JP2003207998A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for preventing nonuniformity in a charging pitch to reduce an electric discharge product and the amount of ozone generation, to obtain the image forming apparatus for normally developing an electrostatic latent image with a proper amount of toner in spite of the change of charging performance in a charging device and also to provide a tandem type image forming apparatus with which the life of a photosensitive drum is prolonged and the cartridge of the photosensitive drum is made usable for a long term. <P>SOLUTION: The image forming apparatus is provided with an image carrier body 2 for carrying the electrostatic latent image, a charging device 1 arranged so as to be brought into contact with the image carrier body, and a developing unit 3 for developing the electrostatic latent image with toner under application of DC voltage. Voltage obtained by superimposing an AC component on a DC component is applied to the charging device and the average charging potential Vhavg (V) of the image carrier body is adjusted to satisfy the range of (1). The frequency f (Hz) of the AC component is adjusted to be equal to or less than 2 kHz and also to satisfy (1) and (2). (1): (Vpc/f)×250+Vdc+50<Vhavg<(Vpc/f)×250+Vdc+200; (2): α<80×(Vpc/f)<SP>-1</SP>(wherein, Vpc is the linear velocity (mm/s) of the image carrier body, Vdc is the development DC voltage (V) of the charging device, and α is resolution (dpi)). <P>COPYRIGHT: (C)2003,JPO

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 provided with a charging device for charging a photosensitive drum or the like before electrostatic latent image formation.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a charging voltage composed of an AC component and a DC component is applied to a contact type roller charging member in order to charge a photosensitive drum before forming an electrostatic latent image. However, there is a problem that unevenness in the charging potential occurs at the drum linear velocity / frequency pitch on the photosensitive drum thus charged. In order to solve such a problem, various proposals have been made to define a frequency range and a drum linear velocity / frequency range.

For example, in JP-A-3-100674, it is necessary to satisfy Vp / L <f <n (limit frequency) in relation to AC voltage frequency f, roller speed Vpc, and roller contact width L. JP-A-3-100675. In the publication, the AC voltage frequency f is set to 1000 Hz or lower or 2500 Hz or higher, and in Japanese Patent Laid-Open No. 3-101764, f / Vp.
It proposes to satisfy c ≧ 5. In addition, JP-A-8
In Japanese Patent Publication No.-328360, the AC voltage + DC is applied to the first charger.
It is proposed that a voltage is applied and the generated charging pitch unevenness is made inconspicuous by applying a DC voltage to the second charger.

In order to make the unevenness of the charging pitch inconspicuous, it is necessary to reduce the drum linear velocity / frequency. When the linear velocity is high, the frequency must be simply increased. This leads to an increase in substances and ozone and easily causes contamination of the charging roller, the photosensitive drum, and the like. Also, when a halftone image was output after running, the required toner amount did not adhere and the density decreased. The above publication does not address this problem.

A case where the charging performance of the charging roller is deteriorated due to changes in use or environment will be described with reference to FIG. As shown in FIG. 8A, when the resistance value between the charging roller and the photosensitive drum increases due to long-term use (cumulative increase in the number of prints) and environmental changes, the charging performance deteriorates and the charging of the photosensitive drum is reduced. The potential Vh is reduced. On the other hand, due to the cumulative increase in the number of prints, the thickness of the photosensitive drum on the surface of the photosensitive drum is reduced, the photosensitive drum capacity is changed, and the charging potential of the photosensitive drum is increased as shown in FIG. After exposure, the potential Vl increases. As a result, the amount of toner attached to the photosensitive drum changes.

To address this problem, Japanese Unexamined Patent Publication No. 8-76561
In the publication, the voltage applied to the charging means is controlled to stabilize the charging potential Vh against changes in the operating environment. However, when the post-exposure potential Vl changes, the contrast potential changes,
As a result, the toner adhesion amount changes. Further, in Japanese Patent Laid-Open No. 6-35302, the fluctuation of the charging potential Vh due to the capacitance change of the photoconductor is corrected by the direct current detection, but the contrast potential fluctuates, and as a result, the toner adhesion amount changes. Further, in Japanese Patent Laid-Open No. 4-181962, in an image forming apparatus in which a bias voltage in which an AC bias is superimposed on a DC bias is applied to a charging member, only the AC component of the applied bias is controlled based on the output value of the potential detecting unit. However, since it is the DC bias that can directly control the charging potential Vh, the charging potential Vh cannot be corrected and stabilized.

Further, when the charging means is of a corona electrode type, it is general to detect the charging potential Vh and the post-exposure potential Vl, adjust the contrast potential and feed it back to the grid voltage Vgrid. -The amount of discharge products generated is larger than that of the charging roller, and at this time, in order to reduce the influence of surface deposits on the potential, polishing by cleaning must be intensified, and even if the above control is performed, the photosensitive drum etc. It was not possible to extend the life of the photoconductor. Further, in the tandem configuration, the amount of ozone / discharge products generated is quadrupled by simple calculation, so that it is difficult to stay and discharge inside the equipment, and the life of the photoconductor is shortened.

Further, in the past, when replacing the photosensitive drum cartridge, the replacement time is determined by the life of the photosensitive drum, not the charging roller. For models with low cost performance, a short replacement cycle does not cause a big problem, but it is high. In the model, it is desired to extend the life of the photosensitive drum and bring it closer to the life of the charging roller to prolong the cartridge replacement cycle. In particular, it has been found that the life of the photosensitive drum is shortened with the corona electrode in the image forming apparatus with the tandem structure, which was conceived to increase the cost performance, and when the charging roller is used with the tandem structure, the cartridge It is desired to extend the life of the photosensitive drum whose life is determined and to use the cartridge for a long time.

[0009]

SUMMARY OF THE INVENTION A first object of the present invention is to provide an image forming apparatus capable of preventing the generation of uneven charging pitch and reducing the amounts of discharge products and ozone. .

A second object of the present invention is to provide a high quality image because the electrostatic latent image can always be developed with an appropriate amount of toner even if the charging performance of the charging device changes due to long-term use or environmental changes. An object is to provide an image forming apparatus capable of forming an image.

A third object of the present invention is to provide an image forming apparatus having a tandem structure in which the life of the photosensitive drum is extended and the cartridge of the photosensitive drum can be used for a long time when a charging roller is used for the charging device. Is.

[0012]

In order to achieve the above object, a first image forming apparatus according to the present invention includes an image carrier for carrying an electrostatic latent image and a moving body before the formation of the electrostatic latent image. A charging device arranged in contact with the image carrier to charge the image carrier, and a developing device for applying a DC voltage to the toner to develop the electrostatic latent image on the image carrier. And an average voltage Vhavg (V) of the image carrier is in the range of the following expression (1) in an image forming apparatus in which a voltage in which an AC component is superimposed on a DC component is applied to the charging device. It is characterized in that it is adjusted to be satisfactory. (Vpc / f) × 250 + Vdc + 50 <Vhavg <(Vpc / f) × 250 + Vdc + 200 (1) where Vpc: linear velocity (mm / s) of the image carrier f: of the AC component 2 kHz or less at frequency (Hz) Vdc: Development DC voltage (V) of the developing device

According to this image forming apparatus, unevenness in the charging pitch occurs due to the difference in height of the charging potential, and the difference in height is 2 ×.
Since (Vpc / f) × 250 (V), uneven charging pitch can be prevented by setting the average charging potential Vhavg in a range satisfying the expression (1) in consideration of occurrence of fogging.

