JPH0756404A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of forming the image of a uniform density, regardless of the cause of fluctuations in dark decay on a photosensitive body film, even if the dark decay is fluctuated caused by many kinds of factors. CONSTITUTION:A detector 26 taking out a leakage current I1c generated by the dark decay on the photosensitive body film 12 and made of a conductive material, etc., is electrically connected without obstructing the rotation of a photosensitive drum 13. The detector 26 is connected to a comparator 27, to detect the variation between an initial leakage current value and the measured leakage current value. The comparator 27 is connected to a controller 28. In a memory 29 connected to the controller 28, the data of the change width DELTAR of the resistance value of a variable resistor 24 previously set correspondence relation with respect to a large number of variations based on the dark decay on the photosensitive body film 12 is stored. The controller 28 changes the resistance value of the variable resistor 24 by its change width DELTAR read out of the memory 29, in accordance with the variation of the leakage current I1c detected by the comparator 27.

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 using electrophotography, and more particularly to an image forming apparatus for forming an image by charging and exposing a single-layer organic photosensitive drum.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic technique has been actively developed as an electrostatic copying apparatus or a printing apparatus.

FIG. 12 is a system diagram of an image forming apparatus 1 using a conventional electrophotographic technique. The image forming apparatus 1 includes a rotatable photosensitive drum 3 having a photosensitive film 2 formed on the surface thereof,
A main charger 4 for uniformly applying a predetermined amount of electric charge to the photoconductor film 2, an optical device 5 for exposing the photoconductor film 2 to form an electrostatic latent image on the photoconductor film 2, and a photoconductor. A developing device 6 for developing the electrostatic latent image on the film 2, a transfer device 8 for transferring the toner image formed on the photoconductor film 2 onto the recording paper 7, and a toner remaining on the photoconductor drum 3 are removed. A cleaning device 9 having a cleaning blade for removing the charges remaining on the photoconductor drum 3 to set the surface potential of the photoconductor drum 3 to a predetermined uniform potential.
Equipped with 0 etc.

According to the image forming apparatus 1, the main charger 4 uniformly applies a predetermined amount of electric charge to the photoconductor film 2, and then the optical device 5 irradiates the photoconductor film 2 with light. An electrostatic latent image is formed on the film 2. Thereafter, the developing device 6 supplies the toner onto the photoconductor film 2 to visualize the electrostatic latent image. The toner image on the photoconductor drum 3 is transferred to the transfer device 8
Is transferred onto the recording paper 7. After the transfer, the toner remaining on the photosensitive drum 3 is removed by the cleaning device 9. Next, the static elimination lamp 10 irradiates the photoconductor film 2 with light to remove the electric charge remaining on the photoconductor film 2 and equalize the surface potential of the photoconductor film 2 to a predetermined potential. After that, the main charger 4 charges the photosensitive drum 3 again. These series of processes are continuously and repeatedly performed according to the rotation of the photosensitive drum 3.

In the prior art, an inorganic material or an organic material is used as a photosensitive material forming the photosensitive film 2. Se-based materials, amorphous Si-based materials, etc. are used as the inorganic materials. In recent years, organic materials are often used in terms of safety and workability. Organic photoreceptors using organic materials are classified into laminated organic photoreceptors and single-layer organic photoreceptors.

The laminated organic photoreceptor has a structure in which a charge generation layer and a charge transport layer are laminated. Among the materials forming the charge transport layer, many materials having a good hole transporting ability have been developed, but a material having an excellent electron transporting ability has not yet been developed. For this reason, most of the laminated organic photoconductors are of the negative charging type. However, when a negative charging type photoconductor is charged by using a charger that uses corona discharge, ozone is often generated, and there is a problem that ozone countermeasures are newly required in terms of safety and environment. was there.

In order to overcome the above problems, a single-layer organic photoreceptor in which a charge generating medium is dispersed in a charge transporting medium has been proposed. In the single-layer organic photoconductor, a positive charge type photoconductor can be easily realized by using a material having a good hole transport ability as the charge transport medium.

[0008]

A single-layer organic photoreceptor is preferable in terms of ease of production as compared with a laminated organic photoreceptor. However, the single-layer photoconductor film generally has a high residual potential even after charge elimination. Further, there is a problem that the charge potential at the time of charging becomes low due to the residual photocarrier showing the high residual potential in the photoconductor film. Further, the photosensitive film having a good charging ability during the period when the use time is short, fatigues as the use time becomes longer,
There is a problem that the number of trap sites increases and the chargeability decreases.

The above-mentioned conventional technique has the following problems. That is, there is a problem that after a predetermined amount of electric charge is applied to the unit area of the photoconductor film 2 by the main charger 4, dark decay occurs in which a part of the electric charge is lost with the passage of time. Therefore, as the photosensitive drum 3 rotates, an arbitrary region of interest on the photosensitive film 2 moves from the charging position (position close to the main charger 4) to the developing position (position close to the developing device 6). In the meantime, the amount of charge in that area will decrease.

