JPH0619279A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a stable output image without having nonuniformity by detecting the uneveness of an electrifying means and taking the proper recovery action of the electrifying means, according to the unevenness. CONSTITUTION:A surface electrometer 11 is provided between an exposing system 3 and a developing unit 4, and the electrification unevenness of a primary electrifier 2 is detected by detecting the electrified state of a photosensitive drum 1. The surface electometer 11 measures potential unevenness in the longitudinal direction of the photosensitive drum 1, and in an electrification uneveness detecting mode. only the driving source of the photosensitive drum, a preexposing means 7, and the primary electrifier 2, are operated, to detect the potential unevenness caused by the discharge uneveness of the primary electrifier 2. At this time, the total current of the primary electrifier is set about 1/2-1/3 that at the time of normally copying, to amplify the soiling (electrification unevenness) of the primary electrifier 2. An uneveness ratio L is calculated from the distribution of the measured surface potential, in the longitudinal direction of the photosensitive drum, and a means for recovering the electrification uneveness of the primary electrifier is selected/operated according to the value of the calculation.

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 of an electrophotographic type or an electrostatic recording type, a laser beam printer or the like, and more particularly to an image forming apparatus having a separation mode for causing unevenness of an output image. It is a thing.

[0002]

2. Description of the Related Art For example, electrophotographic image formation is applied to image forming apparatuses such as black and white copying machines, laser beam printers, and color copying machines. As is well known, the electrophotographic method means that a photosensitive drum as an image carrier is
An electrostatic latent image is formed by the charging process and the exposure process,
This latent image is made into a visible image (toner image) by adhering a developer (toner) in a developing process, and then this toner image is transferred onto a recording material (transfer material) by a transfer process,
In this method, a transfer toner image is fixed on a recording material by a fixing device to obtain an image.

Since these processes in the electrophotographic image forming apparatus utilize electrostatic phenomena such as corona discharge and frictional charging, it is difficult to stably maintain an output image due to dirt, deterioration and the like. Therefore, image deterioration occurs due to uneven discharge or the like during use. For this reason, in the past, regular inspections by service personnel etc.,
All unstable process parts are made into a kit and made into a disposable structure.

In particular, a primary charger that uses corona discharge (a charger that uniformly charges the photosensitive drum before latent image formation),
The transfer charger, which transfers the toner image formed on the photoconductor drum to the recording material, is a phenomenon in which corona discharge is a high-energy destruction phenomenon, which causes various discharge products and also has a dust collection effect. Since it is a phenomenon that occurs, it is easy to get dirty, which is the main cause of uneven discharge.

[0005]

Generally, the smaller the discharge current, the larger the unevenness of the discharge due to the dirt on the corona charger. FIG. 9 is a characteristic diagram showing the relationship between the longitudinal position of the corona charger CH and the corona current I toward the opening of the charger CH at each position in the longitudinal direction. At total current I (I = I + I _S ,
However, I _S is measured by changing the corona current of the corona charger CH toward the shield plate S direction).
As is clear from FIG. 9, the characteristic curve A has a higher total current, but the unevenness at the point P is smaller than that of the characteristic curve B having a low total current.

As a value representing the size of the unevenness of the corona charger, the unevenness ratio L (=, which is the ratio of the total current I _MR at the position where unevenness is generated in FIG. I _MR /
I) can be taken. The characteristic curve of FIG. 10 is obtained by examining the relationship between the value of the unevenness ratio L and the total current of corona discharge. As is clear from FIG. 10, the magnitude of the unevenness becomes a constant value as the total current increases. Further, in the region where the total current is low, the unevenness becomes large. This is because the discharge corona ions that charge the photoconductor drum largely depend on the corona discharge directly above it in the region where the total current is small. It is considered that corona discharge is also involved.

By utilizing this phenomenon, it is possible to amplify and detect discharge unevenness or charging unevenness of uniform charging and transfer charging, and it is possible to detect charging-related unevenness before unevenness occurs in an output image. Can be detected.

