JP3423632B2 - Image forming device - Google Patents

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 used in copying machines, page printers, facsimiles and the like.

More specifically, the present invention relates to an image forming apparatus in which an image forming process including a charging step is applied to an image carrier to form an image, and the image carrier is repeatedly subjected to image formation.

[0003]

2. Description of the Related Art FIG. 1 shows a schematic structure of an example of an image forming apparatus which has been used as an engine of a copying machine or a page printer. The image forming apparatus of this example is a reversal development type / contact charging type laser beam printer.

Reference numeral 1 denotes a main body of an image forming apparatus which is a printer engine.

Reference numeral 2 denotes a cylindrical electrophotographic photosensitive drum as an image bearing member, which is rotationally driven around its axis in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed).

The surface of the photosensitive drum 2 is uniformly charged to a predetermined polarity and potential by the charging device 3 (in this example, negative charging), and then exposed to a light image by the exposure device (laser scanner) 4 to be statically exposed. A latent image is formed.

The charging device 3 is a contact charging device using a charging roller as a contact charging member, and a superposed voltage of a DC voltage (charging DC) and an AC voltage (charging AC) is applied to the charging roller, so that the photosensitive drum 2 is exposed. The surface of is uniformly charged by the contact charging method.

A reversal developing device 5 is provided with a hopper, which is a toner storage device for storing and storing toner (negative toner) 6, and a developing sleeve 8, which is a toner carrier, and is formed on the photosensitive drum 2. Toner 6 is supplied to the formed latent image to perform reversal development. A developing blade 9, which is a toner regulating member, is installed near the developing sleeve 8. Then, by the engine control unit 7 provided with a power supply for driving the image forming apparatus and a high voltage circuit for supplying a bias for forming an image, a DC bias and an AC bias are provided between the photosensitive drum 2 and the developing sleeve 8. Is applied to the developing bias.

Photosensitive drum 2 visualized by toner 6
The upper image is transferred onto a transfer material 11 by a transfer device (transfer roller) 10 to which a transfer bias having a positive polarity is applied.

The transfer material 11 is stored in a paper feed cassette 17, is fed by a paper feed roller 12, and is sent to a transfer device 10 by a registration roller 13 in synchronism with the image on the photosensitive drum 2.

The visible image by the toner 6 transferred from the photosensitive drum 2 side to the transfer material 11 by the transfer device 10 is a transfer material 1.
1 is conveyed to the fixing device 14 together with 1 and is fixed on the transfer material 11 by heat or pressure to form a recorded image. The transfer material 11 that has undergone image fixing is discharged and conveyed to the paper discharge unit 18.

On the other hand, after the transfer, the photosensitive drum 2 is not transferred and is not transferred.
The toner 6 remaining on the top is removed by the cleaning blade 16 in the cleaning device 15.

The surface of the photosensitive drum 2 from which the toner 6 has been removed is charged again by the charging device 3, and the above steps are repeated.

Reference numeral 19 denotes a process cartridge which can be attached to and detached from the image forming apparatus main body 1. The process cartridge of the present example stores four process devices including a photosensitive drum 2 as an image carrier, a charging device 3, a developing device 5, and a cleaning device 15.

By the way, after the printing operation of the image forming apparatus is finished, the operation of making the surface potential of the photosensitive drum 2 uneven and uniform, or returning the toner 6 adhering to the transfer roller 10 as a transfer device to the photosensitive drum 2 side and transferring it. Laura 1
There is a step (hereinafter referred to as a post-rotation step) for performing an operation of cleaning the 0 surface.

A specific example of the post-rotation process will be described with reference to the sequence of FIG.

.. After the printing operation, in order to erase the potential unevenness of the photosensitive drum 2 due to the latent image immediately after printing,
The entire surface of the image area for one round of the photosensitive drum is exposed to change the photosensitive drum potential to the latent image potential. tl is the period during which the entire surface exposure is turned on. The entire surface exposure is performed by the exposure device 4. It is also possible to provide an exposure device dedicated to the whole surface exposure.

