JP3482131B2 - 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 such as a copying machine or a laser printer using electrophotography.

[0002]

2. Description of the Related Art In an image forming apparatus using electrophotography,
The surface of the photoreceptor, which is an image carrier, is uniformly charged, and the surface is imagewise exposed to form an electrostatic latent image according to the exposed image. In order to visualize this electrostatic latent image. In addition, for example, development is performed with a toner that is a colorant. The toner image on the surface of the image carrier formed by this development is transferred to a transfer material (sheet) such as a sheet that is appropriately conveyed, the sheet is separated from the photoconductor, and passed through a fixing device to obtain a hard copy. I try to finish it.

On the other hand, after the toner image is transferred onto the sheet, a part of the toner of the toner image remains on the photoconductor, and the residual toner is cleaned and reused for repeated use of the photoconductor. The charge is removed to remove the residual charge, and these operations are repeated in order, so that the above-described image formation on the photoconductor can be repeatedly used.

The surface potential of the photoconductor has a great influence on 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.

[0005] However, in a general inexpensive photoreceptor, the photoreceptor sometimes new, no particular problem arises if I stable charging means. However, as the image formation is repeated, the charging potential of the first rotation at the beginning of use does not rise to the predetermined potential. As a result, in the image formed by forming the first image, the area of
Surface potential difference between the rotating and subsequent region occurs, the image density of nonuniform, the head of the base is generated, there is a problem of causing image quality degradation.

[0006] In particular, in the image formation using the reversal development, these problems are conspicuously manifested as a halftone density step and a fog step in a white background which is a background. Further, as a photoconductor, it is a phenomenon which occurs remarkably in a general photoconductor which is used for digital use using an inexpensive phthalocyanine compound.

As one means for solving the above-mentioned problems,
In general, a method of rotating the photoconductor plural times while performing the charging and static elimination steps before starting the image process to stabilize the surface potential of the photoconductor by operating the charging unit and the static elimination unit, and then executing the image forming process is common. Is being used for 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,
It becomes impossible to output the hard copy from the first sheet at high speed.

[0008] b As further charging means - in the case of using a contact type charging means such as La method or brush method, a decrease in film thickness of rather large, especially the photoreceptor. Therefore, if the processing such as pre-rotation is performed in order to stabilize the photosensitive member as described above, the number of rotations of the photosensitive member is significantly increased, and the 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. 4-161963, in an image forming apparatus for uniformly charging a photosensitive member by using a contact charging means (roller charging), charging conditions at the first rotation and after the second rotation, An image forming apparatus that changes exposure conditions and developing conditions is disclosed. According to the image forming apparatus of the disclosed technique, image formation can be started from the first time of the photoconductor, and a hard copy with stable image quality can be output from the first sheet. That is, since the charging potential of the first rotation and the charging potential of the second and subsequent rotations can be made substantially equal, and the exposure and development conditions are controlled so that the same image quality is obtained, the image quality is stable while the speed-up processing is performed. Will be able to deal with.

As another method, it is conceivable to use a photoconductor in which the photoconductor surface potential becomes the same after the first and second rotations of the photoconductor due to the start of image formation. As such a photoconductor, Japanese Patent Laid-Open No. 9-12771
There is one disclosed in Japanese Patent No. The photoconductor disclosed in this publication contains a phthalocyanine compound as a charge generating substance in the charge generating layer constituting the photoconductor, and further contains an azo compound to reduce the charging potential at the first rotation as a characteristic of the photoconductor. I am trying to suppress it. Therefore, the image formation is performed from the first rotation of the photosensitive member, so that the speedup can be dealt with.

[0011]

In recent years, digitization of image forming apparatuses has progressed, and many image forming apparatuses employ a reversal development method. Further, there is a demand for speeding up of the image forming apparatus, and in addition to these, a corona charging method (charging means of scorotron method) is widely used as a charging means instead of a contact charging method. .

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 like the contact charging means, and the position where the charging potential is changed becomes unclear. Therefore, it is extremely difficult to accurately switch the charging potential and correct the potential gap at the boundary between the first rotation and the second rotation of the photoconductor. To achieve that,
Position detecting means and means for detecting the surface potential state of the photoconductor,
Further, a means for controlling them is required, but it is very difficult to prevent the potential gap because the charged area cannot be defined as described above.

Therefore, as described in Japanese Patent Application Laid-Open No. 4-161963, the image forming apparatus of the contact charging type cannot be used as it is in the corona charging type.

Therefore, in the image forming apparatus capable of high-speed processing utilizing the corona charging means, after the pre-rotation without image formation is performed to stabilize the charging potential,
It was necessary to carry out the image forming process. Therefore, as compared with 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 required copying time becomes long cannot be solved. Further, since the photoconductor is rotated extra, there is a problem that the life of the photoconductor is shortened.

It should be noted that improving the charge reduction in the first rotation as a characteristic of the photoconductor causes problems such as sensitivity reduction and cost increase. In particular, if the photoconductor disclosed in Japanese Patent Laid-Open No. 9-127711 is used, the speed-up process can be easily performed, but the manufacturing cost and the cost of the photoconductor are increased.
In particular, the production yield and the like for obtaining the photoconductor having the above-mentioned characteristics is a serious problem, and the cost is inevitably high.