In a second image forming apparatus according to the present invention, the image bearing member carrying an electrostatic latent image and the image bearing member for charging the moving image bearing member before the electrostatic latent image is formed are charged. The charging device is arranged so as to be in contact with the carrier, and the developing device for developing the toner of the electrostatic latent image on the image carrier by applying the DC voltage is provided, and the AC component is superimposed on the DC component. In an image forming apparatus in which a voltage is applied to the charging device, the frequency f (Hz) of the AC component is 2 kHz or less and is adjusted so as to satisfy the following formulas (1) and (2). Characterize. (Vpc / f) × 250 + Vdc + 50 <Vhavg <(Vpc / f) × 250 + Vdc + 200 (1) α <80 × (Vpc / f) ⁻¹ (2) where Vpc: the image carrier Linear velocity (mm / s) Vhavg: average charging potential (V) of the image carrier Vdc: development DC voltage (V) of the developing device α: resolution (dpi)

According to this image forming apparatus, unevenness in the charging pitch occurs due to the height difference of the charging potential, and the height difference is 2 ×.
Since (Vpc / f) × 250 (V), the average charging potential Vhavg is set in a range satisfying the expression (1) in consideration of occurrence of fogging, and the range is satisfied by the expression (2). Can be within a range that is not actually harmful in relation to Vpc / f. In addition, the frequency f of the AC component is 2 kHz.
By setting it to be equal to or less than z, it is possible to reduce the generation amount of discharge products and ozone, and to prevent the density reduction of the halftone image formed after running.

The average charging potential Vhavg of the image carrier in the first and second image forming apparatuses can be measured by a surface potential meter in an unexposed state after the surface of the image carrier is charged by the contact charging means. The spot diameter measured by this surface electrometer is as large as several mm.

Further, the third image forming apparatus according to the present invention comprises: a photosensitive member on which an electrostatic latent image is formed by exposure; and the photosensitive member for charging the electrostatic latent image before the electrostatic latent image is formed. In an image forming apparatus including a charging device having a contact type charging member arranged so as to be in contact with a photoconductor, and a developing means for developing an electrostatic latent image with a toner to form an image, a direct current is applied to the contact type charging member. Applying means for applying a bias voltage; charging potential detecting means for detecting the charging potential of the surface of the photoconductor after being charged by the contact type charging member and the potential of the surface of the photoconductor after exposure; The application unit is controlled to apply the contact type charging member under a preset application condition to charge the photoconductor, and the output value of the charging potential detection unit at that time and the output of the charging potential detection unit after exposure Based on value There characterized by comprising a control means for controlling a voltage applied to the applying means during image formation, the by.

According to this image forming apparatus, even if the charging performance of the contact type charging member changes due to long-term use or changes in the environment, the charging of the photosensitive member is controlled by controlling the voltage applied to the contact type charging member. Since the performance can be stabilized without fluctuation, the electrostatic latent image can always be developed with a proper amount of toner, and a high-quality image can be formed.

Further, the fourth image forming apparatus according to the present invention comprises a photoconductor on which an electrostatic latent image is formed by exposure, and the above-mentioned photoconductor for charging the photoconductor before the formation of the electrostatic latent image. In an image forming apparatus including a charging device having a contact type charging member arranged so as to be in contact with a photoconductor, and a developing means for developing an electrostatic latent image with a toner to form an image, a direct current is applied to the contact type charging member. Applying means for applying a bias voltage in which an AC bias is superimposed on the bias, and charging potential detecting means for detecting the charging potential of the surface of the photoconductor after being charged by the contact type charging member and the potential of the surface of the photoconductor after exposure. And controlling the application means at the time of non-image formation to apply the charge to the contact type charging member under a preset application condition to charge the photoconductor, and the output value of the charging potential detection means at that time and the exposure value after exposure. band Based on the output value of the potential detection means, applied DC voltage of said applying means during image formation or, characterized in that it and a control means for controlling the AC applied current and applied DC voltage.

According to this image forming apparatus, even if the charging performance of the contact type charging member changes due to long-term use or changes in the environment, the DC applied voltage to the contact type charging member, or the DC applied voltage and the AC By controlling the applied current, the charging performance of the photoconductor can be stabilized without fluctuation, so that the electrostatic latent image can always be developed with an appropriate amount of toner and a high-quality image can be formed.

In the above-described third and fourth image forming apparatuses, a developing DC bias voltage for setting a predetermined contrast potential from the output value of the charged potential detecting means after exposure is set, and a predetermined fog prevention potential is set. By controlling the applying means so that the applied potential is obtained, for example, the charging potential Vh and the post-exposure potential Vl are detected during non-image formation, and the direct-current developing bias for changing the post-exposure potential Vl to a predetermined contrast potential. The charging performance of the photoconductor can be stabilized by setting the voltage and controlling it by the control means so that it becomes a potential to which a predetermined antifogging potential is added.

Further, a fifth image forming apparatus according to the present invention comprises an exposing means for exposing by pulse width modulation based on image information, and a photoreceptor on which an electrostatic latent image is formed by the exposing by the exposing means. A charging device having a contact type charging member arranged so as to contact the photoconductor to charge the photoconductor before forming an electrostatic latent image, the contact type charging member. An applying means for applying a DC bias voltage to the charging means, a charging potential detecting means for detecting a charging potential of the surface of the photoconductor after being charged by the contact type charging member and a potential of the surface of the photoconductor after exposure, and the contact type A developing unit having a rotating sleeve for developing toner after exposure of at least a part of the charged area of the photoconductor after being charged by a charging member, and a toner adhesion amount in the developed area are detected. And a toner adhesion amount detecting means for controlling the applying means at the time of non-image formation to apply the toner to the contact type charging member under preset application conditions to charge the photoconductor, and the charging potential detecting means at that time First control means for controlling the applied voltage of the applying means during image formation based on the output value and the output value of the charged potential detecting means after exposure, and for controlling the applying means and the developing means during non-image formation. After applying the voltage to the contact type charging member under a preset application condition to charge the photoconductor, the rotation of the sleeve at the time of image formation is determined based on the output value of the toner adhesion amount detection means at the time of toner development. A second control means for controlling at least one of the number, Vac, and pulse width modulation of the exposure means.

According to this image forming apparatus, even if the charging performance of the contact type charging member changes due to long-term use or changes in the environment, the voltage applied to the contact type charging member is controlled to charge the photoreceptor. Since the performance can be stabilized without fluctuation, the electrostatic latent image can be always developed with an appropriate amount of toner, and the toner adhesion amount is detected, and the rotation speed of the sleeve, Vac (applied to the rotating sleeve of the developing means). Since at least one of the developing AC voltage) and the pulse width modulation is controlled, even if the developing property varies due to the Q / M distribution of the toner, the adhesion force to the carrier, the change in the particle size distribution of the toner, etc., the toner adhesion amount can be controlled. The toner adhesion amount can be kept constant, and a high-quality image can be formed.

