JPH11184205A - Electrophotographic device using potential dividing developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a fringe phenomenon and to obtain an image without error printing by performing correction exposure by exposure control in order to restrain an inverse electric field which becomes the cause of the fringe phenomenon. SOLUTION: A laser beam 4 is emitted by an exposure control means 3, a photoreceptor drum 2 is irradiated with the laser beam, and a latent image whose surface potential is different is formed on the drum 2. Then, as to the latent image formed on the drum 2, the toner of two colors whose electrification polarity is different, that is, positively electrified toner as first toner is developed by a first developing machine 5 and negatively electrified toner as second toner is developed by a second developing machine 6 to the latent image by an electrical potential division developing method. The toner of two colors on the drum 2 is transferred to a paper 12 by a transfer machine 8, and fixed on the paper 12 by a fixing machine 9. At this time, a correction exposure deciding circuit 13 inside the means 3 decides whether or not the correction exposure is performed from an image signal 11, and the correction exposure is performed based on the decision result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light amount control method for an electrophotographic apparatus using a potential division developing method of forming electrostatic latent images having different polarities in one exposure operation and performing two-color development.

[0002]

2. Description of the Related Art A conventional laser beam printer is of a type in which one color of toner is developed by one laser beam.
2. Description of the Related Art In recent years, with the development of color laser beam printers, attention has been paid to a potential division developing method that can perform two-color development using one laser and one exposure operation.

[0003] The potential division development method is to charge a photoreceptor and change the exposure amount in three stages of no exposure, weak exposure, and strong exposure according to the color information of the image in exposure, so that the photoreceptor is exposed on the photoreceptor. A three-level electrostatic latent image is formed, and is developed with positively charged toner and negatively charged toner.
This is a method for forming a color toner image.

In an electrophotographic apparatus to which the potential division developing method is applied, a phenomenon in which an image of one color which is not originally developed is developed such that the periphery of the image is bordered by another color toner (hereinafter, referred to as an image).
(Referred to as fringe development).

[0005] The occurrence of fringe development is explained as follows. As shown in FIG. 2A, the surface potential of the photosensitive drum in this potential division developing system is as follows: the charged potential Vca at the place without exposure, the intermediate potential Vw at the place of weak exposure, and the discharge potential at the place of strong exposure. Vda. In the charged potential portion of Vca, the first toner is regularly developed by the developing device to which the developing bias voltage Vb1 is applied. On the other hand, in the discharge potential portion of Vda, the second toner is reversely developed by the developing device to which the developing bias voltage Vb2 is applied. The intermediate potential portion of Vw is a place where no toner is developed and becomes a white image portion. However, as shown in FIG. 2B, the electric field on the photosensitive drum 2 is Vca, V
Since the difference between the potential portion of da and the intermediate potential Vw is large, an electric field in the opposite direction is generated by the edge effect, and the toner of the opposite charge polarity adheres to the electric field. In an electrophotographic process, when an electrostatic latent image is formed for development on a photoreceptor, an electric field for enhancing the latent image and an electric field having a polarity opposite to that of the latent image (hereinafter, referred to as a reverse electric field) are generated. This is because it occurs at the edge of the image and at the periphery of the latent image. Therefore, if the first toner is red and the second toner is black, the originally white image portion around the black image is developed with red, and the originally white image portion around the red image is developed with black. Become so. This is called fringe development, as if the periphery of the black image is bordered in red and the periphery of the red image is bordered in black. This is a printing of a color that should not be formed originally, and erroneous printing results in recording of incorrect information in a printing result, which is a problem to be solved. The fringe development has a characteristic that the development bias voltages Vb1 and Vb2 appear more prominently near the intermediate potential Vw of the weakly exposed location, and decrease as the distance from Vw increases. Therefore, as a means for preventing fringe development, it is conceivable to use this characteristic to separate the developing bias voltages Vb1 and Vb2 from Vw. However, with this means, the developing bias and the potential difference between the image areas where toner adheres, the absolute values of Vca-Vb1 and Vda-Vb2 become smaller, and the amount of toner developed in the original image area decreases, and There is a problem that the concentration decreases. Although fringe development is prevented, the original development becomes insufficient, and it is difficult to solve the fringe development by this means.