According to the present invention, in an image forming apparatus using a general photoconductor and a charging means, simple control can be performed without adding a complicated control device or detection device and omitting the pre-rotation of the photoconductor. Therefore, it is an object of the present invention to provide an image forming apparatus capable of making the surface potential of a photosensitive member uniform, shortening an image forming time, and maintaining good image quality.

Further, an object of the present invention is to provide an optimum image forming apparatus using a digital system (digital exposure) and a corona charging system which can cope with speeding up as a charging means. is there.

[0018]

Achieve Means for Solving the Problems] above objects
Images forming apparatus of the present invention, a charging unit, an exposure means for irradiating light to the image bearing member surface after charging for charging the surface of the image bearing member,
An image forming apparatus comprising image forming process means including developing means for visualizing an electrostatic latent image formed on the surface of the image carrier according to light irradiation of the exposing means. means driven at a high output from the predetermined output the charging means to the first rotation of the image carrier in accordance with the start process by, the second rotation onwards Ru provided with a control means for driving and gradually decreases to a predetermined output.

[0019] Re good to the image forming apparatus according to the above configuration,
When the image forming process is started, the charging means is increased from the predetermined output by the amount corresponding to the decrease in the charging potential in the first rotation caused by repeated fatigue only in the first rotation of the image carrier. Drive gradually. Then, 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 bearing member 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 potentials are substantially the same. As a result, defects such as density difference and fog difference corresponding to the regions of the first and second rotations do not occur on the image. Further, since the image forming process can be started substantially in synchronism with the first rotation of the image bearing member by omitting the pre-rotation of the image bearing member, the consumption of the image bearing member due to the extra rotation is suppressed,
The life etc. can be extended.

Further, in the image forming apparatus having the above-described configuration, the control unit determines whether or not the start of the image forming process by the image forming process unit has passed a predetermined time from the end time of the previous process, and the predetermined process is performed. When the time has not elapsed, the charging means is driven and controlled with a predetermined output from the first rotation of the image carrier. As a result, if the time until the image forming process by the image carrier is restarted due to the end of the image forming process is short, that is, if the predetermined time has not elapsed, the charging unit increases the high output. An attempt is made to prevent an opposite potential difference between the first rotation and the second rotation when driven. That is, when the correction due to excess is eliminated and the start of the image forming process is a short time after the end of the previous image forming process, the image carrier itself remains in 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, after the lapse of a predetermined time, when the image forming process, such as is resumed it will be controlled as described above is executed.

[0021]

[0022]

Further, in the images forming apparatus having the above-described configuration, the drive output of the first rotation by the upper Symbol charging means to be gradually decreased to the predetermined output, and to perform continuously or stepwise. For example, when gradually decreasing the output of the charging means, the predetermined drive output to be applied to the starting 2 rotating onward from said predetermined output higher drive output to impart to the charging means only one rotation of the image carrier by the image forming process If the output is controlled so as to have a continuous (linear or meandering) output gradient over a certain period of time from the end of the first rotation of the output reduction to the start of the second rotation, During this period, the output is continuously returned to the predetermined drive output without interruption.
Therefore, the effect of eliminating the surface potential difference of the image carrier in the boundary region of a predetermined width between the first rotation and the second rotation is promoted.

Then, the output reduction by switching from the drive output higher than the predetermined output given to the charging means to the predetermined drive output given after the second rotation is reduced by 1 only for one rotation of the image carrier by the start of the image forming process. When controlling to make the output gradient stepwise from the end of the first rotation to the fixed period after the start of the second rotation, the output is continuously continuous stepwise from the first rotation to the second rotation. To return to a predetermined drive output. Therefore, it is possible to eliminate the surface potential difference in the above-described open region of the image carrier of the first rotation and that of the second rotation. Moreover, when the output is gradually reduced in stages, the drive control becomes simple.

[0025] In still images forming apparatus having the above structure, the upper Symbol control means, the output reduction is completed first rotation of the charging means switching time of the charging means in the second rotation from the first rotation of the image bearing member It is characterized in that it is controlled to start from the front and complete after the shift to the second rotation.

This can 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 or the like, the output state of the charging unit is gradually reduced from the stage one rotation before, so that the potential difference at the boundary is gradually eliminated. Therefore, it is possible to eliminate the occurrence of a large potential difference on the way.

Further in images forming apparatus having the above structure, as the upper Symbol charging means, it is possible to use a corona charger of scorotron including a grid electrode, said control means controls the charging potential of the image bearing member corona that controls the voltage supplied to the grid electrode of the charger.