It is generally called dark decay that the surface potential of the photoconductor film 2 decreases without exposure. The degree of this dark decay changes depending on various factors such as the charge holding ability of the photoconductor film and the environment in which the image forming apparatus 1 is installed. When the charge holding ability of the photoreceptor film 2 and the environment in which the image forming apparatus 1 is installed are different for each image forming apparatus 1, the degree of dark decay also varies for each image forming apparatus 1. Further, when the charge holding ability of the photosensitive film 2 or the environment in which the image forming apparatus 1 is installed changes with time, the degree of dark decay also changes with time. A change in the degree of dark decay causes a change in the charge amount of the photoconductor film 2 at the developing position, which hinders the formation of an image with a uniform density.

In the conventional image forming apparatus 1, irrespective of the installation environment, and without considering the change over time of dark attenuation,
The same data for compensating for the decrease in surface potential due to dark decay was set for all the image forming apparatuses 1. This data is initial data corresponding to the degree of dark attenuation measured at the time of manufacturing the photosensitive drum 3, for example.

Therefore, when the degree of dark decay changes due to various factors such as the charge holding ability of the photoconductor film and the environment in which the image forming apparatus 1 is installed, the conventional image forming apparatus 1 uses the initial data according to the initial data. However, it is not possible to compensate for the changed dark attenuation, and it becomes impossible to form an image of uniform density. The same applies to the case where the dark decay causes a change over time due to long-term use of the image forming apparatus 1. In this case, the image forming apparatus 1 cannot compensate the fluctuated dark attenuation with the initial data,
It becomes impossible to form an image having a uniform density.

In particular, the positive charging type single-layer organic photoreceptor film has good charging ability and charge retaining ability at the initial stage of use, but the charge ability and charge retaining ability decrease with the lapse of use time. There is a problem of doing. Therefore, there is a problem that the image forming apparatus cannot form a uniform image due to the degree of dark decay in the positive charging type organic photosensitive film changing with time. This is one of the problems to be solved particularly for practical application of the single-layer organic photoreceptor film of the type.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to obtain a uniform density regardless of the cause of the dark attenuation in the photoconductor film due to various causes. An object is to provide an image forming apparatus capable of forming an image.

[0015]

SUMMARY OF THE INVENTION An image forming apparatus according to the present invention comprises a rotatable substrate having a conductive base and a photosensitive film formed on the surface of the base, and the photosensitive member. A charging means for charging the photosensitive film, an exposing means for irradiating the charged photosensitive film with light corresponding to an image, and the exposing means along the rotation direction of the photosensitive member. Developing means arranged on the downstream side of the means, dark decay detecting means for detecting a change in the degree of dark decay based on dark decay in the photoconductor film, and dark decay detecting means Compensation means for compensating for the fluctuation in the degree of dark attenuation based on the fluctuation in the degree of dark attenuation that has been performed is provided, and thereby the object can be achieved.

In the present invention, the dark decay detecting means is
When the leak current flowing from the substrate is detected by the dark decay in the photoconductor film, and the compensating means compensates the fluctuation of the degree of the dark decay based on the leak current detected by the dark decay detecting means. There is.

In the present invention, the charging means may be a scorotron charger including a discharge wire, a shield case and a grid.

In the present invention, the compensating means may include a grid resistor having a variable resistance value, which is connected between the grid and the common potential.

In the present invention, the compensating means may include grid potential adjusting means for adjusting the grid potential of the grid.

In the present invention, the compensating means may control the amount of charging current supplied to the charging means.

In the present invention, the dark decay detecting means is
The detector may be provided with a conductive detector that comes into contact with the base body to extract a leak current, and a comparison unit that reads the current value of the leak current extracted by the detector and compares it with a predetermined initial leak current value. .

In the present invention, the dark decay detecting means is
A detection body having a conductivity that comes into contact with the base body to extract a leak current; and an integrated leak current detection means that integrates leak currents taken out by the detection body over a predetermined period to detect an integrated leak current value. May be provided.

[0023]

In the image forming apparatus of the present invention, the photoconductor member is provided with a conductive base and a photoconductor film formed on the surface of the base. The photoconductor film is charged by the charging means. The charged photoconductor film is exposed by the exposure means to form an electrostatic latent image. The electrostatic latent image on the photoconductor film is developed by developing means. In the photoconductor film of the photoconductor member, dark decay occurs in which the surface potential due to charging by the charging means decreases with time even when no exposure is performed.

The dark decay detecting means detects a variation in the dark decay of the photoconductor film. The compensation means is
Corresponding to the variation in the degree of dark decay of the photoconductor film detected by the dark decay detecting means, the variation in the degree of dark decay near the developing means in the photoconductor film is compensated.

In the present invention, as described above, when the fluctuation of the degree of dark decay of the photoconductor film is detected, the dark decay of the photoconductor film in the vicinity of the developing means is detected based on the detection result. I am trying to compensate the fluctuation of the degree. As a result, when the degree of dark decay changes with time, or when the dark decay varies from image forming apparatus to the image forming apparatus due to the installation environment of the image forming apparatus, etc. When there is a change from the degree immediately after, it is possible to form an image with a uniform image density by compensating for the change over time or the variation in the degree of dark attenuation.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus of the present invention detects the amount of change in the amount of charge on the photoconductor film due to dark decay, and then adjusts various parameters that affect image formation based on the amount of change. As a result, the change with time of the charge amount of the photosensitive film at the developing position is compensated, and an image having a uniform density is formed.

An example of the present invention will be described below in the case of using a positive charging type single-layer organic photoreceptor film as an example.