As another means for solving this problem, a method of using a developer having a low resistance value is disclosed in Japanese Patent Laid-Open No. 1-1896.
No. 64 is proposed. This is based on the fact that the use of a developer having a low resistance value weakens the edge effect and weakens the peripheral electric field in the opposite direction. However, a developer having a too low resistance value causes a secondary problem that the carrier adheres to the photoconductor. The carrier adhered to the photoreceptor causes a gap between the toner image on the photoreceptor and the paper during transfer, thereby lowering the transfer electric field strength and causing transfer failure of the toner image. This means that some characters, images, and the like are missing without being transferred to the paper. Therefore, there is a problem in applying the second means of using a developer having a low resistance value to solve the fringe development.

[0007]

In the prior art, there is no consideration for a reverse electric field generated around and at the edge of an image portion in potential division development, and there is a problem that fringe development occurs. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrophotographic apparatus using a potential division developing system capable of preventing fringe development and obtaining an image without erroneous printing.

[0008]

In the present invention, correction exposure is performed by exposure control in order to suppress a reverse electric field which causes fringe development.

The correction exposure includes three-stage exposure for forming three potential portions, namely, a charged potential portion where toner is normally developed, a discharge potential portion where toner is reversely developed, and an intermediate potential portion where toner is not developed. The white image portion around the portion is exposed with an exposure amount forming a potential between the charging potential and the intermediate potential, and the white image portion around the discharging potential portion forms a potential between the discharging potential and the intermediate potential. By controlling the light amount of the laser so as to perform the exposure with the exposure amount, a sudden change in the potential is reduced, and the generation of the reverse electric field is suppressed. In the correction exposure, a plurality of laser drivers are used as an exposure unit, an exposure amount is set for each of a laser driver for forming an intermediate potential, a discharge potential, and a correction exposure, and a corresponding laser driver is switched according to image data. It is done by. The correction exposure is performed by using a plurality of laser drivers for correction exposure in addition to laser drivers set for exposure to strong exposure and weak exposure.

In the correction exposure, a plurality of laser drivers are used as the exposure means, and an exposure amount weighted to each of the laser drivers is set, and a combination of the laser drivers to be operated is used to perform a strong exposure, a weak exposure, and a correction exposure. This is done by switching.

[0011] The correction exposure may include a strong exposure to the exposure means,
A voltage is generated by converting an exposure amount set value of the weak exposure and the correction exposure into a digital input into an analog signal, and this voltage is used as a reference voltage to control the current to the laser to adjust the exposure amount. This can be done with a laser driver.

Further, in the correction exposure, strong exposure, weak exposure, and correction exposure are performed by controlling the laser emission time of the exposure means and setting the exposure amount.

[0013]

(Embodiment 1) An embodiment of the present invention will be described below.

FIG. 1 is a schematic sectional side view showing a process of an electrophotographic apparatus using a potential division developing system according to the present invention. 1 is a charger, 2 is a photosensitive drum, 3 is an exposure unit,
4 is a laser, 5 is a first developing machine, 6 is a second developing machine, 7 is a pre-transfer charger, 8 is a transfer machine, 9 is a fixing machine, 10 is a cleaner, 11 is an image signal, 12 is paper, and 13 is This is a correction exposure determination circuit.

In the laser printer of the present embodiment, the photosensitive drum 2 using the negatively charged OPC is uniformly charged by the charger 1. Next, a laser 4 is emitted by the exposure control means 3 to irradiate the photosensitive drum 2 with a laser beam.
The latent images Vca, Vw, and Vda are formed at the surface potential of.

Thereafter, the latent image formed on the photosensitive drum 2 is subjected to a first development by a first developing unit 5 by a potential division developing method.
The two color toners having different charging polarities, such as a positively charged toner as the toner and a negatively charged toner as the second toner, are developed by the second developing device 6 into latent images formed on the photosensitive drum 2, respectively. You. At this time, since the charged polarities of the two developed toners are different, the pre-transfer charger 7
The charge polarity of the two-color toner developed is adjusted to the negative polarity. The two-color toner on the photosensitive drum 2 is transferred to the transfer device 8.
Is transferred onto the paper 12. The two-color toner transferred to the paper 12 is fixed on the paper 12 by the fixing device 9. The residual toner remaining on the photosensitive drum 2 without being transferred to the paper 12 is collected by the cleaner 10 and a series of printing processes is completed.