Therefore, an object of the present invention is to detect unevenness of the charging means in the charging unevenness detection operation mode, and to select and execute an appropriate recovery operation of the charging means in accordance with the detected unevenness state. An object of the present invention is to provide an image forming apparatus capable of always obtaining a stable output image without any noise.

[0009]

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier, a primary charging unit that charges the image carrier to a uniform potential, and an exposure according to image information to the image carrier after the primary charging. Means for forming an electrostatic latent image on the image bearing member, developing means for visualizing the formed electrostatic latent image, and recording a visible image on the visualized image bearing member. An image forming apparatus having a transfer unit for transferring to a material has an operation mode capable of detecting the contribution of the primary charging unit with respect to image unevenness, and the contribution detection unit detects the contribution in the operation mode. The image forming apparatus is characterized in that the means for recovering uneven charging of the primary charging means is executed according to the detection output.

[0010]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In each of the following embodiments, the case where the present invention is applied to an image forming apparatus such as an electrophotographic copying machine or a printer will be described. However, an electrophotographic image forming apparatus or a static image forming apparatus having a configuration other than the embodiments is described. It goes without saying that the present invention can be applied to an image forming apparatus of another system such as an electrographic system.

FIG. 1 is a schematic configuration diagram showing a main part of a first embodiment of an image forming apparatus according to the present invention, in which an electrostatic latent image is usually formed, for example, Se, amorphous Si,
It includes a photosensitive drum 1 such as an organic photosensitive member. The photoconductor drum 1 steadily rotates in the direction of the arrow in the figure, and along the rotation direction, a primary charger 2 utilizing the corona discharge phenomenon that uniformly charges the photoconductor drum 1 and an electrostatic latent image formation An exposure system 3 such as a laser scanning optical system, a developing device 4 for developing an electrostatic latent image formed on the photoconductor drum 1 into a visible image, and a visible image (toner image) on the developed photoconductor drum. A transfer charger 5 for transferring the toner to a transfer paper as a recording material, a cleaner 6 for removing the toner remaining on the photosensitive drum 1 in the transfer process,
Pre-exposure means 7 for uniformizing the photosensitive drums 1 prior to the primary charging are provided.

On the other hand, the transfer paper on which the toner image has been transferred is conveyed to the fixing device 10 to fix the toner image on the transfer paper, and then discharged to the outside of the machine.

As the primary charger 2, a scorotron charger in which a discharge wire is surrounded by a shield plate and a grid is provided in an opening is used, and a constant current high voltage power supply unit for applying a high voltage to the discharge wire is used. A constant-voltage high-voltage power supply unit 13 for applying high voltage to the grid 12 and the grid is provided. Further, the developing device 5 uses, for example, a one-component magnetic toner to form a thin layer of this one-component developer on a developing sleeve as a developer carrying member, and this and the photosensitive drum 1
Between the photoconductor drum 1 and the developing sleeve in a non-contact state, the alternating developing bias (AC
+ DC) is applied to develop a latent image, a so-called jumping development method, or a two-component developer composed of a high-resistance carrier and toner is used to form a thin layer of the two-component developer on a developing sleeve. A developing device using a two-component developing brush method or the like is used which is opposed to the photosensitive drum 1 in close proximity and applies an alternating developing bias between the photosensitive drum and the developing sleeve. Further, the cleaner 6 is of a blade cleaning type in which an elastic body such as urethane is brought into contact with the surface of the photosensitive drum against a counter, and the toner remaining on the photosensitive drum is removed by mechanical scraping for cleaning. used.

