JPH11190922A - Picture forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device in which reduction of density and a fogging can be suppressed to the minimum by operating a charging means while radiating a prescribed exposure quantity, deciding charging quantity of the charging means so as to be a desired bright part potential, and using latent image contrast of the maximum limit given by each picture forming device. SOLUTION: The charging quantity of the charging means is decided so as to be a desired bright part potential by operating a charging means while radiating a prescribed exposure quantity. In this device, a potential sensor 6 measures a potential on a photosensitive drum 2 after charging and exposure, and controls applied voltage of a lamp 22 for illuminating a manuscript, applied voltage of a primary charger 4, a developing voltage applied to a developing means 7 from the detected result. And a target value is given to a bright part potential, and charging quantity is controlled using exposure quantity of the maximum limit given by a picture forming device so as to be made the target value. And a dark part potential is a potential when exposure quantity of an exposure device 5 is made the minimum exposure quantity applying charging quantity decided by a bright part potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus for uniformly charging an electrophotographic photosensitive member, forming a latent image by exposure after charging, and visualizing the latent image. More particularly, the present invention relates to an image forming apparatus capable of controlling a photoconductor potential and stabilizing an image.

[0002]

2. Description of the Related Art As a conventional technique, a technique of measuring a photoconductor potential in an image forming apparatus using an electrophotographic photoconductor,
There is a technique for adjusting the amount of charge on the photoconductor and the amount of exposure to the photoconductor.

In order to adjust the charge amount and the exposure amount on the photosensitive member, first, in order to adjust the dark portion potential, the charge amount of the charging means is determined with or without the exposure amount, and then the dark portion potential is adjusted. There is known a method of adjusting the exposure amount so as to obtain a predetermined bright portion potential.

[0004]

Generally, a large number of image forming apparatuses that are manufactured have variations in performance for each component or unit. The following examples can be given as such variations. 1. Exposure amount for a predetermined signal of the exposure unit: In the case of an analog type electrophotography, it is an exposure amount for a lighting voltage of a document illumination lamp. . 2. The performance of the optical system that constitutes the exposure means: the transmittance and the degree of vignetting of lenses and mirrors, the placement accuracy, the aberrations, and the deterioration in efficiency due to contamination over time. 3. Charging amount with respect to applied voltage in charging means: In the case of a corotron type charger, it depends on the distance between the wire and the drum and on the degree of dirt.

[0005] Further, the electrophotographic photosensitive member also has variations in basic characteristics. The charge amount (charging ability) with respect to the applied voltage of the charging means, the change (sensitivity) of the charge amount with respect to the exposure amount, and the minimum charge amount (saturated bright portion potential) with an increase in the exposure amount are exemplified.

Although there are many parameters having variations other than those described above, an image forming apparatus having these variations is usually designed and manufactured with an appropriate margin. That is, various design values are set in consideration of a margin to some extent rather than the performance of one image forming apparatus.

[0007] The potential on the electrophotographic photosensitive member is no exception.
Not only the potential when the exposure amount is absent or minimized after uniform charging by the charging means (hereinafter referred to as “dark portion potential”), but also the potential when the exposure amount corresponding to a white background original is exposed on the photoconductor (hereinafter referred to as “dark portion potential”) The "bright portion potential" is also designed with a margin.

However, such a design value has a disadvantage that basic performance is sacrificed. That is,
The fact that there is a margin in the design value in consideration of the production means that there is a margin in the design value for each of the image forming apparatuses, but that only one of the image forming apparatuses can generally provide a low level of performance. . There were the following problems regarding the photoconductor potential.

The lighting voltage of the original illuminating lamp, which is an exposure means, is determined so as to be set with a certain margin with respect to a design value of power consumption. Therefore, the difference between the dark portion potential and the bright portion potential of the electrophotographic photoreceptor (hereinafter referred to as “latent image contrast”) depends on the exposure amount of the original illumination lamp, that is, the lighting voltage, and therefore, the dark portion potential cannot be sufficiently increased. Or, the bright portion potential cannot be sufficiently reduced. Therefore, although it is often possible to set a margin with only one image forming apparatus, the dark area potential is relatively low in consideration of production,
The bright portion potential must be set relatively high, that is, the latent image contrast must be set small. If the latent image contrast is small, a problem occurs in visualization by the developing means.

That is, in the analog regular development system,
If the dark area potential is low, the image density is reduced and the solid black density is reduced, resulting in an output image with poor image quality. If the light area potential is high, image fouling called fog starts to stand out on a white background. In the digital reversal development method, fogging occurs when the dark part potential is low, and the image density decreases when the light part potential is low.

An object of the present invention is to provide an image forming apparatus
Using the maximum latent image contrast of a single unit, minimizing density reduction and fogging, and controlling the photoconductor potential at a high image level, a high-quality image can always be stably obtained. An object of the present invention is to provide an image forming apparatus.