(Embodiment 1) FIG. 1 is a system diagram showing a configuration of an image forming apparatus 11 according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 11 is a rotation member that is a photoconductor member in which a photoconductor film 12 made of a single-layer organic photoconductor is formed on the surface of a drum base 30 made of a metal material such as aluminum. A main charger 1 which is a charging means for uniformly applying a desired amount of electric charge to the possible photosensitive drum 13 and photosensitive film 12.
4. An optical device 15, which is an exposing means for exposing the photoconductor film 12 to generate light for forming an electrostatic latent image on the photoconductor film 12, and a toner for the electrostatic latent image on the photoconductor film 12. A developing device 16 that is a developing unit for developing, a transfer device 18 that transfers the toner image on the photosensitive drum 13 to the recording paper 17, and the toner remaining on the photosensitive drum 13 after the toner image is transferred. The cleaning device 19 for removing and the electric charges remaining on the photoconductor drum 13 are removed to remove the photoconductor film 12.
A static elimination lamp 20 for equalizing the upper potential to a predetermined potential is provided.

The main charger 14 employs a scorotron charger, and has a discharge wire 21 for corona discharge, a shield case 22 surrounding the discharge wire 21 and opening to the photosensitive drum 13, and a shield case 22. And a metal grid 23 provided in the opening. A power supply 25 for supplying a current required for corona discharge is connected to the discharge wire 21 of the main charger 14.
The shield case 22 is grounded. Grid 23
Is connected to a variable resistor 24 whose one end is grounded.

In this embodiment, as the main charger 14,
By using the scorotron charger, the surface potential at the charging position of the photosensitive drum 13 at the time of charging is
It reaches a predetermined upper limit value and is held at the upper limit value. This is for the following reason. The power supply current Icc from the power supply 25 to the discharge wire 21 is the discharge current Isc to the shield case 22, the discharge current Igc to the grid 23, and the discharge current Ipc to the photosensitive drum 13 due to the discharge.
Will be diverted to. In order for the discharge current from the discharge wire 21 to reach the surface of the photoconductor film 12 via the grid 23,
It is necessary that the surface potential of the photosensitive film 12 is lower than the potential of the grid 23.

When the discharge current Ipc is supplied to the photoconductor film 12 at the charging position by the discharge from the discharge wire 21, the surface potential of the photoconductor film 12 gradually rises. When the rising surface potential substantially matches the potential of the grid 23, thereafter, no discharge occurs between the grid 23 and the photoconductor film 12. The power supply current Icc supplied to the discharge wire 21 is the discharge currents Isc and Igc. Therefore, the surface potential of the photoconductor film 12 is determined by the grid potential of the grid 23, and after reaching the grid potential, it is maintained at a potential substantially close to the grid potential.

On the drum substrate 30 of the photosensitive drum 13, a detector 26 made of a conductive material or the like for extracting a leak current Ilc generated by dark decay in the photosensitive film 12 is formed.
However, they are electrically connected without hindering the rotation of the photosensitive drum 13. The detector 26 is connected to the comparator 27, and detects the difference between the initial leak current value and the measured leak current value (hereinafter, fluctuation amount ΔIlc). Comparator 27
Is connected to a control device 28 including, for example, a microcomputer. A dark attenuation detecting means is configured by including the detector 26 and the comparator 27.

A memory 29 is connected to the control device 28. The memory 29 stores the variation ΔIlc in FIG.
Data of the change width ΔR of the resistance value of the variable resistor 24 having a predetermined correspondence relationship such as the correction curve 31 in the graph of FIG. The control device 28 corresponds to the variation amount ΔIlc of the leak current Ilc detected by the comparator 27, and reads the variable resistor 24 read from the memory 29.
The resistance value of the variable resistor 24 is changed by the resistance value change width ΔR. Compensation means is constituted by including the control device 28, the memory 29 and the variable resistor 24.

The resistance value change width data used when the resistance value of the variable resistor 24 is adjusted is also stored in the memory 29. The control device 28 refers to the resistance value change width data, and then holds the resistance value of the variable resistor 24 at the adjusted value until the condition for adjusting the resistance value of the variable resistor 24 is satisfied. To do. As an example, if the variable resistor 24 has a sliding configuration having a slider (not shown) displaced by a motor (not shown), the controller 28
Rotates the motor bidirectionally to displace the slider and change the resistance value of the variable resistor 24.

The data stored in the memory 29 is determined as follows. At the time of manufacturing the photoconductor film 12, the leak current based on the dark decay of the photoconductor film 12 is measured for a long period of time, or the leak current is used under the environment where the ambient atmosphere such as temperature, humidity and vibration is different. Measure the amount of current fluctuation. Also, changes in the surface potential at the developing position corresponding to various leak current values are measured. A uniform surface potential can be obtained at the developing position by changing the surface potential at the charging position by the amount of change in the surface potential.
The correction curve 31 has a predetermined surface potential V at the developing position.
When d is to be realized, it is set as a resistance value change width ΔR of the variable resistor 24 capable of realizing a change width of the surface potential at the charging position, which corresponds to the variation amount ΔIlc of the leak current Ilc.