As described above, in the present invention, the charging method by corona discharge can be utilized, and at that time, the surface potential difference in the boundary region between the first rotation and the second rotation of the image carrier can be eliminated as described above. In other words, in the case of the corona charger, the charging width of the image carrier cannot be regulated, 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 in that region will not occur. Will tend to occur. However, in the control of the present invention, that is, since the output of the corona charger is gradually reduced to a predetermined output before the end of the first rotation, it is possible to effectively eliminate the surface potential difference in the above-mentioned boundary region and make the potential almost equal. it can. Furthermore, since the voltage supplied to the grid electrode of the corona charger is controlled, it is sufficient to perform voltage control of about several hundreds of V instead of the very high voltage of about tens of thousands of V for corona discharge. Will be easier.

When an organic photoconductor is used as the image bearing member, an inexpensive phthalocyanine compound is used and a general photoconductor for digital images is used.
By driving the charging unit to have a higher output than the predetermined output and to gradually decrease until the output returns to the predetermined output only for the first rotation immediately after the photoconductor is started when the image forming process is stopped for a certain period of time (stopped state of the image forming process). The surface potential difference in the boundary region between the first rotation and the second rotation can be effectively eliminated. In particular, in the case of the above-described organic photoreceptor, the potential difference appears remarkably at the start of the image forming process from the rest time, but this can be effectively eliminated, and the image density does not change in the middle. Similarly, fogging and the like can be eliminated, and the object of the present invention can be effectively achieved by using an inexpensive photoconductor.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments suitable for deepening the 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 photoconductor that is an image carrier when the present invention is carried out and the surface potential of the photoconductor when the present invention is not carried out. Also, FIG.
FIG. 3 is a time chart showing the relationship between the rotation state of the photoreceptor, which is an image carrier for carrying out the invention, and the voltage supplied to the corona charging means. FIG. 3 constitutes an electrophotographic image forming apparatus according to the invention. FIG. 4 is a configuration diagram showing details of the image forming process means, and FIG. 4 is a configuration diagram showing the entire image forming apparatus provided with the image forming process means of FIG.

First, before explaining the 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 horizontally moves below the document table 2, scans the image of the document with the light of the light source 4, and distributes the reflected light from the document to the CCD 5. In this way, the image of the original is read by the CCD 5 and stored in an image memory (not shown) as image data.

The laser unit 6 shown in FIG. 4 comprises a semiconductor laser, a polygon mirror and an fθ lens.
The semiconductor laser is driven on the basis of the image data stored in the above-mentioned image memory, and the light emitted from the semiconductor laser passes through the polygon mirror and the fθ lens to form an image carrier of the process unit 7 which is an image forming process means. The photosensitive member 8 formed in the drum shape is distributed. In the image forming process unit 7, the surface of the photoconductor 8 is charged,
A toner image is formed through the steps of exposure and development. This toner image is transferred to a sheet that is 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 is transferred is heated and pressed by the fixing roller 14 to melt and fix the toner, and then the sheet is ejected to a paper ejection unit including a sorter 15 and the like.

The image forming process unit 7 described above will be described in more detail with reference to FIG. The image forming process unit 7 includes a photoconductor 8 and 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 arranged so as to face the peripheral surface of the photoconductor 8. It is composed of a cleaning blade 20 and a charge eliminating lamp 21. The photoconductor 8 is rotated in the direction of arrow A with the start of the image forming process for image formation. The charger 16 charges the surface of the photoconductor 8 with electric charges of a single polarity. The surface of the photoconductor 8 charged by the charger 16 is exposed by the 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 photoconductor 1 and the transfer unit 18 with controlled timing, and the toner image formed on the surface of the photoconductor 8 is transferred onto the sheet by the action of the transfer unit 18. The peeling device 19 peels the sheet electrostatically adsorbed on the photoconductor 8. Cleaning blade 20
Removes toner remaining on the surface of the photoconductor 1 after transfer. The charge eliminating 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 facing a slit of a slit disk 22 coaxially attached to the photoconductor 8.
Detected by.

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

The charger 16 of the present invention which constitutes the image forming process unit 7 has a case (shield case) 16b in which the surface of the corona discharge electrode 16a in the shape of a wire or a saw blade is open at the surface facing the photoconductor 8. It is provided in an electrically insulated state. Then, a grid electrode 16c which is electrically insulated and held with respect to the case 16a is attached to the open surface of the case 16b to form a corona charger 16 of the scorotron system. 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 unit 6 performs the digital exposure, the area corresponding to the image portion is irradiated with light contrary to the exposure by the analog method. Therefore, it is necessary to develop with the developing device 17 an electrostatic latent image formed by the charging potential being lowered in the area irradiated with light. 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 photoconductor 8 and the developing bias potential supplied to the developing roller 17a constituting the developing device 17 and the laser exposure in the relationship as shown in FIG. Shows the relationship between the electrostatic latent image potentials formed by decreasing the surface potential of the photoconductor 8. That is, the surface of the photoconductor 8 is uniformly charged by the charger 16 to the charging potential V _O (for example, −550V).
Then, when exposed by the irradiation of the laser beam, the charge on the surface of the photoconductor 8 is canceled according to the amount of the light,
An electrostatic latent image is formed at the latent image potential _VL (for example, -100 to -300V). A developing bias potential DVB (for example, −4) is provided between the photoconductor 8 and the developing roller 17a of the developing device 17.
00V) is supplied. This developing bias potential DV
Using the difference between B and the latent image potential V _L as the development potential, for example, negatively charged toner is supplied to the surface of the photoconductor 8 from the development roller 17a. As described above, in the digital copying machine 1 according to the present invention, the reversal development is performed so that the toner is attached to the exposed portion of the surface of the photoconductor 8 to form a toner image.