[0012]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
Charging means for imparting a uniform charge on the electrophotographic photoreceptor,
An exposure unit that exposes the charged electrophotographic photosensitive member to form a latent image; a unit that is downstream of the exposure unit and that measures a potential on the electrophotographic photosensitive member; And a developing unit for visualizing the latent image of the image forming apparatus, the charging unit is operated while irradiating a predetermined amount of exposure with the exposure unit, and the charging unit is operated so that a desired bright portion potential is obtained. An image forming apparatus comprising a photoconductor potential control unit for determining a charge amount of the unit.
According to the invention, the determined charge amount of the charging unit is applied, and the potential on the photoconductor when the minimum exposure amount is irradiated by the exposure unit is set as a dark portion potential.

According to one embodiment of the present invention, the predetermined exposure amount is a maximum exposure amount of the exposure means, and preferably, the absolute value of the desired bright portion potential is 100 V or more, preferably 150 V or less. And

According to another embodiment of the present invention, the applied voltage of the developing potential applied to the developing means is determined by the bright portion potential and the dark portion potential.

According to another aspect of the present invention, a charging means for imparting a uniform charge to the electrophotographic photosensitive member, and an exposing means for exposing the charged electrophotographic photosensitive member to form a latent image, ,
An image forming apparatus downstream of the exposing unit, comprising: a unit for measuring a potential on the electrophotographic photosensitive member; and a developing unit for developing a latent image on the electrophotographic photosensitive member. The charging unit is operated while irradiating a predetermined exposure amount with the unit, the charge amount of the charging unit is determined so as to have a desired light portion potential, and then the determined charge amount of the charging unit is determined. A first photosensitive member potential control means for setting a potential on the photosensitive member when a minimum exposure amount is applied by the exposure means and a dark portion potential; and applying the charge amount of the charging means and Means for adjusting the dark portion potential, which is the potential on the photoconductor when the minimum exposure amount is applied, and then adjusting the exposure amount so as to obtain a predetermined light portion potential on the dark portion potential. Controlling means for controlling the first photosensitive member potential The third charge amount is determined from the charge amount of the charging means obtained by the means and the charge amount of the charging means obtained by the second photoconductor potential control means, and is obtained by the first photoconductor potential control means. An image forming apparatus is provided, wherein a third exposure amount is determined from an exposure amount of the exposure unit and an exposure amount of the exposure unit obtained by the second photoconductor potential control unit. According to the present invention, the third developing potential is obtained from the developing potential of the developing means obtained by the first photosensitive member potential control means and the developing potential of the developing means obtained by the second photosensitive body potential control means. To determine.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an electrophotographic copying machine which is an embodiment of the image forming apparatus according to the present invention. In this embodiment, the electrophotographic copying machine is provided with a cylindrical electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 2 substantially at the center of the apparatus main body 1. The photoconductor drum 2 is rotatably supported by the apparatus main body 1 in the direction of arrow R1. Around the photoconductor drum 2, the potential on the photoconductor drum 2 is erased in order along the rotation direction. An electric device 3, a primary charger (charging means) 4 for uniformly charging the surface of the photosensitive drum 2,
An exposure device (exposure means) 5 for exposing the surface of the photoconductor drum 2 to form an electrostatic latent image, a potential sensor 6 for measuring a potential on the photoconductor drum 2 after exposure, and a photosensor formed on the photoconductor drum 2 A developing device (developing unit) 7 for forming a toner image by attaching toner to the electrostatic latent image; a transfer charger (transfer device) 8 for transferring the toner image onto the transfer material P; And a cleaning device 10 for removing residual toner on the photoconductor drum 2.

A transfer material P to which a toner image is transferred is fed from a feed deck 11. Below the photosensitive drum 2, that is, below the inside of the apparatus main body 1, a paper feed deck 11 for storing the transfer material P is arranged. The transfer material P in the paper feeding deck 11 is fed by a paper feeding roller 12, and is conveyed via a conveying roller 13 and a registration roller 15 to the photosensitive drum 2.
And the transfer charger 8. The transfer material P transfers the toner image from the photosensitive drum 2 here, and is conveyed to the fixing device 17 by the conveyance belt 16. The transfer material P to which the toner image has been transferred by the fixing device 17 is discharged onto a discharge tray 20 by a discharge roller 19 as a final copy.

In this embodiment, the exposure device 6 illuminates the original placed on the platen glass 21 with the original illumination lamp 22 and the reflection plate 23, and reflects reflected light from the original image into mirrors 25a and 25b. , 25c, and after passing through an enlargement / reduction lens 26, the light is guided to the surface of the photosensitive drum 2 via a projection mirror 27. Thus, the uniformly charged surface of the photosensitive drum 2 is exposed to form an electrostatic latent image corresponding to the original image. In order to adjust the amount of exposure to the photosensitive drum 2, a standard white plate 28 is provided on the side of the platen glass 21, and a document illumination lamp illuminates these to set a bright potential on the photosensitive drum 2. It can be formed.