At this time, the correction exposure determination circuit 13 in the exposure control means 3 determines whether or not correction exposure is to be performed from the image signal 11, and performs correction exposure based on the determination result.

FIGS. 2A and 2B are diagrams showing the surface potential and the electric field in the potential division development of this embodiment. The horizontal direction shows the position on the photosensitive drum 2, (a) shows the surface potential, and (b) shows the surface. An electric field corresponding to the potential.

The potential division developing method will be described with reference to FIG. The potential division developing system controls the surface potential of the photosensitive drum 2 to three values. In order to make the surface potential of the photosensitive drum 2 ternary, the exposure amount of the laser
In actuality, the exposure amount is controlled in three stages of unexposed, weakly exposed, and strongly exposed by controlling the exposure in stages. An unexposed portion, a weakly exposed portion, and a strongly exposed portion are formed on the photosensitive drum 2. The surface potential of the photosensitive drum 2 is such that the unexposed portion has a charged potential Vca, the weakly exposed portion has an intermediate potential Vw, and the strongly exposed portion has Discharge potential Vda
Is formed. After the ternary potential is formed, the positively charged toner is developed (normally developed) on the photosensitive drum 2 by the first developing device 5 to which the developing bias voltage Vb1 is applied. Next, the negatively charged toner is developed (reversed development) on the photosensitive drum 2 by the second developing device 6 to which the developing bias Vb2 is applied. Neither toner is developed at the intermediate potential. (Hereinafter, the positively charged toner will be described as red toner, the negatively charged toner will be described as black toner, the normally developed image will be described as a red image, and the reversal developed image will be described as a black image.) The fringe development will be described.

FIG. 2B shows an electric field with respect to the surface potential of the photosensitive drum 2. As shown in FIG. 2B, the electric field enhances the electric field at the edge of the image, and an electric field of the opposite polarity (reverse electric field) is generated in the white image area around the image. When this reverse electric field exceeds the electric field at which development is started, red fringe development occurs in which red toner is developed around the black image, and black fringe development occurs in which black toner is developed around the red image. I do.

FIG. 3 is a diagram showing the surface potential and the electric field when the correction exposure of this embodiment is used.
(B) is an electric field corresponding to the surface potential. FIG. 3A is a diagram showing a surface potential formed by exposure control using correction exposure. By controlling the exposure amount of the laser 4 in four steps of the exposure amount for forming the potentials Vcf and Vdf between the toner development potential and the intermediate potential Vw in addition to the strong exposure and the weak exposure, the unexposed portion, the intermediate potential portion, and the discharge The surface potential is formed in five stages of a potential portion, 20 portions of correction exposure, and 30 portions of correction exposure. FIG. 3 (b)
Indicates an electric field corresponding to the surface potential. The discharge potential Vc is calculated based on the potentials Vcf and Vdf formed by the correction exposure.
The abrupt potential difference between a and the intermediate potential Vw and between the charging potential Vda and the intermediate potential Vw are eliminated, and the electric field intensity at the peripheral portion of the image is reduced, thereby suppressing the generation of the reverse electric field.

FIG. 4 is a diagram showing an example of the configuration of the exposure control means when the correction exposure is not used.

Reference numeral 41 denotes a laser driver for strong exposure, 42 denotes a laser driver for weak exposure, 43 denotes a black image signal, 44 denotes a red image signal, 45 denotes a host, 46 denotes an image signal discriminating circuit, and 47 denotes a host.
Is a white image signal.

The ternary surface potential on the photosensitive drum 2 required for the potential division developing method is realized by controlling the light amount of the laser 4 to two values by switching the two laser drivers 41 and 42. I have.

