JP3064643B2 - Apparatus for detecting thickness of charged object and image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting the thickness of a member to be charged.
It relates 置及 beauty image forming apparatus.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an image carrier as an object to be charged such as an electrophotographic photosensitive member or an electrostatic recording dielectric is subjected to a charging process (the charge removing process is also performed). In the past, a corona charger has been used as an apparatus for performing the above.

In recent years, a charging member (conductive member) such as a roller type (charging roller) or a blade type (charging blade) to which a voltage has been applied is brought into contact with the surface of the member to be charged so that the surface of the member to be charged has a predetermined polarity. A contact (direct) type charging device (for example, Japanese Patent Application Laid-Open No. 63-167380) for charging to a potential has been put to practical use.

[0004] The contact charging device has the advantages of lowering the pressure of the power supply and generating very little corona discharge products such as ozone (ozone-less) as compared with the corona charger.

A conductive roller (charging roller) as a charging member
Is preferably used from the viewpoint of charging stability.

[0006] Further, a charging method (hereinafter, referred to as DC charging) in which the surface of a member to be charged is charged with only a DC voltage (DC voltage) applied to the charging member, and an oscillating voltage (with time) applied to the charging member. There is a charging method (hereinafter, referred to as AC charging, Japanese Patent Application Laid-Open No. 63-149669, etc.) in which an object to be charged is charged with a voltage whose voltage value changes periodically.

[0007] Since contact charging is performed by discharging from the charging member to the member to be charged, charging of the member to be charged is started by applying a DC voltage higher than a certain threshold voltage to the charging member.

[0008] A specific example will be described below.
When the charging roller is brought into pressure contact with the 5 μm OPC photoconductor, as shown in FIG. 5, if a DC voltage of about 640 V or more is applied to the charging roller as a charging member, the surface potential of the photoconductor becomes low. After that, the photosensitive member surface potential linearly increases with a slope of 1 with respect to the applied voltage.

The applied DC voltage of about 640 V at which the surface potential of the photosensitive member starts to rise is the charging start voltage _Vth for the photosensitive member.

From the above, in order to obtain a desired photosensitive member surface potential (charging potential) Vd required for image formation by DC charging, a DC voltage of Vd + _Vth should be applied to the charging roller. become.

In the DC charging, the DC voltage is applied to a charging roller to perform a charging process as an object to be charged.

This is explained as follows. FIG. 6A shows a state in which a charging roller 1 as a charging member is brought into pressure contact with a photosensitive drum 2 in which a layer of a photosensitive member 2a as a member to be charged is formed on the outer peripheral surface of a conductive drum base 2b. FIG. 4 is an enlarged model diagram of a corresponding contact portion in a folded state. Reference numeral 8 denotes a charging bias application power supply.

FIG. 6B shows an electrical equivalent circuit of an air layer having a small gap involved in the discharge between the charging roller 1 and the photosensitive drum 2 and the photosensitive drum. The impedance of the charging roller 1 is smaller than that of the photosensitive drum and air layer and can be ignored. Therefore, it can be understood that the charging mechanism can be simply expressed by the two capacitors C1 and C2.

When a DC voltage is applied to this equivalent circuit, the voltage is proportionally distributed to the impedance of each capacitor, and the voltage Vair applied to the air layer is calculated as follows: Vair = C2 / (C1 + C2) (1) Become.

The air layer has a dielectric breakdown voltage according to Paschen's law. If the thickness of the air layer is g [μm], V
When air exceeds 312 + 6.2 g [V] (2), discharge occurs and charging is performed.

Since the voltage at which discharge occurs for the first time is when the quadratic equation relating to g has a multiple solution when equations (1) and (2) are equal (C1 is also a function of g), The voltage value corresponds to the discharge starting voltage _Vth . V _{th of} the theoretical value thus obtained takes a value very close to the experimental value.

However, in the case of contact charging, the resistance value of the contact charging member fluctuates due to environmental fluctuations, and the photoreceptor as a member to be charged is scraped off (reduced to wear) due to durability and the thickness changes to change the charging start voltage V _th. May fluctuate,
In the case of the DC charging system, it is difficult to stabilize the surface potential of the photoconductor to a desired Vd value.

The AC charging can make contact charging even more uniform. The DC voltage corresponding to a desired Vd is preferably reduced to a peak-to-peak voltage V of 2 × _Vth or more.
An oscillating voltage (V _DC + V _AC ) on which an AC voltage having _PP is superimposed is applied to a charging member to perform a charging process on a member to be charged.
This is for the purpose of smoothing the charging potential by the AC voltage as shown in FIG. 7, and the charging potential can be made more uniform than the DC charging.

The waveform of the AC voltage is not limited to a sine wave.
A rectangular wave, a triangular wave, or a pulse wave may be used. Includes a square-wave voltage formed by periodically turning on and off a DC power supply.

[0020]

For example, in a transfer type image forming apparatus in which an image carrier as a member to be charged is repeatedly used, an image carrier as a member to be charged (photosensitive layer, The dielectric layer and the like are gradually scraped, and the thickness (film thickness) thereof is gradually reduced. The thickness reduction due to the durability of such an image bearing member (hereinafter, referred to as a photoreceptor) as a member to be charged is caused even when the charging of the photoreceptor is performed by DC charging.
The following problem also occurs with C charging.

That is, the amount of charge Q required to charge the photosensitive member to a constant potential Vd is determined by the capacitance C of the photosensitive member, and this charge amount is inversely proportional to the thickness of the photosensitive member.

Therefore, in order to charge the scraped photoreceptor to the same Vd, more charge (charging current) is required than in the initial stage. However, as the charging current increases, the voltage drop due to the impedance of the charging member becomes significant.

Generally, a charging roller as a charging member is
When a pinhole is formed in the photoreceptor, a resistive layer is provided to prevent the charging current from concentrating thereon, and the roller has an impedance value of 10 ⁵ to 10 ⁶ Ω as a roller resistance. Further, if the durability is further increased in a low-temperature and low-humidity environment or the like, the roller resistance further increases, and the increase in the charging current due to the scraping of the photoreceptor is combined with a decrease in Vd of 100 to 200.
V, which may cause image fogging.

As described above, in order to obtain a good image, the thickness of the photoreceptor needs to be about 15 μm or more. If the photoreceptor is further shaved, a stable image cannot be guaranteed. Can be considered beyond the lifetime of

[0025] However the conventional, effective ones less as a means to know the thickness of the photosensitive member directly, a method of calculating indirect photoconductor scraping amount, i.e. the life of the photoreceptor by counting the total rotational speed of the photosensitive drum However, the photoreceptor shaving amount varies depending on the use environment, the state of the cleaning device, and the like, and thus lacks reliability. Also, Japanese Patent Application Laid-Open No. 59-69774
Measures the potential charged by the corona charger with a probe
And the potential and the current flowing during one rotation of the photoreceptor
To detect the thickness of photoreceptor by dark decay characteristics
Is described, but the dark decay characteristics change depending on the temperature and humidity.
Therefore, the method of detecting the film thickness from the dark decay characteristic in this way is
Cannot perform highly accurate detection.

Therefore, the present invention provides an accurate
It is an object of the present invention to provide a highly reliable thickness detection device capable of high thickness detection.

Further, when the thickness of the member to be charged or the image bearing member as the member to be charged is reduced, or the minimum thickness as the service limit (life) is reached, the environmental impact is reduced.
High accuracy and stable detection and take appropriate countermeasures such as warnings to prompt replacement of the charged object or the image carrier. and to provide the images forming apparatus which allows prevent improper charging and image defects such as generation by the fact that the.

[0028]

The present invention SUMMARY OF THE INVENTION is characterized by the following configuration is the thickness detection instrumentation 置及 beauty image forming apparatus member to be charged.

[0029] (1) and the electrode member in contact with the member to be charged, this
Voltage applying means for applying a plurality of different voltages to the electrode members
When, a current detecting means for detecting a current flowing through the electrode member
VI obtained by applying different voltages to the electrode members
An apparatus for detecting a thickness of a member to be charged, wherein the thickness of the member to be charged is detected based on characteristics.

(2) The voltage applied to the electrode member is a DC voltage
Component and AC voltage component are superimposed on each other.
The body is changed from a predetermined first potential V1 to a predetermined second potential V2.
Of DC current flowing through electrode members when charging
The thickness of the member to be charged is detected by
The device for detecting the thickness of a member to be charged according to (1) .