Further, a sixth image forming apparatus according to the present invention comprises an exposing means for exposing by pulse width modulation based on image information, and a photoreceptor on which an electrostatic latent image is formed by the exposing means. A charging device having a contact type charging member arranged so as to contact the photoconductor to charge the photoconductor before forming an electrostatic latent image, the contact type charging member. Means for applying a bias voltage in which an AC bias is superimposed on a DC bias, and a charging potential for detecting the charging potential of the surface of the photoconductor after being charged by the contact type charging member and the potential of the surface of the photoconductor after exposure. A detecting means; a developing means having a rotating sleeve for developing a toner after exposing at least a part of a charged area of the photosensitive member after being charged by the contact type charging member; Toner adhesion amount detection means for detecting the amount of toner adhesion in the image area, and controlling the application means during non-image formation to apply to the contact type charging member under preset application conditions to charge the photoconductor, At the time of image formation, a direct current applied voltage or a direct current applied voltage and an alternating current applied current of the applying means are controlled based on the output value of the charging potential detecting means at this time and the output value of the charging potential detecting means after exposure. The control unit and the applying unit and the developing unit during non-image formation are applied to the contact type charging member under a preset application condition to charge the photoconductor, and then the toner adhesion amount at the time of toner development. Based on the output value of the detection means, the rotational speed of the sleeve, Vac
And second control means for controlling the pulse width control of the exposure means.

According to this image forming apparatus, even if the charging performance of the contact type charging member changes due to long-term use or changes in the environment, a DC applied voltage to the contact type charging member, or a DC applied voltage and an AC By controlling the applied current, the charging performance of the photoconductor can be stabilized without fluctuation, so that the electrostatic latent image can always be developed with an appropriate amount of toner, and the toner adhesion amount can be detected and the rotational speed of the sleeve, Since at least one of Vac and pulse width modulation is controlled, the toner adhesion amount can be kept constant even if the developing property changes due to changes in the toner Q / M distribution, carrier adhesion force, toner particle size distribution, etc. The adhered amount is stable, and a high-quality image can be formed.

In the fifth and sixth image forming apparatuses described above, a developing DC bias voltage for setting a predetermined contrast potential from the output value of the charging potential detecting means after exposure is set, and a predetermined fog is set. It is preferable that the applying unit is controlled so as to have a potential to which a preventive potential is added, and then at least one of the developing unit and the exposing unit is controlled.

In each of the third to sixth image forming apparatuses described above, the contact type charging member is provided with a roller member, and a tandem structure is used so that a color image can be formed, and a tandem using the charging roller member. By performing the above-mentioned control in the configuration, the amount of discharge products and the like attached to the photoconductor can be reduced compared to when a corona electrode is used, and cleaning conditions can be relaxed, so the life of the photoconductor can be extended. Also, the charging performance of the photoconductor can be extended to the life of the photoconductor. Therefore, when the components including the photoconductor and the charging device are configured to be housed in the cartridge that is detachable from the image forming apparatus, the cartridge of the photosensitive drum can be used for a long time.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The first and second embodiments of the present invention will be described below.
Embodiments will be described with reference to the drawings. <First
Embodiment>

FIG. 1 is a schematic side view of the image forming apparatus according to the first embodiment. The image forming apparatus of FIG. 1 includes a photosensitive drum 2 on which a photosensitive layer is formed on the outer peripheral surface thereof and an electrostatic latent image is formed by laser exposure 6, and a photosensitive drum 2 which rotates at a constant rotation speed in a rotation direction R in the figure. Roller 1 of the charging device 12 that charges the surface while sliding on the surface
A developing device 3 having a developing sleeve 3a that rotates while sliding on the surface of the photosensitive drum 2 to develop an electrostatic latent image on the surface of the photosensitive drum 2 with toner to form a toner image; A transfer unit 4 for transferring the toner image remaining on the photosensitive drum 2, a fixing unit 7 for fixing the toner image transferred on the recording medium S, and the like. Equipped with.

The image forming apparatus shown in FIG.
Bias power source 10 of the charging device 12 for applying an AC bias voltage in which a DC component is superimposed with an AC component of frequency f (Hz) to the charging roller 1 to uniformly charge the toner, and a photosensitive member after charging and laser exposure. A surface potential meter 8 for measuring the surface potential of the drum 2, a developing bias power source 11 for applying a developing bias voltage in which an AC component is superimposed on a DC component to the peripheral surface of the developing sleeve 3a, and a surface potential meter 8 are used for measurement. The control unit 9 controls the charging device 12 and the developing device 3 based on the measured value of the surface potential of the photosensitive drum 2. The surface potential meter 8 can measure both the charging potential (Vh) and the post-exposure potential (Vl).

In the control unit 9 of FIG. 1, the measured value Vhavg of the surface potential of the photosensitive drum 2 measured by the surface electrometer 8 is expressed by the following equation (1).
Bias power supply 10 of the charging device 12 so that it is within the range of
To control.

(Vpc / f) × 250 + Vdc + 50 <Vhavg <(Vpc / f) × 250 + Vdc + 200 (1) where Vpc: linear velocity of the photosensitive drum 2 (mm / s) f: charging roller Frequency (Hz) of AC component of bias voltage applied to 1 Vdc: Development DC voltage (V) of development bias voltage applied to peripheral surface of development sleeve 3a

Although the frequency of the AC component of the bias voltage applied to the charging roller 1 has been conventionally adjusted to a frequency at which high resolution does not cause uneven charging pitch, in the above formula (1), uneven charging pitch causes a charging potential. The difference in height is 2 × Vpc / f × 250 (V). Therefore, the average charging potential is set in consideration of the occurrence of fog. By setting the average charging potential Vhavg in a range that satisfies the expression (1), uneven charging pitch can be prevented. By adjusting the DC voltage of the bias power supply 10 of the charging device 12, the average charging potential Vhavg
Can be changed.

Further, the control unit 9 in FIG. 1 controls the frequency f (Hz) of the AC component of the bias voltage applied to the charging roller 1.
Controls the bias power supply 10 of the charging device 12 so as to satisfy the above equation (1) and the following equation (2).

Α <80 × (Vpc / f) ⁻¹ (2) where α: resolution (dpi)

As described above, the uneven charging pitch occurs due to the difference in height of the charging potential, and the difference in height is 2 × (Vpc / f).
Since it is × 250 (V), the average charging potential Vhavg is set in the range that satisfies the formula (1) in consideration of the occurrence of fogging, but by further satisfying the range of the formula (2), the resolution is Vpc. In terms of the relationship with / f, dot reproduction can be set within a range that does not actually cause harm. The frequency f of the AC component of the bias voltage applied to the charging roller 1 can be changed by adjusting the AC voltage generator of the bias power supply 10 of the charging device 12.

Next, the image forming process in the image forming apparatus of FIG. 1 will be described. Rotate the photosensitive drum 2 in the rotation direction R in the figure.
The surface of the charging roller 1 is charged to a charging potential Vh, which is a relatively strong negative voltage, while being rotated to. Next, the surface of the photosensitive drum 2 is exposed by laser exposure means (not shown).
By performing the laser exposure 6 by the laser light from, the potential on the surface of the exposed photosensitive layer of the photosensitive drum 2 changes to the exposure potential Vl. As a result, an electrostatic latent image is formed on the photosensitive drum 2.