Specifically, one laser driver 42
(Weak exposure) to perform weak exposure to form an intermediate potential Vw,
The remaining one laser driver 41 (for strong exposure) performs strong exposure to form a discharge potential Vda. When neither laser driver operates, the charging potential Vca is formed because the laser is in the unexposed state. In this embodiment, the image signal 11 sent from the host 45 is a black image signal 43,
There are two red image signals 44, and these two signals are sent by serial transfer. When both the black image signal 43 and the red image signal 44 are input, the image signal discriminating circuit 46 recognizes the signal as a white image portion and outputs the white image signal 4.
Treated as 7.

In the exposure control means, when the red image signal 44 is inputted, neither of the two laser drivers 41, 42 is selected and the exposure control means is in an unexposed state, and the surface potential on the photosensitive drum 2 is the charged potential Vca. It is formed. When the black image signal 43 is input, the laser driver 41 whose current value for controlling the amount of light of the laser 4 is set to Ib is selected to perform strong exposure, and the surface potential on the photosensitive drum 2 becomes the discharge potential Vda.
Is formed. Further, a black image signal 43 and a red image signal 44
When neither is input, it is recognized as a white image part,
The laser driver 42, which is treated as a white image signal 47 and has a current value for controlling the light amount of the laser 4 set to Iw, is selected to perform weak exposure to form an intermediate potential Vw.

FIG. 5 is a diagram showing a circuit configuration using correction exposure.

Reference numeral 51 denotes a laser driver for the correction exposure 20,
52 is a laser driver for the correction exposure 30, 53 is a black correction signal, and 54 is a red correction signal.

The exposure method controls the amount of exposure to reduce the electric field strength (potential gradient) by switching a plurality of laser drivers one by one for correction exposure in the exposure control unit 3.
The generated reverse electric field is suppressed. In this embodiment, in order to newly form a black correction potential Vdf and a red correction potential Vcf on the photosensitive drum 2 for correction exposure, two current values for setting the light amount of the laser 4 are set to Ifrb and Ifrc, respectively. Laser drivers 51 and 52 are added, and the laser driver 4 for weak exposure is added.
1. The surface potential on the photosensitive drum 2 is changed to a charging potential Vca and an intermediate potential Vw by using a total of four laser drivers: a laser driver 42 for strong exposure, a laser driver 51 for correction exposure 20, and a laser driver 52 for correction exposure 30. , A discharge potential Vda, a black correction potential Vcf, and a red correction potential Vdf.

The image signal 11 from the host side is determined by a correction exposure determination circuit 13 in the exposure control means 3 based on information on the periphery of the target pixel to be exposed, and the exposure amount is set by the laser. One of the drivers 41, 42, 51, 52
To perform an exposure operation. At this time, it is necessary to set the correction exposure amount so that the range of the surface potential formed on the photosensitive drum 2 by the correction exposure is Vb1 to Vw as a measure against black fringe and Vw to Vb2 as a measure against red fringe. Becomes The correction exposure determination circuit 13 uses the black image signal 43 and the white image signal 4 as laser drive signals.
7, one of four signals of black correction signal 53 and red correction signal 54
The logic circuit is configured to output only one signal. By exposure, the surface potential on the photosensitive drum 2 is formed stepwise between the red developing bias Vb1 and the intermediate potential Vw,
Similarly, a stepwise potential is formed between the intermediate potential Vw and the black developing bias Vb2.

As described above, by controlling the light amount of the laser 4 and forming the surface potential on the photosensitive drum 2 in a stepwise manner, a sudden change in the potential is suppressed, and the generation of a reverse electric field which causes fringe development is suppressed. Can be suppressed.

FIG. 6 is a diagram showing the surface potential when the multi-step correction exposure of this embodiment is used. The exposure amount of the laser 4 is added to the strong exposure and the weak exposure, and is controlled in six steps of the exposure amount for forming Vcf1, Vcf2, Vdf1, and Vdf2 between the toner developing potential and the intermediate potential Vw, so that the unexposed portion and the intermediate potential are controlled. Part, discharge potential part, 21 parts of correction exposure, 22 parts of correction exposure, 31 parts of correction exposure
The surface potential is formed in seven stages, ie, 32 parts and 32 parts of correction exposure. By forming a plurality of correction potentials between the toner development potential and the intermediate potential Vw, a change in potential can be reduced, the occurrence of a reverse electric field can be reduced, and the effect of suppressing fringe development can be increased. Further, when the number of correction potentials is increased, a further effect can be obtained.