.. Then, in order to clean the toner 6 adhering to the transfer roller 10, the transfer roller 10 is printed at the time of printing.
A reverse transfer bias (negative in this example) having a reverse polarity to the transfer bias (positive in this example) applied to the transfer roller 3
The toner is applied to the transfer roller 10 for a period of the circumference, and the toner 6 attached to the transfer roller 10 is blown to the photosensitive drum 2 side for cleaning.
The toner 6 transferred from the transfer roller 10 side to the photosensitive drum 2 side is removed from the photosensitive drum 2 surface by the cleaning device 15.

T2 is a period during which the reverse transfer bias for the transfer roller 10 is ON. There is a timing difference between the time when the entire surface exposure is turned off and the time when the reverse transfer bias is turned on, which corresponds to the phase difference between the exposure position and the transfer position of the photosensitive drum 2.

[0020]. And finally, the photosensitive drum 2 again
In order to eliminate the potential unevenness of and the potential becomes 0 V, only the AC voltage is applied to the charging roller 3 (hereinafter, this operation will be referred to as A
C is referred to as static elimination). Since the DC voltage is not superimposed, the surface potential of the photosensitive drum 2 converges to 0V. This is the photosensitive drum 1
The motor as a drive source of the image forming apparatus is turned off when the rotation is completed, and the post-rotation operation is completed.

T3 is the period during which the above-mentioned AC static elimination is ON.
There is a timing difference between the time when the AC charge removal is ON and the time when the reverse transfer bias is OFF, which corresponds to the phase difference between the exposure position and the transfer position of the photosensitive drum 2.

[0022]

By the way, it has been found that horizontal streaks are generated on the image at the photosensitive drum cycle after being left for several days in the state where the entire printing operation is completed.

As a result of studying this, when the AC neutralization of the post-rotation operation is OFF, the AC voltage is + or −.
It can be seen that a voltage higher than the voltage on the side is applied, which causes unevenness in the surface potential of the photosensitive drum, and remains as a memory, and either black streaks or white streaks occur.

The reason why a large voltage is applied when the AC neutralization is OFF is as follows.

That is, in making a sine wave which is a charging AC voltage, it is better to make a sine wave in either polarity than in making a sine wave over both the positive (+) side and the negative (-) side. It can be easily made ((a) in FIG. 3). A means for cutting the direct current component by passing the output waveform through a capacitor ((b) in FIG. 3) and amplifying it to an appropriate Vpp (peak to peak voltage) ((c) in FIG. 3) via a transformer. Is often used.

In this embodiment, at the moment when the charging AC voltage is OFF, the central axis is m → n (0V) as shown in FIG.
Becomes

Since the potential difference g of m → n is amplified and output as it is, the final output becomes a spike waveform and a voltage larger than usual is applied to the photosensitive drum 2 ((b) of FIG. 4). ).

According to the present inventor, the spike voltage is 1.4
When about kV is applied, the potential becomes + 900V only in the applied part, and it is confirmed that it will remain as a memory because it will not be able to converge to 0V even with the subsequent dark decay, and it will occur as a horizontal stripe on the image. is doing.

Here, in order to prevent the spike waveform from being output, the basic waveform created in (a) of FIG. 3 may be created around 0 V as shown in (b) of FIG. 3, but the polarity of the waveform is + (plus). Since there is a negative polarity (-) and negative polarity (-), the number of elements on the electric circuit is increased and the control is complicated, resulting in an increase in cost.

Therefore, an object of the present invention is to make it possible to eliminate AC charges on the surface of an image bearing member without memory in an image forming apparatus without increasing the cost, and to prevent lateral streaks and the like caused by the above-mentioned problem. This is to prevent the generation of images.

[0031]

The present invention is an image forming apparatus having the following configuration.