Next, an image forming operation of the image forming apparatus having the above structure will be briefly described. The photoconductor drum 1 is uniformly charged by the primary charger 2, and an electrostatic latent image corresponding to image information is formed on the photoconductor drum 1 by the exposure system 3. This electrostatic latent image is developed by the developing device 4 to form a visible image. The toner image on the photosensitive drum 1 is transferred by the transfer charger 5 onto a transfer sheet fed from the sheet feeding cassette 8. In this case, the transfer sheet is sent to the transfer area at a predetermined timing in synchronization with the toner image on the photosensitive drum 1 by the registration roller 9. The transfer sheet onto which the toner image has been transferred is conveyed to the fixing device 10, where the toner image is fixed, and the sheet is discharged to a discharge tray (not shown) outside the machine. The toner remaining on the photoconductor drum 1 is cleaned by the cleaner 6 and again pre-exposed by the pre-exposure means 7 to be initialized to prepare for the next image forming operation.

FIG. 11 is a timing chart showing the operation sequence of the pre-exposure means 7, the primary charger 2, the exposure system 3, the developing device 4, the transfer charger 5, and the fixing device 10 during normal image formation. When the drive of the photoconductor drum 1 is mainly considered, the drive of the photoconductor drum 1 is performed by pre-rotation, image formation rotation,
There are three types of post-rotation. The pre-rotation is for stabilizing the electric potential before using the photoconductor drum, and the post-rotation is for performing a process after the photoconductor drum 1 is used to prevent generation of a memory or the like. On the other hand, during image formation rotation, the processes of exposure, development, transfer, and fixing are sequentially performed to form a toner image on the photosensitive drum 1, and the toner image is transferred and fixed on the transfer paper. Is ejected out of the machine.

In this embodiment, a surface potential meter 11 is provided between the exposure system 3 and the developing device 4 as a detecting means for detecting the distribution of corona discharge in the longitudinal direction of the photoconductor drum, and the photoconductor drum 1 is charged. By detecting the state, uneven charging of the primary charger 2 is detected. The detection output of the surface electrometer 11 is input to the control device (CPU) 14. The controller 14 also controls the total current of the constant-current high-voltage power supply unit 12 that controls the total current of the primary charger 2, the constant-voltage high-voltage power supply unit 13 that controls the grid voltage of the primary charger 2, and the total current of the transfer charger 5. The constant current high voltage power supply unit 15 is controlled.

The surface electrometer 11 has means for moving the electrometer 11 in the longitudinal direction of the photosensitive drum 1, and is capable of measuring the potential unevenness in the longitudinal direction of the photosensitive drum 1. The uneven potential caused by uneven discharge is
In general, it has a wide width, and the angle of view of an ordinary surface electrometer is 5 to 1
It can be sufficiently detected with a resolution of about 0 mm. It is desirable that the moving step in the longitudinal direction is about half of this angle of view (area). In the charging unevenness detection mode, as shown in the timing chart of FIG. 2, only the drive source of the photoconductor drum, the pre-exposure means 7, and the primary charger 2 are operated, and the potential unevenness caused by the discharge unevenness of the primary charger 2 is eliminated. Detect. At this time, the total current of the primary charger is 1/2 to 1/3 that of normal copying.
It is set to a degree so that the dirt (uneven charging) of the primary charger 2 is amplified.

The unevenness rate L is calculated from the distribution of the measured surface potentials in the longitudinal direction of the photosensitive drum, and the charging unevenness recovery means, which is unevenness prevention means, is operated according to the calculated value.
The following operations are performed as a means for recovering from unevenness.

[ Recovery means 1 ] The corona discharge current is instantaneously increased to remove dust adhering to the corona charging wire.
Remove dust, etc. Since this is a cleaning that uses physical energy, it is a countermeasure against initial dirt to the extent that dust, dirt, and the like are removed.

[ Recovery Means 2 ] The charger is cleaned by mechanical cleaning means. By wiping the corona discharge wire and the grid with a cleaning member such as a pad, the attached dirt is wiped off by mechanical force. By using a member having a polishing effect as the cleaning member, the adhered dirt can be removed. However, if the frequency is increased, adverse effects such as wear occur.

[ Recovery Means 3 ] The corona discharge wire or the like is automatically fed out and replaced with a new one. Although this is the most effective method, it has the drawback of being costly.

