JPH10133516A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely control the conditions of an image forming process (for instance, the light quantity of image exposure imparted from an exposure device to a photoreceptor) by accurately detecting the thickness of the photoconductive layer of the photoreceptor. SOLUTION: When an image is not formed, an AC voltage is applied to a conductive layer 10 formed on a cleaning blade 6, to make a potential on the photoreceptor 1 uniform. After that, a voltage is applied to an electrifying roller 2, to measure a current-flow between the electrifying roller 2 and the photoreceptor 1 by an ammeter 8, so that an accurate and stable current-flow can be measured. Therefore, the light quantity of the image exposure L imparted from the exposure device 3 to the photoreceptor 1 can be precisely controlled by a controller 12, based on the measured accurate and stable current-flow.

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 to which an electrophotographic system is applied, such as a copying machine, a laser beam printer, and a facsimile.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, etc. to which electrophotography is applied, a drum type electrophotographic photosensitive member (hereinafter simply referred to as a "photosensitive member") as an image carrier has conventionally been used. Many image forming apparatuses have been proposed and put to practical use, in which a charging member is brought into contact with a member to apply a voltage in which alternating current and direct current are superimposed to perform charging. Also, many image forming apparatuses have been proposed and put into practical use, in which the thickness of a photoconductive layer on a photoreceptor is detected to control the conditions of the image forming process (exposure light amount, charging applied voltage, transfer voltage, etc.). .

As a method for detecting the thickness of the photoconductive layer on the photoconductor, for example, a method of detecting the thickness of the photoconductive layer of the photoconductor by detecting the amount of current flowing between the charging member and the photoconductor. For example, it is described in JP-A-5-307315.

[0004]

In the above-described method of detecting the amount of current flowing between the charging member and the photoreceptor in the conventional image forming apparatus, the current flowing through the photoreceptor is determined by the amount of change in the potential of the photoreceptor. Since the thickness (capacity) of the photoconductive layer of the photoconductor is determined, in order to accurately know the thickness of the photoconductive layer, the potential on the photoconductor before the contact between the charging member and the photoconductor is kept at a constant value. There is a need.

[0005] For this reason, in the past, pre-exposure was generally performed to keep the potential on the photosensitive member constant.
However, in order to perform pre-exposure, a space for pre-exposure must be provided between the charging member and the cleaning member that removes deposits on the photoconductor, which is a factor that hinders miniaturization of the apparatus. I was In addition, since a light-emitting device for performing pre-exposure is required, there are also problems such as a rise in temperature due to heat generated by light emission and an increase in energy consumption due to light emission. Furthermore, when the photoconductor is deteriorated and the bright portion potential rises, the light cannot set the potential of the photoconductor to a predetermined value, and a residual potential remains. Since the amount is smaller than without residual potential,
There is also a problem that the thickness of the photoreceptor cannot be known accurately.

Further, when the potential of the photosensitive member is made constant in front of the cleaning member, the thickness of the photosensitive member can be accurately known by charging unevenly due to friction between the cleaning member and the photosensitive member. I couldn't do that.

Further, when charging is performed by applying a voltage in which AC and DC are superimposed on the charging member, a sound having a period that is an integral multiple of the frequency of the AC component is generated. Exceeds 70 mm / sec, charging frequency is 500H
At z or more, the charging sound is mainly doubled at 1000 Hz, which is a very unpleasant sound.

Further, when the image forming apparatus is operated continuously, the residue passing through the cleaning member is accumulated by electrostatic force on the downstream side of the cleaning member in the rotation direction of the photosensitive member, and the image forming apparatus is stopped for a while. When the cleaning member is restarted after the cleaning, the cleaning member tends to rotate around the surface of the photoconductor, and the residue accumulated on the downstream surface of the cleaning member in the rotation direction of the photoconductor is attached by a horizontal line on the photoconductor and charged. There was a possibility that the member was soiled and had adverse effects on charging.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of accurately detecting the thickness of a photoconductive layer of a photoreceptor and controlling the conditions of an image forming process with high accuracy. .