(1) In an image forming apparatus in which an image is formed by applying an image forming process including a charging step by a charging unit that is in contact with the image carrier, and the image carrier is repeatedly subjected to image formation. After mounting the image carrier or the process cartridge storing the image carrier on the main body of the image forming apparatus, or after forming the image, only the AC voltage is applied to the charging means to eliminate the surface potential of the image carrier, More than twice the charging start voltage
Of the peak voltage of the AC voltage having a peak-to-peak voltage, the rotation of the image bearing member is OFF by attenuated after stopping, the image
The peak-to-peak voltage of the AC voltage is
When attenuated, it becomes less than the charging start voltage of the image carrier
The applied voltage immediately before is +300 from the charging start voltage of the image carrier.
It is within the range of V, and the polarity is the charging of the image carrier during image formation.
An image forming apparatus having the same polarity as the voltage .

In the above structure, after the rotation of the image carrier is stopped
The surface potential of the image carrier at the contact position of the charging member is
When the voltage is attenuated, the voltage falls below the charging start voltage of the image carrier.
Determined by the applied voltage immediately before Image bearing due to dark decay
In order for the body surface potential to converge to 0 V, the applied voltage starts charging.
The voltage is within the range of + 300V from the voltage, and the polarity is the charging voltage.
By setting the same polarity as,
It will be about 300V and will converge to 0V due to dark decay.
Is possible. As a result, the surface of the image carrier is uniformly discharged.
And a good image is obtained.

[0034]

[0035] (2) imaging process unit, a charging unit that charges the image bearing member, an exposure means for forming an electrostatic latent image by exposing the charged image carrier, a developer a developer carrying member A developing unit that carries the developer on the top and conveys the developer to a developing unit facing the image carrier, and develops an electrostatic latent image on the image carrier to form a visible image; and a visible image transfer unit. 2. An image forming apparatus according to (1) , further comprising a transfer means for transferring to a transfer material.

[0036] (3) band conductive means, the image forming apparatus superimposes a DC voltage and an AC voltage, characterized in that a contact charging member for charging the image bearing member surface (1) or (2).

In the above structure, the present invention is particularly AC + D.
The effect is great in the contact charging member by the C voltage.

[0038]

[0039]

(4) It is characterized in that the magnitude of the peak-to-peak voltage of the AC voltage changes in a plurality of steps to decrease.
The image forming apparatus according to any one of (1) to (3) .

(5) The plurality of steps in which the magnitude of the peak-to-peak voltage of the AC voltage changes includes a voltage in the range of twice the charging start voltage of the image carrier to +600 V for one cycle or more. The image forming apparatus according to (4) .

In the above-mentioned configurations (4) and (5) , even in the simple voltage attenuating means, the voltage within the range from twice the charging start voltage to +600 V is applied,
The surface potential of the image carrier becomes 0V to 300V which can converge to 0V, and it is possible to prevent the generation of streaks which are defective images.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION In the present embodiment, the apparatus configuration of the image forming apparatus is the same as that shown in FIG.

The post-rotation step is performed in substantially the same manner as the sequence of FIG. 2 described above. That is, after printing is completed, the entire surface exposure is turned on for one rotation of the photosensitive drum (period tl). The photosensitive drum 2 surface potential at this time becomes a latent image potential from the charging potential, the potential gradually released once the high potential state becomes close to 0 V. After that, until the application of the charging AC voltage (AC neutralization) performed at the end of the post-rotation operation, the latent image potential is attenuated by dark decay and converges to 0V.

After completion of the whole surface exposure, a reverse transfer bias (cleaning bias) having a reverse polarity to the transfer bias applied to the transfer roller 10 at the time of printing, that is, in the case of reversal development, a negative bias is applied for 2 to 4 rounds of the transfer roller. (Period t2). As a result, the toner 6 attached to the transfer roller 10 is caused to fly to the photosensitive drum 2 side, and the transfer roller 10 is cleaned. Photosensitive drum 2 at this time
The surface potential of is slightly affected by the cleaning bias of the transfer roller 10, but is almost unchanged.

Next, only the AC voltage is applied from the charging roller 3 for one round of the photosensitive drum (AC neutralization, period t3). At this time, since the DC voltage is 0 V, the photosensitive drum surface potential is 0
It is converged to V and the charge is removed.

Next, the means for gradually attenuating the charged AC voltage for AC neutralization will be described with reference to FIG.