In FIG. 7, the unevenness detection mode is executed and the unevenness ratio L
6 is a flowchart showing an operation sequence of how to execute the plurality of unevenness recovery means 1, 2, 3 which are unevenness prevention means after obtaining the value of The basic idea is
The unevenness recovery means to be executed is selected according to the detected unevenness rate L. The unevenness rate L and the dirt on the charger have a relationship as shown in the characteristic diagram of FIG. 8, and there is a correlation between the degree of dirt on the charger and the unevenness rate. You can estimate the degree. Depending on the degree of this contamination, physical means, mechanical means, and replacement and recovery means are used properly.

First, the unevenness detection mode is started, and in step S1, image forming conditions (photosensitive drum drive source ON,
The non-uniformity detection operation is started when the pre-exposure means is on and the primary charger is on. At this time, as shown in step S2, the total current of the primary charger 2 is set to about 1/2 to 1/3 of the normal copying to set the unevenness amplification mode, and the surface electrometer 11 is set to the longitudinal direction of the photosensitive drum 1. Direction (main scanning direction), the charging state (potential unevenness) on the photosensitive drum 1 in the longitudinal direction is detected, and the unevenness rate L is obtained. Next, in step S3, the obtained unevenness ratio L is compared with the unevenness ratio values L ₁ , L ₂ and L ₃ (L ₁ <L ₂ <L ₃ ) of three preset threshold values. Then
From the comparison result, the stains on the primary charger 2 are confirmed to be A, B, C,
The corresponding processing is executed in four stages of D. That is,
In the case of stage A, it is judged that the unevenness recovery operation is not necessary, and stage B
In the case of No. 3, it is judged that the recovery means 1 is used unevenly, in the case of Step C, it is judged that the recovery means 2 is used, and in the case of Step D, the recovery means 3 is used. When it is determined that there is unevenness, the unevenness recovery operation is executed except in the case of step A.

In this embodiment, the detected unevenness ratio L
Is smaller than the preset minimum threshold unevenness ratio L ₁ (L ≦ L ₁ ) it can be determined that the primary charger 2 is not contaminated, so the unevenness recovery operation is not performed and the detected unevenness ratio is When L is between L ₁ and the unevenness ratio L ₂ of the intermediate threshold value, the dirt is such that the unevenness can be sufficiently recovered by the recovery means 1, so the recovery operation of the recovery means 1 is executed. When the detected unevenness ratio L is between L ₂ and the maximum threshold unevenness ratio L ₃ , the dirt is such that the unevenness can be sufficiently recovered by the recovery means 2, and therefore the recovery means 2 is used. If the detection unevenness ratio L is larger than L ₃ , the recovery operation of the recovery means 3 is executed, and the recovery operation of the recovery means 3 is executed. . Here, the non-uniformity rates L ₁ , L ₂ , and L ₃ of the preset threshold value are values that can prevent non-uniformity by the above operation.

In the first embodiment described above, the surface electrometer 11 detects the charged state of the photosensitive drum 1 to detect the dirt (uneven charging) of the primary charger 2. Next, the primary charging is performed. A second embodiment of the present invention will now be described with reference to FIGS. 3 and 4 in which not only the charging unevenness of the charging device 2 but also the charging unevenness of the transfer charging device 5 can be detected.

FIG. 3 is a schematic configuration diagram showing a main part of an image forming apparatus according to the second embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment of the present invention shown in FIG. 1 except that the surface electrometer 11 is arranged immediately after the transfer charger 5, and therefore the same symbols are given to corresponding parts. The description is omitted unless otherwise necessary. The operation sequence for detecting the charging unevenness of the primary charger 2 is the same as the operation sequence of the first embodiment shown in the timing chart of FIG. The operation sequence for detecting the uneven charging will be described with reference to FIG.