FIG. 7 is a diagram showing a circuit configuration corresponding to a correction exposure method for realizing this embodiment.

Reference numeral 71 denotes a laser driver for the correction exposure 21;
2 is a laser driver for the correction exposure 22, and 73 is a correction exposure 3
1 is a laser driver for correction, 74 is a laser driver for correction exposure 32, 75 is a first black correction exposure signal, 76 is a second black correction exposure signal, 77 is a first red correction exposure signal, and 78 is a second
Is a red correction exposure signal. In this embodiment, in order to form the correction potentials Vcf1, Vcf2, Vdf1, and Vdf2 in addition to the strong exposure and the weak exposure, a laser driver for the correction exposure 21, a laser driver for the correction exposure 22, a laser driver for the correction exposure 31, and a correction exposure 32 laser driver was added, and the surface potential of the photosensitive drum 2 was charged using a total of six laser drivers.
Vca, intermediate potential Vw, discharge potential Vda, first black correction potential Vcf
1, an example is shown in which the second black correction potential Vcf2, the first red correction potential Vdf1, and the second red correction potential V are formed in seven stages.

The image signal 11 from the host side is determined by a correction exposure determination circuit 13 in the exposure control means 3 based on information on the periphery of the target pixel to be exposed. Drivers 41, 42, 71, 72, 7
One of 3, 74 is driven to perform an exposure operation. At this time, it is necessary to set the correction exposure amount so that the range of the surface potential formed on the photosensitive drum 2 by the correction exposure is Vb1 to Vw as a measure against black fringe and Vw to Vb2 as a measure against red fringe. Becomes Further, a correction exposure determination circuit 1
In 3, the black image signal 43, the white image signal 47, the first black correction signal 75, the second black correction signal 76, the first red correction signal 77, and the second red correction exposure signal 78 are used as laser drive signals. The logic circuit is configured to output only one of the six signals.

By exposure, the surface potential on the photosensitive drum 2 is formed in a stepwise manner between the red developing bias Vb1 and the intermediate potential Vw. Similarly, a stepwise potential is also formed between the intermediate potential Vw and the black developing bias Vb2. Is formed. As described above, by controlling the light amount of the laser 4 and forming the surface potential on the photosensitive drum 2 in a stepwise manner, a rapid change in the potential is suppressed, and the generation of a reverse electric field which causes fringe development is suppressed. Can be.

According to the above-described embodiment, since the amount of exposure necessary for forming a potential for each laser driver is set, a stable surface potential can be obtained.

(Embodiment 2) Another embodiment will be described below with reference to FIG.

FIG. 8 is a diagram showing a circuit configuration corresponding to a correction exposure method for realizing this embodiment. 81, 82,
83 is a laser driver weighting the exposure amount to 1: 2: 4, 84, 85, 86 are 20 bits, 21 bits, 2 bits
This is a signal for driving the laser driver assigned with 2 bits. A plurality of laser drivers 81 for exposure;
The figure shows a configuration in which an exposure amount is determined based on peripheral information of a pixel of interest to be exposed using 82 and 83, and an exposure operation is performed by driving a laser driver in combination to achieve the exposure amount. . At this time, the amount of light obtained by the combination of the laser drivers is such that the range of the surface potential formed on the photosensitive drum 2 by exposure is Vb1 to Vw as a measure against black fringe, Vw to Vb2 as a measure against red fringe, and the intermediate potential V
w, it is necessary to set the discharge potential Vda. In this embodiment, three laser drivers 81, 82,
An example is shown in which the light intensity of the laser is controlled by using a combination of these elements 83 to form eight potentials on the photosensitive drum 2.

The current for controlling the light quantity of the laser 4 is
Laser drivers 81, 82, 83 set as I, 2I, 4I
Are used in combination. As a result, the current value, that is, the drive current of the laser 4 can be controlled in eight ways: 0, I, 2I, 3I, 4I, 5I, 6I, and 7I. The combination of the laser drivers is performed by the correction exposure determination circuit 13. As described above, by controlling the light amount of the laser 4 and forming the surface potential on the photosensitive drum 2 in a stepwise manner, a rapid change in the potential is suppressed, and the generation of a reverse electric field which causes fringe development is suppressed. Can be.