As described with reference to FIG. 3A, first, a sine wave is formed as the basic waveform 20 with either polarity. Then, in order to cut the DC component, the current is passed through the capacitor 21 and amplified by the amplifier circuit 22 to a predetermined current or voltage.

On the other hand, a control circuit (not shown) of the image forming apparatus 1 sends a current signal 26 as a reference of the charging AC voltage. As for the signal 28, the signal 26 is the RC circuit 24/25.
The signal 2 of the reference current is compared with the signal 29 sent from the amplifier circuit 22 by the comparison circuit 23.
The signal is amplified by the amplifier circuit 22 until it becomes equal to 8, and is output when it becomes equal.

When the signal 26 is turned off, the signal 28 becomes an attenuation signal with respect to time due to the characteristic of the capacitor 25. Therefore, the signal 29 for comparing the signal 28 with the reference is also attenuated, and the output 27 has a waveform in which the charging AC voltage is gradually attenuated.

The decay time of the signal 28 may be changed by changing the size of the capacitor 25, whereby the decay time of the output can be changed to a desired time.

At the end of the post-rotation operation, after the rotational drive of the photosensitive drum 2 is stopped (after the motor is turned off), the applied AC charge for AC neutralization is attenuated by the means configuration as shown in the above example (FIG. 5). The feature is that it can be turned off.

That is, the motor for driving the photosensitive drum 2 is stopped when AC static elimination is applied for one round of the photosensitive drum.

After the photosensitive drum 2 is stopped, the charging AC voltage applied to the charging roller 3 is gradually converged to 0V.

In this example, the charging A is performed immediately after the photosensitive drum 2 is stopped.
Although the C voltage is attenuated, it is necessary to apply the voltage after the photosensitive drum 2 is completely stopped in consideration of a margin such as rotation due to inertia of the photosensitive drum 2. Therefore, although the charging AC voltage may start to decay several seconds after the photosensitive drum 2 is stopped, it has been confirmed that the effects of the present invention are sufficiently obtained.

However, charging A at the same position of the photosensitive drum 2
If the C voltage is continuously applied, the surface layer of the photosensitive drum 2 is deteriorated. Therefore, it is desirable to attenuate the charging AC voltage within about 2 seconds after the photosensitive drum 2 is stopped.

The potential is uniformly converged to 0 V except the position where the photosensitive drum 2 is in contact with the charging roller 3. At the position where the photosensitive drum 2 is in contact with the charging roller 3, the surface potential of the photosensitive drum 2 is + as the AC voltage periodically changes to the + (plus) and- (minus) sides.
Potential, changing periodically to one potential. The potential at this time has a voltage value obtained by subtracting the charging start voltage from the charging AC voltage.
As the AC voltage is attenuated from the normal voltage, the difference from the charging start voltage is reduced and the surface potential of the photosensitive drum 2 is reduced. Then, when the voltage falls below the charging start voltage, the surface of the photosensitive drum 2 is not charged with electric potential because it is not charged. At this time, the potential of the surface of the photosensitive drum 2 finally becomes
When the lowest voltage that is equal to or higher than the charging start voltage is applied, the potential is charged on the photosensitive drum 2.

In the present invention, the peak-to-peak voltage of the charging AC voltage is gradually attenuated, and a voltage close to twice the charging start voltage is applied so that the surface potential of the photosensitive drum 2 is as low as possible.
The potential is close to V. After that, it converges to 0 V due to the dark attenuation characteristic of the photosensitive layer of the photosensitive drum 2. Therefore, the unevenness of the potential on the surface of the photosensitive drum 2 is eliminated, and it is possible to prevent a defective image due to a memory.

Further, when the voltage between the peaks of the charging AC voltage is attenuated, if the voltage is suddenly dropped, the charging start voltage
The lowest voltage more than twice the charging start voltage becomes a voltage far from twice the charging start voltage , and the surface potential of the photosensitive drum 2 may be from 0 V to a considerably large potential.
When lowering the peak-to-peak voltage of the C voltage ,
It is necessary to apply a voltage value close to twice .