A digital copying machine 1 having a structure as shown in FIG.
In step 1, upon receiving an image formation start command, the surface of the photoconductor 8 is repeatedly subjected to the steps of charging, exposing, developing and transferring. Therefore, on the surface of the photoconductor 8 that has undergone the exposure process, a potential difference is generated between a portion irradiated with laser light and a portion not irradiated with laser light. If the charging process is performed while leaving this as it is, a memory phenomenon in which the potential difference caused by the previous image formation is sequentially accumulated in the electrostatic latent image this time occurs, and the image quality is deteriorated.

Further, in a portion that receives little or no exposure to laser light, the charging potential increases every time the photosensitive drum 1 rotates, and the uniformity of the image formed in each process is impaired. Therefore, the surface of the photoconductor 8 that has completed the transfer process is irradiated with the light of the charge eliminating lamp 21 to remove the electric charge remaining before the charging process by the charger 16 is performed. The photoconductor 8 is compensated so as to always realize a stable image quality state.

As a result, the photoconductor 8 is repeatedly used,
By repeating the image forming process in sequence,
Can 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 generation layer 8b. This electron trap prevents the movement of positive charges, exists in the material itself, and is accumulated in the material due to light fatigue or the like.

Therefore, a local electric field is generated between the electron trap and the substrate 8a of the photoconductor 8 by the irradiation of the light from the static elimination lamp 21, and the carrier injection is increased to lower the surface potential of the photoconductor. Among the electron traps, those accumulated by light fatigue include those that recover by leaving and those that do not recover, and the state of change in the surface potential of the photoreceptor differs depending on the time the photoreceptor drum is left.

For example, as shown in FIG.
The state of the surface potential between the second rotation and the second rotation is the surface of the photoconductor 8 in the state of the image forming process restarted immediately after the end of the previous image forming process, as shown in FIG. The potential is substantially constant in the first and second rotations without any potential difference.

On the other hand, when the image forming process is restarted after, for example, about 10 minutes have passed after the end of the previous image forming process, as shown in FIG. In the region of the second rotation, the charging potential is reduced by about 50V as compared with the charging potential of the second rotation.

When the charging potential is lowered in this manner, the background margin, which is the difference between the charging potential V ₀ and the developing bias potential DVB, is reduced as described with reference to FIG. 6, fogging occurs in the non-image area, and the image quality is reduced. Cause deterioration. When fogging occurs in this way, toner that is not originally required is adsorbed on the surface of the photoconductor drum 1, and the running cost increases due to an increase in toner consumption, and the burden on the cleaning blade 20 increases. There is a problem of early deterioration.

The image density changes midway due to the potential difference of the electrostatic latent image due to the potential decrease. 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 rest, and the surface potential difference in the boundary region between the first rotation and the second rotation when the charger 16 is operated to charge the photosensitive member 8 is restarted. 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 the period corresponding to one rotation of the photoconductor 8. That is, when a series of image forming processes by the digital copying machine 1 is finished, the copying machine 1 is left unattended, and thereafter the image forming start command is received, and the image forming process is restarted, the photoconductor 8 is charged by the charger 16 When charged at
When the characteristic as shown in (A) is exhibited, the drive output by the charger 16 is maintained 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 above-mentioned leaving time becomes long and a predetermined time has elapsed, charging is performed. The charging output of the container 8 is increased while the photosensitive member 8 makes one rotation, and the normal predetermined charging output is obtained from the second rotation.

The above-mentioned predetermined time is the time during which the surface potential of the photoconductor 8 decreases as shown in FIG. 7B even when the charging device 8 charges with a normal charge output. Depends on However, if the photoconductor 8 to be used is decided, as shown in FIG.
The time to fall into the state as shown in (B) is naturally determined by performing a simulation or the like.

As described above, if the control circuit (CPU) 25 on the main body side of the digital copying machine 1 recognizes that the restart of the image forming process is over the predetermined time, as shown in FIG. 1 of the photoconductor 8 in response to the start command of
In the second rotation, the charging output is increased via the power supply control unit 26 for driving the charging device 16 as compared with the case of the normal predetermined output, and in the second rotation, the charging device 8 is drive-controlled by the predetermined charging output. .

FIG. 8 shows the characteristics of the surface potential of the photoconductor 8 at that time.
Shown in. As shown by the solid line in FIG. 8, the charging device 16 in the first rotation can reduce the decrease in the charging potential V _O of the photoconductor 8. In FIG. 8, the curve indicated 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 above, that is, when it is driven at a predetermined charging output. This is equivalent to the characteristic shown in FIG. The solid line in FIG. 8 is according to the present invention, and the charging output of the charger 16 is increased by the first rotation of the photoconductor 8 as shown in FIG. It is when driven.

By controlling in this way, even when the image forming process is restarted after a predetermined time as described above, the surface potential of the photoconductor 8 is made approximately equal to that at the first and second rotations. 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 can be reduced, and a toner image of good density without density change can be formed. Moreover, since the surface potential V _O does not decrease, it is possible to provide a high-quality image in which fogging is prevented.

According to the above configuration, the charging output of the charger 16 is higher than the predetermined output only in the first rotation immediately after the photoconductor 8 is started by the image forming start command after the image forming process is stopped. Even when the image formation by the laser beam is started from the first rotation, the output processing of the Hargo copy maintaining the good image quality can be performed without deteriorating the image quality, and the output processing can be speeded up.

(Best Mode for Carrying Out the Invention) Here, in the case where the image forming process is restarted after a predetermined time elapses as described above, the change in the potential difference between the first rotation and the second rotation of the photosensitive member 8 is performed. Examining the situation in detail, Fig. 1 (B)
It was found that there is a case where a potential gradient is generated between the first rotation and the second rotation, as shown in FIG.

Therefore, as shown in FIG. 8C, the charger 16 is provided in the boundary region between the first rotation and the second rotation of the photosensitive member 8.
The charging output by the control circuit (CPU) 25 is not immediately switched, but is controlled so as to gradually return the charging output to the normal output state as shown in FIG. In other words, by restarting the image forming process,
In a region before and after the boundary between the second rotation and the second rotation (boundary region), a gradient is provided for a certain period T, and the output is gradually reduced so as to be gradually reduced.

As a form of gradually decreasing the output of the charger 16, the output may be linear as shown in FIG. 1 (C), but as shown in FIG. 2 (A). , In order to prevent the potential gap between the first and second rotations of the photoconductor as much as possible and to prevent the potential from changing rapidly, the output starts to decrease in a gentle curve before the completion of the first rotation of the photoconductor. Then , after shifting to the second rotation of the photoconductor, the output reduction is completed and the output is returned to the predetermined output.

Similarly, in the example shown in FIG. 2 (B), the output reduction is gradually started before the first rotation of the photosensitive member is completed, and the output reduction is completed after the second rotation of the photosensitive member. The output is returned to the predetermined level.

As described above, as shown in FIGS. 2 (A) and 2 (B), the charger 8 is gradually reduced from the high output to the predetermined output state. By eliminating the potential gradient between the second rotation and the second rotation, the substantially uniform potential state of FIG. 1A can be obtained. As a result, it is possible to obtain a stable toner image with further improved image quality.
Moreover, since the potential gradient disappears, there is no difference in density due to the electrostatic latent image formed across the first and second rotations, and stable image quality without density change can be obtained.

Particularly, as a charging means for uniformly charging the photoconductor 8, a charging device 1 using a corona charging system is used.
In the case of 6, when the photoconductor 8 is charged, the boundary of the charging width becomes unclear. Therefore, it can be considered that the potential gradient as shown in FIG. However, according to the present invention, by gradually reducing the output by the charger 16 as shown in FIG. 2 (A) or by gradually reducing the output in FIG. 2 (B), within the effective width of the corona discharge. Since the charging is stabilized, and in the case of the present invention, there is no abrupt potential change, the potential gradient can be eliminated and defects such as uneven image density can be prevented.

With the above-described configuration, 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 photoconductor 8 is activated, and the first rotation is performed. Even when the image formation by the laser beam is started from the eyes, the unstable portion of the surface potential which is generated at the boundary between the first rotation and the second rotation can be prevented from being formed, and the image formation state can be uniformly maintained.

Further, in the present embodiment, if the pause of the image forming process is within a predetermined time, for example, 60 seconds (depending on the characteristics of the photoconductor 8), charging is performed only in the first rotation immediately after the photoconductor 8 is started. The output is not driven at a higher output than the predetermined output, and an instruction to reduce the output is not output within a certain period (T) before and after the boundary between the first rotation and the second rotation.
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 the present embodiment, the photosensitive member 1 is removed after being rested in a state close to continuous copying.
It is possible to prevent the charging potential of the first rotation from becoming high due to overcorrection when the charging reduction of the first rotation does not occur.

(Control Circuit Realizing Embodiment of the Present Invention)
Control for realizing the embodiment described above 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 including, includes a microcomputer, and includes a program ROM that stores a control program, a RAM that sequentially stores information generated in the control, and the like.

The CPU 25 has a slit disk 22 formed by a slit sensor 23 for detecting the rotation state of the photoconductor 8.
And Tsu Na to enter through the slit signal output circuit 27 for outputting a detection signal based on the slit detector. Therefore, the CPU 25 can grasp the rotational position of the photoconductor 8 based on the slit detection signal. That is, the detection of the first rotation and the second rotation by the start of the image forming process of the photoconductor 8 can be easily recognized by the slit disc 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 by the rotation of the photosensitive member 8 is recognized as the initial stage of the first rotation, and at that time, the power supply circuit 26 is controlled to charge the charger 16. To start. At the same time, a predetermined voltage is supplied to the grid electrode 16c that controls the surface potential of the photoconductor 8. At this time, grid voltage 16c
Is supplied with a voltage of −510 V as shown in FIG. Then, the voltage is controlled so as to be gradually reduced to -480 V as a voltage which is a predetermined output supplied to the grid electrode 16c before the photoconductor 8 reaches the second rotation.

