JPH08328360A - Electrifying method - Google Patents

Abstract

PURPOSE: To stabilize electrification potential and to apply the invention to a high speed machine by reducing the unevenness of the electrification potential corresponding to the frequency pitch of an AC component generated by primary electrification by secondary electrification. CONSTITUTION: An electrifying device 2 is constituted of a 1st electrifying roll 10 rotatably arranged on an upstream side in the rotating direction of a photoreceptor 1, a 2nd electrifying roll 11 rotatably disposed on a downstream side in the rotating direction of the photoreceptor 1, a 1st power source for electrification 12 impressing voltage obtained by superposing a DC component on the AC component on the roll 10, and a 2nd power source for electrification 13 impressing specified DC voltage on the roll 11. After performing the primary electrification by the roll 10 on which the voltage obtained by superposing the DC component on the AC component is impressed, the secondary electrification by the roll 11 on which DC voltage to discharge at least a part of the uneven potential by electrification corresponding to the frequency pitch of the AC component generated by the primary electrification so as to exceed discharge start voltage is impressed is performed. Thus, the uneven potential by electrification is surely and remarkably reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method for charging an image bearing member composed of an electrophotographic photosensitive member or an electrostatic recording type dielectric, a charging device used in the charging method, and a charging device therefor. The present invention relates to an image forming apparatus including a charging device.

[0002]

2. Description of the Related Art In recent years, as a charging device for charging an image bearing member in an image forming apparatus such as an electrophotographic copying machine, a laser printer, an electrostatic recording device, etc., a charging voltage has been used instead of a corona charger which has been widely used conventionally. Attention has been focused on a contact charging device that charges a surface of an image bearing member by bringing a rotating roll, a brush, a blade, or the like, to which the image is applied, into contact with the image bearing member. As this contact charging device, at present, one charging roll that rotates in contact with the image carrier is used, and charging is performed by applying a voltage in which a DC component is superimposed on an AC component to this charging roll. Things are mainly known.

However, the contact charging device for charging by applying a voltage in which a direct current component is superimposed on an alternating current component to this one charging roll is attracted and separated between the charging roll and the image carrier during the charging. Since the force is generated, there is a problem that the image carrier vibrates to generate noise. Further, since the surface of the image bearing member is deteriorated by the discharge due to the AC voltage, and this surface may be worn away by the rubbing by the cleaning blade, the current value of the voltage applied to the charging roll may be increased. It is not possible to increase the frequency, and as a result, if the AC frequency is lowered to prevent deterioration and wear of the surface of the image carrier, charging unevenness will increase and black streaks will occur on the resulting image. There's a problem. Furthermore, when the charging roll is worn down and the environmental conditions change, the charging start voltage of the charging roll changes and the charging potential itself also changes, causing image quality defects such as density changes and fogging. There is a problem of doing.

Therefore, as a conventional technique for solving the problem in the contact charging device for charging by applying a voltage in which a direct current component is superimposed on an alternating current component to such one charging roll, for example, as an image Using two contact chargers that contact the carrier back and forth to charge, and especially for the second charger, the nip width between the charger and the image carrier is determined by the frequency pitch generated by the charging by the first charger. A charging device has been proposed which prevents charging noise and uneven charging due to the first charging device by being installed so as to be larger than the uneven charging potential unevenness pitch (Japanese Patent Laid-Open No. 4-301861).
Issue). Also, two contact chargers that contact the image carrier before and after to perform charging are used, and in particular, by applying only a constant voltage component to the second charger, charging that prevents uneven charging by the first charger is performed. There is a device proposal (Japanese Patent Laid-Open No. 6-954).
No. 78).

[0005]

However, the above two charging devices have the following problems. That is, first, in the former case, it is possible to reduce the charging potential unevenness by electrically neutralizing the portion of the charging unevenness to some extent by the function of the leveling charging by the second charger, but the charging potential is limited. It only alleviates unevenness,
It is not possible to fundamentally eliminate the uneven charging potential. In particular, when the process speed of the image bearing member is increased, the potential difference between the exposed portion and the non-exposed portion on the image bearing member generated in the previous image forming cycle cannot be sufficiently smoothed, and especially halftone image formation is performed. In this case, an image quality defect such as an unclear density difference occurs.