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and is directed to a rotatable image carrier having a photoconductive layer formed on a surface thereof with a predetermined thickness, and a surface of the image carrier. An image bearing member for charging the image carrier by contacting the image carrier; a power source for applying a voltage to the charging device; and an exposing device for performing image exposure on the image carrier in accordance with input image information. A measuring device configured to measure a current amount between the charging unit and the image carrier when a predetermined voltage is applied to the charging unit from the power supply, and provided to be in contact with a surface of the image carrier. A conductive member, an AC power supply for applying an AC voltage to the conductive member, and current amount data measured by the measurement unit, and setting conditions of an image forming process based on the input current amount data. Control means for controlling During image formation, an AC voltage is applied to the conductive member from the AC power supply to make the potential on the image carrier uniform, and then a voltage is applied to the charging unit from the power supply to cause the charging unit and the image to be charged. The amount of current between the carriers is measured by the measuring unit, the measured current amount data is input to the control unit, and the control unit controls the conditions of the image forming process based on the input current amount data. It is characterized by doing.

[0011] Further, a cleaning means for removing the adhering matter on the image carrier is provided upstream of the charging means in the rotational direction of the image carrier so as to contact the image carrier, and at least one of the cleaning means is provided. The image forming apparatus is characterized in that the conductive member is arranged on a part of a surface that comes into contact with the surface of the image carrier.

The control means stores in advance a relationship between thickness data of the photoconductive layer of the image carrier and light potential data on the image carrier according to the input current amount data. The control means controls the light amount of the image exposure in accordance with the current amount data input based on the relation data.

Further, the power supply applies a voltage obtained by superimposing a direct current to a direct current to the charging means during image formation.

The charging means and the conductive member are arranged at a predetermined interval, and when the image carrier is charged by applying a voltage obtained by superimposing an alternating current and a direct current to the charging means, the charging means and the conductive member are connected to each other. An AC bias voltage is simultaneously applied to the conductive members.

(Operation) According to the structure of the present invention, an AC voltage is applied to the conductive member during non-image formation to make the potential on the image carrier uniform, and then a voltage is applied to the charging means to charge the charging means. By measuring the amount of current between the image carrier and the image carrier, the potential on the image carrier before measuring the amount of current between the charging means and the image carrier is stable, so that an accurate and stable amount of current can be obtained. Can be measured. Therefore, the conditions of the image forming process can be accurately controlled based on the measured and stable current amount.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a main part of an image forming apparatus according to an embodiment of the present invention. In this embodiment, an example of a transfer type laser beam printer using an electrophotographic system is shown. is there.

The image forming apparatus (laser beam printer) shown in FIG. 1 has a rotating drum type photoreceptor 1 as an image carrier and a charging roller 2, an exposing device 3 and a developing device 4 around the photoreceptor 1 as main components. , A transfer device 5 and a cleaning blade 6.

The photoreceptor 1 has a photoconductive layer 1a made of, for example, an organic photoconductor formed on the surface thereof, and a cylindrical conductive base 1b made of, for example, aluminum having the photoconductive layer 1a adhered to the surface. It is driven to rotate at a predetermined peripheral speed (for example, 200 mm / sec) in the direction of arrow A. In the present embodiment, for example, the thickness of the photoconductive layer 1a is 5
0 μm, and the diameter of the conductive substrate 1b is 30 mm.

The charging roller 2 is constituted by providing a medium-resistance rubber layer on a core metal having a diameter of, for example, 8 mm, and is disposed so as to be in contact with the photoconductive layer 1 a on the surface of the photoconductor 1. It is driven and rotated. To the charging roller 2, a voltage obtained by superimposing a direct current on an alternating current is applied from a power source 7 during image formation. The charging roller 2 includes the charging roller 2 and the photosensitive member 1.
An ammeter 8 for measuring a current flowing therebetween is connected.

The exposure device 3 performs an image exposure L according to the input image information on the photosensitive member 1 charged by the charging roller 2. The exposure device 3 includes a laser diode,
A laser beam scanner (not shown) having a polygon mirror or the like is provided, and a laser beam modulated (intensity) in accordance with a time-series electric digital image signal of input image information is output. Photoconductive layer 1
Image exposure L is performed on a, and an electrostatic latent image corresponding to the input image information is formed.

The developing device 4 rotates on a magnet roller, which carries and transports a developing container (not shown) for storing a developer (toner) and a charged toner, and attaches the charged toner to the electrostatic latent image. The developing device 4 is provided with a developing roller 9 provided with a possible non-magnetic sleeve, and the developing device 4 makes toner adhere to the electrostatic latent image to visualize it as a toner image.

The transfer device 5 applies a charge having a polarity opposite to that of the toner image by corona discharge to the back surface of a transfer material such as paper (not shown) to be conveyed, and transfers the toner image to the transfer material by electrostatic force.