In this embodiment, the grid resistance R is adjusted by adjusting the resistance value of the variable resistor 24, and the grid current Igc flowing through the grid 23 is controlled as follows. By controlling the grid current Igc, the discharge current Ipc supplied from the main charger 14 to the photosensitive drum 13 is controlled. As a result, the charging potential of the photosensitive drum 13 is controlled.

That is, the power supply current Icc from the power supply 25 to the discharge wire 21 is the discharge current Isc to the shield case 22 and the discharge current Igc to the grid 23 due to the discharge.
And the discharge current Ipc to the photoconductor drum 13 is divided. As a result, the following expression 1 is established.

[0038]

## EQU1 ## Icc = Isc + Igc + Ipc In the first expression, if the power supply current Icc and the discharge current Isc are constant values, the discharge current Ipc that determines the charging potential on the photoconductor film 2 is discharged to the grid 18. Current I
Determined by gc under negative correlation. The value of this discharge current Igc is determined by the resistance value of the variable resistor 12.

As the main charger 14, a scorotron charger is used in this embodiment. Generally, the photoreceptor film 2
Has a saturated charging potential Vs of 500 to 1000 V, especially 70
It is desirable to carry out main charging so that the voltage is in the range of 0 to 850V. Therefore, when performing corona discharge, 4 to
It is desirable to apply a high voltage of 7 kV to the discharge wire 21 of the main charger 14.

FIG. 3 is a system diagram showing an arrangement state of the photoconductor drum 13, the main charger 14, the developing device 16 and the charge eliminating lamp 20 of this embodiment, and FIG. 4 is a view of the grid 23 of the main charger 14. It is a top view. Charger width W1 of the main charger 14
Is, for example, 22 mm, and the opening width W of the grid 23 is
2 is 16 mm as an example. The distance L1 between the grid 23 and the photoconductor drum 13 is 1.5 mm as an example. An angle θ1 between the downstream end of the main charger 14 with respect to the rotation direction of the photoconductor drum 13 and the developing device 16 along the rotation direction is 120 ° as an example.
An angle θ2 along the rotation direction between the main charger 14 and the upstream end of the main charger 14 in the rotation direction is 30 °, for example. The diameter of the photoconductor drum 13 is, for example, φ78 mm. The grid length L2 of the grid 23 is 320 as an example.
mm. The openings of the grid 23 are formed in a mesh shape, and the opening ratio is 80% as an example.

The optical device 15 used for image exposure is
An optical system including a lens or a reflecting mirror, or a laser light oscillator is used. The developing device 16 includes a developing roller 6 a that supplies the charged toner of the one-component developer or the two-component developer to the surface of the photoconductor film 12. As the transfer device 18, a corona charger similar to the main charger 14 or a contact type charger is used.

Prior to charging the photoconductor film 12, the photoconductor film 12 is neutralized so that the surface potential of the photoconductor film 12 after the neutralization is 100 V or less. Therefore, depending on the type of the photoconductor film 12, the charge removal light amount of the charge removal lamp 20 may be preferably 5 LUX · SEC or more, particularly 10 LUX · SEC or more, on the photoconductor film 12. In particular, the above-mentioned amount of charge removal light is preferable in the photoconductor film 12 of this embodiment. On the other hand, when it is 50 LUX · SEC or more, deterioration of quality occurs due to light fatigue of the photoconductor film 12. As the static elimination lamp 20, any visible light source such as a halogen lamp, a fluorescent lamp, a cold cathode ray tube, or a neon lamp such as red or green can be used. Alternatively, a monochromatic light source such as an LED (light emitting diode) of red, yellow, green or the like can be used.

The photoconductor film 12 of the present embodiment is a positive charging type single layer organic photoconductor film, and is formed by mutually dispersing a binder resin, a charge transport medium and a charge generating substance. As the charge generating substance, any organic photoconductive pigment known per se is used. In particular, phthalocyanine pigments, perylene pigments,
Photoconductive organic pigments such as quinacridone pigments, pyranthrone pigments, disazo pigments and trisazo pigments are used alone or in combination of two or more.

As the charge transport medium, a resin medium in which a charge transport substance is dispersed is used. As the charge transport material, any hole transport material or electron transport material known per se is used for the purpose of the present invention. Examples of suitable hole transport materials are poly-N-vinylcarbazole, phenanthrene, N-ethylcarbazole, 2,5-diphenyl 1,3,4-oxadiazole, 2,5-bis (4
-Diethylaminophenyl) -1,3,4-oxadiazole, bis-diethylaminophenyl-1,3,6-
Oxadiazole, 4,4'-bis (diethylamino)
-2,2'-dimethyltriphenylmethane, 2,4,5
-Triaminophenylimidazole, 2,5-bis (4
-Diethylaminophenyl) -1,3,4-triazole, 1-phenyl-3- (4-diethylaminostyryl) -5- (4-diethylaminophenyl) -2-pyrazoline, p-diethylaminobenzaldehyde- (diphenylhydrazone), etc. , Or a combination of a plurality of these. 2 examples of suitable electron transport materials
-Nitro-9-fluorenone, 2,7-dinitro-9-
Fluorenone, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone, dinitroanthracene, dinitroacridine, It is used in any one of dinitroanthoquinone and the like, or a combination of a plurality thereof.