FIG. 2 is a diagram schematically illustrating the configuration of control means around the control board 100 for measuring and controlling the potential on the photosensitive drum 2.

In the embodiment shown in FIG. 2, a ROM in which a control program is described and a RAM which is a temporary storage element of necessary data on the program are connected to a CPU which is a central element of processing in the control board 100. ing. Also, I / O which is an interface element and A which is a data conversion element
The / D converter and the D / A converter are connected to external peripheral devices, and information is input and output to and from the control board 100. With such a configuration, the potential sensor 6 as the peripheral device in the present invention can measure the potential on the photosensitive drum 2 after the charging and exposure. Then, based on the detection result of the potential sensor 6, the applied voltage of the original illumination lamp 22 and the primary charger 4
And the developing potential applied to the developing means 7 can be controlled.

In the present embodiment, in the image forming apparatus having the above-mentioned configuration, which is an electrophotographic copying machine, the conventional control method which causes a decrease in the latent image contrast is improved, and the maximum latent image of each image forming apparatus is provided. The contrast is used to control the photoconductor potential for minimizing density reduction and fogging.

That is, the charge amount is adjusted while giving the target value to the bright portion potential and using the maximum exposure amount of the image forming apparatus main body so as to reach the target value. The dark portion potential is a potential when the exposure unit is set to the minimum exposure amount while applying the charge amount determined by the light portion potential.

In the present invention, it has been found that setting the light portion potential to an absolute value of 100 V or more, preferably 150 V or less, is the most appropriate potential for the image forming apparatus. In order to obtain the maximum latent image contrast at a constant exposure, it is advantageous to set the bright portion potential as high as possible from the relationship between the exposure and the potential of the electrophotographic photosensitive member. However, it has been found that when the voltage is higher than 150 V, the scattered toner around the photoreceptor flies toward the light portion potential, causing image smearing. The photoreceptor has such a property that the amount of charge held does not decrease linearly with respect to the amount of exposure, and that the photoreceptor has a gentle curve, especially near a light portion potential. Therefore, it can be said that setting the bright portion potential low is a disadvantageous condition in terms of power consumption of the exposure unit when there is no margin in the exposure amount.

The present invention is characterized in that the applied voltage of the developing potential applied to the developing means is determined from the target potential of the light portion potential and the measured potential of the dark portion potential.

In the present invention, in order to maximize the latent image contrast in order to effectively use the capability of each of the image forming apparatus main bodies, the halftone area is determined by the latent image contrast at a predetermined developing potential applied voltage. Causes a concentration fluctuation.
Of course, this is not the case in a binary control image forming apparatus having no halftone area, but it cannot be ignored in a copying machine having a halftone area. Therefore, a method of determining a development potential in consideration of a predetermined target value of a light portion potential and a measured potential of a dark portion potential, that is, a latent image contrast was considered.

Further, regardless of the order of the method for controlling the potential of the photosensitive member of the present invention, the potential control method for adjusting the exposure amount so as to obtain a predetermined bright portion potential on the dark portion potential after adjusting the dark portion potential first. Was performed, and a means for obtaining a desired image level from each parameter obtained by the two control methods was considered. That is, the potential control according to the present invention is referred to as a first control method, and the conventional potential control is referred to as a second control method. After executing these two control methods, the charge amount of the charging unit obtained by the first control method of the photoconductor potential and the charge amount of the charging unit obtained by the second control method of the photoconductor potential are determined from 3 is determined. Further, a third exposure amount is determined from the exposure amount of the exposure unit obtained by the first photoconductor potential control method and the exposure amount of the exposure unit obtained by the second photoconductor potential control method.
And the developing potential of the developing means obtained by the first control method,
From the development amount of the developing means obtained by the second control method,
Is determined.

In the present invention, an image is formed with the third charge amount, exposure amount and development potential thus obtained. As described above, the charge amount, exposure amount and development potential specific to the present invention obtained by the first control method are the most capable conditions for use of the image forming apparatus main body. On the other hand, the charge amount, the exposure amount, and the development potential obtained by the second control method are set values in consideration of production, and the charge amount, the exposure amount, and the development potential obtained in the first control show lower values. . Under the second condition, the image level is lower than the first image level.

Therefore, in the present invention, means for freely setting the image level during this period by a user or a service person has been considered. That is, by determining the third charge amount, the exposure amount, and the development potential between the two types of charge amount, the exposure amount, and the development potential obtained by the first and second control methods, The setting between the first condition having a high image level and the condition common to image forming apparatuses having a low image level can be freely performed.

That is, according to the present invention, the image forming apparatus 1
Using the maximum latent image contrast of one unit, control of the photoconductor potential at a high image level with minimum density reduction and fogging is realized, and a stable, high-quality image is always obtained. Can be.

Next, an image forming apparatus according to the present invention will be described in detail with reference to embodiments.

Embodiment 1 This embodiment will be described as applied to an electrophotographic copying machine provided with the electrophotographic photosensitive member described with reference to FIGS. 1 and 2. That is, the electrophotographic copying machine is provided with a cylindrical electrophotographic photosensitive member, that is, the photosensitive drum 2, and the surface of the photosensitive drum 2 is uniformly charged by the temporary charger 4;
The surface of the photosensitive drum 2 is exposed by an exposure device 5 to form an electrostatic latent image, and this latent image is visualized by a developing device 7.

As described above, the potential on the photosensitive drum 2 after charging and exposure can be measured by the potential sensor 6, and the voltage applied to the original illumination lamp 22 can be determined from the detection result of the potential sensor 6. And the applied voltage of the primary charger 4;
It is possible to control the developing potential applied to the developing means 7.

FIG. 3 shows a photosensitive drum 2 having a different dark portion potential.
7 is an exposure dose-potential curve in the case of using. Even if the photosensitive drum 2 and the image forming apparatus are the same, if the dark part potential (VD) is different, the curve of the potential decrease due to exposure draws a different curve as shown in the figure. However, normally, even if the exposure amount is excessively applied, the potential is not 0 V, but the result is to settle to the saturated bright portion potential (VSL). Generally, the saturated light portion potential is about 10 to 50V. Of course, if the exposure is performed continuously, the voltage drops to about 0 V. However, the potential at the potential sensor 6 does not become 0 V due to the relationship between the exposure system of the image forming apparatus and the rotation speed of the photosensitive drum.

In FIG. 3, the maximum value of the latent image contrast which influences the image level of the image forming apparatus (hereinafter referred to as “maximum latent image contrast”) is the dark portion potential (VD) which is the potential of the black portion and the potential of the white background portion. This is the difference between the saturated light portion potential (VSL), which is the lowest potential. As is clear from the figure, the maximum latent image contrast increases as the dark area potential increases. Further, in an actual image forming apparatus, the exposure amount is limited. When the difference between the bright portion potential and the dark portion potential at the predetermined exposure amount (E1) is called "latent image contrast", the latent image contrast also increases as the dark portion potential increases. In the figure, the relationship of △ V1> △ V2> △ V3 holds. The reason for this is that if the dark part potential is high, a relatively linear characteristic region is used instead of using the characteristics near the saturated light part potential VSL in the exposure amount / potential curve.

FIG. 4 shows an exposure amount / potential curve when photosensitive drums having different exposure sensitivities are used. The photosensitive drums having different exposure sensitivities are photosensitive drums having different potential reduction widths from the dark part potential even with the same exposure amount. In the figure, the photosensitive drum having the characteristic of curve A has a small potential drop width with respect to the exposure amount, and it is necessary to increase the power consumption of the original illumination lamp in order to secure the maximum latent image contrast.

FIG. 5 shows an exposure amount / potential curve when photosensitive drums having different saturated bright portion potentials VSL are used. The saturated bright portion potential VSL may also vary depending on the photosensitive drum, and the maximum latent image contrast will differ even if the dark portion potential is the same. Actually, the photosensitive drums having different sensitivities as shown in FIG. 4 and the photosensitive drums having different saturated bright portion potentials shown in FIG. 5 are not independent from each other, and the sensitivity and the saturated bright portion potential are simultaneously varied. Is a parameter having

FIG. 6 is an exposure / potential curve when three types of photosensitive drums having different sensitivity and saturated bright portion potential are used. The photosensitive drum having the characteristic of curve C is
It can be seen that the photosensitive drum can obtain a large maximum latent image contrast with a small exposure amount as compared with the photosensitive drum having the characteristic of the curve B which is manufactured most in production. Conversely, the photosensitive drum having the characteristic of the curve A cannot obtain a maximum latent image contrast unless the exposure amount is increased as much as possible.

By the way, in consideration of the productivity of the image forming apparatus, there is a case where the photosensitive drum having the characteristic of the curve A must be used due to the production yield and the like. In the related art, the following control method is executed even in such a case.

FIG. 7 is a flowchart showing a control procedure of the photoconductor potential in the prior art.

According to the prior art, first, the original illumination lamp 22 shown in FIG. 1 is turned off (m1), and the primary charger 4 is turned on with the initial applied voltage (m2). The photoconductor potential at this time is measured by the potential sensor 6 (m3), and it is compared whether or not the dark portion potential VD is a target value (m4). If not, the voltage applied to the primary charger 4 is changed (m5), and charging and measurement are repeated again. The application voltage of the primary charger 4 is adjusted a predetermined number of times to adjust the applied voltage of the primary charger 4 so as to reach the target dark portion potential, and the applied voltage of the primary charger 4 is determined (m6). That is, the amount of charge on the photosensitive drum 2 by the primary charger 4 is determined.

Next, O is determined by the voltage determined by the primary charger 4 described above.
N (m7), the standard white plate 28 in FIG. 1 is illuminated (m8) while the original illumination lamp 22 is turned on with the applied voltage of the initial value. The potential of the photoconductor at this time is measured by the potential sensor 6 (m9), and it is compared whether the bright portion potential VL is a target value (m10). The document illumination lamp 22 is not the target value.
Is changed (m11), and exposure and measurement are repeated again. The voltage applied to the document illumination lamp 22 is determined a predetermined number of times by adjusting the voltage applied to the document illumination lamp 22 so as to reach the target bright portion potential (m1
2). That is, the photosensitive drum 2 by the document illumination lamp 22
To determine the amount of exposure.

As described above, in the prior art, the control method is to first adjust the dark area potential, determine the charge amount, and then adjust the light area potential to determine the exposure amount. In this control method, a target value is provided for the dark portion potential, that is, the dark portion potential is constant. At the same time, in the process of adjusting the amount of exposure, a target value is provided for the bright portion potential, that is, the bright portion potential is constant. Such a control method has the following problems.

In the process of determining the exposure amount, when a photosensitive drum having a characteristic represented by a curve A is used as shown in FIG. A bright portion potential other than the potential is used. In FIG. 6, the photosensitive drum having the characteristics represented by the curves B and C has a characteristic in which the upper limit of the exposure amount Emax is lower than the bright portion potential of the curve A. However, considering production, the target value of the bright portion potential is VL. Must. If it is set to be equal to or lower than VL, the photosensitive drum having the characteristic represented by the curve A exceeds the upper limit of the power consumption of the original illumination lamp.

Accordingly, the latent image contrast is determined by the photosensitive drum having the curve A.
This can be said to be a less preferable control method in that the set value is affected by components that are not so many in production, and there is a margin for most other components.

It has been found that a small latent image contrast is disadvantageous for image density and fog. When the developing potential in the developing means is defined for the latent image contrast which is the difference between the dark part potential and the bright part potential, the difference between the dark part potential and the developing potential is the density contrast, and the difference between the developing potential and the bright part potential is the fog contrast. is there. Usually, the development potential refers to only a DC bias among the development bias generated by superimposing a DC bias and an AC bias applied to the developing unit. In the present invention, it is a potential located between a dark portion potential and a bright portion potential. Density contrast and fog contrast are accompanied by the disadvantage that, when the contrast is small, the density is slightly increased. Therefore, each of the density contrast and the fog contrast requires a large amount. In other words, if the latent image contrast, which is the sum of the density contrast and the fog contrast, is small, the condition is disadvantageous for the density and the fog.

In the case where the positively charged amorphous silicon photosensitive member used in this embodiment is used by the conventional potential control method, the dark portion potential VD at the potential sensor position is set to 4
The condition of 20 V and the bright portion potential VL of 60 V were the conditions for obtaining a bright portion potential at the maximum exposure amount of the photoreceptor having the characteristic represented by the curve A. That is, in the related art, the latent image contrast is 360 V, and no more can be obtained.

Therefore, in the present invention, emphasis is always placed on maximizing the capability without leaving any remaining power of the components.
The image level can be maintained at the highest level.

FIG. 8 is a flowchart showing a control procedure of the photoconductor potential in the present invention.

First, according to the present invention, the standard white plate 28 in FIG. 1 is illuminated while the original illumination lamp 22 shown in FIG. 1 is turned on at the maximum exposure amount (n1). Then, the primary charger 4 is turned ON with the applied voltage of the initial value (n2). The photoconductor potential at this time is measured by the potential sensor 6 (n3), and it is compared whether or not the bright portion potential VL is a target value (n4). If it is not about the target value, the voltage applied to the primary charger 4 is changed (n5), and charging and measurement are repeated again. The voltage applied to the primary charger 4 is adjusted a predetermined number of times to adjust the voltage applied to the primary charger 4 so as to reach the target bright portion potential, and the voltage applied to the primary charger 4 is determined (n6). That is, the amount of charge on the photosensitive drum 2 by the primary charger 4 is determined. Next, the above-mentioned primary charger determination voltage is turned on (n7), and the original illumination lamp 22 is turned off.
(N8). The photosensitive potential at this time is measured by the potential sensor 6 (n9), and the dark portion potential VD is detected (n1).
0). Such a potential control method according to the present invention has the following advantages.

FIG. 9 is an exposure / potential curve when the potential control method of the present invention is executed using three types of photosensitive drums having different sensitivities and saturated bright portion potentials. In the present invention, the voltage applied to the primary charger 4 is adjusted so that the bright portion potential VL is set to the target value at the maximum exposure amount Emax.
The value of L is constant. On the other hand, since the dark portion potential is detected by the voltage applied to the primary charger 4 in a state where the bright portion potential is adjusted,
As shown in the figure, the potentials of the curves B and C are higher than in the conventional case. That is, since there is no target value in the dark portion potential, it is possible to obtain a large latent image contrast on drums other than the photosensitive drum showing the characteristic represented by the curve A. Therefore, conditions favorable for density and fog are obtained.