At this time, the recognition (detection) before reaching the second rotation of the photosensitive member 8 is a predetermined time from the time when the slit sensor 23 detects the slit to one rotation. Therefore, on the CPU 25 side, the position of the photoconductor 8 facing the charger 8 can be easily grasped by using an internal timer or the like for the time before one rotation is made after the slit is detected. Then, the voltage supplied to the grid electrode 16c as shown in FIG. 1 can be easily controlled. Therefore, the time point 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, and control as shown in FIG. It can be performed.

Further, the CPU 25, which is the control circuit, knows that the image forming process is executed by inputting the slit signal from the slit detection circuit 27. Then, the end of the image forming process can be grasped by setting the digital copying machine 1 to the standby state by the end of its own control. From this point on, the CPU 25 naturally uses the internal timer to count that the image forming process is paused. As shown in FIG. 1 (B), this count indicates that a predetermined time has elapsed in which a charging potential difference is generated between the first rotation and the second rotation when charging is performed by the charger 16 via the photoconductor 8. The CPU 25 recognizes it. By this recognition, if there is a command to start the image forming process, as shown in FIG.
6 drive output control is executed. The control is as described above.

By the control as described above, it is possible to form an excellent image without causing a potential difference in the boundary region between the first rotation and the second rotation of the photoconductor 8 as described with reference to FIG.

(Other Embodiments of the Present Invention) In the embodiments of the present invention described above, when the photoconductor 8 is charged when the image forming process is restarted after a predetermined time, the first rotation and the second rotation are performed. This is done in order to eliminate the difference in the charged potential with the eyes.

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

In order to solve this, the same control as that of the above-described embodiment is performed to eliminate the potential difference between the first rotation and the second rotation.

That is, in the digital copying machine 1, the photoconductor 8
By exchanging, it is set only the rotational speed accumulation counter of cumulative counting the number of times of rotation. In order to control the image forming process as shown in FIG. 10 according to the count content of the cumulative counter, the charger 16 in the first rotation
The control is performed so that the increase in output due to 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. To remember. That is, FIG. 10 (A)
By referring to the table shown in (1), the number of rotations of the photoconductor 8 is compared with the content of the cumulative counter, and the voltage is increased to the charging device 16 according to the counted content of the cumulative counter to control the supply. Then, after the second rotation, the drive control is performed in a predetermined output state as described in the above embodiment.

In order to realize this, referring to FIG. 3, in order to count the number of rotations of the photosensitive member 8, the slit signal from the slit sensor 23 is used to accumulate the slit signal.
Set 8 and count. Since this slit signal is output every time the photosensitive member 8 makes one rotation, the cumulative counter 28
Counts the cumulative number of rotations.

Then, as shown in FIG. 10 (A), a table (R which stores the relationship between the cumulative rotation speed of the photoconductor 8 and the voltage corresponding to the increase in the driving output of the charger 16 at that time is stored.
The OM) 29 is connected to the CPU 25. Based on the counter number of the accumulating counter 28, the CPU 25 refers to the table 29 and fetches the data of the drive output for the increased amount of the charger 16. Then, the voltage supplied to, for example, the grid electrode 16c of the charger 16 is controlled via the power supply circuit 26.

Therefore, if the above control is briefly described,
In the charger 16 using the scorotron method, the increased amount is added to the grid electrode 16c to control the supply.
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 is calculated from the count value of the cumulative counter 28.
If the CPU 25 recognizes that it is necessary to increase −20 V with reference to the above, the voltage of the predetermined output −4.
The voltage of -500V added to 80V is applied to the grid electrode 1
Supply control to 6c. This is Ri Oh <br/> in the first rotation of the photosensitive member 8 gradually drive control so as to gradually decrease to -480V at the second rotation of the boundary region.

If the relationship in FIG. 10A is tabulated in the ROM 29, very fine control becomes possible.
However, if it is very difficult to supply the subdivided voltage as shown in FIG. 10 (A) to the grid electrode 16c, as shown in FIG. 10 (B) or (C), for example, the grid electrode It is also possible to control the voltage supplied to 16c stepwise by making unit amounts determined such as 5V and 10V correspond to the cumulative rotation speed of the photoconductor 8 or the cumulative value at the time of cumulative rotation. Even if the ROM table 29 as shown in FIG. 10B or 10C is used, the same operational effect can be expected, and at the same time, the load on the ROM, that is, the storage capacity can be reduced, and the configuration can be inexpensive.

As described above, according to the structure of another embodiment of the present invention, even if the potential change as shown in FIG.
The potential difference in the first rotation and the second rotation can be effectively resolved.
Therefore, even when image formation is started from the first rotation of the photoconductor 8 by the charger 16 to perform uniform charging and digital exposure with laser light, the image quality is not significantly deteriorated over a long period of time, and 1 It is possible to provide an image having a constant image quality from the first sheet, and it is possible to increase the image forming speed.

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

In the description of another embodiment of the present invention, in consideration of the usage state of the photoconductor 8, that is, the decrease in the surface potential of the photoconductor 8 from the start of use, the first and second rotations are taken into consideration. By controlling the voltage of the charging device 16 of FIG. This requires the same control even when the image forming process of the photoconductor 8 is left for a predetermined time without being started as described in the embodiment of the present invention. Therefore, as a matter of course, the output control of the charger 16 is controlled according to the usage status of the photoconductor, for example, the cumulative rotation speed or the cumulative rotation time shown in FIG. 9, and the output of the charger 16 after the photoconductor 8 is left for a predetermined time. If the control is performed together, more effective control can be performed.

That is, with the start of the image forming process after the photoconductor 8 is left for a predetermined time, the charging output of the charger 16 is controlled by further adding the increment corresponding to the cumulative rotation speed of the photoconductor 8. By doing so, the potential drop due to the standing for a predetermined time and the cumulative rotation speed (or 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 can be prevented. In addition, it is possible to perform stable charging under a constant potential state and provide a stable image.

Further, the charging potential of the photoconductor 8 gradually decreases depending on the cumulative rotation speed or cumulative rotation time as shown in FIG. Therefore, although the surface potential of the photoconductor 8 is used as a reference for the charging control performed in the second rotation, the voltage control of the charging device in the first rotation is performed. However, not only this control, the charging device 16 in the second rotation is performed. By performing the voltage control in the same manner as above, a more stable charging potential of the photoconductor 8 can be expected. That is, as shown in FIG. 9, since the charging potential decreases, it can be predicted that the potential cannot be maintained even if the charging control is performed by the voltage control that is always determined in the second rotation. Therefore, the charging control for the second rotation is performed similarly to the charging control for the first rotation. In this case, naturally, the charging output for the charging control in the second rotation is controlled to be smaller than the charging output in the first rotation. The degree of this change can be easily implemented by previously measuring the characteristics of the charging potential due to long-term use of the photoconductor 8 and controlling the output state of the charger 16 in the second rotation.

(Other Aspects According to Embodiments of the Present Invention) In the above-described embodiments, the charger 16 according to the corona charging method, particularly the scorotron method, has been described as an example. Instead of such a configuration of the charger 16, a corona charger using a corotron system that performs corona discharge can be used in the same manner.

This charger is the same as the charger 16 shown in FIG. 3 except that the grid electrode 16c does not exist. When controlling the charging output by the charger in this case, naturally, it can be performed by controlling the high voltage supplied to the corona discharge electrode 16b. Further, by supplying a predetermined voltage to the case 16a and controlling the voltage, the charging output by corona discharge can be controlled. That is, it is possible to easily control the charging potential of the photoconductor 8.

In the present invention, the charger 16 in the case of utilizing the corona charging method has been described. This is effective in the case where the photoconductor 8 is uniformly charged at high speed, and the charging width cannot be defined, so that 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 method,
That is, even when the charging roller 30 as shown in FIG. 11 is used, the present invention can be used as it is.

In this case, the charging control is provided so that an image can be formed from the first rotation of the photoconductor 8 by starting the image forming process, and the contact time between the photoconductor 8 and the charger 26 is shortened so that the surface potential becomes unstable. It is possible to prevent a portion from being formed on the surface of the photoconductor 8 and maintain a uniform image formation state, and further to significantly increase the number of copies per life of the photoconductor 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, it is possible to form a toner image at a surface potential with a small potential gradient, and a density change. You can easily get good quality images.

The structure of the roller charger 30 will be briefly described. A stainless steel core bar 30a having a diameter of about 6 mm.
Then, a conductive layer 30b of polyurethane rubber having a thickness of about 3 mm is formed by mixing an appropriate amount of alumina, and 1
It is composed of a coating layer 30c coated with insulating nylon having a thickness of about 0 to 20 μm. In particular, the total resistance value of the roller charger 30 is 10 ⁶ Ω · cm and JI
A charging roller having an S-A hardness of 30 ° and a diameter of about 12 mm can be used.

Further, the accumulation of electron traps of the organic photoconductor 8 described above is likely to occur in a phthalocyanine compound which is a general charge generating material for the photoconductor, and these photoconductors 8 generally undergo processes such as pre-charging. It was generally added. However, according to the present invention, even when the image formation by the laser beam is started from the first rotation,
It is possible to prevent a portion having an unstable surface potential from being formed on the surface of the photoconductor 8 and to maintain a uniform image formation state.

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

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

[0092]

[Table 1]

In Table 1 above, according to the prior art, the life of the photoconductor is shortened because the photoconductor is pre-rotated. Therefore, it is necessary to replace the photoconductor frequently within the usage limit of the device. Therefore, even if there is no price difference between the photoconductors,
It is disadvantageous because it increases the total running cost.

Further, in the case of applying the reversal development, the toner consumption is accompanied during the pre-rotation of the photosensitive member, and the toner consumption amount increases, which is also disadvantageous in this respect.

In this respect, according to the present invention, since the life of the photoconductor 8 is extended and the pre-rotation process of the photoconductor 8 is not necessary, the toner is used only during the image formation by the image forming process, which is very advantageous. 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 photo conductor 8 is further extended, and the total photo conductor is increased. 8 cost down.

1 and 2 for explaining the embodiment of the present invention, the end of the first rotation of the photoconductor 8 is the charger 1.
The output of the charger 16 is controlled so as to be gradually reduced from a high output to a predetermined output even before the position 6 is passed. Therefore, when the end of the first rotation of the photoconductor 8 is before the charger 16 passes, for example, when the time for the photoconductor 8 to make one turn is about 1 second (1000 msec), the charger 16 is moved from 25 msec before the charger 16. The output is gradually reduced to 25 from that point.
Drive control is performed with a predetermined output after 0 msec. That is, FIG.
Further, the time T in FIG. 2 is set to about 250 msec, and the time T is gradually decreased to return from the high output to the predetermined output. This time T is about 1 for one rotation of the photoconductor 8.
It corresponds to about / 4, and the time when the gradual reduction is started corresponds to about 1/40.

Such a time may be set according to the characteristics of the photoconductor 8, and particularly when the corona charger 16 is used, the charging width cannot be regulated, which is very effective.

[0098]

According to the image forming apparatus of the present invention, an abrupt change in the potential difference is prevented between the first rotation and the second and subsequent rotations, and the image forming process is accelerated without deteriorating the image forming state. There are advantages that you can get started with. Further, it is possible to prevent fogging from occurring in the non-image forming area on the surface of the photoconductor, prevent waste of toner, reduce running costs, and prolong the life of the cleaning device.

[0099]

[0100]

[0102] Further, with respect to aging of the resume or the image bearing member of the process of the image bearing member, a charging output when gradually decreasing from a high output state to a predetermined output state, stepwise or continuously performed so that Thus, the 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 uniformly maintained.

The boundary between the first rotation and the second rotation is reduced 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 charged potential difference in the area can be more effectively eliminated, and even when the image formation is performed using the areas of the first rotation and the second rotation, the image quality does not deteriorate such that the image density changes in the middle. .

[0103]

[0104]

[Brief description of drawings]

FIG. 1 is provided for explaining an embodiment according to the present invention, in which drive control of a charging unit shows a state of a surface potential of a photoconductor at the first and second rotations of the photoconductor. It is the characteristic view which also showed what was made by the prior art.

FIG. 2 is a timing chart for explaining an embodiment for driving and controlling a charger that executes 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 block diagram of a digital copying machine showing the overall structure of an image forming apparatus including the image forming process means shown in FIG.

5 is a cross-sectional view provided for explaining one specific example of the organic photoreceptor structure of the photoreceptor that constitutes the image forming process means shown in FIG.

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

FIG. 7 is a view for explaining the embodiment of the present invention, in which a potential difference is generated between the first rotation and the second rotation of the photoconductor due to the restart and is not generated depending on the pause time of the image forming process. It is a characteristic view which shows the relationship in a case.

FIG. 8 relates to an embodiment of the present invention and includes a photosensitive member 1
FIG. 9 is a characteristic diagram showing a change state of the surface potential of the photoconductor when the charging output of the charger of the second rotation is increased more than the predetermined charging output of the second and subsequent rotations.

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

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

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

[Explanation of symbols]

1 Digital copier (image forming device) 7 Image forming process unit (image forming process means) 8 Photoconductor (image carrier) 16 Charging device (charging means) 16a Case (shield plate) 16b Corona discharge electrode 16c grid electrode 17 Developing device 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)

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tomoko Kanazawa 22-22 Nagaike-cho Naganocho, Abeno-ku, Osaka, Osaka Prefecture Sharp Corporation (72) Inventor Yoshihide Shimoda 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Sharp Corporation (72) Inventor Masaru Nakamura 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) Reference JP-A-6-59547 (JP, A) JP-A-5-188674 (JP, A) JP-A 2-91666 (JP, A) JP-A 5-297672 (JP, A) JP-A 7-244421 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/02 G03G 15/00 303

Claims (2)

(57) [Claims] 1. A charging means for charging the surface of the image bearing member, an exposing means for irradiating the charged surface of the image bearing member with light, and an electrostatic member formed on the surface of the image bearing member according to the light irradiation of the exposing means. In an image forming apparatus comprising an image forming process means including a developing means for converting a latent image into a visible image, the charging means is activated at the first rotation of the image carrier in response to the start of the process by the image forming process means. The control means is driven at a higher output than a predetermined output, and is gradually reduced to a predetermined output after the second rotation, and the control means drives the charging means from the first rotation to the second rotation of the image carrier. An image forming apparatus characterized in that the output of the charging means at the time of switching is controlled to start before the completion of the first rotation and complete after the transition to the second rotation. 2. The image forming apparatus according to claim 1, wherein the driving output for the first rotation by the charging unit is gradually or continuously reduced to the predetermined output, and is continuously or stepwise.