Specifically, when the charging start voltage of the charging roller is 550V, 1100Vpp to 1700Vpp is applied for one cycle or more. The surface potential of the photosensitive drum 2 at this time is
It is −300V to 0V.

In the study by the present inventor, it was confirmed that if the surface potential of the photosensitive drum 2 is about −300V, it converges to 0V within several hours due to dark decay. If the charging AC voltage is applied to the surface of the photosensitive drum in the next printing operation, it does not become a memory on the surface of the photosensitive drum for a few hours.
There is no unevenness in the potential, and no stripes appear on the image.

Therefore, the surface potentials of the contact portion of the charging roller 3 and the photosensitive drum 2 other than the contact portion are both 0 V, and no electric charge is accumulated in the memory, so that a good image can always be provided.

Even if the next printing operation starts before the surface potential of the photosensitive drum 2 at the contact portion of the charging roller 3 converges to 0V, the charging voltage for one or more rounds of the photosensitive drum is applied before image formation. By applying the voltage, the surface potential of the photosensitive drum 2 becomes uniform.

Specific examples 1 to 3 and comparative examples of the sequence of the image forming apparatus will be described below. In all examples, common settings for the image forming apparatus 1 are as follows.

A. Reversal development method, using charging device with charging roller 3 b. Process speed: 8 ppm c. Photosensitive drum 2: φ30 mm OPC drum d. Charging AC voltage: 600 Hz, constant current control with 600 μA sine wave e. Charging DC voltage: -600V f. Charging start voltage: 550V In the image forming apparatus 1, when only the DC voltage was applied to the charging roller 3 and the surface potential of the photosensitive drum 2 at that time was measured and confirmed, the charging start voltage was 550V.

The basic sequence of the post-rotation operation is the same as that described in FIG. In the following examples and comparative examples,
As AC neutralization, charging AC is applied for one round of the photosensitive drum to neutralize the surface of the photosensitive drum 2 and A after the photosensitive drum 2 is stopped.
The mode of attenuation change of the C voltage will be described.

As an evaluation method, the photosensitive drum 2 was left to stand for 24 hours in a state where the photosensitive drum 2 was post-rotated once, and then a solid black or halftone image was output to confirm the occurrence of streaks.

<Embodiment 1> (FIG. 6) FIG. 6 shows the form of attenuation change of the AC voltage after the photosensitive drum 2 in this embodiment is stopped.

In this embodiment, after the photosensitive drum 2 is stopped, the charging AC voltage is gradually attenuated to 0V.

In this embodiment, the voltage is converged from 2000 Vpp to 0 V in 60 ms. At this time 34Vpp / m
The voltage was dropped at s.

The surface potential of the photosensitive drum 2 at the contact portion of the charging roller 3 immediately after the post-rotation of this embodiment was -10V.

<Embodiment 2> (FIG. 7) FIG. 7 shows a form of attenuation change of the AC voltage after the photosensitive drum 2 in this embodiment is stopped.

In the present embodiment, the decay time of the charging AC voltage was shortened until the spike voltage generated when the charging AC voltage was turned off was equal to or higher than the charging start voltage. That is, the surface potential of the photosensitive drum 2 at the contact portion of the charging roller 3 is the potential charged by the last spike voltage, and the charging AC voltage is attenuated to such an extent that a spike voltage that does not cause image defects is output. Is what made it faster.

To accelerate the decay time, the capacitance of the capacitor 25 in the circuit shown in FIG. 5 may be reduced.

The present embodiment also has an effect that the decay time can be shortened to 0 V as in the first embodiment. As a result, deterioration of the photosensitive drum 2 due to charging can be prevented, and abrasion of the surface layer of the photosensitive drum 2 can be suppressed.

In this embodiment, the charging AC application is 2000V.
It was turned off by converging from pp to 800 Vpp. The voltage peak of the spike waveform generated at OFF is -5
It was 80V. At this time, 48 Vpp / up to 800 Vpp
The voltage was dropped in ms.

Then, it was confirmed that the surface potential of the photosensitive drum 2 at the contact portion of the charging roller 3 immediately after the post-rotation was -28V.