On the other hand, in the latter case, it is said that only the constant voltage component is applied to the second charger, but in practice, the same DC voltage as the DC component applied to the first charger is applied. Even if a DC voltage of this level is applied and charging is performed by the second charger, it is not possible to sufficiently eliminate the charge potential unevenness caused by the first charger, and the pattern of microscopic potential unevenness is also seen on the image. There is a problem that light and shade consisting of is generated. Further, there is a possibility that the charge potential unevenness of the first charger can be corrected (leveled to some extent) by the injected charges, but there is a problem that the potential unevenness cannot be substantially eliminated. Furthermore, even in the case of this charging device, there is a limit in practical adaptability to speeding up of the process speed (about 100 mm / s in process speed), and there is a problem that it cannot be applied to a so-called high speed machine.

Therefore, the object of the present invention is to sufficiently reduce the charging unevenness caused by charging by applying a voltage in which a direct current component is superimposed on an alternating current component so that a uniform image can always be obtained without image quality defects. In addition, the charging method, the charging device, and the image forming apparatus can be applied to a high-speed machine, and the charging potential can be stabilized regardless of changes in environmental conditions and film loss of the image carrier over time. To provide.

[0008]

According to the charging method of the present invention, the surface of an image bearing member before the formation of an electrostatic latent image is brought into contact with the surface of the image bearing member.
This is a contact charging method of separately charging, and the charging corresponding to the frequency pitch of the AC component generated by the primary charging after the primary charging is performed by the contact charging means in which the voltage in which the DC component is superimposed on the AC component is applied. At least a part of the potential unevenness exceeds the discharge start voltage, and secondary charging is performed by the contact charging means to which a direct current voltage for discharging is applied.

In this charging method, both primary charging and secondary charging may be performed by one contact charger, but primary charging and secondary charging are individually performed by using two contact chargers. It is desirable to do. The DC voltage at which at least a part of the charging potential unevenness exceeds the discharge start voltage and is discharged means that the voltage difference between the peak potential of the charging potential unevenness due to the primary charging and the charging potential due to the secondary charging is 30 V or less, preferably 10 V or less. It is a DC voltage that

Further, the charging device of the present invention is a contact charging device which contacts an image carrier before an electrostatic latent image is formed and charges the surface thereof in two steps. Is applied to apply a voltage that superimposes the voltage on the image carrier to perform primary charging, and at least part of the charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging by the first charging device starts discharge. And a second charger for performing secondary charging of the image bearing member by applying a direct current voltage for discharging over the voltage.

Further, in the image forming apparatus of the present invention, the image carrier on which the electrostatic latent image is formed and the image carrier on which the electrostatic latent image is not formed are arranged so as to come in contact with each other. And a second charger, and an image forming apparatus comprising first and second voltage applying means for applying a voltage to each of the first and second chargers, wherein the first voltage applying means is , A voltage in which a direct current component is superimposed on an alternating current component is applied to a first charger that performs the above-mentioned charging, and the second voltage applying means is a charger that corresponds to the frequency pitch of the alternating current component generated by the primary charging of the first charger. It is characterized in that a direct current voltage at which at least a part of the potential unevenness exceeds the discharge start voltage and is discharged is applied to the second contact charger.

In such a charging method, charging device and image forming apparatus, it is desirable that the DC voltage applied to the contact charging means for performing the secondary charging should correspond to the frequency pitch of the AC component generated by the primary charging. A direct-current voltage is applied so that the entire potential irregularity exceeds the discharge start voltage and is discharged.

Further, in such a charging method, a charging device and an image forming apparatus, it is desirable that the DC voltage applied to the contact charging means for carrying out the secondary charging is detected by detecting the current value flowing into the charging means. The current value is controlled to be constant.

Further, in such a charging method, charging device and image forming apparatus, the types of the first charging device and the second charging device are not particularly limited, but preferably the first charging device is It is a blade-shaped, brush-shaped or film-shaped contact charger, and the second charger is a roll-shaped contact charger.