According to this embodiment described above, there is no need to use a laser driver corresponding to a step of a required potential, and there is an effect that hardware can be reduced.

Embodiment 3 Hereinafter, another embodiment will be described with reference to FIG.

FIG. 9 is a diagram showing a circuit configuration corresponding to a correction exposure method for realizing this embodiment.

Reference numeral 91 denotes a V / I converter, and 92 denotes a D / A converter. As a correction exposure method, a configuration is shown in which the V / I converter 91 is used for exposure, and the reference voltage of the V / I converter 91 is analog-converted to a digital input to finely control the amount of light. .

The image signal 11 from the host is determined by the correction exposure determination circuit 13 on the basis of information on the periphery of the pixel of interest to be exposed, and a digital signal is output to provide the required exposure. The signal is converted into an analog output by the D / A converter 92. V / I conversion 91
Since the laser drive current is set based on the input reference voltage, the analog output signal is converted to V / I
The V / I converter 91 is driven using the reference voltage as the reference voltage, and the current value for controlling the light amount of the laser 4 is adjusted to form the surface potential on the photosensitive drum 2. The range of surface potential formed on the photoreceptor by exposure is a measure against black fringe
Vb1 to Vw, Vw to Vb2 as red fringe measures, intermediate potential Vw,
It is necessary to set the discharge potential Vda.

When this method is used, a high-speed D / A converter 92 is required. For example, a D / A converter operable at 500 MHz may be used for video signal processing.

As described above, by controlling the light amount of the laser 4 and forming the surface potential on the photosensitive drum 2 in a stepwise manner, a sudden change in the potential is suppressed, and the generation of a reverse electric field which causes fringe development is suppressed. Can be suppressed.

According to the above-described embodiment, since the analog output obtained by the digital input can be set finely, the changing portion of the image can be smoothly changed.
The generation of a reverse electric field can be eliminated.

Embodiment 4 Hereinafter, another embodiment will be described with reference to FIG.

FIG. 10 is a diagram showing a circuit configuration corresponding to a correction exposure method for realizing this embodiment, and shows an example in which the amount of light is controlled by the time for emitting the laser 4 to suppress fringe development. is there. 101 is a waveform generator, 1
02 is a comparator and 103 is a D / A converter.

In order to control the amount of light according to the light emission time, there is a method using pulse modulation as an example. The waveform generating circuit 101 generates a sawtooth wave and inputs it to the comparator 102, and generates a pulse by applying a voltage to the other comparator input as a threshold voltage. Since this pulse width can be controlled by changing the threshold voltage, it is realized by setting the threshold voltage by the correction exposure determination circuit 13. D / A converter 103 for setting the threshold voltage
And so on.

As described above, by controlling the light amount of the laser 4 and forming the surface potential on the photosensitive drum 2 in a stepwise manner, a rapid change in the potential is suppressed, and the generation of a reverse electric field which causes fringe development is suppressed. Can be suppressed.

According to the present embodiment, the generation of the reverse electric field which causes the fringe development can be suppressed, and the fringe development can be solved. Therefore, a high-quality two-color print image can be obtained.

[0054]

According to the present invention, the occurrence of a reverse electric field which causes fringe development can be suppressed, and the fringe development can be solved.
Therefore, fringe-free printing can be performed, and high-quality two-color printing can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electrophotographic apparatus.

FIG. 2 is a diagram showing a potential and an electric field on a photosensitive drum of a potential division developing system.

FIG. 3 is a diagram showing a potential and an electric field on a photosensitive drum by a correction exposure.

FIG. 4 is a configuration diagram of an exposure unit when correction exposure is not used.

FIG. 5 is a configuration diagram of an exposure unit when using correction exposure.

FIG. 6 is a diagram showing a potential and an electric field on a photosensitive drum by multi-level correction exposure according to an embodiment of the present invention.

FIG. 7 is a configuration diagram of an exposure unit when multi-level correction exposure is used.

FIG. 8 is a configuration diagram of an exposure unit when using multilevel correction exposure.

FIG. 9 is a configuration diagram of an exposure unit when using multi-level correction exposure.

FIG. 10 is a configuration diagram of an exposure unit when multi-level correction exposure is used.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Charging device, 2 ... Photoconductor drum, 3 ... Exposure control means, 4 ... Laser, 5 ... First developing machine, 6 ... Second developing machine, 7 ... Pre-transfer charger, 8 ... Transfer device, 9 ... Fixing vessel,
10 cleaner, 11 image signal, 12 paper, 1
3. Correction exposure determination circuit, 41, 42, 51, 52, 7
1, 72, 73, 74, 81, 82, 83 laser driver, 43 black image signal, 44 red image signal, 45
... Host, 46... Image signal discriminating circuit, 47... White image signal, 53... Black correction signal, 54.
First black correction signal, 76... Second black correction signal, 77.
A first red correction signal, 78... A second red correction signal, 84,
85, 86 ... Digital 3-bit signal, 91 ... V / I conversion, 92, 103 ... D / A converter, 101 ... Waveform generation circuit, 102 ... Comparator.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Ito 1060 Takeda, Hitachinaka-shi, Ibaraki Prefecture Within Hitachi Koki Co., Ltd.

Claims (4)

[Claims] 1. A photoconductor is charged, and a three-stage electrostatic image composed of a charged potential portion, a discharge potential portion, and a potential portion therebetween is formed on the photoconductor by exposure means using a laser. In an electrophotographic apparatus using a potential division developing method of developing a toner at a potential portion, in addition to the exposure for forming the three-stage potential portion, a white image portion around the potential portion where the toner is developed is defined as a toner development potential. Exposure is performed with an amount of light that forms a potential between the intermediate potentials, an exposure amount is set for each laser driver using a plurality of laser drivers, and by switching each laser driver, a charging potential, a discharging potential, and an intermediate potential are set. And an exposure device for forming a plurality of potentials between a toner development potential and an intermediate potential. 2. A photoconductor is charged, and a three-stage electrostatic image including a charging potential portion, a discharging potential portion, and a potential portion intermediate between the charging potential portion and the discharging potential portion is formed on the photoconductor by an exposure unit using a laser. In an electrophotographic apparatus using a potential division developing method of developing toner at a potential portion, in addition to the exposure for forming the three-stage potential portion, a white image portion around the toner development potential portion is moved between a toner development potential and an intermediate potential. Exposure is performed with the amount of light that forms the potential of the laser, a plurality of laser drivers are used, and the amount of laser is set by a combination of laser drivers to be operated. The charging potential, the intermediate potential, the discharging potential, the toner developing potential, and the intermediate potential An electrophotographic apparatus provided with an exposure unit for forming a potential between the two. 3. A photoconductor is charged, and a three-stage electrostatic image composed of a charged potential portion, a discharge potential portion, and a potential portion therebetween is formed on the photoconductor by exposure means using a laser. In an electrophotographic apparatus using a potential division developing method of developing toner at a potential portion, in addition to the exposure for forming the three-stage potential portion, a white image portion around the toner development potential portion is moved between a toner development potential and an intermediate potential. Exposure is performed with a light amount that forms the potential of the toner image, and in addition to the charging potential, the intermediate potential, and the discharging potential, a digital image signal is converted into an analog signal to form a potential between the toner developing potential and the intermediate potential. An electrophotographic apparatus, comprising: an exposure unit for setting an exposure amount of the image. 4. A photoconductor is charged, and a three-stage electrostatic image composed of a charged potential portion, a discharge potential portion, and a potential portion therebetween is formed on the photoconductor by exposure means using a laser. In an electrophotographic apparatus using a potential division developing method of developing toner at a potential portion, in addition to the exposure for forming the three-stage potential portion, a white image portion around the toner development potential portion is moved between a toner development potential and an intermediate potential. And an exposure means for changing the laser emission time to form a charging potential, an intermediate potential, a discharging potential, and a potential between the toner developing potential and the intermediate potential. An electrophotographic apparatus characterized by the following.