The photosensitive drum 2 used in this embodiment
Is used in the potential control method according to the present invention, in the photosensitive drum 2 having the characteristic of the A curve, the dark part potential VD at the potential sensor position is 420 V and the light part potential V
L was 60V. However, in the photosensitive drum 2 having the characteristic of the curve B which is produced most in production, the dark portion potential VD is 460V, that is, the latent image contrast is 400V.
And it becomes possible to make it larger than the prior art. Further, with the photosensitive drum 2 having the characteristic represented by the curve C, the dark portion potential VD can be set to 500 V and the latent image contrast can be set to 440 V.

It should be noted that the potential control method of the present invention always exerts the maximum capability with respect to variations other than those of the photosensitive drum, so that it is possible to obtain a latent image contrast higher than that of the prior art.

Embodiment 2 In Embodiment 1, the bright portion potential VL is set to 60
V was set. In this embodiment, the bright portion potential VL is set to 100 V
As described above, a potential control method characterized by desirably setting the voltage to 150 V or lower will be described.

As described with reference to FIG. 3, even when the same photosensitive drum 2 is used, if a different dark portion potential is applied, the latent image contrast changes. This is because a relatively linear characteristic region is used in the exposure amount-potential curve without using the characteristics near the saturated bright portion, so that the photoreceptor potential is greatly reduced by exposure. Although the photoconductor drum 2 has various compositions, it has been found that the potential having a substantially linear characteristic region is 100 V or more. Therefore, when a bright portion potential of 100 V or more is used, the latent image contrast can be efficiently obtained.

However, the higher the bright portion potential VL, the higher the latent image contrast can be.
It turns out that there is another evil. That is, in the case of the image forming apparatus of the present invention in which the bright portion potential VL is a white background, when the VL is high, the scattered toner is easily attached. Various metal members arranged near the photoconductor drum 2 are often grounded at the main body, that is, grounded. Therefore, when the bright portion potential VL is high, the electric field between the photoconductor drum and the metal member causes It will fly to the drum side. It has been found that these values become remarkable at about 150 V or more when an actual image forming apparatus is used.

In the actual photosensitive drum 2, 15
At about 0 V and 150 V or more, the exposure amount / potential curve is relatively linear in both settings, and it is known that there is not much difference in the obtained latent image contrast. I will. Therefore, the light portion potential V
It is important that L is set to 100 V or more, preferably 150 V or less. In this embodiment, the bright portion potential VL is set to 120 V
And

Table 1 shows a comparison between the prior art (Comparative Example 1) and Examples 1 and 2. Here, the bright portion, the dark portion potential and the latent image contrast when the photosensitive drum having the most mass-produced characteristics among the three types of photosensitive drums shown in FIG. 6 are used.

[0059]

[Table 1]

As shown in the first embodiment, in the prior art, since the potential is determined based on the photosensitive drum having the characteristic A, the latent image contrast is smaller than that in the first embodiment.
On the other hand, in the present embodiment, since the potential is set so as to use a relatively straight line portion of the exposure / potential curve, the obtained dark portion potential is higher than a mere 60 V increase, and as a result, the latent image contrast is larger than that of the first embodiment. It became possible to take.

Embodiment 3 In this embodiment, a description will be given of a means for determining a developing potential which affects an actual image level in the latent image contrast obtained in Embodiments 1 and 2.

It should be noted that, with respect to the latent image contrast which is the difference between the dark portion potential and the bright portion potential, the difference between the dark portion potential and the development potential is the density contrast, and the difference between the development potential and the bright portion potential is the fog contrast. did. Since the density contrast and the fog contrast are each accompanied by an adverse effect such as an increase in density and fog when the contrast is small, it is desirable that both of them be as large as possible.

If the fog contrast is above a certain level,
Since the fog level does not change much, only the development contrast tends to be large. However, it has been found that another problem arises when only the latent image contrast and the development contrast among them are increased.

The light portion potential VL is formed on the photosensitive drum from the dark portion potential VD to the light portion potential VL depending on the amount of exposure, but the halftone potential (VHT) is naturally formed also for the density of the halftone document. Since the halftone potential is governed by the exposure amount, it depends only on the exposure / potential curve of the photosensitive drum, and cannot change only the halftone potential. Therefore, when the dark part potential is high and the development contrast is wide, the halftone potential is high, and at a constant development potential, the halftone has a desirable density or more.

Therefore, in the present embodiment, the halftone density is made uniform by modulating the developing potential in accordance with the latent image contrast.