In the present invention, the image carrier is a photoconductor, a dielectric or the like, and the image carrier may be in the form of a drum or a belt. Further, as the contact charging means for performing the primary charging, for example, a transfer roll, a cleaning blade or the like may be used as the charging device instead of the normal charging device.

[0016]

According to such a technical means, at least a part of the charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging exceeds the discharge start voltage by the secondary charging and is discharged (desired. Therefore, the unevenness of the charging potential is reliably and significantly reduced. In this respect, for example, in the technique described in Japanese Patent Laid-Open No. 6-95478, only the same potential as the DC component of the first charging is applied to the second charger, so that the second charger is actually used. Even if the electric charge is injected by the charger and the electric potential unevenness can be smoothed to some extent, the electric discharge does not occur as in the case of applying the discharge start voltage based on Paschen's law as in the present invention. Is not substantially resolved. That is, in the conventional charging by the charge injection of the second charger, if there is a microscopic variation in the surface or volume resistance of the charging means, the variation pattern is reflected as charging unevenness. As a result, the image appears as light and shade.

As the DC voltage applied to the contact charging means for carrying out the secondary charging, the DC voltage at which the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging exceeds the discharge start voltage and is discharged. When applying,
The uneven charging potential generated by the primary charging is completely eliminated.
Moreover, even when the actual charge potential of the image carrier falls below the target potential (insufficient) due to changes in environmental conditions and film loss of the image carrier over time, the peaks of the frequency pitch of the AC component Alternatively, since the valley portion protrudes from the charging potential due to the DC voltage at the time of secondary charging, the average value of the charging potential of the image carrier approaches the target potential, and the charging potential of the image carrier can be stabilized. it can.

Further, in the case of detecting the current value flowing into the charging means for the DC voltage applied to the contact charging means for carrying out the secondary charging and controlling the current value to be constant, the image carrying member is charged. The charging potential can be stabilized more reliably.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of an image forming apparatus to which the present invention is applied. In this image forming apparatus, a charging device 2, an image exposure device 3, a developing device 4, a transfer roll 5, and a cleaning device 6 are arranged in this order around a drum-shaped photosensitive member 1 serving as an image carrier that rotates in the arrow direction. The main part is constructed. In the figure, reference numeral 7 is a recording sheet, and 8 is a transfer power source for applying a predetermined voltage to the transfer roll 5.

The charging device 2, as shown in FIG. 1 and FIG.
With respect to the first charging roll 10 rotatably arranged on the upstream side in the rotation direction of the photosensitive member 1, the second charging roll 11 rotatably arranged on the downstream side in the rotation direction, and the first charging roll 10. And a second charging power source 13 that applies a predetermined DC voltage to the second charging roll 11, and a first charging power source 12 that applies a voltage in which a direct current component is superimposed on an alternating current component.

First charging roll 10 and second charging roll 1
As shown in FIG. 2, in each case 1, a rubber layer 15 and a surface layer 16 are sequentially formed on a conductive support shaft 14 made of iron, copper, stainless steel, aluminum or the like. The rubber layer 15 is formed using EPDM rubber in which conductive particles such as carbon black are dispersed, polyurethane rubber in which an ion conductive agent such as LiClO ₄ is dispersed, and the like. Also,
The surface layer 16 is set to have a volume resistance value of 10 ⁵ to 10 ⁹ Ω, and is made of a synthetic material such as polyamide, polyurethane, polyethylene or acrylic in which conductive particles such as carbon black and aluminum are dispersed. Resin or L
It is formed by using polyurethane rubber or the like in which an ion conductive agent such as iClO ₄ is dispersed. The thickness of the surface layer 16 is appropriately set within the range of 1 to 50 μm. The charging rolls 10 and 11 may be provided with a pressure resistant layer between the rubber layer 15 and the surface layer 16 in order to prevent leakage due to pinholes, if necessary. The breakdown voltage layer is formed of a material obtained by adding SnOx or the like coated with BaSO ₄ to a cyan resin, a byron resin, or the like, and its thickness is appropriately set within the range of 10 to 50 μm.