<Third Embodiment> (FIGS. 8 and 9) FIG. 8 shows a form of attenuation change of the AC voltage after the photosensitive drum 2 in this embodiment is stopped.

In this embodiment, the charging AC voltage value was switched and turned off in 6 steps.

As means for changing the magnitude of the charging AC voltage stepwise, for example, a plurality of transistors 33 as shown in FIG.
・ 34 and resistors 31 and 32 are installed, and each transistor 3
By sending the signals 35 and 36 to 3 and 34 stepwise, the magnitude of the signal 28 can be reduced stepwise.

The 6-step switching values are switched from 2000 Vpp to 1700 Vpp immediately after the start of the post-rotation, and 1700 Vpp to 1400 Vpp and 1400 Vpp every 20 ms.
→ 1100Vpp, 1100Vpp → 800Vpp, 8
00Vpp → 500Vpp, 500Vpp → 0V. It is 100 ms up to 0V.

In the present embodiment, the surface of the photosensitive drum 2 is charged by applying 1100 Vpp, which is at least twice as high as the charging start voltage, to the charging roller 3, and thereafter the charging start voltage is set at twice or less. That is, finally, the surface potential of the photosensitive drum 2 at the contact portion of the charging roller 3 immediately after the rear rotation is 110.
The charging potential was -5 V when applied at 0 Vpp.

<Comparative Example> (FIG. 10) As a comparative example, comparison is made using the conventional means for removing the surface potential of the photosensitive drum 2 by the charging AC.

As shown in FIG. 10, when the charging AC voltage was applied for one round of the photosensitive drum, it was turned off. The spike waveform generated at this time was -1300V. At this time, the surface potential of the photosensitive drum 2 at the contact portion of the charging roller 3 is about 1
It was 50V.

The results of Examples 1 to 3 and Comparative Example are shown in Table 1.
Shown in.

[0086]

[Table 1]

The spike voltage as in the comparative example of Table 1 is -1.
White stripes are generated when the voltage is 300 V, whereas the charge A
Same as Example 1 in which C voltage is attenuated to 0V
It was confirmed that in Example 2 in which the charging AC voltage was attenuated until the spike voltage became −580 V, a good image was obtained without appearing as white stripes on the image.

As described above, in the charge removal of the surface of the photosensitive drum 2 by applying the charging AC voltage during the post-rotation, the charging AC voltage is attenuated after the rotation driving of the photosensitive drum is stopped. It is possible to prevent the generation of streaks, which is the memory of the memory, and obtain a stable image.

<Others> 1) In the present embodiment, the AC charge removal in the post-rotation operation has been described, but in the present invention, the image carrier 2 or the process cartridge 19 in which the image carrier is stored is attached to the image forming apparatus main body 1. It is needless to say that the same effect can be obtained in the AC neutralization in the leveling process performed later.

The process cartridge includes at least one of charging means, developing means and cleaning means,
The image carrier is made into a cartridge so that it can be attached to and detached from the main body of the image forming apparatus. It also means that at least the developing means and the image carrier are made into a cartridge so that it can be attached to and detached from the main body of the image forming apparatus.

2) The image bearing member is not limited to the electrophotographic photosensitive member, but may be an electrostatic recording dielectric member, an intermediate transfer member or the like, and the principle and process of forming a toner image on them are arbitrary.

3) The developing method and means of the electrostatic latent image are arbitrary, and it is needless to say that regular developing may be used instead of the reversal developing of the embodiment.

4) An image display device (display) in which a toner image is formed and carried on the surface of the image carrier, the toner image forming section is positioned on the reading display section to display an image, and the image carrier is repeatedly used for image formation. There is also. The image forming apparatus of the present invention includes such an image display apparatus.

5) The contact charging member is not limited to the roller type,
It may be a blade type, a rod type, a brush type, a magnetic brush type or the like.

As the waveform of the AC bias component of the charging bias applied to the contact charging member, a sine wave, a rectangular wave, a triangular wave or the like can be appropriately used. Further, it may be a rectangular wave formed by periodically turning on / off the DC power supply. Thus, as the waveform of the AC voltage, a bias whose voltage value periodically changes can be used.

Even if the contact charging member is not necessarily in contact with the surface of the image carrier with pressure contact force,
As long as the dischargeable area determined by the gap voltage and the Paschen curve is reliably ensured, a non-contact and very close arrangement may be adopted. In the present invention, this case is also in the category of contact charging.

[0097]

As described above, according to the present invention, an image forming apparatus that applies an image forming process including a charging step to an image carrier to perform image formation, and the image carrier is repeatedly subjected to image formation. In the above, the surface of the image bearing member can be AC-erased without a memory without increasing the cost, and it is possible to prevent the occurrence of a defective image such as a horizontal stripe due to the AC static-eliminating memory.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus.

FIG. 2 is a diagram showing a sequence of a post-rotation operation.

FIG. 3 is a diagram showing a process of generating a charging AC voltage.

FIG. 4 is an explanatory diagram of spike waveform generation.

FIG. 5 is a circuit example for gradually attenuating a charged AC voltage for AC neutralization.

FIG. 6 is a diagram showing a decay state of a charging AC voltage in the first embodiment.

FIG. 7 is a diagram showing a decay state of a charging AC voltage in the second embodiment.

FIG. 8 is a diagram showing a decay state of a charging AC voltage in Example 3.

FIG. 9 is an example of a circuit for attenuating a charged AC voltage for AC neutralization in multiple stages.

FIG. 10 is a diagram showing a state in which a charging AC voltage is turned off in a comparative example.

[Explanation of symbols]

1 ... Image forming device, 2 ... Photosensitive drum (image carrier),
3 ... Charging roller, 4 ... Exposure device, 5 ... Developing device,
6 ... Toner, 7 ... Engine control unit, 8 ... Development sleeve, 9 ... Development blade, 10 ... Transfer roller, 11
Transfer material, 14 fixing device, 15 cleaning device, 16 cleaning blade

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroyuki Sakakibara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Incorporated (56) Reference JP-A-1-232371 (JP, A) JP-A-8-190251 (JP, A) JP-A-9-80870 (JP, A) JP-A-8-146848 (JP, A) JP-A-53-49988 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 21/06 G03G 15/02

Claims (5)

(57) [Claims] 1. An image forming process is performed by applying an image forming process including a charging process by a charging unit that contacts an image carrier.
In the image forming apparatus to be subjected to imaging the image bearing member is repeatedly, the image bearing member, or after mounting the process cartridge in which the image bearing member is stored in the image forming apparatus main body, or after the image formation, only AC voltage to the charging means Apply the voltage to eliminate the surface potential of the image carrier, and the peak-to-peak voltage that is at least twice the charging start voltage.
The peak-to-peak voltage of the AC voltage with a rotation drive of the image bearing member is OFF by attenuated after stopping, the rotation of the image bearing member is the peak voltage of the AC voltage after stopping
When the voltage is attenuated, the voltage falls below the charging start voltage of the image carrier.
Immediately before application, the applied voltage is +30 from the charging start voltage of the image carrier.
Within the range of 0 V, the polarity is the band of the image carrier during image formation.
An image forming apparatus having the same polarity as an electric voltage . 2. An image forming process means, a charging means for charging the image carrier, an exposing means for exposing the charged image carrier to form an electrostatic latent image, and a developer on the developer carrier. And a developing unit for carrying the developer to a developing unit facing the image carrier to develop an electrostatic latent image on the image carrier to form a visible image, and a visible image in the transfer unit. The image forming apparatus according to claim 1, further comprising transfer means for transferring to a transfer material. 3. The image forming apparatus according to claim 1, wherein the charging unit is a contact charging member that charges the surface of the image bearing member by superposing a DC voltage and an AC voltage. 4. The image forming apparatus to the magnitude of the peak voltage of the AC voltage claims 1, characterized in that changes to decrease direction in a plurality of stages 3. 5. The plurality of steps in which the magnitude of the peak-to-peak voltage of the AC voltage changes includes a voltage within a range from twice the charging start voltage of the image carrier to +600 V for one cycle or more. The image forming apparatus according to claim 4 .