As shown in the timing chart of FIG.
When the charging unevenness of the transfer charger 5 is detected, only the drive source of the photosensitive drum 1, the pre-exposure means 7, and the transfer charger 5 are operated, and the corona discharge of the transfer charger 5 causes the photosensitive drum 1 to move.
Is charged, and the potential unevenness in the longitudinal direction on the photosensitive drum 1 is measured by an electrometer 11 arranged immediately after the transfer charger 5. At this time, the transfer current of the transfer charger 5 is set to about 1/2 to 1/3 of the operating current at the time of normal copying, and the charging unevenness is detected in the unevenness amplification mode to obtain the unevenness rate L. The sequence for performing the operation of recovering the charging unevenness of the transfer charger 5 from the obtained unevenness rate L is the same as the unevenness recovery operation execution sequence of the primary charger 2 described above with reference to FIG. The description is omitted.

Next, a third embodiment of the present invention in which uneven charging is detected without using a surface electrometer will be described with reference to FIGS. 5 and 6.

FIG. 5 is a schematic configuration diagram showing a main part of an image forming apparatus according to a third embodiment of the present invention. In this embodiment, an optical detecting means 16 is provided in the developing device 4 instead of the surface electrometer. Since it has the same configuration as the first and second embodiments of the present invention shown in FIGS. 1 and 3 except that it is arranged immediately after that,
Corresponding parts are designated by the same reference numerals and the description thereof will be omitted unless necessary.

In this embodiment, when detecting uneven charging of the primary charger 2, as shown in the timing chart of FIG. 6, the drive source of the photosensitive drum 1, the pre-exposure means 7, the transfer charger 5, and Only the developing device 4 is operated. First, the photosensitive drum 1 is initialized by the pre-exposure means 7, and then the photosensitive drum 1 is charged by the corona discharge of the primary charger 2. Next, the photoconductor drum 1 is developed by the developing device 4, and a developer (toner) is attached to the charged charges on the photoconductor drum 1 to form a visible image (toner image).
Is irradiated with light from the optical detection means 16 disposed immediately after, and the unevenness of the visible image is optically detected from the reflected light,
This is for detecting the situation of potential unevenness of the photosensitive drum 1. That is, by scanning the optical detection means in the longitudinal direction of the photosensitive drum 1, the unevenness of the toner adhesion amount is detected,
From this, uneven charging of the primary charger 2 is detected. In the present embodiment as well, similar to the first and second embodiments, the charging current of the primary charger 2 is set to about 1/2 to 1/3 of the operating current at the time of normal copying and the unevenness is amplified. It goes without saying that the mode is set to facilitate detection of uneven charging. Further, the unevenness rate L is obtained from the detected charging unevenness, and the operation for recovering the uneven charging of the primary charger 2 is executed from this unevenness rate L. This operation sequence may be the same as the unevenness recovery operation execution sequence described above with reference to FIG. 7.

As described above, in this embodiment, the charging unevenness of the primary charger 2 is detected by converting it into the surface potential of the photosensitive drum 1 and the toner adhesion amount. Can be amplified. That is,
By setting the developing bias to a potential having a large inclination (γ characteristic) in the characteristic of the toner adhesion amount with respect to the surface potential of the photosensitive drum 1, it is possible to amplify the unevenness of the potential when converting it to the unevenness of the toner adhesion. In general, half of the maximum density in the density area is an area where γ stands.

In each of the above-described embodiments, the case where the present invention is applied to the electrophotographic image forming apparatus has been described. However, other various image forming apparatuses of the electrophotographic system, the electrostatic recording method and the like are also used. It is needless to say that the present invention can be applied to the image forming apparatus of the above method and the same operational effect can be expected. Further, it is needless to say that the judgment criterion for the magnitude of the unevenness rate L, the means for recovering unevenness, the unevenness recovery operation execution sequence, etc. are not limited to those of the embodiment and can be variously changed.