(3) DC of vibration voltage applied to electrode member
The voltage component is a voltage corresponding to a desired charging potential of the member to be charged.
The AC voltage component is a DC voltage applied to the electrode member.
At least twice as high as the charging start voltage V _th of the member to be charged
(2) The apparatus for detecting the thickness of a member to be charged according to (2), wherein

(4) DC of vibration voltage applied to electrode member
Switching the voltage component between the first voltage V1 and the second voltage V2
The device for detecting the thickness of a member to be charged as described in (2) or (3), further comprising means for detecting the thickness of the member to be charged.

(5) A charging member which comes into contact with the member to be charged,
Voltage applying means for applying a plurality of different voltages to the charging member
And current detecting means for detecting a current flowing through the charging member.
And VI obtained by applying different voltages to the charging member.
Detecting the thickness of the member to be charged based on the characteristics.
Device for detecting the thickness of an object to be charged.

(6) The voltage applied to the charging member is a DC voltage
Component and AC voltage component are superimposed on each other.
The body is changed from a predetermined first potential V1 to a predetermined second potential V2.
Of DC current flowing through charging member when charging
The thickness of the member to be charged is detected by
(5) The apparatus for detecting a thickness of a member to be charged according to (5) .

(7) DC of vibration voltage applied to charging member
The voltage component is a voltage corresponding to a desired charging potential of the member to be charged.
The AC voltage component was obtained by applying a DC voltage to the charging member.
At least twice as high as the charging start voltage V _th of the member to be charged
(6) The apparatus for detecting the thickness of a member to be charged according to (6), wherein

(8) DC of vibration voltage applied to charging member
Switching the voltage component between the first voltage V1 and the second voltage V2
The device for detecting the thickness of an object to be charged according to (6) or (7), further comprising:

(9) Image Carrier and Band in Contact with Image Carrier
Applying a plurality of different voltages to the charging member and the charging member
Voltage applying means and current for detecting current flowing through the charging member
Detecting means for applying different voltages to the charging member.
Detecting the thickness of the image carrier based on the obtained VI characteristics.
An image forming apparatus comprising:

(10) The voltage applied to the charging member is a DC voltage.
This is an oscillating voltage in which the voltage component and the AC voltage component are superimposed.
The holding body is moved from a predetermined first potential V1 to a predetermined second potential V2.
Measurement of the DC current flowing through the charging member when charging
The thickness of the image carrier is detected by a constant
The image forming apparatus according to (9).

(11) The oscillating voltage applied to the charging member
The flowing voltage component is a voltage corresponding to a desired charging potential of the image carrier.
The AC voltage component is a DC voltage applied to the charging member.
At least twice the charging start voltage _Vth of the image carrier
The image according to (10), wherein the image has a voltage between blocks.
Forming equipment.

(12) The vibration voltage applied to the charging member
Switching the flowing voltage component between a first voltage V1 and a second voltage V2
(10) or (1),
The image forming apparatus according to 1).

[0041]

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[0044]

[0045]

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[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

< Operation > That is, when an electrode member (charging member) is brought into contact with a member to be charged and a voltage is applied to the member to be charged in a DC or AC manner, the thickness of the member to be charged and the flow to the electrode member. The DC charging current has a correlation as described in the embodiments described later. Focusing on this, the present invention focuses on the electrode member (charging
And a plurality of different voltages are applied to the electrode member.
Voltage applying means and current for detecting current flowing through the electrode member
And detecting means for applying different voltages to the electrode members.
Detecting the thickness of the member to be charged based on the obtained VI characteristics.
The thickness of the member to be charged is electrically detected by the structure of the device for detecting the thickness of the member to be charged.
The thickness can be detected.

In a charging device for a member to be charged or an image forming apparatus of a transfer system, the thickness of the member to be charged or the image bearing member as the member to be charged is reduced to a reduced thickness or a lower limit thickness as a usage limit. reached was that the obtained take appropriate measures processing such as alert to exchange by detecting less <br/> precisely and stably environmental impact member to be charged or image bearing member, using the member to be charged or image bearing member Despite reaching the limit, it is possible to prevent the occurrence of charging failure or image failure due to continued use, etc.

[0066]

【Example】

First Embodiment (FIGS. 1 to 4) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 2 denotes an electrophotographic photosensitive drum as an image carrier, which is driven to rotate at a process speed (rotational peripheral speed) of 95 mm / sec in a clockwise direction indicated by an arrow a.

The photoreceptor drum 2 of this embodiment is formed by coating a layer of an OPC photoreceptor 2a on the outer periphery of an aluminum drum 2b (conductive drum base) having a diameter of 30 mm. A carrier transport layer (Carrier Transfer Layer: hereinafter referred to as CT layer) having a thickness d = 25 μm
Is arranged.

In the present embodiment, a polycarbonate resin is used as a binder for the CT layer, and the CT layer is gradually scraped by durable paper passing, and its thickness decreases.

Reference numeral 1 denotes a charging roller as a primary charging member of the photosensitive drum 2, which is formed on a core 1a, a conductive elastic layer (conductive rubber layer) 1b formed on the outer periphery thereof, and further formed on the outer periphery thereof. It consists of a high resistance layer 1c.

Both ends of the cored bar 1a are supported and arranged substantially in parallel with the photosensitive drum 2, and are brought into pressure contact with the surface of the photosensitive drum 2. In the case of this embodiment, the rotation of the photosensitive drum 2 is accompanied. No driven rotation.

Reference numeral 8 denotes a power source for applying a charging bias to the charging roller 1. The power source 8 applies a predetermined charging bias to the charging roller 1 via the cored bar 1 a to apply a charging bias to the photosensitive member 2 a of the rotating photosensitive drum 2. The outer peripheral surface is contact-charged to a predetermined polarity and potential.

In the high-resistance layer 1c on the outer periphery of the charging roller 1, when a low-voltage defect such as a pinhole exists or occurs in the photosensitive member 2a, the charging current concentrates on this portion, and the potential on the surface of the charging roller drops. And prevents the occurrence of horizontal streak-like charging failure.

Next, a laser beam 3 (laser intensity-modulated according to a time-series electric digital pixel signal of target image information) output from a laser beam scanner (not shown) is provided on the charged surface of the rotating photosensitive drum 2. By performing the scanning exposure using light, the exposed portion of the photoconductor 2a is discharged, and an electrostatic latent image of image information is formed on the surface of the photoconductor 2a.

Next, the latent image is reversely developed with a one-component magnetic toner by a developing device 4 of a jumping development system, and the exposed portion of the surface of the photoconductor 2a is visualized by the adhesion of the toner.

At the position of the transfer roller 5, the toner image is
The image is transferred onto the surface of the transfer material 9 fed at a predetermined timing from a paper feed mechanism (not shown) to a pressure nip portion (transfer portion) between the photosensitive drum 2 and the transfer roller 5. In this embodiment, a transfer bias of 3 kV is applied to the transfer roller 5 by the transfer bias application power supply 10.

The transfer material 9 that has passed through the transfer section is the photosensitive drum 2
The toner image is separated from the surface and sent to the fixing device 7, where the toner image is fixed by pressurizing and heating, and output as an image formed product (print, copy).

After the transfer of the toner image onto the transfer material 9, the surface of the photosensitive drum 2 is scraped off by a cleaning blade (urethane rubber counter blade) of a blade-type cleaning device 6 to remove contaminants such as untransferred toner and paper powder. The surface is then cleaned and repeatedly provided for image formation.

The printer of this embodiment is a cartridge in which four process devices, ie, the photosensitive drum 2, the charging roller 1, the developing device 4, and the cleaning device 6, are collectively attached to and detachable from the printer main body. It is a detachable type.

(2) Detection of Thickness of Photoconductor 2a As described above with reference to FIG. 5, when a DC voltage is applied to the charging roller 1, the photoconductor 2a is charged when the applied voltage is equal to or higher than the charging start voltage _Vth. Is started, and thereafter, the photoconductor surface potential increases linearly at the same rate as the increase ΔV of the applied voltage (ΔVd). Here if the applied voltage V is that the following areas V _th is referred to as A region, V _th or more B region.

In the area A, the applied voltage is small and the voltage divided into the air layer cannot exceed the dielectric breakdown voltage based on Paschen's law. Area.