As the binder resin, various resins, for example, styrene-based polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-
Maleic acid copolymer, acrylic polymer, styrene-acrylic copolymer, styrene-vinyl acetate copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy Examples of various polymers include resins, polycarbonates, polyarylates, polysulfones, diallylphthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, polyether resins, phenol resins, and photocurable resins such as epoxy acrylates and urethane acrylates. To be done. A photoconductive polymer such as poly-N-vinylcarbazole can also be used as the binder resin.

The charge generating substance to be present in the photosensitive film 12 is suitably in the range of 0.1 to 50 parts by weight, particularly 0.5 to 30 parts by weight, per 100 parts by weight of the binder resin. It is suitable that the charge transport substance is in the range of 20 to 500 parts by weight, particularly 30 to 200 parts by weight, per 100 parts by weight of the binder resin. The thickness of the photoreceptor film 12 is preferably in the range of 10 to 40 μm, particularly 22 to 32 μm in view of high surface potential, printing durability and sensitivity.

As the drum substrate 30 made of metal of the photosensitive drum 12, an aluminum tube or an aluminum tube obtained by alumite treatment is generally used. In the present invention, the drum substrate 30 is not limited to the above metal, and any material having conductivity may be used. Examples include conductive resins and conductive films.

The organic photoreceptor layer as the photoreceptor film 12 is formed by using resin as N, N-dimethylformamide, N, N-.
Amide-based solvents such as dimethylacetamide; cyclic ethers such as tetrahydrofuran and dioxane; dimethyl sulfoxide; aromatic solvents such as benzene, toluene, xylene; ketones such as methyl ethyl ketone; N-methyl-
2-Pyrrolidone: dissolved in a solvent such as phenol or phenol such as cresol, and the charge generating substance is dispersed in the solvent to obtain a coating composition. This composition is applied to the conductive drum substrate 30 to form the photoconductor film 12.

The present invention has a remarkable advantage in the case of a positive charging type organic single layer photoreceptor, and the positive charging type also has an advantage that less ozone is generated at the time of main charging. In the case of the positive charging type, it is preferable to use a perylene pigment, an azo pigment or a combination thereof as the charge generating substance, and to use 2,6-dimethyl-2 ', 6-diter as the charge transporting substance.
a diphenoquinone derivative such as t-butyldiphenoquinone,
3,3′-dimethyl-N, N, N ′, N′-tetrakis-4-methylphenyl (1,1′-biphenyl) -4,
It is preferable to use diamine compounds such as 4′-diamine, fluorene compounds, and hydrazone compounds.

Below, referring to the flow chart,
The operation of this embodiment will be described.

FIG. 5 is a flow chart showing the operation of the image forming apparatus 11 of this embodiment, and FIG. 6 shows the leak current detecting operation and the surface potential correcting operation at the charging position in this embodiment. 3 is a flowchart illustrating in detail.
The operation described below is performed by the image forming apparatus 11 of this embodiment.
However, as an example, in the case of an electrostatic copying machine, this is performed during the warm-up period after the main power is turned on, or during the period when the copying operation is not performed. When it is performed during the warm-up period, it is not necessary to independently set an operation period for the correction operation of the present embodiment described below, and it is possible to prevent waste of time for the copying operation.

At step a1 in FIG. 5, the main power source is turned on. In step a2, the dark attenuation amount is measured as described later in detail. In step a3, it is judged whether the measured dark attenuation amount is equal to a predetermined initial value of the dark attenuation amount. Here, the initial value of the dark attenuation amount is a dark attenuation amount at the time of manufacturing an electrostatic copying machine which is an example of the image forming apparatus 11, and means a dark attenuation amount that has not changed with time. If the determination in step 3 is negative, it means that the dark attenuation amount has changed over time, etc., and in step a4, a correction operation described later in detail is executed. After completion of the correction operation, step a5
At this time, the electrostatic copying machine is set to a standby state in which copying operation is possible, and the copying operation is executed at step a6. At step a7, the copying operation is completed and the main power supply is cut off. If the determination is affirmative in step a3, in step a5, the electrostatic copying machine is set to a standby state in which copying operation is possible. Thereafter, the processing of steps a6 and a7 is performed.

At step b1 in FIG. 6, the main power source is turned on. In step b2, the photosensitive drum 13 starts rotating, and the main charger 14 is supplied with the discharge current Icc from the power supply 25. Optical device 15, developing device 1
6, the transfer device 18, the cleaning device 19, the static elimination lamp 20, etc. are all stopped. In step b3, the process stands by until the photosensitive drum 13 makes one rotation (for example, about 1 to 6 seconds). When the main motor of the image forming apparatus 11 of this embodiment is pulse-driven, the measurement of the waiting period may be realized by counting the pulses used for driving the main motor. Further, the image forming apparatus 11 may separately use a timer or a counter for measuring the waiting period.

The waiting period is set in order to wait until the charging on the entire surface of the photosensitive film 12 is completed.
As described above, the main charger 1 composed of the scorotron
When the photoconductor drum 13 is charged by means of 4, when the entire surface of the photoconductor film 12 is not charged to the saturated charging potential Vs, the discharge current Ip from the main charger 14 to the photoconductor film 12
c is flowing. As a result, carrier movement or recombination occurs in the photoconductor film 12, and even if the current from the photoconductor drum 13 is measured, the current is equivalent to the leak current in the photoconductor film 12. Not expected to be.