The cleaning blade 6 has its tip abutting on the surface of the photoreceptor 1 to clean the surface of the rotating photoreceptor 1 such as residual toner after transfer. Direction of rotation (arrow A
Direction) A conductive layer 10 is formed on the downstream surface.
The tip of the conductive layer 10 is in contact with the surface of the photoconductor 1, and an AC power supply 11 is connected to the conductive layer 10.

The exposure device 3 and the ammeter 8 have a control device (CP
U) 12 are connected. The control device 12 stores in advance the relationship between the thickness data of the photoconductive layer 1 a of the photoconductor 1 and the light potential data on the photoconductor 1 according to the current amount data input from the ammeter 8. The means 12 controls the amount of image exposure L given to the photoreceptor 1 from the exposure device 3 in accordance with the current amount data input based on these relationship data (details will be described later).

Next, the operation of the above-described image forming apparatus according to the present embodiment will be described.

At the time of image formation, the photosensitive member 1 is driven to rotate in the direction of arrow A by driving means (not shown). At this time,
A voltage obtained by superimposing an alternating current and a direct current is applied to the charging roller 2 from a power source 7 to charge the surface of the photoconductor 1 to a predetermined negative potential. The applied voltage at this time is, for example, a frequency of 1600
It is obtained by superimposing a DC voltage of -700 V on an AC voltage of 2000 V in Hz.

Then, an image exposure L is given from the exposure device 3 to the charged photosensitive member 1 to form a positive electrostatic latent image corresponding to the input image information. This photoconductor 1
The developing device 4 attaches a negatively charged toner having the same polarity as the electrostatic latent image to the upper electrostatic latent image and develops the toner image. At this time, the amount of image exposure L from the exposure device 3 is controlled by the thickness of the photoconductive layer 1 a of the photoconductor 1, that is, the current flowing between the charging roller 2 and the photoconductor 1 measured by the ammeter 8. It is controlled by the controller 12 based on the amount (the details will be described later).

When the toner image on the photoreceptor 1 reaches the transfer device 5, a transfer material (not shown) is transported between the photoreceptor 1 and the transfer device 5 at this timing. A positive charge is provided on the back side of
The toner image on the photoconductor 1 is transferred to the front surface side. The transfer material onto which the toner image has been transferred is conveyed to a fixing device (not shown), and the transferred toner image is fixed on the transfer material as a permanently fixed image by the fixing device and discharged. On the other hand, the surface of the photoreceptor 1 after the transfer of the toner image is cleaned by removing the residual toner and other attached matter by the cleaning blade 6, and the surface is initialized by a static eliminator (not shown). Hereinafter, the above-described steps are similarly repeated.

Next, control of the amount of image exposure L from the exposure device 3 to the photoconductor 1 based on the thickness of the photoconductive layer 1a of the photoconductor 1 will be described.

FIG. 2 is a graph showing the relationship between the thickness of the charge transport layer (CT layer) of the photoconductive layer 1a of the photoreceptor 1, the light potential on the photoreceptor 1, and the DC current flowing through the charging roller 2. Yes,
This is data when a constant DC voltage of -1.4 kV is applied from the power supply 7 to the charging roller 2. In FIG. 2, graph 1
Is the relationship between the thickness of the charge transport layer (CT layer) of the photoconductive layer 1a of the photoconductor 1 and the DC current flowing through the charging roller 2,
Graph 2 shows the charge transport layer (C) of the photoconductive layer 1a of the photoreceptor 1.
4 shows the relationship between the thickness of the (T layer) and the light portion potential on the photoconductor 1.

FIG. 3 shows the amount of light (E) and the amount of light (E) when image exposure L is performed after charging the photosensitive member 1 by applying a DC constant voltage of -1.4 kV from the power supply 7 to the charging roller 2. The relationship (EV curve) with the bright portion potential (V) of one surface was measured before and after the endurance of 60,000 sheets.
Graph 4 shows the relationship between the amount of light after the endurance and the light portion potential. In FIG. 3, a graph 5 shows a relationship (EV curve) between the light quantity and the light-portion potential after 10,000 sheets of durability.
The control of the amount of image exposure L given from the exposure device 3 onto the photoreceptor 1 is performed based on the graphs shown in FIGS.

That is, the photoreceptor 1 rotates at the time of non-sheet passing (non-image formation), such as at the time of multi-rotation before, and a DC constant voltage bias is applied to the charging roller 2 from the power supply 7. The DC current flowing between the charging roller 2 and the photoconductor 1 at this time is measured by an ammeter 8
As shown in the graph 1 of FIG. 2, it was 50 μA before the endurance, but was 60 μA after passing 10,000 sheets.
Became. As a result, as shown in the graph 2 of FIG. 2, the thickness of the charge transport layer (CT layer) of the photoconductive layer 1a of the photoconductor 1 is reduced.
From about 30 μm to about 25.4 μm (Graph 1
A → B) at this time, the bright portion potential on the photoreceptor 1 is -15
From about 0 V to about -250 V (C in graph 2)
→ D). When these results are applied to FIG. 3, the state of the point P on the graph 3 changes to the state of the point Q on the graph 5 which is the EV curve after the 10,000 sheets endurance due to the 10,000 sheets endurance. Will be.

At this time, in order to secure a bright portion potential of -150 V, it is necessary to be in the state of the point R on the graph 5, and a light amount of about 1.4 (lux · sec) is required.
Further, after the end of 60,000 sheets, it is necessary to change to the state of the point E on the graph 4 in order to secure a bright portion potential of -150 V, and the light amount of about 2.3 (lux · sec) is required. Required.

As described above, by detecting the DC current flowing through the charging roller 2 with the ammeter 8, the amount of light required to secure the light portion potential on the photosensitive member 1 is calculated, and based on these graphs. For example, the charging roller current shown in FIG.
A graph showing the relationship between kV DC constant voltage) and the amount of light required to secure the light portion potential is obtained. In the control device 12,
For example, the relationship data between the current and the light amount as shown in FIG. 4 is stored in advance, and when the current amount data is input from the ammeter 8, the stored relationship data between the current and the light amount as shown in FIG. The amount of image exposure L given to the photoconductor 1 from the exposure device 3 is controlled based on the exposure.

It is important to know the exact thickness of the photoconductive layer 1a of the photoreceptor 1 for optimal control and, consequently, for optimal image formation. For that purpose, it is essential that the potential of the photoconductor 1 in front of the charging roller 2 is stable.
For this reason, in the present embodiment, the cleaning blade 6
A conductive layer 10 on the surface of the photosensitive member 1 on the downstream side in the rotation direction
When an image is not formed (when the thickness of the photoconductive layer 1a of the photoconductor 1 is detected), an AC bias voltage (for example, an AC voltage of 2000 V at a frequency of 1600 Hz) is applied from the AC power supply 11 to the conductive layer 10. , And discharge is caused between the photosensitive member 1 and the surface potential of the photosensitive member 1.

The conductive layer 1 provided on the cleaning blade 6
By applying an AC bias voltage of 0 to make the charge of the photosensitive member 1 uniform, the cleaning blade 6 and the photosensitive member 1 that are generated when the charge is made uniform before the cleaning of the photosensitive member 1 by the cleaning blade 6, for example. The surface potential of the photosensitive member 1 rises due to the friction of
There is no possibility that the thickness of the photoconductive layer 1a of the photoconductor 1 is erroneously detected due to a change in the amount of current between the photoconductor 1 and the photoconductor 1. Therefore, even in the case where the charge removal is made uniform by pre-exposure, which has been widely performed conventionally, the problem of temperature rise due to the pre-exposure light source does not occur. Does not occur.

As described above, in the present embodiment, an AC voltage is applied to the conductive layer 10 during non-image formation (when the thickness of the photoconductive layer 1a of the photoconductor 1 is detected) to reduce the potential on the photoconductor 1 After uniforming, by applying a voltage (DC voltage) to the charging roller 2 and measuring the amount of current between the charging roller 2 and the photoconductor 1, before measuring the amount of current between the charging roller 2 and the photoconductor 1 Since the potential on the photoreceptor 1 is stable at this time, an accurate and stable current amount can be measured. Therefore, the amount of image exposure L given to the photoconductor 1 from the exposure device 3 can be accurately controlled based on the measured and stable amount of current, so that stable image formation can be performed regardless of the number of image formations. It can be performed.

In the above embodiment, the photosensitive member 1
The method of detecting the film thickness of the photoconductive layer 1a by applying a DC voltage and measuring the current value of the DC current flowing at that time was used. However, the current value of the AC current flowing at that time by applying the AC voltage was Can be measured.

In the above-described embodiment, the photosensitive member 1
The AC bias voltage is applied to the conductive layer 10 provided on the cleaning blade 6 only when the thickness of the photoconductive layer 1a is measured. However, the AC bias voltage is applied periodically every several image forming operations. This makes it possible to blow off the deposits accumulated on the downstream side in the rotation direction of the photoconductor 1 through the cleaning blade 6 by the electric field, so that a large amount of deposits are prevented from being accumulated on the photoconductor 1 and the apparatus is stopped. The surface of the photoconductor 1 will not be stained at the time of restarting later.

The charging roller 2 and the conductive layer 10 are arranged at a predetermined interval, and when the photosensitive member 1 is charged by applying a voltage obtained by superimposing an alternating current and a direct current to the charging roller 2,
By simultaneously applying an AC bias voltage to the photoconductor 1 and the conductive layer 10, vibration caused by the charging of the photoconductor 1 is cancelled, and noise generated due to the charging of the photoconductor 1 can be reduced.

[0042]

As described above, according to the present invention,
After applying an AC voltage to the conductive member during non-image formation to make the potential on the image carrier uniform, by applying a voltage to the charging unit and measuring the amount of current between the charging unit and the image carrier, The amount of current between the charging means and the image carrier can be accurately measured. Therefore, it is possible to accurately control the conditions of the image forming process, for example, the amount of image exposure, based on the measured and stable current amount, so that stable image formation can be performed regardless of the number of times of image formation. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a main part of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a relationship between a film thickness of a photoconductive layer of a photoconductor, a bright portion potential on the photoconductor, and a DC current flowing through a charging roller.

FIG. 3 is a diagram illustrating an example of a relationship between a light amount at the time of image exposure and a surface potential of a photoconductor.

FIG. 4 is a diagram illustrating an example of a relationship between a current flowing through a charging roller and a light amount necessary for securing a bright portion potential on a photoconductor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image carrier (photoreceptor) 1 a photoconductive layer 1 b conductive substrate 2 charging means (charging roller) 3 exposure means (exposure apparatus) 4 developing device 5 transfer device 6 cleaning means (cleaning blade) 7 power supply 8 measuring means (current 9) developing roller 10 conductive member (conductive layer) 11 AC power supply 12 control means (control device)

Claims (5)

[Claims] 1. A rotatable image carrier having a photoconductive layer formed on a surface thereof with a predetermined thickness, a charging unit that contacts the surface of the image carrier and charges the image carrier, and a voltage is applied to the charging unit. And an exposure unit for performing image exposure on the image carrier in accordance with input image information, when a predetermined voltage is applied to the charging unit from the power supply. Measuring means for measuring the amount of current between the charging means and the image carrier; a conductive member provided to contact the surface of the image carrier; and an AC power supply for applying an AC voltage to the conductive member. Inputting current amount data measured by the measuring means,
Control means for controlling the conditions of the image forming process based on the input current amount data, wherein an AC voltage is applied to the conductive member from the AC power source during non-image formation, and the image carrier is After making the above potential uniform, a voltage is applied to the charging unit from the power supply, a current amount between the charging unit and the image carrier is measured by the measurement unit, and the measured current amount data is controlled by the control unit. An image forming apparatus configured to control an image forming process by the control unit based on the input current amount data. 2. A cleaning means for removing an adhering substance adhered on the image carrier is provided upstream of the charging means in a rotation direction of the image carrier so as to contact the image carrier, and at least one of the cleaning means is provided. The image forming apparatus according to claim 1, wherein the conductive member is disposed on a part of a surface that contacts a surface of the image carrier. 3. The control means stores in advance a relationship between thickness data of the photoconductive layer of the image carrier and light potential data on the image carrier according to the input current amount data. 2. The image forming apparatus according to claim 1, wherein the control unit controls a light amount of the image exposure according to the current amount data input based on the relationship data. 3. 4. The image forming apparatus according to claim 1, wherein the power supply applies a voltage obtained by superimposing a direct current on an alternating current to the charging unit during image formation. 5. The image forming apparatus according to claim 1, wherein the charging unit and the conductive member are arranged at a predetermined interval, and the charging unit is charged by applying a voltage obtained by superimposing an alternating current and a direct current to the charging unit. The image forming apparatus according to claim 1, wherein an AC bias voltage is simultaneously applied to each of the conductive members.