After that, when the photosensitive drum 2 passes the position of the surface electrometer 8, its surface potential is measured. next,
The developing sleeve 3a of the developing device 3 rotates, and the toner charged to a negative potential is supplied while the developer slides on the surface of the photosensitive drum 2, and the toner is adsorbed to the surface of the photosensitive drum 2. This adsorption is performed by applying a developing AC bias while holding the developing device 3 containing toner at the developing DC bias potential Vdc. Since the surface portion of the photosensitive drum 2 which has been exposed to the exposure potential Vl has a potential higher than the developing DC bias potential Vdc by the contrast potential (Vdc-Vl), toner having a negative charge (developing DC bias potential Vdc) is used. Are attracted toward the photosensitive drum 2 by the action of an electric field. Therefore, the toner adheres to the exposed surface of the photosensitive drum 2. In this way, a toner image is formed from the electrostatic latent image on the photosensitive drum 2.

The toner image formed on the photosensitive drum 2 is
When the recording medium S such as recording paper conveyed from the direction a in FIG. 1 passes between the transfer unit 4 and the photosensitive drum 2, it is transferred onto the recording medium S by the transfer unit 4. The recording medium S to which the toner image is transferred is then fixed by the fixing device 7 and then discharged to the outside of the apparatus. The surface of the photosensitive drum 2 after the transfer to the recording medium S is then cleaned by wiping off the residual toner by the photosensitive member cleaning blade 5, and then the surface of the photosensitive drum 2 is discharged to remove the charge. The surface of is made into an electrically uniform initial state.

In the image formed on the recording medium as described above, the photosensitive drum 2 is in the range satisfying the above expression (1).
By controlling the average charging potential Vhavg, the unevenness of the charging pitch is not observed and a high quality image can be obtained.

Further, by controlling the frequency f of the AC component of the bias voltage applied to the charging roller 1 within a range satisfying the above-mentioned formula (1), the amount of discharge products and ozone generated can be reduced. Therefore, it is possible to prevent the charging roller 1, the photosensitive drum 2, the developing sleeve 3a and the like from being contaminated. Also,
By satisfying the range of Expression (2), the resolution of the formed image does not decrease.

[0042]

EXAMPLES The image forming apparatus of FIG. 1 will be further described below with reference to Examples 1 and 2 and Comparative Examples 1, 2 and 3. 2 is a schematic diagram showing the relationship between Vhavg and Vdc in the case of Example 1, FIG. 3 is a schematic diagram showing the relationship between Vhavg and Vdc in the case of Comparative Example 2, and FIG. FIG. 6 is a diagram showing a relationship between a circumferential distance of a photosensitive drum and Paschen's discharge voltage during charging in Examples and Comparative Examples. FIG. 5 shows the potential fluctuation pitch (Vpc / f) and the screen resolution α in the second embodiment.
It is a figure which shows the relationship of.

First, the relationship between the frequency f of the AC component of the AC bias voltage and the pitch unevenness will be described with reference to FIG.
In FIG. 1, the diameter of the photosensitive drum 2 is 60 mm, the diameter of the charging roller 1 is 14 mm, Vpc is 200 mm / s, and f is 0.5 kHz, and a direct current component and an alternating current component of frequency f (Hz) are applied to the charging roller 1. When the superimposed AC bias voltage of 1.6 kV is applied, the charging potential is determined on the output side as shown by the circle A in FIG. 4, and the charging potential fluctuates in the cycle of the AC component. In FIG. 4, the outlet side is the outlet side of the charging roller, and the inlet side is the entrance side to the charging roller.

In FIG. 4, when the frequency f of the AC component of the AC bias voltage is 0.5 kHz, the potential fluctuation amount is about 20.
It is 0V, but if the frequency is changed to 1kHz, the fluctuation is about 1
It becomes 00V. Also, 50V at 2kHz and 2 at 4kHz
It becomes 12.5 V at 5 V and 8 kHz. Frequency f is 0.5
When the frequency is kHz, the photosensitive drum advances by 0.4 mm in one cycle, but 0.4 mm near Vdc of the Paschen curve in FIG.
The discharge potential difference corresponding to the width is the potential fluctuation amount. That is, if the frequency f is doubled, a discharge potential difference corresponding to a width of 0.2 mm is obtained.

As a result of visually confirming the sample of the recording medium on which the image is formed, it is 400 dp at the frequency f0.5 kHz.
With respect to the i halftone image input, only the lines having a pitch of 0.4 mm are developed. On the other hand, the frequency is 1
When the frequency is raised to kHz, a 0.2 mm pitch period is confirmed, but dots between pitches are also recognized. Furthermore,
Dots are surely formed when the frequency is raised to 2 kHz and 0.1 mm
If the pitch period is looked closely, it is improved to the extent that it can be seen. Three
The pitch is unknown at frequencies above kHz. As described above, when the frequency f of the AC component of the AC bias voltage applied to the charging roller 1 is increased, the charging pitch unevenness disappears, but then, the amount of discharge products and ozone generated increases.

<Example 1>

In FIG. 1, the linear velocity Vp of the photosensitive drum 2 is
c is set to 200 mm / s, and the frequency f of the AC component of the bias voltage applied to the charging roller 1 is set to 500 Hz, which produces a small amount of discharge products and ozone, and Vpc / f
× 250 = 100. At this time, the above formula (1) is
Vdc + 150 <Vhavg <Vdc + 300.

As shown in FIG. 2, the average charging potential Vhavg of the photosensitive drum 2 is set within the range of the formula (1) to prevent fogging and the exposure lowers the charging potential to the developing DC bias potential Vdc or less. Under this condition, the density change of the halftone image was examined after running for 5 kP at a printing rate of 5%. As a result, the density did not decrease and the charging pitch unevenness was not noticeable.

On the other hand, as Comparative Example 1, Vhavg is Vdc
When +150 (V) and f is set to 3 kHz,
The charge pitch unevenness is not noticeable because the frequency f is high, but when the density change of the halftone image was examined after running for 5 kP at a printing rate of 5%, a density decrease occurred. In addition, filming occurs in which toner adheres to the photosensitive drum.

As Comparative Example 2, Vhavg is Vdc
When the voltage is set lower than +150 (V) by 50 V and the other conditions are the same as those in the first embodiment, the potential in the low (low) region of the charging potential Vh is the same as Vdc, as shown in FIG. And a fogging occurred. Also, Vhavg is Vdc +
When the voltage is set higher than 300 (V) by 100 V, the potential in the high region of the charging potential Vh is Vdc + 500.
In some cases, even after exposure, the potential did not drop below Vdc even after exposure, and toner did not adhere.

<Example 2>

As in Example 1, Vpc was 200 mm /
s and f are set to 500 Hz, (Vpc / f) × 250
= 100 and the above equation (1) is Vdc + 150 <Vhavg
<Vdc + 300. As a result, fogging is prevented and the potential is lowered to Vdc or less by exposure. Furthermore, within the range of this formula, f is 2kHz, 1kHz, 500H
In the range where the resolution α satisfies the above equation (2), that is, in the C-2 region below the bold line in FIG. 5, instead of z and 333 Hz, the exposure potential is sufficiently Vdc even in the portion where the charging potential Vh is high. It decreased to the following level, and the dot reproduction was good.

On the other hand, in the range where the resolution α does not satisfy the above equation (2), that is, in the case of the comparative example 3 which is the C-1 region above the thick line in FIG. 5, the dot diameter is small in the portion where the charging potential Vh is high. Then, the potential of the exposed portion did not drop below Vdc and the dots could not be reproduced.

Further, f is 3 kHz (potential fluctuation pitch Vp
When c / f = 0.067 mm), the density was reduced in the whole halftone image when running 5000p, but when f was 500 Hz and 333 Hz,
Even after running at 5000p, the density did not decrease in the whole halftone image.

Generally, an image forming apparatus such as a copying machine or a printer is equipped with a function of changing the image resolution depending on the type of the original. For an original mainly composed of character images, the resolution is increased and sharp edges are reproduced in detail. In addition, the resolution is lowered in the photographic image so that the gradation is smoothly expressed, and in the prior art, the frequency of the AC component of the bias voltage applied to the charging roller is adjusted to a frequency that does not cause uneven charging pitch at high resolution. However, since it is not necessary to forcefully raise the frequency in an image with reduced resolution, the frequency f is adjusted so as to satisfy the equations (1) and (2) as in the above-described second embodiment. By adjusting the frequency according to the image resolution, it is possible to prevent the occurrence of density decrease in the halftone image, and it is possible to set the frequency to a lower level. We can reduce the generation amount of emissions.

<Second Embodiment>

FIG. 6 is a diagram showing a schematic structure of a tandem color image forming apparatus according to the second embodiment.
The image forming apparatus of FIG. 6 includes an image forming system (100Y, 100M, 100C, 100K) of four colors (Y, M, C, K) and an intermediate transfer belt system. As shown in FIG. 6, a four-color image forming system (yellow color component 100Y, magenta color component 100M, cyan color component 100C, black color component 10) is used.
Although the image formation of each color is performed at 0K), the configuration of the image formation system 100K for the black color component will be described together with the operation.

Photosensitive drum 2 in image forming system 100K
K rotates in the rotation direction R in the figure, and charges the surface of the photosensitive drum 2K to a charging potential which is a relatively strong negative voltage by the charging roller 1K arranged so as to contact the surface of the photosensitive drum 2K. Next, the charged photosensitive drum 2K is
Laser exposure 6 by laser light from the exposure unit 22 (FIG. 7)
When the surface of the photosensitive drum 2K is exposed with K, the potential of the exposed portion changes to the exposure potential because the photosensitive layer film is formed on the photosensitive drum 2K. As a result, the photosensitive drum 2
An electrostatic latent image consisting of dots is formed on K.

The developing device 3K has the same construction as that of the developing device 3 shown in FIG. 1, and a developing sleeve similar to the developing sleeve 3a shown in FIG. 1 rotates and slides on the surface of the photosensitive drum 2K to develop a developing bias power source. 21 (FIG. 7) supplies toner charged to a negative potential, and this toner is adsorbed on the surface of the photosensitive drum 2K. This adsorption is performed by applying a developing AC bias while holding the developing device 3K containing black toner at the developing DC bias potential. The surface portion of the photosensitive drum 2K that has been exposed to the exposure potential is
Since the contrast DC potential is higher than the development DC bias potential, the negatively charged toner is attracted toward the photosensitive drum 2 by the electric field effect. Therefore, the toner adheres to the exposed surface of the photosensitive drum 2K. In this way, a toner image is formed from the electrostatic latent image on the photosensitive drum 2K.

This toner image is transferred to the intermediate transfer belt 150 by the primary transfer roller 4K, and the surface of the photosensitive drum 2K after the transfer is the photosensitive member cleaning blade 5.
The residual toner is wiped off and cleaned by K. Then, the surface of the photosensitive drum 2K is discharged to remove the history, and the surface of the photosensitive drum 2K is brought into an electrically uniform initial state.

In the same manner as the photosensitive drum 2K, the electrostatic latent image is developed on each of the photosensitive drums 2C, 2M and 2Y with the toners of C, M and Y to form a toner image. The image forming system 100Y for the yellow color component, the image forming system 100M for the magenta color component, and the image forming system 100C for the cyan color component.
Has the same configuration as that of the above-described image forming system 100K, the same portions are denoted by the same reference numerals, and the last Y, M, and C are used to distinguish them.

As shown in FIG. 6, the intermediate transfer belt system includes an intermediate transfer belt 150, an intermediate transfer belt support roller 90, and
100, an intermediate transfer belt driving roller 110, an intermediate transfer belt tension roller 120, a secondary transfer backup roller 70, and a secondary transfer roller 80 facing the secondary transfer backup roller 70.

When the intermediate transfer belt drive roller 110 is rotated by a power not shown, the intermediate transfer belt 150 is rotated.
Moves in the direction AA in FIG. 1 in synchronism with each rotation of the photosensitive drums 2Y, 2M, 2C, and 2K. In this order of progress, the yellow color component in the color image between the photosensitive drum 2Y and the primary transfer roller 4Y. Toner image is transferred to the photosensitive drum 2M
Image of the magenta color component is transferred between the primary transfer roller 4M and the primary transfer roller 4M, the toner image of the cyan color component is transferred between the photosensitive drum 2C and the primary transfer roller 4C, and the primary transfer image is transferred to the photosensitive drum 2K. The black toner image is transferred to and from the roller 4K. The intermediate transfer belt 150 to which these four color components have been transferred passes between the secondary transfer roller 80 and the secondary transfer backup roller 70, but at this time, between the secondary transfer roller 80 and the intermediate transfer belt 150. The image on the intermediate transfer belt 150 is secondarily transferred onto a recording medium (not shown) such as a recording sheet supplied at a timing. An image is thus formed on the recording medium, and the image formed on the recording medium is fixed and becomes the final image.
The intermediate transfer belt 150 after the secondary transfer is cleaned by the intermediate transfer cleaning blade 50, and the next image transfer can be performed.

FIG. 7 is a block diagram relating to control of the image forming apparatus of FIG. As shown in FIG. 7, the image forming apparatus of FIG. 6 has a surface electrometer 1 capable of measuring the surface potential of each of the photosensitive drums 2K, 2C, 2M and 2Y after charging and after exposure.
8, a bias power source 20 for applying a DC bias voltage or a bias voltage obtained by superimposing an AC bias on a DC bias to each charging roller 1K, 1C, 1M, 1Y, and each developing unit 3K, 3C, 3M, 3Y A developing bias power source 21 for applying a developing bias voltage to the sleeve, and pulse width modulation based on image information for each laser exposure 6K, 6
An exposure unit 22 that performs C, 6M, and 6Y, and a toner adhesion detection unit 23 that detects the amount of toner adhesion in the developing area of each photosensitive drum after toner development by each developing device are provided. The toner adhesion detector 23 can be composed of, for example, an optical sensor. This optical sensor is installed at a position where the toner adhesion amount on the intermediate transfer belt 150 can be detected, and it is detected when the pressure of the secondary transfer roller 80 is released.

The image forming apparatus of FIG. 6 further receives the measured values from the surface electrometer 18 and the toner adhesion detector 23, and based on these input values, the bias power source 2
0, a developing bias power source 21, and a control unit 19 for controlling the exposure unit 22. The control unit 19 controls the following,
,,It can be performed.

When a DC bias voltage is applied to each charging roller from the bias power source 20, the charging potential Vh and the post-exposure potential Vl are detected at the time of non-image formation, and the development direct current is set to change the post-exposure potential Vl to a predetermined contrast potential. The bias voltage is set, and the DC bias voltage of the bias power supply 20 is controlled so that the potential becomes a potential to which a predetermined anti-fogging potential is added.

When an AC bias voltage is superimposed on the DC bias voltage from the bias power source 20 and applied to each charging roller, the charging potential Vh and the post-exposure potential Vl are detected during non-image formation, and the post-exposure potential Vl provides a predetermined contrast. The developing DC bias voltage for setting the potential is set, and the bias power supply 20 is set to a potential to which a predetermined fog prevention potential is added.
The DC bias voltage, or the DC bias voltage and the AC bias current are controlled.

When a DC bias voltage is applied from the bias power source 20 to each charging roller, the charging potential Vh and the post-exposure potential Vl are detected during non-image formation, and the direct-current development is performed to change the post-exposure potential Vl to a predetermined contrast potential. The bias voltage is set, and the DC bias voltage of the bias power supply 20 is controlled so that the potential becomes a potential to which a predetermined anti-fogging potential is added. Next, the toner adhesion amount on the belt is detected, and the sleeve rotation speed of each developing device, Vac, and pulse width modulation (P
WM). The former control stabilizes the potential of the photosensitive drum, and the latter control stabilizes the toner adhesion amount.

When an AC bias voltage is superimposed on the DC bias voltage from the bias power source 20 and applied to each charging roller, the charging potential Vh, the intermediate potential Vm, and the post-exposure potential Vl are detected during non-image formation, and the intermediate potential Vm and Post-exposure potential V
A developing DC bias voltage for setting a predetermined contrast potential from 1 is set, and a DC bias voltage of the bias power source 20 is set so that the potential becomes a potential to which a predetermined fog prevention potential is added.
Alternatively, the DC bias voltage and the AC bias current are controlled. Next, the toner adhesion amount on the belt is detected, and the sleeve rotation speed of each developing device, Vac, and pulse width modulation (P
WM). The former control stabilizes the potential of the photosensitive drum, and the latter control stabilizes the toner adhesion amount.

By the above or control, even if the charging performance of each charging roller changes due to long-term use or environmental changes, it is possible to stabilize the charging performance of each photosensitive drum without fluctuation. Further, by the above control or, even if the developing property is changed (due to the Q / M distribution of the toner, the adhesive force to the carrier, the change in the particle size distribution of the toner), the toner adhesion amount can be made constant.

Further, in the case of the image forming apparatus having the tandem structure as shown in FIG. 6, by using the charging roller and performing the above-mentioned respective controls, the discharge to each photosensitive drum is increased as compared with the case where the corona electrode is used. Since the amount of products and the like attached is reduced and the cleaning conditions can be relaxed, the life of the photosensitive drum can be extended, and the charging performance of the photosensitive drum can be extended to the life of the charging roller. Therefore, when the photosensitive drum and the charging roller are housed in the cartridge and the cartridge is configured to be detachable from the image forming apparatus, the life of the photosensitive drum is extended to the life of the charging roller, so that the cartridge can be used for a long period of time.

As described above, the control section 19 of FIG.
Even if the charging performance of each charging roller changes due to long-term use or changes in the environment, the bias power source 20 is controlled, the voltage applied to each charging roller is controlled, or the sleeve rotation of each developing device is controlled. By controlling the number, Vac, and pulse width modulation (PWM) in the exposure unit, the charging performance of each photosensitive drum can be stabilized without fluctuation, and an electrostatic latent image can always be developed with an appropriate amount of toner, and high quality is achieved. Images can be formed.

[0073]

Embodiments Next, each of the above-mentioned controls in the image forming apparatus shown in FIGS. 6 and 7 will be described with reference to Embodiments 3, 4, 5, and 6, respectively.

<Example 3>

The setting conditions of Example 3 are as follows. -Each photosensitive drum: outer diameter 60 mm, drum surface speed: 21
0 mm / s ・ Each charging roller: A cylindrical body in which an elastic body with an outer diameter of 14 mm and a length of 330 mm is combined around a stainless steel cored bar with an outer diameter of 8 mm ・ Initial application condition to each charging roller: DC-1350V

The optimum potential of each photosensitive drum was adjusted as follows.

(A) At the time of non-image formation, a predetermined constant voltage is applied to each charging roller from a bias power source to charge each photosensitive drum, and the charging potential Vh after solid exposure and the potential Vl after exposure are measured.

(B) The developing direct current bias Vdc is set by the developing bias power source 21 to a potential obtained by adding the contrast potential (500 V) to the post-exposure potential Vl.

(C) The charging potential Vh is corrected and set to a potential obtained by adding the fogging prevention voltage (150 V) to the developing DC bias Vdc.

(D) From the predetermined constant voltage and the charging potential Vh measured by each surface electrometer 18 at that time, the applied voltage for setting the corrected charging potential Vh in (c) is calculated.

(E) The calculated applied voltage value is fed back to the bias power source 20 to adjust the bias voltage applied to each charging roller. As a result, a stable and optimal charging potential is always obtained during image formation.

In order to obtain the charging potential Vh corrected in (c) above, the control unit 19 is composed of a CPU, and the applied voltage of the bias power source 20 and the resistance data are stored in the CPU.
The corrected applied voltage can be determined by collating with the estimated resistance value obtained from the measured Vh. Alternatively, the same operation may be performed with two or more predetermined applied voltages, and the applied voltage for obtaining the corrected Vh may be calculated from the difference between the applied voltages and the measured Vh difference.

<Example 4>

The setting conditions of the fourth embodiment are as follows: initial application condition to each charging roller is DC-750V, AC 2 kHz, 5 mA.
Same as Example 3 except that

The optimum potential of each photosensitive drum was adjusted as follows.

(A) At the time of non-image formation, a predetermined DC constant voltage and AC constant current are applied from the bias power source 20 to each charging roller for charging, and the charging potential Vh after solid exposure and the potential Vl after exposure are measured.

(B) The developing bias power source 21 sets the developing DC bias Vdc to a potential obtained by adding the contrast potential (500 V) to the post-exposure potential Vl.

(C) The charging potential Vh is corrected and set to a potential obtained by adding the fogging prevention voltage (150 V) to the developing DC bias Vdc.

(D) From the predetermined constant voltage and the charging potential Vh measured by each surface electrometer 18 at that time, the applied voltage for setting the corrected charging potential Vh in (c) is calculated.

(E) The calculated applied voltage value is fed back to the bias power source 20 to adjust the DC bias voltage to each charging roller. As a result, a stable and optimal charging potential is always obtained during image formation. Alternatively, the DC bias voltage and the AC bias current may be adjusted.

When the control unit 19 is composed of the CPU as described above, the data of the DC applied voltage and the resistance of the bias power supply 20 are stored in the CPU, and the data is compared with the estimated resistance value obtained from the measured Vh. The correction applied voltage can be determined. The AC bias current can be calculated from a current value table for the number of prints (the number of image formations). Alternatively, the same operation may be performed with two or more predetermined applied voltages, and the applied voltage for obtaining the corrected charging potential Vh may be calculated from the difference between the applied voltages and the measured Vh difference.

<Example 5>

The setting conditions of the fifth embodiment are as follows. -Each photosensitive drum: outer diameter 60 mm, drum surface speed: 21
0 mm / s ・ Each charging roller: A cylindrical body in which an elastic body with an outer diameter of 14 mm and a length of 330 mm is combined around a stainless steel cored bar with an outer diameter of 8 mm ・ Each charging roller initial application condition: DC-750 V ・ Each initial exposure condition : 250 μW

The optimum potential of each photosensitive drum was adjusted as follows.

(A) At the time of non-image formation, a predetermined constant voltage is applied to each charging roller from a bias power source to charge each photosensitive drum, and the charging potential Vh after solid exposure and the potential Vl after exposure are measured.

(B) The developing direct current bias Vdc is set by the developing bias power source 21 to a potential obtained by adding the contrast potential (500 V) to the post-exposure potential Vl.

(C) The charging potential Vh is corrected and set to a potential obtained by adding the fogging prevention voltage (150 V) to the developing DC bias Vdc.

(D) From the predetermined constant voltage and the charging potential Vh measured by each surface electrometer 18 at that time, the applied voltage for setting the corrected charging potential Vh in (c) is calculated.

(E) The calculated applied voltage value is fed back to the bias power source 20 to adjust the bias voltage applied to each charging roller. As a result, a stable and optimal charging potential is always obtained during image formation.

When the control unit 19 is composed of a CPU, the applied voltage of the bias power source 20 and the resistance data are stored in the CPU, and the estimated resistance value obtained from the measured charging potential Vh is collated. The correction applied voltage can be determined. Alternatively, the same operation is performed with two or more predetermined applied voltages, and the correction V is calculated from the difference between the applied voltages and the measured Vh difference.
You may make it calculate the applied voltage for making it h.

Next, the optimum toner adhesion amount on the belt was adjusted as follows.

(F) At the time of non-image formation, a toner image is formed under the above-mentioned developing bias conditions (Vdc is the above value, sleeve rotation speed, Vac is a predetermined value).

(G) The toner rotation speed and Vac to be corrected are calculated from the predetermined sleeve rotation speed, Vac and the toner adhesion amount measured by the toner adhesion detection unit 23 at that time.

(H) This calculated value is used as the developing bias power supply 2
Feed back to 1 and develop under optimum developing bias conditions. As a result, a stable toner adhesion amount is always obtained during image formation.

When the control unit 19 is constituted by the CPU as described above, the data of the toner adhesion amount with respect to the rotational speed and Vac is stored in the CPU, and the corrected rotational speed and Vac are checked by collating with the measured toner adhesion amount. Can be determined. Alternatively, a predetermined number of rotations of 2 or more, Va
The same operation may be performed in c, and the sleeve rotation speed and Vac for obtaining the corrected toner adhesion amount may be calculated from the difference amount between a plurality of conditions and the measured toner adhesion amount difference.

The control of the pulse width modulation (PWM) in the exposure section 22 can be performed as follows.

(I) A plurality of latent images in which PWM is changed are produced at the time of non-image formation, and a toner image is formed under the above developing conditions (Vdc, Vac, sleeve rotation speed).

(J) The γ curve inverse correction value is calculated from the predetermined γ curve and the toner adhesion amount of each PWM measured by the toner adhesion detection unit 23.

(K) Exposure is performed under the condition that the inverse correction value determined at the time of image formation is applied to obtain a stable and optimum γ curve.
Thereby, a stable toner adhesion amount may be obtained at the time of image formation.

<Example 6>

The setting conditions of Example 6 are as follows: initial application condition to each charging roller is DC-750V, AC 2 kHz, 5 mA.
Same as Example 5 except that

The optimum potential of each photosensitive drum was adjusted as follows.

(A) At the time of non-image formation, a predetermined DC constant voltage and AC constant current are applied from the bias power source 20 to each charging roller for charging, and the charging potential Vh after solid exposure and the potential Vl after exposure are measured.

(B) The developing direct current bias Vdc is set by the developing bias power source 21 to a potential obtained by adding the contrast potential (500 V) to the post-exposure potential Vl.

(C) The charging potential Vh is corrected and set to a potential obtained by adding the fogging prevention voltage (150 V) to the developing DC bias Vdc.

(D) From the predetermined constant voltage and the charging potential Vh measured by each surface electrometer 18 at that time, the applied voltage for setting the corrected charging potential Vh in (c) is calculated.

(E) The calculated applied voltage value is fed back to the bias power source 20 to adjust the DC bias voltage to each charging roller. As a result, a stable and optimal charging potential is always obtained during image formation. Alternatively, the DC bias voltage and the AC bias current may be adjusted.

Next, the optimum toner adhesion amount on the belt was adjusted as follows.

(F) At the time of non-image formation, a toner image is formed under the above-mentioned developing bias conditions (Vdc is the above value, sleeve rotation speed, Vac is a predetermined value).

(G) The toner rotation speed and Vac to be corrected are calculated from the predetermined sleeve rotation speed, Vac and the toner adhesion amount measured by the toner adhesion detection unit 23 at that time.

(H) The calculated value is used as the developing bias power supply 2
Feed back to 1 and develop under optimum developing bias conditions. As a result, a stable toner adhesion amount is always obtained during image formation.

The optimum .gamma.-curve may be corrected as described above to control the pulse width modulation (PWM) in the exposure unit 22 so that a stable toner adhesion amount is always obtained during image formation.

[0123]

According to the present invention, it is possible to provide an image forming apparatus capable of preventing the generation of uneven charging pitch and reducing the amounts of discharge products and ozone.

Further, even if the charging performance of the charging device changes due to long-term use or environmental changes, an electrostatic latent image can always be developed with an appropriate amount of toner and a high-quality image can be formed. A device can be provided.

Further, it is possible to provide an image forming apparatus having a tandem structure in which the life of the photosensitive drum is extended and the cartridge of the photosensitive drum can be used for a long time when a charging roller is used for the charging device.

[Brief description of drawings]

FIG. 1 is a side view schematically showing a main part of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between Vhavg and Vdc in the case of the first embodiment.

FIG. 3 is a diagram showing a relationship between Vhavg and Vdc in the case of Comparative Example 2;

FIG. 4 is a diagram showing the relationship between the circumferential distance of the photosensitive drum and the discharge voltage of Paschen at the time of charging in Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 5 shows the potential fluctuation pitch (Vpc /
It is a figure which shows the relationship between f) and screen resolution (alpha).

FIG. 6 is a side view schematically showing a main part of an image forming apparatus having a tandem structure according to a second embodiment of the present invention.

FIG. 7 is a control block diagram in the image forming apparatus in FIG.

FIG. 8 is a diagram (a) for explaining the problems of the conventional technique;
(B) and (c).

[Explanation of symbols]

1 charging roller 2 photosensitive drum (image carrier,
Photoconductor) 3 developing device 3a developing sleeve 8, 18 surface potential meter 9, 19 control unit 10, 20 bias power supply 11, 21 developing bias power supply 22 exposure unit 23 toner adhesion detection unit 1Y, 1M, 1C, 1K charging roller 2Y, 2M, 2C, 2K photosensitive drum (image carrier,
Photoreceptor) 3Y, 3M, 3C, 3K Developing device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/06 101 G03G 15/04 120 2H200 15/08 501 F term (reference) 2H027 DA02 DA09 DE05 DE07 DE09 EA01 EA02 EA04 EA05 EB04 EC06 EC18 EF09 2H030 AA05 AB02 AD02 AD16 BB02 BB13 BB34 BB36 BB42 2H073 AA02 AA03 BA04 BA13 BA23 BA27 BA28 CA03 CA22 2H076 AB02 DA07 DA12 DB07 FA12 DB12 DB07 FA12 DB12 DB07 DB12 DB07 DB12 DB12 DB12 GA34 GA44 GA47 GA57 GB12 HA02 HA29 HB12 HB22 JA02 JC03 JC07 JC12 PA03 PA08 PA09 PA11 PA19 PA24 PB04 PB20

Claims (9)

[Claims] 1. An image bearing member carrying an electrostatic latent image, and a charging member arranged in contact with the image bearing member for charging the moving image bearing member before the formation of the electrostatic latent image. An apparatus and a developing device for applying a DC voltage to the electrostatic latent image on the image carrier to develop the toner, and a voltage in which an AC component is superimposed on a DC component is applied to the charging device. In the image forming apparatus described above, the average charging potential Vhavg (V) of the image carrier is adjusted so as to satisfy the following range. (Vpc / f) × 250 + Vdc + 50 <Vhavg <(Vpc / f)
× 250 + Vdc + 200 where Vpc: linear velocity of the image carrier (mm / s) f: frequency of the AC component (Hz) of 2 kHz or less Vdc: developing DC voltage of the developing device (V) 2. An image bearing member carrying an electrostatic latent image, and a charging member arranged so as to contact the image bearing member for charging the moving image bearing member before the formation of the electrostatic latent image. An apparatus and a developing device for applying a DC voltage to the electrostatic latent image on the image carrier to develop the toner, and a voltage in which an AC component is superimposed on a DC component is applied to the charging device. In the image forming apparatus described above, the frequency f (Hz) of the AC component is 2 kHz or less and is adjusted so as to satisfy the following two expressions. (Vpc / f) × 250 + Vdc + 50 <Vhavg <(Vpc / f)
× 250 + Vdc + 200 α <80 × (Vpc / f) ⁻¹ where Vpc: linear velocity of the image carrier (mm / s) Vhavg: average charging potential of the image carrier (V) Vdc: the development DC voltage of developing unit (V) α: Resolution (dpi) 3. A photoconductor on which an electrostatic latent image is formed by exposure to light, and a contact arranged to contact the photoconductor to charge the photoconductor before the formation of the electrostatic latent image. An image forming apparatus comprising: a charging device having a charging device; and a developing device for developing an electrostatic latent image with an image to form a toner image; an applying device for applying a DC bias voltage to the contact charging member; Charging potential detecting means for detecting the charging potential of the surface of the photoconductor after being charged by the charging member and the potential of the surface of the photoconductor after exposure, and the application condition preset by controlling the applying means during non-image formation To charge the photoconductor by applying it to the contact type charging member, and based on the output value of the charging potential detecting means at that time and the output value of the charging potential detecting means after exposure, the applying means of the applying means Applied voltage An image forming apparatus comprising: a control unit that controls pressure. 4. A photoconductor on which an electrostatic latent image is formed by exposure, and a contact arranged to contact the photoconductor to charge the photoconductor before the formation of the electrostatic latent image. An image forming apparatus comprising: a charging device having a charging device; and a developing device for developing an electrostatic latent image with toner to form an image, wherein a bias voltage in which an AC bias is superimposed on a DC bias is applied to the contact charging member. Applying means, a charging potential detecting means for detecting a charging potential of the surface of the photoconductor after being charged by the contact type charging member and a potential of the surface of the photoconductor after exposure, and controlling the applying means during non-image formation. Then, by applying to the contact type charging member under a preset application condition to charge the photoconductor, based on the output value of the charging potential detection means at that time and the output value of the charging potential detection means after exposure, image An image forming apparatus comprising: a control unit that controls a direct-current applied voltage or a direct-current applied voltage and an alternating-current applied current of the applying unit during formation. 5. A developing DC bias voltage for setting a predetermined contrast potential from the output value of the charging potential detecting means after exposure is set, and the applying means is set so as to have a potential added with a predetermined fog prevention potential. The image forming apparatus according to claim 3, which is controlled. 6. An exposure unit that exposes by pulse width modulation based on image information, a photoconductor on which an electrostatic latent image is formed by the exposure by the exposure unit, and an electrostatic latent image formed on the photoconductor. A charging device having a contact type charging member arranged to contact the photoreceptor for precharging;
In an image forming apparatus including: an applying unit that applies a DC bias voltage to the contact-type charging member; a charging potential of the photoconductor surface after being charged by the contact-type charging member and a potential of the photoconductor surface after exposure. A charging potential detecting means for detecting a charge, a developing means having a rotating sleeve for developing a toner after exposing at least a part of a charged area of the photoreceptor after being charged by the contact type charging member, and a toner in the developing area. Toner adhesion amount detecting means for detecting the adhesion amount, and for controlling the applying means at the time of non-image formation to apply to the contact type charging member under a preset application condition to charge the photoconductor, and the charging at that time First control means for controlling the applied voltage of the applying means during image formation based on the output value of the potential detecting means and the output value of the charged potential detecting means after exposure. After the non-image formation, the application means and the development means are controlled to apply the toner to the contact type charging member under a preset application condition to charge the photoconductor, and then the toner adhesion amount at the time of toner development. An image comprising: a second control unit that controls at least one of the rotational speed of the sleeve, Vac, and pulse width modulation of the exposure unit based on the output value of the detection unit during image formation. Forming equipment. 7. An exposure unit that exposes by pulse width modulation based on image information, a photoconductor on which an electrostatic latent image is formed by the exposure by the exposure unit, and an electrostatic latent image formed on the photoconductor. A charging device having a contact type charging member arranged to contact the photoreceptor for precharging;
In an image forming apparatus including: an applying unit that applies a bias voltage in which an AC bias is superimposed on a DC bias to the contact-type charging member; and a charging potential of the surface of the photoconductor after being charged by the contact-type charging member and after exposure. A charging potential detecting means for detecting the potential of the surface of the photoconductor, and a developing means having a rotating sleeve for developing toner after exposure of at least a part of the charged area of the photoconductor after being charged by the contact type charging member. A toner adhering amount detecting means for detecting the toner adhering amount in the developing area; and controlling the applying means during non-image formation to apply the toner to the contact type charging member under preset application conditions to charge the photoconductor. Then, based on the output value of the charging potential detecting means at that time and the output value of the charging potential detecting means after exposure, the applying means at the time of image formation. A first control unit for controlling a DC applied voltage or a DC applied voltage and an AC applied current; and controlling the applying unit and the developing unit during non-image formation to apply the contact type charging member under preset application conditions. After charging the photoconductor, based on the output value of the toner adhesion amount detection means at the time of toner development, the second embodiment of controlling the rotational speed of the sleeve, Vac and the pulse width control of the exposure means at the time of image formation. An image forming apparatus comprising: a control unit. 8. A developing direct current bias voltage for setting a predetermined contrast potential from an output value of the charging potential detecting means after exposure is set, and the applying means is set so as to have a potential added with a predetermined fog prevention potential. 8. The image forming apparatus according to claim 6, wherein the image forming apparatus is controlled and then at least one of the developing unit and the exposing unit is controlled. 9. The image forming apparatus according to claim 3, wherein the contact-type charging member includes a roller member, and has a tandem structure so that a color image can be formed. .