On the other hand, when the photosensitive film 12 is charged to the saturated charging potential Vs over the entire surface, most of the discharge from the discharge wire 21 of the main charger 14 goes to the shield case 22 and the grid 23. Discharge current Isc, I
gc flows. The discharge current Ipc to the photoconductor film 12 in such a state is the leak current Il in the photoconductor film 12.
matches c. At this time, the leak current Ilc is in a constant steady state. Accordingly, by measuring the current flowing from the photoconductor drum 12, it is possible to measure the current equivalent to the leak current Ilc in the photoconductor film 12.

If the determination in step b3 is affirmative, in step b4 the leak current I in the photosensitive film 12 is detected.
lc is taken out from the drum substrate 30 by the detector 26 and measured by the comparator 27. In step b5, it is judged whether or not the dark attenuation amount at the time of measurement of the photoconductor film 12, which is represented by the measured leak current Ilc, is equal to a predetermined initial value of the dark attenuation amount.

If the determination in step b5 is negative, it means that the dark attenuation has changed with time and the like, and in step b6, the correction operation described below is executed. That is, based on the leak current Ilc obtained by the measurement and the initial value at the time of manufacturing the leak current, the fluctuation width ΔIl between the leak current Ilc obtained by the measurement and the initial value.
c is detected by the comparator 27. Control device 28
Reads out the variation width ΔR of the resistance value of the variable resistor 24 corresponding to the fluctuation width ΔIlc based on the fluctuation width ΔIlc of the leak current Ilc detected by the comparator 27. Based on the resistance value change data, the control device 28 described above drives the motor or the like, for example, to change the resistance value of the variable resistor 24 by the change width ΔR. Dark decay is
Since the resistance value of the variable resistor 24 increases with time, a change in the resistance value of the variable resistor 24 results in an increase in the resistance value.

Due to the increase in the resistance value of the variable resistor 24, the grid current Igc of the grid 23 is suppressed.
As a result, as described in relation to the first equation, the discharge current Ip to the photoconductor film 12 due to the discharge from the discharge wire 21.
c increases. As a result, the potential at the charging position of the photosensitive drum 13 directly below the main charger 14 rises. On the other hand, the potential at the developing position of the photoconductor drum 13 facing the developing device 16 changes from the leak current Ic to the leak current Ic due to the change with time of the leak current Ilc, particularly the increase of the leak current.
It decreases by the increase of lc. In this embodiment, the potential at the developing position can be maintained at a predetermined potential by increasing the potential at the charging position of the photosensitive drum 13. As a result, a uniform image density can be realized in the photoconductor drum 13 even if the leak current Ilc changes with time.

When the correction process in step b6 is completed, in step b7, the image forming apparatus 11 enters a standby state in which a copying operation is possible. When the copy operation is executed and completed in step b8, the main switch is cut off and the operation of the image forming apparatus 11 is stopped in step b9. Then, the process returns to step b1.

If the determination is affirmative in step b5, the process proceeds to step b7, and the above-mentioned step b7 is executed.
Perform the following processing.

According to the measurement by the present inventor, the potential at the developing position of the image forming apparatus of the prior art which does not measure the leak current Ilc and adjust the charging potential of the photosensitive drum 3 as in the present embodiment. And the image forming apparatus 11 of this embodiment.
Comparing the electric potential at the developing position with that of the electrostatic copying machine, the results shown in FIG. 7 were obtained. Line 32 in FIG. 7 is for the prior art and line 33 is for the present embodiment. As can be seen from FIG. 7, in the prior art, the potential at the developing position gradually decreases with use, whereas in the image forming apparatus 11 of this embodiment, the potential at the developing position is constant.

As a result, it is possible to realize the image forming apparatus 11 in which the image density is maintained constant in the regular developing method and the fog phenomenon which is the uneven image density is prevented in the reversal developing method.

The waiting period in step b3 may be at least one revolution. Therefore, as a modified example of the present embodiment, the waiting period may be set to a predetermined plurality of rotations, and the average of the leakage current values during the plurality of rotations may be calculated.

As a modification of the present embodiment, the temperature of the photosensitive drum 13 may be raised when measuring the leak current. In the photoconductor drum 13 of the image forming apparatus 11 as an electrostatic copying machine, the photoconductor drum 13
Condensation on the surface of the photosensitive drum 13 may cause disappearance of charges distributed on the photoconductor drum 13 or destruction of the formed electrostatic latent image. Therefore, in order to prevent dew condensation on the photoconductor drum 13, a heater is installed in the photoconductor drum 13.

It has been confirmed that the leak current of the photoconductor film 12 increases as the temperature rises. Therefore, when the temperature of the photoconductor drum 13 is increased by using the heater when performing the operation of measuring the leak current, the level of the leak current measured increases, so the resolution of the leak current detection is improved. You can
The accuracy of the correction operation can be improved.