In FIG. 9, when the halftone original is projected on the photosensitive drum, the photosensitive member potential at the exposure amount EHT is the halftone potential in the case of three types of photosensitive drums having different sensitivities and saturated bright portion potentials. Are VHTA, VHTB, VH
It is significantly different from TC. If the developing potential is changed in accordance with the halftone potential, the halftone density can be kept constant. Therefore,

[0067]

(Equation 1) Is defined. Here, α and β are design fixed values. In this embodiment, α is 0.45 and β is +20 V.

In the present invention, the control is performed by setting the target value of the bright portion potential VL, so that the only parameter that affects the development potential VDC is the substantial dark portion potential VD. Since the thus determined developing potential is adjusted in conjunction with each halftone potential in the halftone exposure EHT as shown in FIG. 9, the halftone density can be kept constant. Further, the photosensitive drum having the characteristics represented by the curves B and C has a fog contrast higher than that of the photosensitive drum having the curve A, so that the fog can be further reduced. Further, the development contrast, which is the difference between the dark portion potential and the development potential, can still have a magnitude larger than that of the related art.

Therefore, according to the method of controlling the developing potential in consideration of the halftone potential according to the present embodiment, the stabilization of the halftone density, the stabilization of the fog, and the stabilization of the density can be achieved simultaneously. .

Fourth Embodiment In the first and second embodiments, a potential control method capable of obtaining a latent image contrast wider than that of the conventional technique will be described. In the third embodiment, fog, density and halftone density will be stabilized. The method of setting the developing potential obtained by the above method has been described. These control methods of the present invention are methods devised so as to exhibit the maximum capability of each image forming apparatus.

Incidentally, the control method in the state where the density is low according to the prior art is not a completely meaningless control method. This is because the lower the density, the lower the toner consumption. An image forming apparatus also needs a stable supply of high density,
On the other hand, there is a conflicting requirement that the consumption of toner should be as small as possible.

Therefore, in the present embodiment, a potential control method which executes the potential control method according to the prior art and the present invention, respectively, and enables a user or a serviceman of the image forming apparatus to arbitrarily adjust the image level will be described. I do.

In this embodiment, the potential control method according to the present invention shown in FIG. 8 and the potential control method according to the prior art shown in FIG. 7 are successively executed. The order does not matter. For convenience, when the potential control method of the present invention is a first potential control method and the potential control method of the prior art is a second potential control method, the controlled value and the target value are detected or set as shown in Table 2. It is set in advance. The respective parameters are denoted by reference numerals 1 and 2.

[0074]

[Table 2]

As described in the first to third embodiments, the first potential control method according to the present invention is controlled so that the values of all parameters become large. The parameters output during actual use of the image forming apparatus determine the image level, the applied voltage Vchg of the primary charger 4 which controls the dark area potential, the applied voltage Vlamp of the original illumination lamp 22 which controls the dark area potential, and the image level. This is the development potential VDC. In this embodiment, by changing these three parameters, the characteristics of the two control methods can be used in a distribution according to preference.

That is, in this embodiment, the distribution rate is defined as a parameter for numerically characterizing the two control methods. Here, the distribution ratio is shown as a percentage, named ε%, and 0% is the first
Only the control method of (1) uses parameters obtained by only the second control method for 100%. In other words, if the value is 50% or less, the priority is given to the parameter obtained by the first control method, and it can be said that the image level is set closer to stabilization of high density. On the other hand, if it is greater than 50%, the parameter is the priority obtained by the second control method, and although the density is low, the setting is to reduce the toner consumption. The distribution ratio ε may be opened to a user as a switch or input data (not shown) of the operation unit of the image forming apparatus, or may be operated by a serviceman as a switch or input data (not shown) inside the image forming apparatus. . Of course, it may be operated from outside via an electric interface.

In this embodiment, the third control is performed using the distribution ratio ε from the parameters obtained by the first and second control methods.
It is characterized by creating the parameters of

That is, the third parameter of this embodiment is defined as follows.

[0079]

(Equation 2) The third parameter defined in this way is always set between the first and second parameters, and since the three parameters are interlocked with each other, the characteristics of the first and second potential control methods are always maintained. , According to the distribution ratio ε.

As described in the above embodiments,
According to the present invention, it is possible to maximize the capability of each of the image forming apparatus main bodies and increase the image level. That is, the charge amount can be adjusted while giving the target value to the bright portion potential and using the maximum exposure amount of the image forming apparatus main body so as to reach the target value. The dark portion potential is a potential when the exposure unit is set to the minimum exposure amount while applying the charge amount determined by the light portion potential. In this way, the latent image contrast, which is the difference between the dark portion potential and the bright portion potential, can be obtained wider than in the prior art.
In addition, the target value of the light portion potential is 100 V or more, preferably 150 V or more.
By setting V or less, it is possible to achieve both a further increase in the latent image contrast and suppression of toner adhesion to the light portion potential.

In the present invention, the development potential of the developing means is also changed according to the latent image contrast, so that the potential control takes into account the halftone density.