In the image forming apparatus of this embodiment,
First, after the primary charging and the secondary charging are sequentially performed so that the surface of the rotating photoconductor 1 becomes a predetermined charging potential by the two charging rolls 10 and 11 of the charging device 2, the surface of the charged photoconductor is obtained. On the other hand, the image exposure device 3 performs exposure according to image information to form an electrostatic latent image. Next, the photoconductor 1 on which the electrostatic latent image is formed is developed by the developing device 4 to form a toner image on its surface, so that the toner image passes between the photoconductor 1 and the transfer roll 5. Is transferred to the recording paper 7 supplied to the recording paper 7. On the other hand, the photoconductor 1 after the transfer has the cleaning blade 6 a of the cleaning device 6.
The residual toner is removed by the method described above, and the apparatus stands by for the next image forming process.

Next, the following test was conducted in order to investigate the charging performance of the charging device 2. That is, the photoconductor 1
Of the first charging roll 10 at a rotation speed of 300 mm / s.
1500Vp-p, 500H for DC component of -660V
The state of the charging potential when the photoconductor 1 is charged by the charging device 2 after the condition in which the voltage in which the AC component of z is superimposed is applied and the DC voltage of -1340V is applied to the second charging roll 11. I checked about. At this time, the discharge start voltage (at normal temperature and pressure) was -600V. The result is shown in Figure 3.
And shown in FIG. FIG. 3 shows the state of the charge potential on the surface of the photoconductor immediately after passing through the first charging roll 10, and FIG. 4 shows the state of the charge potential on the surface of the photoconductor immediately after passing through the second charging roll 11.

As shown in FIGS. 3 and 4, the charging potential unevenness (solid line portion in FIG. 3) corresponding to the frequency pitch of the AC component generated by the primary charging of the first charging roll 10 is the second charging roll 11. Due to the secondary charging of (1), part of the uneven charge potential (dotted line portion in FIG. 4) exceeds the discharge start voltage and is discharged. As a result, the charging potential state shown by the solid line in FIG. 4 is obtained, and it can be seen that the uneven charging potential at the time of primary charging is reduced. In the case of this embodiment, the potential difference S between the peak value of the charging potential during the primary charging and the charging potential (-740V) during the secondary charging is 10 V or less. No unpleasant noise was generated during this charging. In addition, when an image was formed through charging under such conditions, the obtained image was of good quality with no density difference or black streaks. Furthermore, the process speed is 30
Smooth charging could be performed even at a high speed of 0 mm / s.

Next, as the DC voltage applied to the second charging roll 11 in the charging device 2 of the above-described embodiment, the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging of the first charging roll 10 is whole. Is a direct current voltage (-1380 in this example) that causes the discharge to exceed the discharge start voltage.
The state of the charging potential when the photoconductor 1 was charged under the same conditions as in the above-mentioned example except that V) was applied was examined.
Results are shown in FIG.

As shown in FIG. 5, the charging potential unevenness (dotted line portion in the figure) corresponding to the frequency pitch of the AC component generated by the primary charging of the first charging roll 10 is equal to that of the second charging roll 11. By the secondary charging, all of the charging potential unevenness exceeds the discharge start voltage and is discharged. As a result, a uniform charging potential state (-780) shown by the solid line in the figure is obtained.
V), which means that the uneven charging potential at the time of primary charging is completely eliminated. No unpleasant noise was generated during this charging. When images were formed through charging under these conditions, the obtained images were of extremely high quality with no density difference or black streaks.

Next, in the second charging roll 11 in the charging device 2 of the above embodiment, the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging of the first charging roll 10 has the discharge start voltage. In the case of applying a DC voltage that discharges beyond, the above example (FIG. 5) applies a DC voltage that discharges to the same polarity (negative electrode) side as the polarity of the primary charging potential, whereas it is opposite to the primary charging. The state of the charging potential when the photosensitive member 1 was charged by applying a DC voltage (-180 V in this example) that discharges to the polarity (positive electrode) side was examined. In this case, the first charging roll 10 has -90.
A voltage obtained by superimposing an AC component of 1500 Vp-p and 500 Hz on a DC component of 0 V was applied. The discharge start voltage (at room temperature and normal pressure) at this time was + 600V. FIG. 6 shows the results.