(Second Embodiment) FIG. 8 is a system diagram of an image forming apparatus 11a according to a second embodiment of the present invention. This embodiment is similar to the first embodiment, and the corresponding parts are designated by the same reference numerals. In this embodiment, as in the first embodiment, in order to adjust the potential at the charging position of the photoconductor drum 13, the discharge current I from the main charger 14 to the photoconductor drum 13 is adjusted.
control pc. The feature of this embodiment is that the grid 23 and
As an example, the varistor 34 is connected to a common potential such as a ground potential. In the present embodiment, the varistor 34
Of the grid voltage V of the grid 23 by adjusting the control voltage of
g is controlled. In the first embodiment,
It has been described that when the surface potential of the photosensitive drum 13 substantially matches the grid potential Vg of the grid 23, the discharge wire 21 does not discharge to the photosensitive drum 13. Therefore, the surface potential of the photosensitive drum 13 can be controlled by adjusting the grid voltage Vg.

The varistor 34 is constructed by using a constant voltage element such as a Zener diode, and the input current is cut off while the input voltage is less than the control voltage. When the input voltage becomes equal to or higher than the control voltage, the input current flows almost without resistance, and the terminal voltage between the input terminal and the output terminal of the varistor 34 maintains the voltage determined by the control voltage constant. .

In this embodiment, the same detector 26, comparator 27, controller 28 and memory 29 as those used in the first embodiment are used.
And a leak current detecting operation similar to the leak current detecting operation in the first embodiment.

In the present embodiment, the correction curve 3 in the graph of FIG. 9 is set in the memory 29 for the variation amount ΔIlc of the leak current Ilc due to dark decay in the photoconductor film 12.
The varistor 3 having a predetermined correspondence relationship such as 5
Data of the change width ΔVg of the control voltage of No. 4 is stored. The control device 28 changes the control voltage of the varistor 34 by the control voltage change width ΔVg of the varistor 34 read from the memory 29, corresponding to the variation amount ΔIlc of the leak current Ilc detected by the comparator 27.

The control voltage change width data used when the control voltage of the varistor 34 is adjusted is also stored in the memory 29.
Memorized in. The control device 28 refers to the control voltage change width data, and then holds the control voltage of the varistor 34 at the adjusted value until the condition for adjusting the control voltage of the varistor 34 is satisfied.

With this embodiment as well, the same effects as those described in the first embodiment can be achieved.

As another embodiment of the present invention, the variable resistor 24 and the varistor 34 may be used together. Specifically, in the circuit shown in FIG. 8, the variable resistor 24 is connected in series between the varistor 34 and the ground potential. In this embodiment, the control voltage of the varistor 34 and the resistance value of the variable resistor 24 may be individually adjusted to adjust the grid current Igc or the grid voltage Vg of the grid 23.

(Third Embodiment) FIG. 10 shows a third embodiment of the present invention.
3 is a block diagram showing the configuration of the image forming apparatus 11b of FIG.
The present embodiment is similar to each of the above-mentioned embodiments, and corresponding parts are designated by the same reference numerals.

In the image forming apparatus 11b of this embodiment,
As the main charger 14, for example, a corotron charger is used, and in addition, a scorotron charger, a contact type charger, or the like is used. Hereinafter, an example using the Corotron charger will be described. The main charger 14 is
A discharge wire 21 that performs corona discharge and a shield case 22 that surrounds the discharge wire 21 and is open to the photosensitive drum 13 side are provided. The shield case 22 is grounded. A power supply 36 for supplying a power supply current Icc required for corona discharge is connected to the discharge wire 21 of the main charger 14. A variable resistor 37 is connected to the power supply 36. The power supply 36 changes the current value of the power supply current Icc in accordance with the resistance value set in the variable resistor 37 and outputs it.

The surface potential of the photosensitive drum 13 at the charging position is determined by the power supply current Icc in this embodiment unless the surface potential is saturated. Therefore, in this embodiment, by adjusting the resistance value of the variable resistor 37, the surface potential of the photosensitive drum 13 at the charging position is controlled.

One end of the detector 26 is connected to the drum base 30 of the photosensitive drum 13, and the other end of the detector 26 is connected to the integrating ammeter 38. The detection signal from the integrating ammeter 38 is supplied to the control device 28. Control device 2
A memory 29 is connected to 8. The memory 29 stores data of an appropriate current value of the power supply current Icc corresponding to the integrated amount of the leak current Ilc measured by the integrated ammeter 38 in a relationship as shown by the correction curve 39 in FIG.

The integrating ammeter 38 is
As will be described later, the current from the photosensitive drum 13 is detected,
Leakage current I due to dark decay in the photoconductor film 12
The integrated amount of lc is detected. The control device 28 reads an appropriate value of the power supply current Icc corresponding to the integrated amount of the leak current Ilc from the memory 29 based on the integrated amount of the leak current Ilc, and sets the variable resistor 3 to the appropriate value.
Adjust 7. A specific example of the adjusting operation is described in Example 1 as an example.
It may be due to the driving of the motor in. It is considered that the cumulative amount of current measured by the cumulative ammeter 38 during a certain period is substantially proportional to the amount of charge lost from the entire surface of the photosensitive film 2 during the certain period. In this embodiment, the degree of dark decay in the photoconductor film 12 is detected by measuring the integrated current amount based on this idea. In this embodiment, specifically, the amount of change in dark decay over time is detected by measuring how the integrated current amount per unit time changes over time. . As a modified example of this embodiment, the leak current ΔIlc in the photoconductor film 12 is measured by using a normal ammeter, and the instantaneous value of the leak current Ilc obtained by the measurement is input to the control device 28. Alternatively, the control device 28 may integrate the leak current Ilc obtained by the measurement.

If the initial surface potential at the charging position of the photosensitive drum 13 by the main charger 14 is adjusted on the basis of the integrated current amount per unit time, the surface at the developing position where the developing device 16 develops is performed. The potential can be maintained at the desired level. In the present embodiment, the power supply current Icc corresponding to the correction curve 39 of FIG. 11 is supplied from the power supply 36 to the main charger 14 based on the measured integrated current amount. Specifically, by adjusting the resistance value of the variable resistor 37 connected to the power source 36, the power source current Icc from the power source 36 to the main charger 14 is changed. As a result, the surface potential at the charging position of the photoconductor film 12 by the main charger 14 is adjusted.

Also in such an embodiment, the same effects as those described in the above-mentioned embodiments can be achieved.

In the above embodiments, the drum-shaped substrate on which the photosensitive film is formed is used as the photosensitive member, but a belt-shaped substrate on which the photosensitive film is formed may be used.

Although the image forming apparatus of the present invention is described as an electrostatic copying machine in the above embodiments, the image forming apparatus of the present invention can form an image by an electrophotographic method regardless of the electrostatic copying machine. Any image forming apparatus may be used.

[0082]

According to the present invention, after the variation in the degree of dark decay on the photosensitive drum is detected, the degree of the dark decay near the developing means on the photosensitive drum is detected based on the detection result. I am trying to compensate for the fluctuation of. As a result, when the dark decay changes with time, or when the dark decay varies depending on the installation environment of the image forming apparatus and the like, the dark decay may occur immediately after the photoconductor film is manufactured. When it changes from the degree, it is possible to form an image having a uniform image density by compensating for the time-dependent change in the degree of dark attenuation or the variation.

[Brief description of drawings]

FIG. 1 is a system diagram of an image forming apparatus 11 according to a first embodiment of the present invention.

FIG. 2 is a graph illustrating data stored in a memory 29.

FIG. 3 is a system diagram showing an arrangement state of the present embodiment.

FIG. 4 is a plan view of a grid 23 of the main charger 14.

FIG. 5 is a flowchart illustrating the operation of this embodiment.

FIG. 6 is a flowchart illustrating the operation of this embodiment.

FIG. 7 is a graph illustrating the effect of this embodiment.

FIG. 8 is a system diagram of an image forming apparatus 11a according to a second embodiment of the present invention.

FIG. 9 is a graph illustrating data stored in a memory 29.

FIG. 10 is a system diagram of an image forming apparatus 11b according to a third embodiment of the present invention.

11 is a graph illustrating data stored in a memory 29. FIG.

FIG. 12 is a system diagram of a conventional image forming apparatus 1.

[Explanation of symbols]

 11, 11a, 11b Image forming device 12 Photosensitive film 13 Photosensitive drum 14 Main charger 16 Developing device 19 Cleaning device 20 Discharge lamp 21 Discharge wire 22 Shield case 23 Grid 24 Variable resistor 25, 36 Power supply 27 Comparator 28 Control Device 29 Memory 30 Drum Base 34 Varistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Yamazato 1-22-28 Tamazo, Chuo-ku, Osaka Mita Industrial Co., Ltd. (72) Inventor Takuji Terada 1-2-28 Tamatsukuri, Chuo-ku, Osaka Mita Within Kogyo Co., Ltd.

Claims (8)

[Claims] 1. A rotatable photoconductor member comprising a conductive substrate and a photoconductor film formed on the surface of the substrate, and a photoconductor film which is disposed in the vicinity of the photoconductor member. Charging means for charging, exposing means for irradiating the charged photoconductor film with light corresponding to an image, and developing means arranged downstream of the exposing means along the rotation direction of the photoconductor member. And a dark decay detecting means for detecting a variation in the degree of dark decay based on the dark decay in the photoconductor film, and a variation in the degree of dark decay detected by the dark decay detecting means. An image forming apparatus comprising: a compensating unit that compensates for the fluctuation of the degree of dark attenuation. 2. The dark decay detecting means detects a leak current flowing from the substrate by dark decay in the photoconductor film, and the compensating means based on the leak current detected by the dark decay detecting means. The image forming apparatus according to claim 1, wherein the fluctuation of the degree of dark attenuation is compensated. 3. The image forming apparatus according to claim 1, wherein the charging unit is a scorotron charger including a discharge wire, a shield case, and a grid. 4. The image forming apparatus according to claim 2, wherein the compensating unit includes a grid resistor having a variable resistance value, the grid resistor being connected between the grid and a common potential. 5. The image forming apparatus according to claim 2, wherein the compensating unit includes a grid potential adjusting unit that adjusts a grid potential of the grid. 6. The image forming apparatus according to claim 1, wherein the compensating unit controls the amount of electric current supplied to the charging unit for charging. 7. The dark decay detection means reads the current value of the leak current taken out by the detector, which has a conductivity with which the leak current is brought into contact with the substrate, and a predetermined initial leak current. The image forming apparatus according to claim 1, further comprising a comparing unit that compares the value. 8. The dark decay detection means integrates and integrates a conductive detection body that comes into contact with the base body to extract a leakage current, and a leakage current extracted by the detection body over a predetermined period. The image forming apparatus according to claim 1, further comprising an integrated leak current detection unit that detects a leak current value.