[0033]

As described above, according to the image forming apparatus of the present invention, when detecting the unevenness of the charging means, the unevenness is detected while the charging current (voltage) is lowered and the unevenness is amplified. Therefore, even small irregularities can be detected, and the recovery processing operation is executed by switching the irregularity recovery means according to the detected irregularity state, so irregularities are not generated in the charging means. It can be surely prevented. Therefore, there is an effect that a stable image without image unevenness can be maintained for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a main part of a first embodiment in which the present invention is applied to an electrophotographic image forming apparatus.

FIG. 2 is a timing chart showing an operation sequence of the first embodiment of FIG.

FIG. 3 is a schematic configuration diagram showing a main part of a second embodiment of the image forming apparatus according to the present invention.

FIG. 4 is a timing chart showing an operation sequence of the second embodiment of FIG.

FIG. 5 is a schematic configuration diagram showing a main part of a third embodiment of the image forming apparatus according to the present invention.

FIG. 6 is a timing chart showing an operation sequence of the third embodiment of FIG.

FIG. 7 is a flowchart for explaining the operation sequence of the unevenness detection mode in the image forming apparatus according to the present invention.

FIG. 8 is a characteristic diagram showing the relationship between the dirt on the corona charger and the unevenness rate.

FIG. 9 is a characteristic diagram showing the relationship between the longitudinal position of the corona charger and the corona current toward the opening of the corona charger at each position in the longitudinal direction.

FIG. 10 is a characteristic diagram showing the relationship between the total current of the corona charger and the unevenness rate L.

FIG. 11 is a timing chart showing an operation sequence during image formation in the electrophotographic image forming apparatus.

[Explanation of symbols]

 1 Photoreceptor Drum 2 Primary Charger 3 Exposure System 4 Developer 5 Transfer Charger 6 Cleaner 7 Pre-exposure Means 8 Paper Feed Cassette 9 Registration Roller 10 Fixer 11 Surface Potential Meter 12 Constant Current High Voltage Power Supply Unit 13 Constant Voltage High Voltage Power Supply Unit 14 Control device 15 Constant current high voltage power supply unit 16 Optical detection means

Claims (7)

[Claims] 1. An image carrier, a primary charging unit that charges the image carrier to a uniform potential, and after the primary charging, the image carrier is exposed according to image information, Means for forming an electrostatic latent image on the image carrier, developing means for developing the formed electrostatic latent image, and transfer the visualized visible image on the image carrier to a recording material. And an image forming apparatus including a transfer unit for performing an operation mode capable of detecting the degree of contribution of the primary charging unit with respect to image unevenness. In the operation mode, the contribution degree is detected by the contribution degree detection unit, and the detection is performed. An image forming apparatus, which executes a charging unevenness recovery unit of the primary charging unit according to an output. 2. The image forming apparatus according to claim 1, wherein the detection unit is a surface potential detection unit that is movably installed in the longitudinal direction of the image carrier. 3. The image forming apparatus according to claim 1, wherein the detection unit is a developer adhesion amount detection unit installed so as to be movable in a longitudinal direction of the image carrier. 4. The current or voltage of the charging means is set to be smaller than the operation current or voltage during normal image formation in the operation mode in which the contribution of the charging means to the image unevenness is detected. The image forming apparatus according to item 1. 5. The image forming method according to claim 1, wherein the developing bias for the developing unit is set to a value in which γ of the developing characteristic is raised in the operation mode in which the contribution of the charging unit to the image unevenness is detected. apparatus. 6. The transfer means is a transfer charging means, and further has an operation mode capable of detecting a contribution degree of image unevenness of the transfer charging means, and the contribution degree detecting means detects the contribution degree in the operation mode. Then, the image forming apparatus according to claim 1, wherein the charging unevenness recovery unit of the transfer charging unit is executed according to the detection output. 7. The current or voltage of the transfer charging means is set to be smaller than the operation current or voltage at the time of normal image formation in the operation mode in which the contribution of the transfer charging means to the image unevenness is detected. The image forming apparatus according to claim 6.