As shown in FIG. 6, even when a direct-current voltage is applied to the second charging roll 11 so as to discharge it to the side opposite to the polarity (positive electrode) opposite to the polarity of the primary charging potential, it is generated by the primary charging. All of the charging potential unevenness (dotted line portion in the figure) corresponding to the frequency pitch of the AC component is discharged to a uniform charging potential state (-780V), and the charging potential unevenness at the time of the next charging may be completely eliminated. Recognize. And even in this case, no unpleasant noise is generated at the time of charging,
Further, even when an image is formed through charging under such conditions, the obtained image is of high quality with no density difference or black streaks.

With respect to the second charging roll 11 in the charging device 2 as in the above-described two examples, the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging of the first charging roll 10 is the discharge start voltage. When a DC voltage that causes discharge is applied, the charging potential of the photoconductor can be stabilized even if environmental conditions (temperature and humidity) change.

That is, in the case of a charging device which charges the photoconductor 1 only with one charging roll to which a DC voltage is applied (even when charging is performed by the second charging roll 11), the process shown in FIG.
As shown in (1), since the discharge start voltage at the time of charging changes due to the change in environmental conditions, the charge potential on the surface of the photoconductor also changes. That is, even if charging is performed with the same applied voltage (-1380 V), the charging potential is about 50 between high temperature and high humidity (28 ° C, 85% RH) and low temperature and low humidity (10 ° C, 30% RH).
V will also be different. On the other hand, according to the embodiment (in the case of FIG. 5), as shown in FIG. 8, even if the environmental condition is changed from high temperature and high humidity to low temperature and low humidity, the peak of uneven charging potential generated by the primary charging is generated. Since the portion (or the valley portion) protrudes from the charging potential (-740V) due to the secondary charging, the average value of the charging potential approaches that of the target potential (-780V). The two-dotted line in FIG. 8 shows the charging potential (-730 V) under low temperature and low humidity when charging is performed with only one charging roll to which a DC voltage is applied. In this way, the charging potential of the photoconductor can be stabilized. The effect of stabilizing the charging potential can be obtained in the same manner even when the film thickness on the surface of the photoconductor is reduced. It should be noted that the effect of stabilizing the charging potential with respect to such environmental changes is such that in the above-mentioned conventional technique (Japanese Patent Laid-Open No. 6-95478, etc.), an average potential close to the desired charging potential is obtained, and the potential unevenness due to the frequency pitch is uneven. As a result, it cannot be obtained.

FIG. 9 shows another embodiment of the charging device to which the present invention is applied. Charging device 20 of this embodiment
Has the same configuration as the charging device 2 of the above-described embodiment except that the current detection circuit 30, the control circuit (CPU) 31, and the voltage variable device 32 are added to form the second charging power source 130. Reference numeral 33 in the drawing indicates a DC power supply.

In the charging device 20 of this embodiment, the voltage applied to the second charging roll is controlled as follows. FIG.
As shown in 0, first, the voltage variator 22 is fixed to a predetermined applied voltage value, and a constant DC voltage is applied from the DC power supply 33 to the second charging roll 11 (step S).
1). At this time, the current detection circuit 30 causes the charging roll 11
The current value flowing into is detected, the detection signal is A / D converted, and then input to the control circuit 31 (S2). Control circuit 3
It is judged whether or not the current value detected in 1 is the specified current value (S3), and if it is not the specified value, the voltage variator 32 corrects the applied voltage value (S4). FIG. 11 shows the relationship between the charging potential on the surface of the photoconductor and the specified current value to the second charging roll. As shown in FIG. 11, the relationship between the charging potential and the specified current value is almost constant without being affected by environmental conditions such as high temperature and high humidity or low temperature and low humidity. As described above, the applied voltage is controlled while monitoring the current value, and if the current value detected in step S3 is as specified, the control ends. By controlling the voltage applied to the second charging roll in this way, the charging potential on the surface of the photoconductor can be further stabilized.

FIG. 12 shows another embodiment of the charging device of the present invention. The charging device 21 of this embodiment is a charging blade 17 as a first charging device and a second charging device.
The structure is almost the same as that of the above-described embodiment (in the case of FIG. 2) except that No. 18 is applied. As the first charger and the second charger, a charging brush or a charging film may be applied instead of the above-mentioned charging blade. This charger 21 can be applied in place of the charging device 2 in the above-described embodiment (in the case of FIG. 2).

FIG. 13 shows another embodiment of the charging device of the present invention. The charging device 22 of this embodiment is a charging blade 17 (or a charging brush or a charging film) as the first charging device. And the charging roll 1 as the second charger.
The structure is almost the same as that of the above-described embodiment (in the case of FIG. 2) except that the first embodiment is applied. This charger 22 can be applied in place of the charging device 2 in the above-described embodiment (in the case of FIG. 2). The reason why the charging roll 11 is applied as the second charging device is that it is effective in stabilizing the charging potential of the photoconductor evenly as compared with a charging blade or the like. Since a low-cost charging blade or the like other than the charging roll is applied as the first charging device as in this embodiment and the charging roll is applied as the second charging device, the charging potential is stabilized and the charging device is reduced. The cost can be reduced at the same time.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention described in the claims. Is possible.

For example, in the above-described embodiment, the case where the primary charging and the secondary charging are individually performed by using the two contact charging devices as the charging device has been exemplified, but the charging device of the present invention is
In the embodiment shown in FIG. 1, only one of the charging rolls 10 and 11 is used, and the photosensitive member 1 is rotated twice during charging so that primary charging is performed in the first rotation and secondary charging is performed in the second rotation. It may be configured. Further, the charging device of the present invention may be configured so that, for example, the transfer roller 5 and the cleaning blade 6a are also used as the contact charging means for performing the primary charging, instead of the charging roll 10 in the above embodiment.

[0038]

As described above, according to the present invention (charging method, charging device, and image forming apparatus), the secondary charging causes uneven charging potential corresponding to the frequency pitch of the AC component generated in the primary charging. Since it can be surely reduced, it is possible to reduce the noise generated by the vibration of the image carrier, and also to set the current value and the AC frequency of the voltage applied to the contact charging means performing the primary charging to appropriate values. By doing so, it is possible to suppress deterioration and wear of the image carrier surface,
It is possible to prevent the generation of black stripes on the image due to uneven charging. Moreover, such an effect can be obtained in a comparable manner even when it is applied to a high-speed machine having a process speed of 300 mm / s, for example, and it is excellent in adaptability to the high-speed machine.

As the DC voltage applied to the contact charging means for performing the secondary charging, the DC voltage at which the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging exceeds the discharge start voltage and is discharged. When applying,
It is possible to completely eliminate the uneven charging potential generated by the primary charging.
Moreover, even when the actual charge potential of the image carrier falls below the target potential (insufficient) due to changes in environmental conditions and film loss of the image carrier over time, the peaks of the frequency pitch of the AC component Alternatively, since the valley portion protrudes from the charging potential due to the DC voltage at the time of secondary charging, the average value of the charging potential of the image carrier approaches the target potential, and the charging potential of the image carrier can be stabilized. it can.

Further, in the case of detecting the current value flowing into the charging means for the DC voltage applied to the contact charging means for carrying out the secondary charging and controlling the current value to be constant, the image carrying member is charged. The charging potential can be stabilized more reliably.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main part showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram showing a charging device applied to the device of FIG.

FIG. 3 is a diagram showing a charged state of a surface of a photoconductor immediately after passing through a first charging roll.

FIG. 4 is a diagram showing a charged state of the surface of the photoconductor immediately after passing through a second charging roll.

FIG. 5 is a diagram showing a charged state of the surface of the photoconductor immediately after passing through the second charging roll, when the whole is discharged to the negative polarity side.

FIG. 6 is a diagram showing a charged state of the surface of the photoconductor immediately after passing through the second charging roll, when the whole is discharged to the positive polarity side.

FIG. 7 is a diagram showing a charging state with respect to environmental changes when charging is performed by one charging roll to which a DC voltage is applied.

FIG. 8 is a diagram showing a charged state with respect to environmental changes when charged by the charging device of the present invention.

FIG. 9 is a schematic configuration diagram showing another embodiment of the charging device of the present invention.

FIG. 10 is a flowchart showing a method of controlling the voltage applied to the second charging roll by the charging device of FIG.

FIG. 11 is a correlation diagram showing the relationship between the specified current value to the second charging roll and the charging potential on the surface of the photoconductor.

FIG. 12 is a schematic configuration diagram showing another embodiment of the charging device of the present invention.

FIG. 13 is a schematic configuration diagram showing another embodiment of the charging device of the present invention.

[Explanation of symbols]

1 ... Image carrier, 2, 20, 21, 22 ... Charging device, 1
0, 14 ... First contact charger, 11, 15 ... Second contact charger, 12 ... First voltage applying means, 13, 130 ... Second voltage applying means, 30 ... Current detecting means, 31 (32) ... Voltage Control means.

[Procedure amendment]

[Submission date] April 4, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasutomo Ishii 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (12)

[Claims] 1. A contact charging method in which an electrostatic latent image is contacted with an image carrier before the electrostatic latent image is formed and the surface thereof is charged in two steps, and a voltage in which a DC component is superimposed on an AC component is applied. After the primary charging by the contact charging means, at least a part of the charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging exceeds the discharge start voltage, and the contact charging means applies a DC voltage to discharge the discharge. A charging method characterized by performing secondary charging. 2. The charging method according to claim 1, wherein the primary charging and the secondary charging are individually performed using two contact chargers. 3. A contact charging device for charging a surface of an image bearing member before the formation of an electrostatic latent image by charging the surface in two steps, wherein a voltage in which a direct current component is superimposed on an alternating current component is applied. The first charger that performs the primary charging of the image carrier and the direct current that discharges at least part of the charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging by the first charger exceeds the discharge start voltage. A charging device comprising: a second charger that applies a voltage to perform secondary charging of the image carrier. 4. An image carrier on which an electrostatic latent image is formed, and first and second chargers arranged in front and back so as to contact the image carrier on which the electrostatic latent image is not formed, An image forming apparatus comprising first and second voltage applying means for applying a voltage to each of the first and second chargers, wherein the first voltage applying means superimposes a direct current component on an alternating current component. The applied voltage is applied to the first charging device that performs the previous charging, and the second voltage applying means discharges at least a part of the charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging of the first charging device. An image forming apparatus, characterized in that a direct current voltage which exceeds a starting voltage and is discharged is applied to a second contact charger. 5. The charging method according to claim 1, wherein the DC voltage applied to the contact charging means for performing the secondary charging starts the discharge of the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging. A charging method characterized in that it is a direct-current voltage that discharges over a voltage. 6. The apparatus according to claim 3, wherein a DC voltage is applied to the second charger so that the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging exceeds the discharge start voltage and is discharged. A charging device characterized by: 7. The apparatus according to claim 4, wherein the second voltage applying unit applies a DC voltage at which the entire charging potential unevenness corresponding to the frequency pitch of the AC component generated by the primary charging exceeds the discharge start voltage and is discharged. An image forming apparatus characterized by applying to a second charger. 8. The method according to claim 5, wherein the direct current voltage applied to the contact charging means for carrying out the secondary charging is controlled so that the current value flowing into the charging means is detected to be constant. A charging method characterized by the above. 9. The apparatus according to claim 6, wherein the second charger detects a current value flowing into the charger and applies a DC voltage controlled so that the current value becomes constant. Characteristic charging device. 10. The apparatus according to claim 7, wherein the second voltage applying means controls a detecting means for detecting a current value flowing into the second charger and a DC voltage applied so that the current value becomes constant. An image forming apparatus, comprising: 11. The apparatus according to claim 6, wherein the first charger is a blade-shaped, brush-shaped or film-shaped contact charger, and the second charger is a roll-shaped contact charger. Charging device. 12. The apparatus according to claim 7, wherein the first charger is a blade-shaped, brush-shaped or film-shaped contact charger, and the second charger is a roll-shaped contact charger. Image forming apparatus.