In the area B, the discharging from the charging roller 1 to the photosensitive member 2a is actually performed, and the applied voltage V and the photosensitive member surface potential Vd are not affected by the thickness and environment of the photosensitive member.
ΔV = ΔVd because the voltage increases linearly at the slope 1.

On the other hand, as shown in FIG. 2, the graphs showing the relationship between the applied voltage V and the charging current I are the same with respect to the non-charging in the A region, but are the same in the B region. The inclination changes depending on the thickness d of 2a.

This is due to the fact that the same Vd
This shows that the charging current I required for charging up to is different. With respect to the photoconductor surface potential Vd and the charging current I, the following calculation is established.

The thickness of the photosensitive member 2a is d, the relative permittivity is ε, the permittivity in vacuum is ε0, the effective charging width of the contact charging member is L,
Assuming that the process speed is Vp, the photosensitive member 2a
Is calculated, and the following relational expression is derived.

Charged charge amount Q = ∫I · dt = C · Vd → Charge current I = d / dt (C · Vd) where dC / dt = ε · ε0 · L · Vp / d, Vd = Const. Therefore, the charging current I = ε · ε0 · L · Vp · Vd / d (3) In equation (3), ε, ε0, L, Vp, and d are constants, and it is known that ΔV = ΔVd for the B region. Therefore, ΔI = ε · ε0 · L · Vp · ΔVd / d = Ε · ε0 · L · Vp · ΔV / d (4) It is found that the slope of the straight line of the VI graph is represented by ・ · ε0 · L · Vp / d in the B region. Was.

Therefore, in this embodiment, the charging roller 1 as the primary charging member of the photosensitive drum 2 is also used as an electrode member for detecting the thickness of the photosensitive drum, and the voltage V applied to the charging roller 1 in the region B is reduced. The charging current I flowing at that time is measured at two points, the inclination of the straight line of the VI characteristic is calculated from this relationship, and the thickness of the photoconductor 2a is detected.

In this embodiment, since the photosensitive member 2a having an initial film thickness of 25 μm is used, the initial V _th is 640 V,
Since _Vth decreases as the photoreceptor 2a is scraped, if the applied voltage is 640 V or more, it can be regarded as the B region.

As can be seen from the above equation (3), it is possible to detect the film thickness similarly by measuring I and Vd. However, to measure Vd, a photoconductor surface potential measuring device is separately provided in the printer body, and another hardware such as a power supply is required.

The conditions for performing the above control are as follows. Since the relationship between the charging potential and the charging current is not clear unless the potential of the photosensitive member is a certain value at the time of measurement, image exposure was performed and the potential was set to 0. Perform the measurement in the state. The time for applying each voltage is set to be equal to one rotation of the photosensitive drum in order to eliminate the influence of noise and the like, and the current measured during this period is averaged.

The measurement of the film thickness of the photosensitive member 2a by this control is performed during the pre-rotation of the photosensitive drum 2, and the sequence is such that the image formation is not adversely affected.

In order to perform this control, VI-
It is necessary to measure the relationship between the characteristic inclination and the film thickness d of the photoconductor 2a. Therefore, the thickness d of the photoconductor 2a is 15 μm each.
The measurement was performed using the photosensitive drums 2 having m, 17 μm, 21 μm, and 25 μm.

FIG. 2 shows a typical example of 15 μm and 2 μm.
The VI characteristics when the photoconductor thickness d is 5 μm are shown.

Normal environment of 25 ° C. × 60% RH (hereinafter referred to as N
/ N environment), high temperature and high humidity environment of 32.5 ° C. × 85% RH (hereinafter referred to as H / H environment), 15 ° C. × 10% RH
In low temperature and low humidity environment (hereinafter referred to as L / L environment),
Although the intercept of the graph changes, the inclination is constant, and it has been experimentally proved that the graph depends only on the film thickness d of the photoconductor 2a.

FIG. 3 shows an experimental value graph (a) in which the relationship between the film thickness d and the gradient is graphed based on the gradients for the above five film thicknesses.

For reference, in equation (4), ε = 3 and ε0 = as values corresponding to the printer in this embodiment.
8.85 × 10 ⁻¹² , L = 20 cm, Vp = 95 mm /
The value of the theoretical equation obtained by substituting sec is plotted and shown as a theoretical equation graph (b). Although there were some errors, they agreed with the experimental values. In the present embodiment, the control is performed based on the experimental value graph (a) actually obtained by the experiment instead of the theoretical expression graph (b).

In this embodiment, the relationship between the photoconductor thickness d and the gradient of the VI characteristic in the graph (a) of FIG. 3 is stored in the ROM of the printer control unit (not shown). -I
The photosensitive member thickness d can be calculated from the characteristic slope, and the slope is 32 × 10 ⁻³ μA /, which is equivalent to 15 μm, which is the lower limit of the photosensitive member thickness d at which a good image can be obtained.
Warning indicator light (not shown) on the front of the printer when it exceeds V
And a host computer (not shown)
, A signal for notifying the life of the photoconductor is sent.

The operator recognizes that the photosensitive member (photosensitive drum) has reached the end of its life by this warning display or further prohibiting the printer operation. In this case, the operator replaces the process cartridge 11 with a new or old one. This makes it possible to accurately detect the life of the photoreceptor and prevent the occurrence of charging failure and image defect due to use of the photoreceptor even though it has reached the usage limit.

(3) Printer Endurance Test Example An example of an actual endurance test is shown below.

First, during the pre-rotation of the printer, two voltages V1 and V2 higher than the discharge starting voltage _Vth are applied to the charging roller 1 as shown in FIG.
Is measured. Here, since V1 and V2 need to be in the B region, a voltage of 640 V or more is selected in this embodiment, and V1 = 1000 [V] and V2 = 1500 [V].

The slope of the VI characteristic in the region B is calculated by (I2-I1) / (V2-V1).

In the initial stage of durability, the photosensitive member film thickness d is 25 μm.
m, it was determined that I1 = 5.5 μA and I2 = 14 μA, and the slope was 17 × 10 ⁻³ μA / V.

When this control was performed when 15,000 sheets were passed in the N / N environment, I1 = 16 μA, I2 = 32 μA, and the slope became 32 × 10 ⁻³ μA / V, which was set in advance. Since the value exceeded the value, the printer turned on the warning indicator light and issued a warning to the host computer to stop using the printer.

At this time, when the thickness d of the photosensitive member was measured, it was about 15 μm, and it was proved that this control was appropriate.

As described above, in this embodiment, the gradient of the VI characteristic is measured by measuring the voltage V applied to the contact charging member and the charging current I flowing at this time, and the film thickness d of the photosensitive member 2a is measured. Can be detected.

As a result, the film thickness (lifetime) of the photosensitive member 2a, which has not been conventionally provided with an appropriate method, can be easily detected without newly taking a special device configuration or the like.

In this embodiment, the charging roller 1 as a primary charging member is used also as an electrode member for detecting the thickness of the photosensitive member, but the conductive transfer roller 5 is used as an electrode member for detecting the thickness of the photosensitive member. It is also possible to perform the same control as a double use.

Further, as shown in the second embodiment, the same control can be performed by disposing a dedicated electrode member for detecting the thickness of the photosensitive member.

<Second Embodiment> (FIG. 8) This embodiment is an example of an apparatus provided with a dedicated electrode member for detecting the thickness of the photosensitive member.

In the case where the charging roller 1 as the primary charging member of the photosensitive member is also used as the electrode member for detecting the thickness of the photosensitive member as in the first embodiment, the description will be made in the first embodiment. As described above, it is necessary to apply two voltages V1 and V2, respectively. Further, there is a problem that the film thickness cannot be detected at the time of image formation, but this problem can be solved by providing a dedicated electrode member.

This embodiment is an example of an apparatus having such a configuration. FIG. 8A is a partially cutaway top view of a main part of the apparatus.
(B) is a side view thereof.

At a position between the cleaning device 6 and the charging roller 1, an exposure lamp 12 as a photoconductor discharging means and a contact electrode member with respect to the surface of the photoconductor 2 a are provided upstream and downstream in the rotation direction a of the photoconductor drum. And a pair of first and second contacts 13 and 14 are provided.

The first and second contacts 13 and 14 are arranged at intervals in the generatrix direction of the photosensitive drum 2 and are in contact with the surface of the photosensitive member 2a. Each contact of this embodiment has a width of 1
cm is a blade-shaped conductive member, and the material of the blade is a urethane paint (trade name: EMURALON, manufactured by Acheson Japan) with a thickness of 20 μm, which is made of urethane rubber.
Is applied.

As the photosensitive member discharging means 12, an AC charger with a DC offset voltage of 0V can be used. The contacts 13 and 14 may be in the form of a roller, a pad, or the like.

Different voltages are applied to the first and second two contacts 13 and 14, respectively, so that the flowing current can be measured. Since the voltage to be applied needs to be in the region B shown in FIG. 6, 1000 V is applied to the first contact 13 and 1500 V is applied to the second contact 14 in this embodiment.

The configuration of the printer of this embodiment is the same as that of the printer of the first embodiment (FIG. 1), but the charging of the photosensitive drum 2 by the charging roller 1 is performed by the following DC voltage and AC voltage. AC charging by application of the superposed oscillation voltage.

DC voltage: -700 V (corresponding to Vd) AC voltage: Peak-to-peak voltage V _PP = 1900 V Frequency f = 550 Hz Sine wave Using this apparatus, the thickness d of the photosensitive member 2a is 15 μm in advance.
The measurement was performed using the photosensitive drum 2 which was found to be the following. During the measurement, the exposure lamp 12 was turned on, and the surface potential of the photoconductor 2a when passing through the first and second contacts 13 and 14 for measuring the film thickness was about 0V.

At this time, 0.8 μA is applied to the first contact 13 to which a DC voltage of 1000 V is applied, and 1.6 to the second contact 14 to which a DC voltage of 1500 V is applied.
A current of μA flowed. VI calculated by this value
The slope of the characteristic was 1.6 × 10 ⁻³ μA / V.

Since the slope of the VI characteristic is proportional to the effective charging width L as expressed by the above equation (4), this value is the first
32 × 10 ⁻³ obtained under the same conditions in the embodiment of FIG.
Correspondence can be taken with 1/20 of μA / V.

From the above results, in this embodiment, when the calculated slope exceeds 1.6 × 10 ⁻³ μA / V, it is considered that the film thickness of the photoconductor is 15 μm, which is the lifetime, and
A warning shall be given.

Actually, when 12,000 sheets were passed in the H / H environment, the inclination exceeded 1.6 × 10 ⁻³ μmA / V, so a warning was displayed and the operation of the printer was prohibited. When the film thickness of the photoreceptor at this time was measured, it was 15 μm, which proved that the present method was appropriate.

As described above, in this embodiment, the provision of the dedicated contact electrode members 13 and 14 for measuring the thickness of the photosensitive member makes it possible to detect the thickness of the photosensitive member even during image formation. Further, as in the first embodiment in which the charging roller 1 serving as the primary charging member has a function of also using the electrode member for detecting the thickness of the photosensitive member, control is performed such that two-stage voltages are separately applied. No longer needed.

Third Embodiment (FIGS. 9 to 12) (1) Configuration of Image Forming Apparatus The configuration of a printer as an image forming apparatus is the same as that of the printer of the first embodiment (FIG. 1). .

However, in the case of this embodiment, the charging of the photosensitive member 2a is performed by AC charging.

In this embodiment, in order to perform AC charging, an oscillating voltage obtained by superimposing an AC voltage on a DC offset voltage is applied to the charging roller 1. As the DC voltage, V2 = −700 V corresponding to a desired dark portion potential of the photoconductor is used. As the AC voltage, the discharge starting voltage V _th
In this example, a constant voltage of 1800 V was used because a peak-to-peak voltage that is twice or more than that required was used. Regarding this voltage, it is also possible to perform AC constant current control in order to remove the influence of the change in the impedance of the charging roller 1 as the charging member.

(2) Detection of Thickness of Photoreceptor 2a In the electrophotographic process, as a pretreatment for forming an image,
In order to remove the potential history of the photoreceptor, it is general to perform charge elimination during pre-rotation. As the charge removing means, pre-exposure can be performed.
In a device that performs charging, it is possible to make the potential of the photoconductor 0 V by superimposing an AC voltage with a DC voltage of V1 = 0 by utilizing the convergence of the potential.

Next, in order to form an image, the DC offset voltage is set to V2 = − in this embodiment as shown in the sequence of FIG.
The charging is performed as 700. At this time, FIG.
As shown in (1), a DC current required to raise the surface potential of the photosensitive member by Vcontrast flows for one rotation of the photosensitive drum. −
Once charged to 700 V, no charging DC current flows unless there is a change in the photoconductor surface potential (image exposure is not performed and dark decay is ignored).

The charging DC current flowing at this time is theoretically calculated as follows.

The thickness of the photosensitive member 2a is d, the relative dielectric constant is ε, the dielectric constant in vacuum is ε0, the effective charging width of the contact charging roller 1 is L, the process speed is Vp, and the photosensitive member surface potential is 0 → V.
When it is increased to d, the capacitance C of the photoconductor 2a is calculated from this, and the following relational expression is derived.

Charge amount: Q = ∫I · dt = C · Vcontrast → Charging current: I = d / dt (C · Vcontrast) dC / dt = ε · ε0 · L · Vp / d, and Vcontrast is V
Since d is the charging current: I = ε ・ ε0 ・ L ・ Vp ・ Vd / d (5) Since ε, ０0, L, Vp, d, and Vd can be regarded as constants, 0 → Vd The charging current I for charging is d
Is inversely proportional to.

In this embodiment, ε = 3, ε0 = 8.85 ×
10 ^-12 [F / m], L = 230 mm, Vp = 95 mm
/ Sec, Vd = 700 [V], so that d = 25
At μm, I = 16 μA.

Actually, using the photosensitive drums 2 having different thicknesses d of the photosensitive members 2a, the H / H environment, the N / N environment, the L / L
FIG. 11 shows the result of measuring the d-I relationship in the environment. It can be seen from this that the d-I relationship does not depend on the environment, as theoretically.

Based on the result, a means is provided for warning the life of the photosensitive drum when the current amount corresponding to the CT film thickness of 15 μm, which is considered to be the life of the photosensitive body 2a, is exceeded.

In FIG. 11, since the amount of current I required for charging is 27 μA when the film thickness is 15 μm in each environment, as shown in the DC current detection circuit 100 (thickness detection circuit) in FIG. When the voltage V generated at both ends of the 10 kΩ resistor 16 exceeds 0.27 V corresponding to 27 μA, a warning indicator light 20 on the front of the printer main body linked to this.
Is turned on.

Specifically, the voltage V across the 10 kΩ protection resistor 16 of the power supply 8 is set to Vref = 0.2 of the reference voltage 17.
7V, and when there is an output of the comparator 18, D
A signal indicating the life of the photosensitive drum is sent to the C controller 19 to turn on the warning indicator lamp 20. In this embodiment, V is a value obtained by averaging the signal for one rotation of the drum after the DC offset voltage is increased from 0 to Vd in synchronization with the sequence of the printer body (see FIG. 9). When an endurance test was actually performed, V was increased by endurance paper passing, 10,000 sheets were passed in each environment, and a warning was issued when the CT layer was cut by 10 μm and the remaining layer became 15 μm, and excessive cutting was performed. It is possible to prevent the occurrence of image defects due to the above.

<Fourth Embodiment> (FIGS. 13 to 15) In this embodiment, before the AC charging of the photosensitive member 2a by the charging roller 1, the surface potential of the photosensitive member is removed by a pre-exposure or a discharging means such as an AC corona charger. And the contact charging roller 1
It is characterized by detecting a current flowing when charged to a constant potential Vd by C charging.

As shown in the third embodiment, as a method of determining the two potentials V1 and V2 necessary for flowing the charging current, changing the DC voltage of the AC charging from V1 to V2 is equivalent to the potential convergence. Although it is advantageous from the viewpoint of performance, this is not possible in the case of an apparatus configuration having no means for changing the DC voltage. It is not necessary to take a DC voltage variable configuration.

That is, in such a system, V1 can be given by a static eliminator or pre-exposure means.

More specifically, when an AC corona charger is used as the charge removing means, the surface potential of the photosensitive member can be converged to about 0 V, so that V1 = 0, as in the third embodiment. Assuming that V2 = −700, it is possible to detect the photoconductor thickness d by measuring the current I flowing for charging at 700 V. In the present embodiment, the photoconductor drum of the charging roller 1 can be detected as shown in FIG. An AC corona neutralizer 21 serving as a neutralizing means is provided on the upstream side in the rotation direction, and the same effect as in the first embodiment can be obtained only by attaching the neutralizer 21.

FIG. 14 shows an example in which a pre-exposure device 22 is used in place of the AC corona neutralizer 21 described above. Considering a system in which static elimination is performed by pre-exposure, it is possible to always converge the pre-charge potential to a predetermined value V1 by giving exposure before charging. At this time, there is a residual potential on the photoreceptor 2a, and it is difficult to set V1 = 0. is necessary.

In this embodiment, the exposure amount is 0.5 μJ /
cm ² and the residual potential V1 = −100 at this time, a current for charging the charging roller 1 from V1 to V2 always flows. In this case, Vcontrast = 6
Since the voltage is 00 V, the relationship between the film thickness d of the photoconductor 2a and the charging DC current I is different from that of the third embodiment and is as shown in FIG. In this embodiment, 23 μA corresponding to a film thickness of 15 μm is used.
The setting is such that a warning about the life of the photosensitive drum is issued when the current becomes larger.

When the durable paper passing was actually performed with this apparatus configuration, it was confirmed that a warning was issued after passing 10,000 sheets regardless of the environment.

<Fifth Embodiment> (FIGS. 16 to 18) In this embodiment, similarly to the third embodiment, the charging of the photosensitive member 2a is performed by AC charging, and the current flowing by switching the DC voltage is changed. I is measured to detect the film thickness d of the photoreceptor 2a. However, unlike the third embodiment, V1 = −700, V2 = 0, and the DC current flowing during static elimination is detected to detect the film thickness d. Perform detection.

In principle, when charging from 0 to Vd, Vd
Although the currents flowing during the zero charge removal should be equal, a low breakdown voltage defect 23 such as a pinhole on the photoreceptor 2a (FIG. 16)
In this case, erroneous measurement can be significantly reduced by using this embodiment.

When the current is measured during charging as in the third embodiment, if a pinhole 23 exists on the photosensitive member 2a, the leak current I _Leak not actually contributing to charging flows into this portion 23 excessively. ((A) of FIG. 16) causes an erroneous measurement. In order to prevent this, in the third embodiment, the average value of one round of the photosensitive drum after the start of charging in which a current flows is measured.

However, when the current flowing at the time of static elimination of Vd → 0 is measured as in the present embodiment, the potential of the pinhole portion 23 is 0 [V], which is the same as that of the photoconductor supporting substrate 2b. 1 and the pinhole 2
No DC current flows into 3 (FIG. 16 (b)), and it is possible to substitute the measurement of the maximum value without measuring the average value.

More specifically, as shown in FIG. 17, the current flowing in one rotation of the drum in the post-rotation in the post-rotation for setting the drum potential to 0 V in order to erase the potential history after the image formation is completed is measured. At this time, as described above, there is no need to consider the noise current due to the pinhole section 23, so that the averaging circuit is not necessary. ) Only needs to be provided with a circuit for comparing Vref with Vref, and the cost can be reduced.

An example in which image output is actually performed will be described. Using the configuration of this embodiment, measurement was performed on the photoconductor drum 1 having the pinhole 23 on the photoconductor 2a. As a result, a current flows into the pinhole 23 at the start of charging during pre-rotation. In addition, the DC current waveform is noisy, and the maximum value measurement includes an erroneous measurement. However, in the DC current waveform at the time of static elimination during post-rotation, no current flows into the pinhole, so that no noise is generated and the maximum value can be measured with sufficient accuracy.

In the third to fifth embodiments, the photosensitive member 2
a is charged by AC charging, and a constant amount of charge potential of the photoconductor 2a is Vcontrast. A DC current flowing when charging or discharging is measured to measure a thickness d of the photoconductor 2a. By giving a warning when the following occurs, it is possible to prevent the occurrence of image defects in electrophotography.

This is because high-precision film thickness detection can be realized only by measuring the DC current without providing a special means for measuring the film thickness as in the prior art, so that the cost can be reduced. It is possible to obtain a highly reliable effect.

<Sixth Embodiment> (FIGS. 19 to 21) In this embodiment, similarly to the fifth embodiment, a low breakdown voltage defect portion 23 such as a pinhole exists in the photosensitive member 2a as a member to be charged. In this case, it is possible to prevent a decrease in the accuracy of detecting the thickness of the photosensitive member in the case of performing the operation.

In this embodiment, a DC bias: -700 V AC voltage: 2000 V _PP , 550 Hz, a sine wave superimposed vibration voltage is applied to the charging roller 1 by the charging bias applying power source 8 (FIG. 19) to The photoreceptor 2a is subjected to primary charging by AC charging to Vd = -700.

The relationship between the thickness d of the photosensitive member 2a and the charging current I is derived from the following equation. Assuming that the thickness of the photoconductor is d, the relative dielectric constant is ε, the dielectric constant in a vacuum is ε0, the effective charging width of the contact charging member is L, and the process speed is Vp, the capacitance C of the photoconductor is calculated from this. The following relational expression is derived.

Charge amount: Q = 帯 電 I · dt = C · Vd
(Vd is the amount of change in potential) By this, charging current: I = d (C · Vd) / dt dc / dt = ε · ε0 · L · Vp / d, Vd = Cons
t. Therefore, charging current: I = εεε0 ・ L ・ Vp ・ Vd / d (6)

In the equation (6), ε, ε0, L, Vp,
Since d is a constant and Vd = ΔV, ΔI = ε · ε0 · L · Vp · Vd / d (7) is derived, and ε · ε0 · L · Vp · Vd / d is V− It can be seen that the slope of the straight line of the I graph is obtained.

Therefore, the DC voltage V applied to the charging roller 1 as a charging member and the charging current I flowing at that time are measured at two points, and the slope of the straight line of the VI characteristic is calculated from this relationship to obtain the photosensitive member 2a. Can be detected.

In such detection of the photoconductor thickness d, it is necessary to measure the charging current I. However, if the pinhole 23 is opened on the photoconductor 2a, the contact current is measured as described in the fifth embodiment. Due to the charging, current concentrates on the pinhole 23, and an excess current different from the actual charging current flows, and the film thickness d cannot be detected correctly.

Therefore, the present embodiment has a frequency filter in the measuring circuit which could not use the maximum value of the current due to the rush current in the charging current measurement for the film thickness detecting circuit 100 until now. This suppresses the inrush current, measures the maximum value of the charging current, and detects the film thickness correctly.

The actual circuit configuration is like the low-pass filter (LPR) 101 in FIG.

The time for measuring the current for detecting the film thickness is set to π × drum diameter / Vp = π × 30/95 = 1 sec because one rotation of the photosensitive drum is used to eliminate the influence of noise and the like. Since the current during this period is ideally a rectangular wave, the frequency is as shown in FIG. 20A and is 0.5 Hz. Further, for example, a pinhole having a diameter of 1 mm is
If it is opened upward, it will be as shown in FIG. 3B, and the frequency at this time will be 47.5 Hz. Therefore, in this case, a frequency filter that cuts at least 47.5 Hz and passes 0.5 Hz may be used. Actually, since a larger pinhole may be opened, the LPF 101 in FIG. 19 is designed as a filter that cuts 10 Hz or more with a margin.

In this embodiment, the LPF 101 is used. However, the same effect can be obtained by using a BPF (Band Pass Filter), and this does not limit the gist of the present invention. The current measuring circuit having the LPF 101 was inserted on the ground side of the power supply 8 for applying a charging bias voltage to the charging roller 1 in order to avoid a high-voltage load, influence on charging and mixing of current other than charging current.

When the charging current was actually measured, the film thickness 2
When charging from 0 V to 700 V with a 5 μm photoconductor, I =
It was 16 μA. Also, as shown in FIG. 21A, a current value of about 40 to 60 μA was detected where the pinhole was opened, but as shown in FIG. And no longer measured.

As a result, when measuring the charging current for detecting the film thickness, it is possible to eliminate the influence of the rush current due to the pinhole or the like.

<Seventh Embodiment> In this embodiment, the primary charging process of the photosensitive member by the charging roller 1 is performed by DC charging in the printer (FIG. 19) of the sixth embodiment.

In the DC charging, as described above, the charging roller 1 is charged with Vd + V in order to obtain the photosensitive member surface potential Vd.
_th voltage must be applied. Therefore, the DC current flowing through the pinhole becomes larger than that in the case of the AC charging of the sixth embodiment, and the error in detecting the film thickness becomes larger. That is, it is necessary to insert a filter circuit.

The relationship between the charging current I and the film thickness d in DC charging is known from the equation (7) in the sixth embodiment since it is known that ΔV = ΔVd in the region above _Vth. You. In other words, in the even V _th or more regions DC charging ε · ε
0 · L · Vp / d is the slope of the straight line in the VI graph.

Therefore, the voltage V applied to the charging roller 1 and the charging current I flowing at that time are measured at two points in the region equal to or higher than V _th, and the slope of the straight line of the VI characteristic is calculated from this relationship. The thickness d of the body 2a can be detected.

Since the time for measuring the charging current and the frequency of the rush current due to the pinhole do not change, the filter used in this embodiment may be the same as that shown in the sixth embodiment.

When the charging current was actually measured,
μm photoreceptor, the photoreceptor surface potential Vd is changed from 0 V to 700
Current flowing to raise up to V were also 16μA with the sixth embodiment. This is a value when the surface of the photosensitive member is set to 0 V by the charge removing device before charging, and _Vth + vd = 640 + 700 = 1340 V is applied to the charging roller 1.

At this time, the inrush current flowing through the pinhole is about 1
20 μA was measured, but the inrush current was not measured by using the circuit of this embodiment.

As a result, the photosensitive member film thickness can be correctly detected by DC charging, which has been greatly affected by the rush current such as a pinhole.

As described above, in the sixth and seventh embodiments, the use of the filter 101 makes it possible to prevent an inrush current flowing in the DC current detecting circuit for detecting the thickness of the photosensitive member. This prevents a malfunction of the film thickness detecting circuit using the charging current, and makes it possible to obtain high reliability.

<Eighth Embodiment> (FIGS. 22 to 24) (1) Image Forming Apparatus FIG. 22 is a schematic configuration diagram of an image forming apparatus of the present embodiment.
The image forming apparatus of this embodiment has the same configuration as the laser beam printer (FIG. 1) of the first embodiment.

However, in this embodiment, the primary charging of the photosensitive member 2a by the charging roller 1 is performed by AC charging. The transfer bias application power source 10 for the transfer roller 5 is D
It comprises a C power supply 10A, an AC power supply 10B, and a switching circuit 10C for selectively switching between the power supplies 10A and 10B with respect to the charging roller 1.

The AC charging of the photoreceptor 2a is applied to the charging roller 1 from the power supply 8 to a DC voltage of V ₂ = −700 V corresponding to a desired dark portion potential of the photoreceptor. 1 as a peak-to-peak voltage of twice or more of V _th
The oscillation was performed by applying an oscillating voltage on which a constant voltage AC voltage of 800 V was superimposed. In order to eliminate the influence of the change in the impedance of the charging roller 1, it is possible to apply a voltage to the charging roller by an AC constant current control method.

The switching circuit 10C of the transfer bias application power supply 10 is switched to the DC power supply 10A side during transfer, and the DC power supply 10A
The transfer is performed by applying a transfer DC voltage of kV. When the switching circuit 10C is switched to the AC power supply 10B, the AC power supply 10
When an AC voltage of 2000 V _PP is applied from B, the transfer roller 5 functions as a charge removing member, and the photosensitive layer 2 a of the rotating photosensitive drum 2 is discharged to V ₁ = 0 V.

The other structure and the image forming process are the same as those in FIG.

(2) Detection of Thickness of Photoconductor 2a FIG. 23 shows a timing chart of thickness detection of the photoconductor 2a.

First, the switching circuit 10C of the transfer bias applying power source 10 is switched to the AC power source 10B side, and the photosensitive member 2a of the rotating photosensitive drum 2 is discharged by the transfer roller 5 (V1 = OV). Then, the photoreceptor 2 having been neutralized
a is charged to V2 = −700 V by the charging roller 2. At this time, a DC current required to raise the photoconductor surface potential from 0 V to -700 V flows through the charging roller 1 (hatched portion in FIG. 20). Otherwise, the charging DC current does not flow unless there is a change in the photoconductor surface potential.
The theoretical calculation formula of the charging DC current flowing at this time is the same as the formula (5) described in the third embodiment.

That is, the thickness of the photosensitive member is d, the relative permittivity is ε,
Dielectric constant in vacuum ε0, effective charging width of contact charging roller 1 is L, process speed is Vp, photoconductor surface potential is 0 →
When the voltage is increased to Vd, the electrostatic capacity C of the photoconductor is calculated from this, and the following relational expression is derived.

Charge amount: Q = ∫I · dt = C · Vcontrast → Charging current: I = d / dt (C · Vcontrast) dC / dt = ε · ε0 · L · Vp / d, and Vcontrast is V
d, charging current: I = εεε0 ・ LＬVp ・ Vd / d (5) Since ε, ０0, L, Vp, d, and Vd can be regarded as constants, 0 → Vd The charging current I for charging
Is inversely proportional to.

In this embodiment, ε = 3, ε0 = 8.85 ×
10 ^-12 [F / m], L = 230 mm, Vp = 95 mm
/ Sec, Vd = 700 [V], so that d = 25 μ
At m, I = 16 μA.

Actually, using the photosensitive drums 2 having different thicknesses d of the photosensitive members 2a, the H / H environment, the N / N environment, the L / L
The result of the measurement of the d-I relationship in the environment is the same as that of FIG. 11, and it can be seen that the d-I relationship does not depend on the environment as theoretically.

Based on the result, a means is provided for warning the life of the photosensitive drum when the current amount corresponding to the CT film thickness of 15 μm, which is considered to be the life of the photosensitive body 2a, can be exceeded.

In FIG. 11, each environment is 15 μm
Since the amount of current I required for charging when the film thickness is 27 μA is 27 μA, the voltage V generated across the 10 kΩ resistor 16 by I is 27 μA as in the detection circuit 100 of FIG.
When the voltage exceeds 0.27 V, the warning light 20 on the front of the printer body is turned on.

That is, specifically, the voltage V across the protection resistor 16 of 10 kΩ of the power supply 8 is changed to the voltage Vref of the reference voltage 17.
Compared with 0.27 V, when the output of the comparator 18 is received, a signal of the photosensitive drum life is sent to the DC controller 19, and the warning lamp 20 is turned on.

As shown in FIG. 23, the detection of the DC current was performed for a time corresponding to a hatched portion where the charging DC current was flowing.

In this embodiment, one rotation of the photosensitive drum is used as the charging time by the charging roller 1, and the DC current detection uses a value obtained by averaging detection signals during this period.

When an endurance test was actually performed, V was increased by endurance passing, a warning was issued when the CT layer was cut by 10 μm and the remaining 15 μm was reached after passing 10,000 sheets in each environment, and It has become possible to prevent the occurrence of image defects due to excessive shaving.

The above-described sequence can be set for pre-processing, post-processing, etc. of the image forming process after the image forming apparatus is turned on.

In the above sequence, as shown in FIG. 24, assuming that the time until the portion of the photosensitive member 2a from which the charge is removed by the transfer roller 5 reaches the charging position by the charging roller 1 is T ₀ , the charging of the charging roller 1 is performed. The on / off timing is set to T from the charge removal on / off timing by the transfer roller 5.
_This indicates that the operation can be extended to the timing shifted by ₀ . Naturally, the detection of the current flowing through the charging roller 1 can be similarly extended.

It is needless to say that the charge elimination ON time of the transfer roller 5 can be set arbitrarily.

<Ninth Embodiment> (FIG. 25) In this embodiment, the transfer bias application power supply 10 in the printer (FIG. 22) of the eighth embodiment is replaced with a variable DC power supply 10D and an AC power supply 10.
B is changed to a series power supply.
Is the same as

In this embodiment, a DC voltage of 3 kV and a 2,000 V
_The transfer is executed by applying the superimposed oscillation voltage with the AC voltage of _PP .

At the time of non-transfer, the variable DC power supply 10D is set to 0V so that the transfer roller 5 is supplied with 2000V of the AC power supply 10B.
_When only the AC voltage of _PP is applied, the transfer roller 5 functions as a charge removing member, and the photosensitive layer 2a of the rotating photosensitive drum 2 becomes V1.
= 0.

That is, also in this embodiment, as shown in the eighth embodiment, the surface potential of the photosensitive drum 2 can be eliminated (V1 = 0) by the transfer roller 5, and the photosensitive member shown in FIG. A film thickness detection sequence can be realized.

Also in this embodiment, the charging potential of the photosensitive member by the charging roller 1 is set to V ₂ = −700 V, and FIG.
When the paper was actually passed using the detection circuit 100 shown in (1), it was confirmed that a warning was issued after 10,000 sheets were passed.

<Tenth Embodiment> (FIG. 26) In this embodiment, the transfer bias applying power source 10 in the printer of the eighth embodiment (FIG. 22) is changed to only the variable DC power source 10D. The device configuration is the same as that of FIG.

In this embodiment, at the time of transfer, a transfer DC voltage of 3 kV is applied to the transfer roller 5 from the power supply 10 to execute transfer.

The variable DC of the transfer bias applying power source 10
By adjusting the voltage of the power supply 10D, the rotating photosensitive drum 2 is adjusted.
It is possible to eliminate the surface potential of the photosensitive member 2a.

However, the uniformity of static elimination is slightly impaired as compared with the case where the AC power supply 10B is used as in the eighth and ninth embodiments, but the film thickness d of the photosensitive member 2a is detected. Is not enough to affect the charging current.

When the charging potential of the photosensitive member 2a by the charging roller 1 is set to V2 = -700V, 1500 is applied to the transfer roller 5.
By applying V, the photoconductor surface potential can be eliminated as V1 = 0.

Therefore, also in this embodiment, the photosensitive member film thickness detecting sequence shown in FIG. 23 can be realized. However, as described above, the charge elimination (V1 = 0) loses some smoothness, so that the DC current flowing through the charging roller 1 includes some noise, but this is a level that does not cause any problem in practical use.

The endurance was performed using the detection circuit 100 shown in FIG. However, in the eighth and ninth embodiments, the film thickness detection level of the photosensitive member 2a is set to 15 μm, that is, the DC current is set to 27 μA. DC
The current was 23 μA.

As a result, a warning was issued when 9000 sheets were passed. After the durability test, the thickness of the photoreceptor was measured to be 9 μm, and it was 16 μm, and it was confirmed that a warning was issued before reaching the dangerous thickness of 15 μm.

<Eleventh Embodiment> (FIGS. 27 and 28) In the present embodiment, the transfer bias applying power source 10 in the printer (FIG. 22) of the eighth embodiment is replaced by a positive polarity DC power source 10A for the transfer bias. And a DC power supply 10E having a negative polarity opposite to the transfer bias, and both power supplies 10A
10E is replaced with a switching circuit 10C for selectively switching connection to the transfer roller 5, and the other configuration is the same as that of FIG.

In the present embodiment, at the time of transfer, the switching circuit 10C is switched to the DC power supply 10A having a positive polarity, so that a transfer DC voltage of 3 kV is applied to the transfer roller 5 and transfer is performed.

By switching the switch circuit 10C in the power supply 10 to the DC power supply 10E having the negative polarity, the photosensitive member surface potential can be set to V1.

However, since a DC voltage is applied, the surface potential V1 of the photoreceptor is not
In some cases, the charging uniformity is slightly impaired and the surface potential V1 becomes uneven in a minute portion as compared with the case where a superimposed power supply is used.

The charge potential of the photosensitive member by the charging roller 1 is set to V2
= −700 V, and the power supply 10E to the transfer roller 5
To apply a -900 V to make the surface potential of the photosensitive member V1 = -10.
It can be 0V.

Therefore, in the present embodiment, similarly to the eighth embodiment, the photosensitive member film thickness detection sequence shown in FIG. 28 can be realized.

Since the DC current I flowing through the charging roller 1 is | V2−V1 | = 600 V, the relationship with the photosensitive member film thickness d is different from those of the eighth to tenth embodiments (FIG. 11). 15 in the case of the fourth embodiment. However, since the charging potential V1 includes some slight unevenness as described above, the charging DC current I includes some noise, but at a level that does not cause any problem in practical use.

Endurance was performed using the detection circuit 100 shown in FIG. However, from the relationship shown in FIG. 15, the film thickness detection level was set to 15 μm, that is, the charging DC current I was set to 23 μA.
The DC current corresponding to 8 μm was 19 μA.

As a result, a warning was issued when 9000 sheets were passed. When the film thickness of the photoreceptor was measured after the endurance, a warning was issued. When the photoreceptor film thickness was measured after the endurance, it was cut by 9 μm and found to be 16 μm. Although the detection accuracy was inferior to those of the eighth and ninth examples, it was confirmed that a warning was issued before the critical film thickness became 15 μm.

Further, in this embodiment, the negative polarity DC power supply 10E is used, but an AC superimposed power supply may be used instead. Further, the transfer bias applying power supply 10 (10A, 10D) shown in FIG. 25 of the ninth embodiment may be used instead of the positive polarity DC power supply 10A. In short, the circuit configuration is not limited as long as V1 is realized.

<Twelfth Embodiment> (FIGS. 29 to 31) In this embodiment, as shown in FIG. 29, the charging bias application power supply 8 for the charging roller 1 is changed to a DC power supply 8A, an AC power supply 8B, and an AC power supply 8B. The power supply 8B comprises a DC power supply 8A and a switching circuit 8C for selectively switching and connecting the ground.

Similar to the power supply of the eleventh embodiment (FIG. 27), the transfer bias application power supply 10 includes a positive DC power supply 10A for the transfer bias and a negative DC power supply 10E having the opposite polarity to the transfer bias. , This power supply 10A.1
0E is selectively connected to the transfer roller 5 by a switching circuit 10C. The other device configuration is the same as that of FIG.

At the time of the primary charging process of the photosensitive member 2a, the switching circuit 8C of the charging bias applying power source 8 is switched to the DC power source 8A side, and the DC power source 8A and the AC power source 8B are connected in series to , DC voltage -70
A superimposed oscillation voltage of 0 V and an AC voltage of 1800 V _PP is applied, and the photosensitive member 2a of the rotating photosensitive drum 2 is driven to have Vd = −70.
It is charged by AC charging to 0V.

In the transfer bias application power source 10, the switching circuit 10C is switched to the DC power source 10A having a positive polarity at the time of transfer, and a transfer bias of 3 kv is applied to the transfer roller 5 to perform transfer.

By switching the switching circuit 10C of the transfer bias applying power source 10 to the DC power source 10E having the negative polarity, the photosensitive member surface potential can be set to V1 as in the eleventh embodiment (FIG. 27). It is.

When the switching circuit 8C of the charging bias applying power source 8 is switched to the ground side, only the AC voltage of the AC power source 8B is applied to the charging roller 1, and the photosensitive member surface potential is eliminated to V2 = 0V.

In this embodiment, the charge potential of the photosensitive member by the transfer roller 5 is set to V1 = −700 V, and the charge can be removed (V2 = 0) by the charging roller 1.

Therefore, in the present embodiment, similarly to the eighth embodiment, the photosensitive member film thickness detecting sequence shown in FIG. 30 can be realized.

Here, the DC current I flowing through the charging roller 1
Changes the potential from V1 = -700V to V2 = 0V, so that a current having a polarity different from that of the eighth to eleventh embodiments flows. As in the tenth embodiment, since the charging potential V1 includes some slight unevenness, the charging DC current I includes some noise, but at a level that does not pose any problem in practical use.

Endurance was performed using the detection circuit 100 shown in FIG. The detection circuit shown here merely changes the polarity of Vref of the reference voltage 17 of the detection circuit shown in FIG. Further, from the relationship shown in FIG.
μm, that is, a DC current of 27 μA, but considering the above noise component, it is expected to be safe and a DC current of 18 μm is required.
3 μA.

As a result, a warning was issued when 9000 sheets were passed. When the film thickness of the photoreceptor was measured after the endurance, it was cut by 9 μm and found to be 16 μm. It was confirmed that a warning was issued before the critical film thickness of 15 μm was reached.

In the present embodiment, the charging bias application power source 8 is not limited to this, and it is natural that V2 can be set using a DC power source or the like having a variable DC level. Further, the transfer bias applying power source 10 is not limited to this, but may be any power source that can be charged to V1.

As in the eighth to twelfth embodiments, using the AC contact charging device 1 and the transfer device 5, the transfer device 5 charges the charged object to the first potential (including static elimination). After that, the thickness of the member to be charged is detected by measuring the DC current flowing through the contact charging member 1 when the member to be charged is charged to the second potential (including static elimination) by the contact charging device. By giving a warning when the following occurs, it is possible to prevent the occurrence of an image defect in the image forming apparatus.

Although the apparatus of the first to twelfth embodiments uses the photosensitive drum 2 having a negative polarity, the photosensitive drum 2 may have an anode polarity or a bipolar polarity. Absent. Furthermore, the transfer roller 5 has been described as a transfer device, but the transfer device is not limited to this, and a transfer device such as a transfer belt and a transfer corona can be used as appropriate.

Although the charging roller 1 is used as the charging device, any member that can realize contact DC charging and AC contact charging may be used.

[0231]

As described above, according to the present invention, it is possible to accurately and stably detect the thickness of a member to be charged with a simple device and circuit configuration with little influence on the environment . In an image forming apparatus, it is possible to accurately and stably detect when the thickness of a member to be charged or an image carrier as a member to be charged has reached a lower thickness or a lower limit as a service limit with little environmental influence.
It is possible to take appropriate countermeasures such as warnings to prompt the replacement of the image carrier, and prevent the occurrence of charging failure and image failure due to the continued use of the image carrier despite reaching the usage limit. This makes it possible to configure a highly reliable device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a printer as a first embodiment.

FIG. 2 is a VI characteristic diagram when a photoconductor thickness is changed.

FIG. 3 is a correlation diagram between a photoconductor thickness and a slope of a VI characteristic.

FIG. 4 is a VI characteristic diagram showing control.

FIG. 5 is a diagram showing a relationship between a voltage applied to a charging member and a charging potential.

6A is an enlarged model diagram of a contact portion between a photosensitive drum and a charging roller, and FIG. 6B is an equivalent circuit diagram of a discharge phenomenon.

FIG. 7 is a diagram illustrating a relationship between a voltage applied to a charging member and a photoconductor surface potential when AC charging is performed.

FIG. 8A is a partially cutaway top view of a photoconductor film thickness measuring unit in the second embodiment, and FIG. 8B is a side view thereof.

FIG. 9 is a control sequence diagram of a printer as a third embodiment.

FIG. 10 is a diagram showing a relationship between an AC voltage, a DC voltage, and a DC current.

FIG. 11 is a diagram illustrating a relationship between a photoconductor thickness d and a DC current I.

FIG. 12 is a conceptual diagram of a DC current detection circuit configuration.

FIG. 13 is a schematic configuration diagram of a printer as a fourth embodiment.

FIG. 14 is a main part diagram of another configuration example.

FIG. 15 is a diagram showing the relationship between the photoconductor thickness d and the DC current I.

FIGS. 16A and 16B show the occurrence of a leak current due to a pinhole in a printer as a fifth embodiment;
Explanation model diagram of the prevention

FIG. 17 is a control sequence diagram.

FIG. 18 is a relationship diagram of AC voltage, DC voltage, and DC current.

FIG. 19 is a schematic configuration diagram of a printer as a sixth or seventh embodiment.

FIG. 20 (a) and (b) are diagrams of the elapsed time and period of the measured current.

21 (a) and (b) are measured current diagrams before and after using a frequency filter.

FIG. 22 is a schematic configuration diagram of a printer as an eighth embodiment.

FIG. 23 is a photoconductor film thickness detection sequence diagram.

FIG. 24 is an extended sequence diagram thereof.

FIG. 25 is a schematic configuration diagram of a printer as a ninth embodiment.

FIG. 26 is a schematic configuration diagram of a printer as a tenth embodiment.

FIG. 27 is a schematic configuration diagram of a printer as an eleventh embodiment.

FIG. 28 is a photoconductor thickness detection sequence diagram.

FIG. 29 is a schematic configuration diagram of a printer as a twelfth embodiment.

FIG. 30 is a photoconductor film thickness detection sequence diagram.

FIG. 31 is a conceptual diagram of a DC current detection circuit configuration.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Charging roller as a charging member 2.2a Photosensitive drum or photosensitive body as a charged member 3 Laser beam 4 Developing device 5 Transfer roller 6 Cleaning device 7 Fixing device 8 Charging bias application power source 9 Transfer material 10 Transfer bias application power source 11 Process cartridge 12.21.22 Exposure lamp or corona discharger for static elimination 13.14 First and second contacts (electrode members) 100 DC current detection circuit (film thickness detection circuit) 101 Low-pass filter (frequency filter circuit)

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Furuya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Norio Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-59-69774 (JP, A) JP-A-63-149668 (JP, A) JP-A-3-163370 (JP, A) JP-A-63-208881 (JP, A A) JP-A-1-232371 (JP, A) JP-A-4-101182 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B ⁷ /00-7/34 G01B 21 / 00-21/32 G03G 13/02 G03G 15/02

Claims (12)

(57) [Claims] And the electrode member to 1. A contact member to be charged, and a voltage applying means for applying a different voltage to the electrostatic <br/> pole member,
Have a current detection means for detecting a current flowing through the electrode member
The VI characteristics obtained by applying different voltages to the electrode members
An apparatus for detecting the thickness of an object to be charged, wherein the thickness of the object to be charged is detected based on the property . 2. A voltage applied to an electrode member is a DC voltage component.
And an AC voltage component superimposed on the charged object.
From a predetermined first potential V1 to a predetermined second potential V2
By measuring the DC current flowing through the electrode member when charging
And detecting the thickness of the member to be charged.
3. The apparatus for detecting a thickness of an object to be charged according to claim 1. 3. A DC voltage of an oscillating voltage applied to an electrode member.
The component is a voltage corresponding to a desired charging potential of the member to be charged.
When the DC voltage is applied to the electrode member, the AC voltage component
Peak-to-peak voltage more than twice the charging start voltage V _th of the member to be charged
3. The apparatus according to claim 2, wherein the apparatus has a pressure . 4. A DC voltage of an oscillating voltage applied to an electrode member.
A method for switching the components between the first voltage V1 and the second voltage V2
4. The device for detecting the thickness of a member to be charged according to claim 2, wherein the device has a step. 5. A charging member in contact with a member to be charged,
Voltage applying means for applying a plurality of different voltages to the electrical member,
And a current detecting means for detecting a current flowing through the charging member.
The VI characteristics obtained by applying different voltages to the charging member
You and detecting the thickness of the member to be charged on the basis of sex
A device for detecting the thickness of an object to be charged. 6. A voltage applied to the charging member is a DC voltage component.
And an AC voltage component superimposed on the charged object.
From a predetermined first potential V1 to a predetermined second potential V2
Measurement of DC current flowing through charging member when charging
6. The method according to claim 5, wherein the thickness of the member to be charged is detected.
The thickness detecting apparatus of the member to be charged according to. 7. A DC voltage of an oscillating voltage applied to a charging member.
The component is a voltage corresponding to a desired charging potential of the member to be charged.
And the AC voltage component is when a DC voltage is applied to the charging member.
Peak-to-peak voltage more than twice the charging start voltage V _th of the member to be charged
7. The apparatus according to claim 6, wherein the apparatus has a pressure . 8. A DC voltage of an oscillating voltage applied to a charging member.
A method for switching the components between the first voltage V1 and the second voltage V2
8. The device for detecting the thickness of an object to be charged according to claim 6, wherein the device has a step. 9. An image bearing member, and a charging section in contact with the image bearing member.
Material and a voltage to apply a plurality of different voltages to this charging member
Application means and current detection for detecting the current flowing through the charging member
Means for applying different voltages to the charging member.
Detecting the thickness of the image carrier based on the VI characteristics
Characteristic image forming apparatus. 10. A voltage applied to the charging member is a DC voltage component.
This is the oscillating voltage obtained by superimposing the AC voltage component on the image carrier.
From a predetermined first potential V1 to a predetermined second potential V2.
For measuring DC current flowing through charging member when charging with
The thickness of the image carrier is detected more.
10. The image forming apparatus according to 9. 11. A DC voltage of an oscillating voltage applied to a charging member.
The pressure component is a voltage corresponding to a desired charging potential of the image carrier.
Yes, the AC voltage component is when a DC voltage is applied to the charging member.
Between the peaks at least twice the charging start voltage V _th of the image carrier
11. The image form according to claim 10, having a voltage.
Equipment. 12. A DC voltage of an oscillating voltage applied to a charging member.
Switching the voltage component between the first voltage V1 and the second voltage V2
12. The method according to claim 10, further comprising:
An image forming apparatus according to claim 1.