Further, the third parameter obtained from the potential control for setting the target values for the dark part potential and the light part potential according to the prior art and the potential control according to the present invention are calculated, and the characteristics of each of the two potential controls are distributed. It is possible to output the image level that has.

[0083]

As described above, the image forming apparatus according to the present invention comprises a charging means for imparting a uniform charge on an electrophotographic photosensitive member, and a latent image by exposing the charged electrophotographic photosensitive member to light. An exposure unit for forming an image, a unit downstream of the exposure unit for measuring a potential on the electrophotographic photosensitive member, and a developing unit for visualizing a latent image on the electrophotographic photosensitive member. Means for activating the charging means while irradiating a predetermined exposure amount by the means, and having a photoconductor potential control means for determining the charging amount of the charging means so as to attain a desired bright portion potential. By using the maximum latent image contrast of each unit, minimizing density reduction and fogging, controlling the photoconductor potential at a high image level, it is possible to always obtain a high quality image stably. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic copying machine as one embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram schematically illustrating a configuration of a control unit around a control substrate for measuring a potential on a photosensitive drum.

FIG. 3 is a diagram illustrating an exposure amount / potential curve when photoconductors having different dark part potentials are used.

FIG. 4 is a diagram showing an exposure amount / potential curve when photoconductors having different exposure sensitivities are used.

FIG. 5 is a diagram illustrating an exposure dose-potential curve when photoconductors having different saturated bright portion potentials are used.

FIG. 6 is a diagram showing an exposure dose-potential curve when three types of photoconductors having different sensitivities and saturated bright portion potentials are used.

FIG. 7 is a flowchart showing a control procedure of a photoconductor potential in the related art.

FIG. 8 is a flowchart showing a control procedure of a photoconductor potential in the present invention.

FIG. 9 is a diagram showing an exposure / potential curve when the potential control means of the present invention is executed using three types of photosensitive members having different sensitivities and saturated bright portion potentials.

[Explanation of symbols]

2 Electrophotographic photoreceptor (photoreceptor drum) 4 Charging means (primary charger) 5 Exposure means (exposure device) 6 Potential sensor 7 Developing means (developing apparatus) 22 Exposure means (document illumination lamp) 28 Standard white plate 100 Control means (Control board)

Claims (8)

[Claims] A charging means for applying a uniform charge to the electrophotographic photosensitive member; an exposing means for exposing the charged electrophotographic photosensitive member to form a latent image; An image forming apparatus comprising: a unit for measuring a potential on the electrophotographic photoreceptor; and a developing unit for developing a latent image on the electrophotographic photoreceptor. An image forming apparatus comprising: a photoconductor potential control unit that operates the charging unit while irradiating the photosensitive member, and determines a charge amount of the charging unit so that a desired bright portion potential is obtained. 2. The method according to claim 1, wherein the determined charge amount of the charging unit is applied, and a potential on the photoconductor when the exposure unit irradiates a minimum exposure amount is a dark portion potential. 1 image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the predetermined exposure amount is a maximum exposure amount of the exposure unit. 4. An absolute value of the desired bright portion potential is 100 V
2. The image forming apparatus according to claim 1, wherein: 5. An absolute value of the desired bright portion potential is 150 V
The image forming apparatus according to claim 4, wherein: 6. The image forming apparatus according to claim 2, wherein an applied voltage of a developing potential applied to said developing unit is determined based on said bright portion potential and said dark portion potential. . 7. A charging means for imparting a uniform charge to the electrophotographic photoreceptor, an exposure means for exposing the charged electrophotographic photoreceptor to form a latent image, and a charging means provided downstream of the exposure means. An image forming apparatus comprising: a unit for measuring a potential on the electrophotographic photoreceptor; and a developing unit for developing a latent image on the electrophotographic photoreceptor. The charging means is operated while irradiating, the charge amount of the charging means is determined so as to have a desired light portion potential, and then the determined charge amount of the charging means is applied, and the exposure means A first photoreceptor potential control means for setting the potential on the photoreceptor when the minimum exposure amount is irradiated to a dark portion potential; and applying the charge amount of the charging means, and setting the minimum exposure amount by the exposure means. Adjust the dark area potential, which is the potential on the photoconductor when irradiated And a second photosensitive member potential control means for adjusting an exposure amount so as to obtain a predetermined bright part potential on the dark part potential. The charging means obtained by the first photosensitive body potential control means And a third charge amount is determined from the charge amount of the charging unit obtained by the second photoconductor potential control unit, and the exposure amount of the exposure unit obtained by the first photoconductor potential control unit is determined. An image forming apparatus that determines a third exposure amount from an exposure amount of the exposure unit obtained by the second photoconductor potential control unit. 8. A third developing potential is determined from a developing potential of the developing means obtained by the first photoconductor potential control means and a developing potential of the developing means obtained by the second photoconductor potential control means. The image forming apparatus according to claim 7, wherein: