JP2000056543A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a surface potential difference between a first and second rotations of a photoreceptor when charging the photoreceptor. SOLUTION: In an image forming process part 7 forming a toner image by charging a photoreceptor 8 by use of a charger 16, performing digital exposure using a laser beam, and reversely developing, using a developing device 17, an electrostatic latent image formed by the exposure, a charging output produced by the charger 16 is controlled to become high during a first rotation of the photoreceptor 8 and get lower during the second rotation thereof. Thereby a potential difference between the first and second rotations and a potential gradient are eliminated, and a toner image of stable picture quality with constant density can be formed by the developing device 17 from the first rotation of the photoreceptor 8.

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 such as a copying machine or a laser printer using an electrophotographic method.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic method,
The surface of the photoreceptor, which is an image carrier, is uniformly charged, and the surface is exposed to an image to form an electrostatic latent image corresponding to the exposed image. For example, development is performed using toner as a colorant. The toner image on the surface of the image carrier formed by the development is transferred to a transfer material (sheet) such as a sheet of paper that is appropriately conveyed, the sheet is separated from the photoconductor, and passed through a fixing device to form a hard copy. I try to finish.

On the other hand, after the toner image is transferred to the sheet, a part of the toner image remains on the photoconductor, and in order to use the photoconductor repeatedly, the residual toner is cleaned, The static elimination for removing the remaining charge is performed, and these operations are repeatedly performed in order, so that the above-described image formation on the photosensitive member can be repeatedly used.

[0004] The surface potential of this photoreceptor greatly affects image formation. That is, in order to always obtain the same image quality state, it is important to stabilize the surface potential of the entire photoconductor.

However, in general, inexpensive photoreceptors, when the photoreceptor is new, no particular problem occurs if the charging means is stable. However, as the image formation is repeated, the charging potential at the first rotation of the first use does not rise to the predetermined potential. As a result, a surface potential difference occurs between the first rotation area and the second and subsequent rotation areas of the photoconductor in the image formed by the first image formation, resulting in non-uniform image density and fogging of the background. However, there is a problem that image quality is reduced.

[0006] These problems are conspicuously exhibited as a density difference of a halftone and a fog difference of a white background which is a background particularly in image formation using reversal development. In addition, this phenomenon is a phenomenon that occurs remarkably in general photoconductors that are used for digital applications using inexpensive phthalocyanine compounds.

[0007] One means for solving the above-mentioned problems is as follows.
Generally, a photoreceptor is rotated plural times while executing a charging and discharging process before the image process is started, a charging unit and a discharging unit are operated to stabilize the surface potential of the photoreceptor, and then an image forming process is generally performed. Has been used in many ways. In this case, the start time of the image forming process is delayed, and the output time of the first hard copy becomes very long. for that reason,
The hard copy from the first sheet cannot be output at high speed.

Further, when a contact-type charging means such as a roller method or a brush method is used as the charging means, the thickness of the photosensitive member is particularly greatly reduced. Therefore, if processing such as pre-rotation is performed in order to stabilize the photoconductor as described above, the number of rotations of the photoconductor is greatly increased, and deterioration of image formation is promoted. This also results in shortening the life of the photoconductor.

Therefore, according to Japanese Patent Application Laid-Open No. Hei 4-161963, in an image forming apparatus for uniformly charging a photoreceptor using a contact charging means (roller charging), charging conditions for a first rotation and a second rotation and thereafter are described. An image forming apparatus that changes exposure conditions and development conditions is disclosed. According to the image forming apparatus of the disclosed technology, image formation can be started from the first time of the photoconductor, and a hard copy with more stable image quality can be output from the first sheet. In other words, the charging potential in the first rotation and the charging potential in the second and subsequent rotations can be made substantially equal, and the exposure and development conditions are controlled so as to obtain the same image quality. Will be able to respond.

As another technique, it is conceivable to use a photoconductor in which the surface potential of the photoconductor after the first rotation and the second rotation after the start of image formation becomes the same. As such a photoreceptor, Japanese Patent Laid-Open Publication No.
There is one disclosed in Japanese Patent Application Laid-Open Publication No. 1 (1999). The photoreceptor described in this publication contains a phthalocyanine compound as a charge generation substance in a charge generation layer constituting the photoreceptor, and further contains an azo compound to reduce the charge potential of the first rotation as a photoreceptor characteristic. I am trying to suppress it. For this reason, image formation is performed from the first rotation of the photoreceptor, so that high-speed operation can be handled.

[0011]

In recent years, digitization of image forming apparatuses has progressed, and many image forming apparatuses employ a reversal developing system. In addition, there is a demand for an increase in the speed of the image forming apparatus, and in addition to this, a corona charging method (a scorotron-type charging means) rather than a contact charging method is widely used as a charging means. .

By the way, in the corona charging means, it is very difficult to define the effective width of charging, that is, to make a boundary, as in the case of the contact charging means, and the position at which the charging potential is changed becomes unclear. Therefore, it is extremely difficult to correct the potential gap by switching the charging potential accurately at the boundary between the first rotation and the second rotation of the photoconductor. To achieve that,
Position detection means and means for detecting the surface potential state of the photoconductor,
Further, a means for controlling them is required. However, as described above, it is very difficult to prevent a potential gap from occurring because the charged area cannot be defined.

Therefore, as described in Japanese Patent Application Laid-Open No. Hei 4-161963, an image forming apparatus using a contact charging method cannot be used as it is in a corona charging method.

For this reason, in an image forming apparatus capable of performing high-speed processing using corona charging means, the pre-rotation without image formation is performed to stabilize the charging potential.
It was necessary to perform an image forming process. Therefore, compared to the case where an image is formed from the first rotation, an extra time is required before outputting a hard copy, and the above-described problem that the copying time becomes longer cannot be solved. In addition, there is a problem that the life of the photoconductor is shortened because the photoconductor is rotated extra.

[0015] Improving the charge reduction in the first rotation as a characteristic of the photoreceptor causes problems such as a decrease in sensitivity and an increase in cost. In particular, if the photosensitive member described in Japanese Patent Application Laid-Open No. 9-127711 is used, high-speed processing can be easily performed, but the manufacturing cost and the cost of the photosensitive member increase.
In particular, the production yield for obtaining a photosensitive member having the above-described characteristics is a major problem, and the cost is inevitably increased.

According to the present invention, in an image forming apparatus using a general photosensitive member and a charging unit, simple control can be performed without adding a complicated control device or detecting device and omitting the pre-rotation of the photosensitive member. Accordingly, an object of the present invention is to provide an image forming apparatus which can make the surface potential of the photoreceptor uniform, shorten the image forming time, and maintain good image quality.

Another object of the present invention is to provide an optimum image forming apparatus using a digital method (digital exposure) and using a corona charging method capable of coping with high speed as a charging means. is there.

[0018]

According to the present invention, there is provided an image forming apparatus configured to achieve the above-mentioned object, comprising: a charging unit for charging a surface of an image carrier; and a surface of the image carrier after charging. Comprising: an exposure unit for irradiating light with light; and a developing unit for visualizing an electrostatic latent image formed on the surface of the image carrier according to the irradiation of light from the exposure unit. In the forming apparatus, the charging unit is driven at a higher output than a predetermined output at the first rotation of the image carrier in accordance with the start of the process by the image forming process unit, and is gradually reduced to the predetermined output after the second rotation. It is characterized by comprising a control means for performing.

According to the image forming apparatus having the above-described configuration, when the image forming process is started, only the first rotation of the image carrier corresponds to a decrease in the charging potential in the first rotation caused by repeated fatigue or the like. For this reason, the charging means is driven while gradually decreasing from a state where the output has increased beyond a predetermined output. After the second rotation of the image carrier, the charging means is driven with the original predetermined output. Therefore, the surface potential of the image carrier is gradually reduced to a predetermined output by the charging means at the boundary between the first rotation and the second rotation, so that there is no potential difference at the boundary and the potential is substantially the same. As a result, defects such as a density difference and a fog difference corresponding to the first and second rotation regions do not occur on the image. Further, since the image forming process can be started substantially in synchronization with the first rotation of the image carrier without omitting the pre-rotation of the image carrier, consumption of the image carrier due to extra rotation is suppressed,
Life can be extended.

In the image forming apparatus having the above-mentioned configuration, according to the second aspect of the present invention, the control means sets the start of the image forming process by the image forming process means from the end of the previous process. It is determined whether or not a predetermined time has elapsed. If the predetermined time has not elapsed, the charging means is controlled to be driven at a predetermined output from the first rotation of the image carrier. In other words, if the time until the image forming process by the image carrier is restarted by the end of the image forming process is short, that is, if the predetermined time has not elapsed, the driving by the increased high output by the charging unit is performed. This prevents the occurrence of a reverse potential difference between the first rotation and the second rotation. In other words, if the correction due to excess is eliminated and the image forming process is started for a short time from the end of the previous image forming process, the image carrier itself maintains a stable state, and the correction of the charging unit by the first rotation is performed. Even if control is not required, normal image formation can be performed from the first rotation. However, when the image forming process is restarted after a predetermined time has elapsed,
The control as described in claim 1 is executed.

According to the third aspect of the present invention, in the image forming apparatus having the above-described configuration, the control means includes means for counting the number of rotations or the cumulative value of the rotation time of the image carrier; A drive output of the charging unit applied only to the first rotation of the image carrier every time the image forming process is started based on the counting result of the counting unit, and a predetermined drive output applied gradually and reduced after the second rotation. And a table in which the difference of the charging means increases with the progress of the cumulative value. At the start of the image forming process, the relation between the cumulative value of the coefficient means and the driving output of the charging means in the first rotation by the table is provided. The driving is controlled based on

According to such a configuration, the cumulative value of the number of rotations or the rotation time of the image carrier corresponding to each image formation is counted by the counting means. Then, based on the calculation result of the counting means, the difference between the driving output of the charging means applied only for one rotation of the image carrier at the start of the image forming process and the predetermined driving output applied for the second and subsequent rotations is calculated by the above accumulation. A table of a relationship that increases as the value progresses is prepared in advance. Therefore, even in the case where the amount of charge reduction in the first rotation of the image carrier increases in accordance with the change with time,
Since the charging output of the first rotation increases in accordance with the characteristics, the surface potential of the image carrier after the second rotation can be controlled to be substantially the same. As a result, the image bearing member is charged by driving the charging means from the first rotation over a long period of time, so that the image forming process can be started and the image output of the first sheet can be accelerated. In addition, the image quality in this case is stable, and a stable image without image density change and without fogging can always be provided.

According to the fourth aspect of the present invention, the driving output of the first rotation by the charging means is gradually reduced to a predetermined output. I try to do it step by step. For example, when the output of the charging unit is gradually reduced, a drive output higher than a predetermined output to be applied to the charging unit for only one rotation of the image carrier due to the start of the image forming process is changed from a drive output to a predetermined drive output to be applied to the second and subsequent rotations. If the output is controlled so as to have a continuous (linear, meandering) output gradient over a certain period from before the end of the first rotation of the switching output reduction to the start of the second rotation, the output from the first rotation to the second rotation is reduced. The output continuously returns to a predetermined drive output without interruption. Therefore, the effect of eliminating the surface potential difference of the image carrier in the boundary region having a predetermined width in the first rotation and the second rotation is promoted.

Then, the output reduction of the switching from the drive output higher than the predetermined output applied to the charging means to the predetermined drive output applied to the second and subsequent rotations for only one rotation of the image carrier by the start of the image forming process is reduced by one. In the case where the output is controlled so as to have a gradual output gradient over a certain period after the end of the second rotation and after the start of the second rotation, the output is continuously continuous without interruption between the first and second rotations. To return to the predetermined drive output. Therefore, it is possible to eliminate the surface potential difference in the above-described open area of the image carrier in the first rotation and the second rotation. In addition, when the output is gradually reduced stepwise, the drive control is simplified.

According to a fifth aspect of the present invention, in the image forming apparatus having the above-described structure, the control means controls the charging at the time of switching of the charging means in the first to second rotations of the image carrier. The output of the means is controlled to be started before the completion of the first rotation and to be completed after the shift to the second rotation.

This makes it possible to more effectively eliminate the surface potential difference in the boundary region between the first rotation and the second rotation of the image carrier. In other words, when the charging unit cannot regulate the charging width and the like, the output state of the charging unit is gradually reduced from the stage before one rotation, so that the potential difference at the boundary is gradually eliminated. It is possible to eliminate the occurrence of a large potential difference on the way.

In the image forming apparatus having the above-mentioned structure, according to the present invention, the charging means is a scorotron type corona charger having a grid electrode, and the control means is an image bearing device. It is characterized in that a voltage supplied to a grid electrode of a corona charger for controlling a charging potential of a body is controlled.

As described above, in the present invention, a charging method using corona discharge can be used, and at that time, as described above, the surface potential difference in the boundary region between the first rotation and the second rotation of the image carrier can be eliminated. In other words, in the case of the corona charger, the charging width of the image carrier cannot be specified, and even if the output is switched at the boundary between the first rotation and the second rotation of the image carrier, the potential difference is generated in that region. Tend to occur. However, the control of the present invention, that is, in order to gradually reduce the output of the corona charger to a predetermined output from before the end of the first rotation, it is necessary to effectively eliminate the surface potential difference in the boundary region and make the surface potential substantially the same. it can. Further, in order to control the voltage supplied to the grid electrode of the corona charger, it is sufficient to perform voltage control of several hundred volts instead of very high voltage of tens of thousands of volts for performing corona discharge. Becomes easier.

When an organic photoreceptor is used as the image carrier, an inexpensive phthalocyanine-based compound may be used, and even if a general photoreceptor for digital use is used,
By driving the charging means at a higher output than the predetermined output and gradually decreasing it until returning to the predetermined output, only during the first rotation immediately after the photosensitive member is started when the image forming process is stopped for a predetermined time or more (stopped state of the image forming process), The surface potential difference in the boundary region from the first rotation to the second rotation can be effectively eliminated. In particular, in the case of the above-described organic photoreceptor, at the start of the image forming process from the stop, the potential difference appears remarkably, but this can be effectively eliminated, and the image density does not change midway. , Fogging and the like can be similarly solved, and the object of the present invention can be effectively achieved by using an inexpensive photoreceptor.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments for better understanding of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a characteristic diagram showing the relationship between the state of the surface potential of a photosensitive member as an image carrier when the present invention is implemented and the surface potential of the photosensitive member when the present invention is not implemented. FIG.
FIG. 3 is a time chart showing the relationship between the rotation state of a photoreceptor serving as an image carrier and the voltage supplied to a corona charging means for carrying out the present invention, and FIG. 3 shows an electrophotographic image forming apparatus according to the present invention. FIG. 4 is a block diagram showing details of the image forming process means, and FIG. 4 is a block diagram showing the entire image forming apparatus provided with the image forming process means of FIG.

First, before describing an embodiment of the present invention,
An image forming apparatus according to the present invention will be described with reference to FIG. As shown in FIG. 4, a digital copying machine 1, which is an image forming apparatus using an electrophotographic system, reads an image of a document placed on a document table 2 on the upper surface of the device from an optical system unit 3. The optical system unit 3 moves horizontally below the document table 2, scans the image of the document with the light from the light source 4, and distributes the reflected light from the document to the CCD 5. Thus, the image of the document is read by the CCD 5 and stored as image data in an image memory (not shown).

The laser unit 6 shown in FIG. 4 includes a semiconductor laser, a polygon mirror, and an fθ lens.
The semiconductor laser is driven based on the image data stored in the above-described image memory, and the light emitted from the semiconductor laser passes through a polygon mirror and an fθ lens to an image carrier of a process unit 7 serving as an image forming process unit. The light is distributed to the photosensitive member 8 formed in a drum shape. In the image forming process section 7, the surface of the photoconductor 8 is charged,
A toner image is formed through each step of exposure and development. This toner image is transferred to a sheet as a transfer material fed from the paper feed cassettes 9 to 12 and the paper feed tray 13. The sheet on which the toner image has been transferred is heated and pressed by the fixing roller 14 to melt and fix the toner, and then is discharged to a paper discharge unit including a sorter 15 and the like.

The image forming process section 7 described above will be described in further detail with reference to FIG. The image forming process unit 7 includes a photoconductor 8, a charger 16, a developing device 17, a transfer device 18, a peeling device 19, which is a corona charging unit according to the present invention and is disposed to face the peripheral surface of the photoconductor 8. It is constituted by a cleaning blade 20 and a static elimination lamp 21. The photoconductor 8 is rotated in the direction of arrow A at the start of the image forming process for image formation. The charger 16 charges the surface of the photoconductor 8 with a charge of a single polarity. The surface of the photoconductor 8 charged by the charger 16 is exposed to laser light from the laser unit 6 to form an electrostatic latent image. This electrostatic latent image is visualized by supplying toner from the developing device 17.

A sheet is conveyed between the photoreceptor 1 and the transfer unit 18 at a controlled timing, and the toner image formed on the surface of the photoreceptor 8 is transferred onto the sheet by the transfer unit 18. The peeler 19 peels off the sheet electrostatically attracted to the photoconductor 8. Cleaning blade 20
Removes toner remaining on the surface of the photoconductor 1 after transfer. The charge removing lamp 21 removes electric charges remaining on the surface of the photoconductor 8. The rotation of the photoconductor 8 is performed by a photosensor 23 including a photointerrupter or the like facing a slit of a slit disk 22 mounted coaxially with the photoconductor 8.
Is detected by

The photosensitive member 8 has, for example, an organic photosensitive layer. The structure will be described with reference to FIG.
The photoreceptor 8 is formed on a conductive substrate 8a made of aluminum having a thickness of 1 mm and having a thickness of about 1 μm, and a charge (carrying) layer 8b formed to a thickness of about 0.5 μm and a film of about 25 μm. This is a function-separated type organic photoconductor in which the charge (carrier) transfer layer 8c is laminated in this order. For the carrier generating layer 8b, a mixture of a phthalocyanine pigment as a carrier generating agent and a polyvinyl butyral resin as a binder resin in a weight ratio of 1: 1 is used. The carrier transfer layer 1c is made of a mixture of a hydrazone-based material as a carrier transport agent and a polycarbonate resin as a binder resin at a weight ratio of 1: 1. The diameter of the drum of the photoconductor 8 is, for example, 65 mm.

The charger 16 of the present invention constituting the image forming process unit 7 has a case (shield case) 16b in which the surface facing the photosensitive member 8 is open to a wire or saw-toothed corona discharge electrode 16a. It is provided in an electrically insulated state. A grid electrode 16c, which is electrically insulated from the case 16a and is held, is attached to the open surface of the case 16b to constitute a corona charger 16 of the scorotron type. The grid electrode 16c controls the surface potential of the photoconductor 8, and the charging potential is determined by the voltage supplied to the grid electrode 16c.

In the image forming apparatus shown in FIG. 4, since the laser exposure is performed by the laser unit 6, the area corresponding to the image portion is irradiated with light, contrary to the exposure by the analog method. Therefore, the developing device 17 needs to develop the electrostatic latent image formed by the lowering of the charging potential in the light-irradiated area. Therefore, the developing device 17 needs to perform reversal development.

In order to realize the reversal development by the developing device 17, the surface potential of the photosensitive member 8, the developing bias potential supplied to the developing roller 17a constituting the developing device 17 and the laser exposure in the relationship shown in FIG. Shows the relationship between the electrostatic latent image potential and the surface potential of the photoreceptor 8 formed by the lowering. That is, the surface of the photoconductor 8 is uniformly charged by the charger 16 to the charging potential V _O (for example, −550 V).
Then, when receiving exposure by laser light irradiation, the charge on the surface of the photoconductor 8 is canceled according to the magnitude of the light amount,
An electrostatic latent image is formed at the latent image potential _VL (for example, -100 to -300 V). A developing bias potential DVB (for example, −4) is applied between the photoconductor 8 and the developing roller 17 a of the developing device 17.
00V) is supplied. This developing bias potential DV
Using the difference between B and the latent image potential _VL as a developing potential, for example, negatively charged toner is supplied to the surface of the photoconductor 8 from the developing roller 17a. As described above, in the digital copying machine 1 according to the present invention, the reversal development in which the toner is adhered to the exposed portion of the surface of the photoreceptor 8 to form a toner image is enabled.

Digital copier 1 having the structure shown in FIG.
In step (2), upon receiving an instruction to start image formation, the charging, exposure, development, and transfer steps are repeatedly performed on the surface of the photoconductor 8. Therefore, a potential difference is generated between a portion irradiated with the laser beam and a portion not irradiated with the laser beam on the surface of the photoconductor 8 after the exposure process. If the charging step is performed while the image is left as it is, a potential difference caused by the previous image formation causes a memory phenomenon in which the potential difference is sequentially accumulated in the current electrostatic latent image, thereby deteriorating the image quality.

Further, in a portion which receives little or no laser light exposure, the charging potential rises every time the photosensitive drum 1 rotates, and the uniformity of an image formed in each process is impaired. Therefore, the surface of the photoreceptor 8 after the transfer process is irradiated with light from the charge removing lamp 21 so as to remove the remaining charge before receiving the charging process by the charger 16. The photoconductor 8 is compensated so as to always realize a stable image quality state.

Thus, the photoconductor 8 is repeatedly used,
By repeating the image forming process sequentially,
It is possible to output a hard copy while constantly maintaining a constant image quality.

The embodiment of the present invention in the digital copying machine 1 shown in FIG. 4 configured as described above will be described in detail below.

(Embodiment of the Present Invention) It is generally known that the photoreceptor 8 having a phthalocyanine pigment used in the digital copying machine 1 according to the present invention has an electron trap in the carrier generating layer 8b. The electron trap hinders the transfer of positive charges, and exists in the material itself and is accumulated in the material due to light fatigue or the like.

As a result, a local electric field is generated between the electron trap and the substrate 8a of the photoreceptor 8 by the irradiation of light from the charge removing lamp 21, and the injection of carriers increases to lower the surface potential of the photoreceptor. Among the electron traps, those accumulated by light fatigue include those that recover by leaving them unrecovered and those that do not recover, and the state of change in the surface potential of the photoreceptor differs depending on the time that the photoreceptor drum is left.

For example, as shown in FIG.
In the state of the surface potential at the rotation and the second rotation, immediately after the end of the previous image forming process, and in the state of the image forming process restarted, as shown in FIG. The potential is substantially constant without a potential difference between the first rotation and the second rotation.

On the other hand, when the image forming process is restarted after the previous image forming process is completed, for example, after about 10 minutes, as shown in FIG. In the region of the second rotation, the charging potential is lower by about 50 V than the charging potential of the second rotation.

When the charging potential decreases in this way, the background margin, which is the difference between the charging potential V ₀ and the developing bias potential DVB, decreases as described with reference to FIG. It causes deterioration. In addition, when such fogging occurs, toner that is not originally required adheres to the surface of the photosensitive drum 1, and the running cost increases due to an increase in toner consumption, and the load on the cleaning blade 20 increases. There is a problem of early deterioration.

Further, the image density changes halfway due to the potential difference of the electrostatic latent image due to the potential drop. That is, the amount of toner attached changes greatly. As a result, a density difference occurs in the formed toner image, and the image quality is greatly deteriorated.

Therefore, in the present invention, the image forming process is restarted after a predetermined period of pause, and the surface potential difference at the boundary region between the first and second rotations when the photoconductor 8 is charged by operating the charger 16. In order to solve the problem, the drive output by the charger 16 is set to be larger than the predetermined drive output after the second rotation in a period corresponding to one rotation of the photoconductor 8. That is, a series of image forming processes by the digital copying machine 1 is completed, the copying machine 1 is left unattended, and thereafter, a start command of image formation is received, and when the image forming process is restarted, the photoconductor 8 is charged to the charger 16. Fig. 7
In the case of exhibiting the characteristic as shown in (A), the drive output by the charger 16 is kept in a predetermined output state. If the surface potential of the photoconductor 8 becomes as shown in FIG. 7B when the image forming process of the copying machine 1 is restarted after the elapse of the predetermined time and the predetermined time has elapsed, the charging is performed. The output of the charging unit 8 is increased during one rotation of the photoconductor 8, and is set to a normal predetermined output from the second rotation.

The above-mentioned predetermined time is a time during which the surface potential of the photosensitive member 8 decreases as shown in FIG. Depends on However, once the photoconductor 8 to be used is determined, FIG.
The time to fall into the state as shown in FIG. 3B is naturally determined by performing a simulation or the like.

As shown in FIG. 3, when the control circuit (CPU) 25 of the main body of the digital copying machine 1 recognizes that the restart of the image forming process is longer than the predetermined time, the image forming process is started. In response to the start command of the photoconductor 8
In the second rotation, the charging output is increased through the power supply control unit 26 for driving the charger 16 in the case of the normal predetermined output, and in the second rotation, the driving of the charger 8 is controlled with the predetermined charging output. .

FIG. 8 shows the characteristics of the surface potential of the photosensitive member 8 at that time.
Shown in As shown by the solid line in FIG. 8, a decrease in the charged potential V _O of the photoconductor 8 by the charger 16 in the first rotation can be reduced. In FIG. 8, the curve shown by the broken line is the photosensitive member 8
3 shows the charging potential (surface potential) of the photoconductor 8 when the output from the charger 16 is constant from the first rotation of the photoconductor 8, that is, when the photoconductor 8 is driven at a predetermined charging output. This is equivalent to the characteristic shown in FIG. The solid line in FIG. 8 indicates that according to the present invention, the charging output of the charger 16 is increased at the first rotation of the photoconductor 8 as shown in FIG. It is when driving.

By controlling as described above, even when the image forming process is restarted after a predetermined time as described above, the surface potential of the photosensitive member 8 is set to be substantially equal between the first rotation and the second rotation. Can be. As a result, when digital exposure is performed by the laser unit 6, the amount of decrease in the electrostatic latent image potential _VL at that time is reduced, and a toner image of good density without density change can be formed. In addition, since there is no decrease in the surface potential V _O , it is possible to provide a high quality image in which fogging or the like is prevented.

According to the above configuration, after the image forming process is stopped, the charging output of the charger 16 is higher than the predetermined output only during the first rotation immediately after the photosensitive member 8 is started by the image forming start command. Even when the image formation by the laser beam is started from the first rotation, the output processing of the hargo copy which maintains the good image quality can be performed without deteriorating the image quality, and the output processing can be accelerated.

Here, as described above, when the image forming process is restarted after the elapse of a predetermined time, the change in the potential difference between the first rotation and the second rotation of the photosensitive member 8 and the subsequent rotations is described. Fig. 1 (B)
As shown in FIG. 7, it was found that a potential gradient might occur between the first rotation and the second rotation.

For this reason, as shown in FIG. 8C, the charger 16 is located at the boundary between the first rotation and the second rotation of the photosensitive member 8.
Is not immediately switched by the control circuit (CPU) 25, but is controlled so as to gradually return the charge output to a normal output state as shown in FIG. 1C. That is, by restarting the image forming process, 1
In a region (boundary region) before and after the boundary between the second rotation and the second rotation, the output is gradually decreased by providing a gradient for a certain period T.

The output of the charger 16 may be gradually reduced gradually to reduce the output linearly as shown in FIG. 1C, or as shown in FIG. 2A. In order to prevent the potential gap between the first and second rotations of the photoconductor from being generated as much as possible and to prevent the potential from abruptly changing, the output of the photoconductor starts to decrease more smoothly than before the completion of the first rotation. Then, after the photosensitive member shifts to the second rotation, the output reduction is completed and the output is returned to the predetermined output.

Similarly, in the example shown in FIG. 2B, the output starts decreasing stepwise before the completion of the first rotation of the photosensitive member, and is completed after the shift to the second rotation of the photosensitive member. To return to the predetermined output.

As described above, by gradually decreasing the charger 8 from a high output to a predetermined output state as shown in FIGS. 2A and 2B, the charging device 8 shown in FIG. The potential gradient between the first and second rotations is eliminated, and the almost uniform potential state shown in FIG. As a result, it is possible to obtain a stable toner image with more excellent image quality deterioration.
In addition, since the potential gradient is eliminated, there is no density difference due to the electrostatic latent image formed so as to extend over the first rotation and the second rotation, and a stable image quality without density change can be obtained.

In particular, as a charging means for uniformly charging the photosensitive member 8, a charger 1 using a corona charging method is used.
In the case of 6, when the photoconductor 8 is charged, the boundary of the charging width is not clear. Therefore, it is conceivable that a potential gradient as shown in FIG. However, according to the present invention, the output is gradually reduced by the charger 16 as shown in FIG. 2A or the output is reduced stepwise as shown in FIG. Since the charging is stabilized, and in the case of the present invention, there is no sudden change in the potential, the potential gradient can be eliminated, thereby preventing defects such as uneven image density.

With the above arrangement, in the embodiment of the present invention, after the image forming process is stopped, the charging output is driven at a higher output than the predetermined output only for the first rotation immediately after the start of the photosensitive member 8. Even when the image formation by the laser beam is started from the eyes, it is possible to prevent the formation of the unstable portion of the surface potential which occurs at the boundary between the first rotation and the second rotation, and to maintain the uniform image formation state.

In this embodiment, if the image forming process is stopped for a predetermined period of time, for example, 60 seconds (depending on the characteristics of the photosensitive member 8), only the first rotation immediately after the photosensitive member 8 is started is charged. The output is not driven at a higher output than the predetermined output, and a command to decrease the output during a certain period (T) before and after the boundary between the first rotation and the second rotation is not output,
When the image forming process is restarted after the elapse of the predetermined time, the drive control of FIG. 1 described above is performed.

By such means, in this embodiment, after the photosensitive member is stopped in a state close to a continuous copy,
In the case where the charge reduction at the rotation does not occur, it is possible to prevent the charging potential at the first rotation due to the excessive correction from increasing.

(Control Circuit Realizing Embodiment of the Present Invention)
Control for realizing the above-described embodiment will be described with reference to FIG. That is, the image forming process unit 7
The CPU 25, which is a control circuit for controlling the microcomputer including a microcomputer, comprises a microcomputer, and includes a program ROM storing a control program, a RAM sequentially storing information generated in the control, and the like.

The CPU 25 has a slit disk 22 by a slit sensor 23 for detecting the rotation state of the photoconductor 8.
Is input via a slit signal output circuit 27 that outputs a detection signal based on the slit detection. Therefore, the CPU 25 can grasp the rotational position of the photoconductor 8 based on the slit detection signal. That is,
First rotation and second rotation of the photosensitive member 8 due to the start of the image forming process
The detection of the rotation eye can be easily recognized by the slit disk 22 and the slit detection signal from the detection circuit 27 output from the slit sensor 23.

That is, the time when the slit sensor 23 detects the slit of the slit disk 22 due to the rotation of the photoreceptor 8 is recognized as the initial stage of the first rotation, and at that time, the power supply circuit 26 is controlled and the charging by the charger 16 is performed. To start. At the same time, a predetermined voltage is supplied to the grid electrode 16c for controlling the surface potential of the photoconductor 8. At this time, the grid voltage 16c
For example, a voltage of -510 V as shown in FIG. Then, before the photosensitive member 8 reaches the second rotation, the voltage is controlled and gradually reduced to -480 V as a predetermined output voltage supplied to the grid electrode 16c.

At this time, the recognition (detection) before reaching the second rotation of the photoconductor 8 is a predetermined time during one rotation from the time when the slit sensor 23 detects the slit. Therefore, the CPU 25 can easily grasp the position of the photoconductor 8 facing the charger 8 by using an internal timer or the like for the time before one rotation from the slit detection time. Then, the voltage supplied to the grid electrode 16c and the like as shown in FIG. 1 can be easily controlled. Therefore, the point in time before the initial position of the second rotation of the photoconductor 8 passes through the charger 8 can be easily grasped by receiving the slit detection signal and performing time counting or the like. It can be performed.

The CPU 25, which is a control circuit, knows that an image forming process will be executed by inputting a slit signal from the slit detecting circuit 27. The end of the image forming process can be grasped by setting the digital copier 1 to the standby state by the end of its own control. From this point on, the CPU 25 naturally counts that the image forming process is paused using the internal timer. As shown in FIG. 1B, when the charging is performed by the charging device 16 through the photoconductor 8 as shown in FIG. 1B, a predetermined time during which a charging potential difference occurs between the first rotation and the second rotation is passed. The CPU 25 recognizes. Based on this recognition, if there is a command to start the image forming process, as shown in FIG.
6 is performed. The control is as described above.

With the above-described control, a good image can be formed without causing a potential difference in the boundary area between the first rotation and the second rotation of the photosensitive member 8 as described with reference to FIG.

(Other Embodiments of the Present Invention) In the above-described embodiments of the present invention, when the photosensitive member 8 is charged when the image forming process is restarted after a predetermined time, the first rotation and the second rotation The purpose is to eliminate the difference in the charged potential with the eyes.

On the other hand, the change in the surface potential difference after the first and second rotations of the image forming process in a unit of time, not a unit of a predetermined time such as several minutes as described above, is examined over a longer period. As shown in FIG. 9, the initial change with time is large and the change after that is a gradual change. It can be seen that the potential difference after the rotation increases further.

To eliminate this, the same control as that of the above-described embodiment is performed, so that the potential difference generated between the first rotation and the second rotation can be eliminated.

That is, the digital copying machine 1 includes the photosensitive member 8
A counter is provided for counting the number of rotations before replacing the. In order to control the image forming process as shown in FIG. 10 according to the count content of the accumulation counter, the charging device 1 at the first rotation is used.
The control is performed such that the increase in output due to 6 is added to the normal output.

That is, FIG. 10A shows the increase in the output of the charger 16 corresponding to the cumulative number of rotations in FIG. 9, and the relationship of such characteristics is stored in a table such as a ROM in advance. And memorize it. That is, FIG.
With reference to the table shown in FIG. 5, the number of rotations of the photoconductor 8 is compared with the content of an accumulation counter, and the voltage of the accumulation counter is increased and supplied to the charger 16 in accordance with the count content. After the second rotation, drive control is performed in a predetermined output state as described in the above-described embodiment.

In order to realize this, a description will be given with reference to FIG. 3. In order to count the number of rotations of the photoreceptor 8, the slit signal from the slit sensor 23 is accumulated by a cumulative counter 2.
8 is counted. Since this slit signal is output each time the photoconductor 8 makes one rotation, the accumulation counter 28
Accumulates and counts (accumulated value) the number of rotations.

Then, as shown in FIG. 10A, a table (R) storing the relationship between the cumulative number of rotations of the photosensitive member 8 and the voltage of the increase in the drive output of the charger 16 at that time is stored.
OM) 29 is connected to the CPU 25. The CPU 25 fetches the drive output data of the increment of the charger 16 based on the count number of the accumulation counter 28 with reference to the table 29. Then, a voltage supplied to, for example, the grid electrode 16 c of the charger 16 is controlled via the power supply circuit 26.

Therefore, the above control will be briefly described as follows.
In the charger 16 using the scorotron method, the supply is controlled by adding the increased amount to the grid electrode 16c.
For example, when the voltage supplied to the grid electrode 16c at the normal predetermined output after the second rotation is -480 V, the table 29
, If the CPU 25 recognizes that it is necessary to increase -20V, the voltage of the predetermined output -4
A voltage of -500V added to 80V is applied to the grid electrode 1
6c. This is the first rotation of the photoconductor 8, and the drive control is performed so that the voltage gradually decreases to -480 V in the boundary region of the second rotation.

If the relationship in FIG. 10A is tabulated in the ROM 29, very fine control is possible.
However, if it is extremely difficult to supply a divided voltage as shown in FIG. 10A to the grid electrode 16c, for example, as shown in FIG. 10B or FIG. The voltage supplied to 16c may be controlled in a stepwise manner in correspondence with the cumulative number of rotations of the photoconductor 8 or the cumulative value at the time of cumulative rotation for each unit amount determined as 5V or 10V. The same operation and effect can be expected by using such a ROM table 29 as shown in FIG. 10B or 10C, and at the same time, the load on the ROM, that is, the storage capacity can be reduced, and the configuration can be made inexpensively.

As described above, according to the configuration of the other embodiment of the present invention, even if the potential change as shown in FIG.
The potential difference between the first rotation and the second rotation can be effectively eliminated. Therefore, even when image formation is started from the first rotation of the photoconductor 8 by the charger 16 and digital exposure with laser light is started, the image quality is not significantly degraded for a long period of time, An image having a constant image quality from the first sheet can be provided, and the image forming speed can be increased.

In this control, as shown in FIGS. 2A and 2B, if the photosensitive member 8 is gradually lowered from a state before the first rotation to a predetermined output state, as shown in FIG. )
It is possible to obtain stable image quality with no change in density without generating a potential gradient as shown in FIG.

In the description of the other embodiment of the present invention, the use state of the photoconductor 8, that is, the surface potential of the photoconductor 8 gradually decreases from the start of use, is considered in the first rotation and the second rotation. By controlling the voltage of the charger 16, there is no difference in the charged potential of the photoconductor 8. This requires the same control even when the image forming process of the photoreceptor 8 is left without being started for a predetermined time as described in the embodiment of the present invention. Therefore, naturally, the output of the charger 16 is controlled by increasing the output of the charger 16 according to the use condition of the photoconductor, for example, the cumulative rotation speed or the cumulative rotation time shown in FIG. If control is performed together, more effective control can be performed.

That is, with the start of the image forming process after the photosensitive member 8 has been left for a predetermined time, the increment according to the cumulative number of rotations of the photosensitive member 8 is further added to control the charging output of the charger 16. By doing so, the potential drop due to the standing for a predetermined time and the cumulative number of rotations (or the cumulative rotation time) of the photoconductor 8 can be eliminated at the same time, and the potential difference between the first rotation and the second rotation is prevented. In addition, charging can be performed in a stable and constant potential state, and a stable image can be provided.

The charging potential of the photosensitive member 8 gradually decreases as shown in FIG. 6 depending on the cumulative number of rotations or the cumulative rotation time. For this reason, the voltage control of the charger in the first rotation is performed based on the charging control performed in the second rotation based on the surface potential of the photoconductor 8. By performing the voltage control in the same manner, a more stable charging potential of the photoconductor 8 can be expected. That is, since the charging potential is reduced as shown in FIG. 9, it can be predicted that the potential cannot be maintained even if the charging control is performed by the constant voltage control in the second rotation. Therefore, the charging control for the second rotation is performed in the same manner as the charging control for the first rotation. In this case, the charging output for the second rotation charging control is naturally controlled to be smaller than the charging output for the first rotation. The degree of this change can be easily implemented by previously measuring the characteristics of the charging potential during long-term use of the photoconductor 8 and controlling the output state of the charger 16 in the second rotation.

(Other Embodiments According to the Embodiment of the Present Invention) In the above-described embodiment, the charger 16 based on the corona charging system, in particular, the scorotron system has been described as an example. Instead of such a configuration of the charger 16, the present invention can be similarly implemented by using a corona charger of a corotron type that performs corona discharge.

This charger has the same configuration as the charger 16 shown in FIG. 3, but without the grid electrode 16c. In this case, the charging output by the charger can be controlled by controlling the high voltage supplied to the corona discharge electrode 16b. Also, by supplying a predetermined voltage to the case 16a and controlling the voltage, the charging output by corona discharge can be controlled. That is, the potential at which the photoconductor 8 is charged can be easily controlled.

In the present invention, the charger 16 in the case where the corona charging method is used has been described. This is effective when the photosensitive member 8 is uniformly charged at a high speed. Further, the charging width cannot be defined, and the potential difference due to the switching control of the charging control between the first rotation and the second rotation cannot be eliminated. explained. However, as a charger, a contact charging system,
That is, the present invention can be used as it is even when the charging roller 30 as shown in FIG. 11 is used.

In this case, the start of the image forming process is provided with a charge control capable of forming an image from the first rotation of the photosensitive member 8, the contact time between the photosensitive member 8 and the charger 26 is shortened, and the surface potential becomes unstable. It is possible to prevent the portions from being formed on the surface of the photoreceptor 8 and maintain the uniformity of the image formation, and it is possible to significantly increase the number of copies per life of the photoreceptor 8. That is, also in the roller charger 30, by performing the charging control as shown in FIG. 1 and the charging control as shown in FIG. 10, a toner image can be formed at a surface potential having a small potential gradient, , And high quality images can be easily obtained.

The structure of the roller charger 30 will be briefly described in the following.
Then, a conductive layer 30b of polyurethane rubber having a thickness of about 3 mm obtained by mixing an appropriate amount of alumina is formed,
It is composed of a coating layer 30c coated with insulating nylon having a thickness of about 0 to 20 μm. In particular, the overall resistance value of the roller charger 30 is 10 ⁶ Ω · cm and JI
A charging roller having an SA hardness of about 30 ° and a diameter of about 12 mm can be used.

The above-mentioned accumulation of electron traps on the organic photoreceptor 8 is likely to occur in a phthalocyanine compound generally used as a charge generating material for the photoreceptor. It was common to add. However, according to the present invention, even when image formation by laser light is started from the first rotation,
It is possible to prevent an unstable portion of the surface potential from being formed on the surface of the photoreceptor 8 and maintain an image forming state uniformly.

Therefore, in the above-described embodiment, the excellent effect of the image forming control of the present invention was confirmed, and a comparison was made with the image forming state when image forming is performed from the first rotation in the conventional case.

The results of the comparison are shown in Table 1 below. In Table 1, what is shown as the prior art is a case where the photoreceptor 8 is pre-rotated, the charging device 8 and the like are simultaneously operated to perform pre-processing, and then image formation is performed. This is a result when an image is formed by performing exposure together with charging by the charger 16 or 26 from the rotation.

[0092]

[Table 1]

In Table 1, according to the prior art, the life of the photosensitive member is shortened because the photosensitive member is pre-rotated. Therefore, it is necessary to frequently replace the photoconductor within the usage limit of the apparatus. Therefore, even if there is no price difference between the photosensitive members, the total running cost is disadvantageously high.

Further, when the present invention is applied to reversal development, toner consumption occurs at the time of pre-rotation of the photosensitive member, so that the amount of toner consumption increases.

In this regard, according to the present invention, the life of the photosensitive member 8 is extended, and the pre-rotation processing of the photosensitive member 8 is not required. It is. Further, in the present invention, the same applies to the contact charging 26 and the non-contact corona charging 16. By using the non-contact charger 16, the life of the photoconductor 8 is further extended and the total photoconductor The cost of 8 goes down.

In FIGS. 1 and 2 illustrating the embodiment of the present invention, the end of the first rotation of the photosensitive member 8 is the charging device 1.
Before passing through the position 6, the output of the charger 16 is controlled to gradually decrease from the high output to the predetermined output. Therefore, when the end of the first rotation of the photoconductor 8 is just before passing through the charger 16, for example, when the time for the photoconductor 8 to make one rotation is about 1 second (1000 msec), the charging device 16 is moved from 25 msec before. The output is gradually reduced, and 25
Drive control is performed with a predetermined output after 0 msec. That is, FIG.
In addition, the time T in FIG. 2 is set to about 250 msec, and is gradually reduced after the time T to return from the high output to the predetermined output. This time T is about 1 for one rotation of the photoconductor 8.
/ 4, and the point in time when the gradual decrease is started corresponds to about 1/40.

Such a time may be set in accordance with the characteristics of the photoreceptor 8, and is particularly effective when the corona charger 16 is used because the charging width cannot be regulated.

[0098]

According to the image forming apparatus of the present invention, an abrupt change in potential difference is prevented from occurring between the first rotation and the second and subsequent rotations, and the image forming process can be quickly performed without deteriorating the image forming state. There are advantages that can be started. Further, it is possible to prevent the occurrence of fogging in the non-image forming area on the surface of the photoreceptor, prevent the waste of toner, reduce the running cost and extend the life of the cleaning device.

When the resumption of the image forming process has not passed the predetermined time, the charging control by the charger is not executed. The image forming process can be started at an early stage without deteriorating an image forming state such as a fog or a fog step.

Further, a sudden change in the potential difference between the first rotation and the second and subsequent rotations is prevented from occurring for a long period of time, and even when the characteristics of the photosensitive member change with time, the image formation is maintained while maintaining a uniform image formation state. There is an advantage that processing can be started quickly.

Further, when the charging output is gradually reduced from the high output state to the predetermined output state in response to the resumption of the process of the image bearing member or the aging of the image bearing member, the charging is performed stepwise or continuously. Thus, an unstable portion of the surface potential generated at the boundary between the first rotation and the second rotation can be smoothly and effectively eliminated, and the image formation state can be maintained uniformly.

Also, by gradually decreasing the drive output higher than the predetermined output before the first rotation and returning to the predetermined output after the second rotation, the boundary between the first rotation and the second rotation is obtained. The charging potential difference in the region can be more effectively eliminated, and even when image formation is performed using the first and second rotation regions, image quality deterioration such as a change in image density in the middle does not occur. .

In the case where corona discharge is used as the charging means, problems such as a decrease in the film thickness of the image carrier are naturally reduced, so that the service life can be extended, the running cost can be reduced, and the image carrier can be reduced. It can be expected to reduce the use cost.

In particular, when an organic photoreceptor is used as the image carrier, even if an inexpensive phthalocyanine compound is used, the image forming process can be quickly performed without deteriorating the image forming state such as the density step and the fog step from the first rotation. Being able to start has the advantage that the number of drum revolutions can be reduced and the number of copies per drum life can be significantly increased.

[Brief description of the drawings]

FIG. 1 is provided for describing an embodiment of the present invention, in which the driving control of a charging unit is shown by the state of the surface potential of a photoconductor at the first rotation and the second rotation of the photoconductor. FIG. 9 is a characteristic diagram showing the characteristics of the related art.

FIG. 2 is a timing chart for explaining an embodiment for controlling driving of a charger for executing an image forming process according to the present invention.

FIG. 3 is a configuration diagram for explaining a configuration of an image forming process unit according to the present invention.

FIG. 4 is a configuration diagram of a digital copying machine showing an overall structure of an image forming apparatus including the image forming process unit shown in FIG.

FIG. 5 is a cross-sectional view for explaining a specific example of an organic photoconductor structure of a photoconductor constituting the image forming process unit shown in FIG. 3;

FIG. 6 is a potential explanatory diagram illustrating a principle for forming a toner image by reversal development in the image forming process unit shown in FIG. 3;

FIG. 7 is a view for explaining an embodiment of the present invention, in which a potential difference occurs between the first rotation and the second rotation of the photoconductor due to restart according to the pause time of the image forming process, and does not occur. FIG. 9 is a characteristic diagram showing a relationship in the case.

FIG. 8 relates to an embodiment of the present invention, and illustrates one of the photoconductors.
FIG. 11 is a characteristic diagram illustrating a change state of the surface potential of the photoconductor when the charging output of the charger at the rotation is increased from a predetermined charging output after the second rotation.

FIG. 9 is a view for explaining another embodiment of the present invention, and is a view showing the relationship between the cumulative value of the rotation time of the photoconductor and the amount of decrease in the charging potential in the first rotation.

FIG. 10 is a diagram illustrating a relationship between a cumulative value of a rotation time of a photoconductor and an increase in output of a first rotation by a charger in order to realize another embodiment of the present invention.

FIG. 11 is a perspective view for explaining the structure of a roller charger using a contact charging system as the charger according to the present invention.

[Explanation of symbols]

 1 Digital Copier (Image Forming Apparatus) 7 Image Forming Process Unit (Image Forming Process Means) 8 Photoconductor (Image Carrier) 16 Charger (Charging Means) 16a Case (Shield Plate) 16b Corona Discharge Electrode 16c Grid Electrode 17 Development Apparatus 22 Slit disk 23 Slit sensor 25 CPU (control means) 26 Power supply circuit 27 Slit detection circuit 28 Cumulative counter (counting means) 29 Table (ROM)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazushige Morita 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Tomoko Kanazawa 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Yoshihide Shimoda Yoshihide Shimoda 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Masaru Nakamura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation F term (reference) 2H003 BB11 CC01 DD03 EE12 2H027 DA40 DA41 EA01 ED02 ED03 EE02 EE08 EF06 ZA01

Claims (6)

[Claims] A charging means for charging the surface of the image carrier; an exposure means for irradiating the charged surface of the image carrier with light; and an electrostatic member formed on the surface of the image carrier in response to the light irradiation of the exposure means. An image forming apparatus comprising: an image forming process unit including a developing unit that visualizes a latent image, wherein the charging unit is turned on the first rotation of the image carrier in response to the start of the process by the image forming process unit. An image forming apparatus comprising: a control unit configured to drive at a higher output than a predetermined output and to gradually reduce the output to a predetermined output after the second rotation. 2. The control means determines whether or not the start of the image forming process by the image forming process means has passed a predetermined time since the end of the previous process. 2. The image forming apparatus according to claim 1, wherein the charging unit is driven and controlled at a predetermined output from the first rotation of the image carrier. 3. The control means includes means for counting the number of rotations or the cumulative value of the rotation time of the image carrier, and one rotation of the image carrier every time the image forming process is started based on the counting result of the counting means. A drive output of the charging means to be applied only to the eyes,
A table in which a difference from a predetermined drive output to be gradually reduced and applied after the second rotation is increased with the progress of the cumulative value, wherein at the start of the image forming process, the cumulative value of the coefficient means and 3. The image forming apparatus according to claim 1, wherein the driving control is performed based on a relationship with a driving output of a first rotation of the charging unit by the table. 4. The image forming apparatus according to claim 1, wherein the drive output of the first rotation by the charging means is performed continuously or stepwise so as to be gradually reduced to a predetermined output. 5. The control means according to claim 1, wherein the output of the charging means at the time of switching of the charging means from the first rotation to the second rotation of the image carrier is started before the completion of the first rotation. 2. The image forming apparatus according to claim 1, wherein the control is performed so as to be completed after the transfer. 6. The charging means is a scorotron-type corona charger having a grid electrode, and the control means controls a voltage supplied to a grid electrode of the corona charger for controlling a charging potential of the image carrier. The image forming apparatus according to claim 1, wherein: