JPH05307287A - Image forming device - Google Patents

Abstract

PURPOSE:To detect the environment, applied conditions, and dispersion in sensitivity at the time of manufacturing a body to be charged by precisely detecting the conditions of the body to be charged such as the potential of an exposing part and the thickness of a film on the body to be charged in an image forming device applying an image forming process including a charging processing operation to the body to be charged as an image carrier and outputting a formed image. CONSTITUTION:In the image forming device applying the image forming process including the charging processing operation, to the body to be charged 2 as the image carrier to output the formed image, when the potential VL of the exposing part obtained by exposing the body to be charged 2 whose surface is electrostatically charged to a potential VD is electrostatically charged up to a potential V1 by the contact charging, a direct current IDC flowing from a power source to a contact-charge member 1 is measured, and the potential VL is detected based on the measured direct current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process of charging an object to be charged as an image bearing member (including a charge removing process) such as an electrophotographic apparatus (electrostatic copying machine) and printer. The present invention relates to an image forming apparatus that outputs an image formed product (copy, print) by applying an image forming process including the image forming process.

[0002]

2. Description of the Related Art Conventionally, in an image forming process such as electrophotography and electrostatic recording, as a charging processing means (charging device) for an electrophotographic photosensitive member and an electrostatic recording dielectric which are charged members as an image carrier. Corona chargers have been used.

In recent years, a contact charging device has been put into practical use instead. This is for the purpose of ozone-less, low power consumption, etc. Among them, a roller charging method using a conductive roller as a charging member is particularly preferably used from the viewpoint of stability of charging. In roller charging, a conductive elastic roller (charging roller) is brought into pressure contact with a member to be charged, and a high voltage is applied to the member to charge the member to be charged.

Specifically, since the charging is performed by the discharge from the contact charging member to the member to be charged, the charging is started by applying a voltage higher than a certain threshold voltage. This voltage is called the charging start voltage V _th .

As an example, the thickness of the member to be charged is 25
When the charging roller is brought into pressure contact with the OPC photosensitive member (layer) of μm, the surface potential of the photosensitive member starts to rise when a voltage of about 640 V or higher is applied, and thereafter, with respect to the applied voltage. With the inclination of 1, the surface potential of the photoconductor increases linearly.

From the above, in order to obtain the desired photoreceptor surface potential V _D required for electrophotography, it is sufficient to apply a DC voltage (DC voltage) of V _D + V _{th to} the charging roller. Become. In this way, the method of applying only the DC voltage to the contact charging member to carry out charging is referred to as "contact DC charging".

However, in contact DC charging, the resistance value of the contact charging member fluctuates due to environmental changes, and when the film thickness changes due to abrasion of the photoconductor (photosensitive layer), the value of the charging start voltage V _th fluctuates. Therefore, it is difficult to set the surface potential of the photoconductor to the desired value V _D.

For this reason, as disclosed in Japanese Patent Laid-Open No. 63-149669, a DC voltage corresponding to the desired photoreceptor surface potential V _D has a peak of 2 × V _th or more as disclosed in JP-A-63-149669. A charging method (hereinafter referred to as "contact AC charging") in which an oscillating voltage (a voltage whose voltage value changes periodically with time) superimposed on an AC component having an inter-voltage is applied to the contact charging member is used. This is for the purpose of leveling the potential by the AC component, and the potential of the charged body is AC.
It converges to V _D , which is the center of the potential peak, and is not affected by disturbances such as the environment.

[0009]

[Problems to be Solved by the Invention]

(A) ZnO, CdS, Se, a is used for the photoconductor used for electrophotography.
-Many of which use inorganic materials such as Si and those which use organic materials (OPC) have been put to practical use in recent years, but all of them are sensitive due to factors such as usage environment, accumulation of light exposure, photoconductor scraping, etc. There was a problem that was changed. Also,
Even if the same material is used, it is difficult to keep the exposed portion potential _VL constant because of variations in manufacturing the photoreceptor.

If such a change in the photosensitivity occurs in an electrophotographic apparatus using a laser beam, especially in a printer, there are problems that the image density is not constant, the line width is changed, and the font (font) becomes dirty. Will occur.

In order to prevent this, conventionally, a method of providing a means for measuring the surface potential of the photoconductor has been used. However, this causes an increase in cost, a low-priced machine and a small size because an extra space is taken. It was difficult to adapt to the machine.

Further, conventionally, in order to correct variations in manufacturing the photosensitive member, the sensitivity of the photosensitive drum is measured in advance, and the apparatus is adjusted so as to obtain an exposure amount suitable for each, or a cartridge type method. In that case, a so-called "sensitivity frame" indicating the drum sensitivity was attached to each cartridge, and the main body of a printer or the like took a method of adjusting the optimal exposure amount by reading the sensitivity frame.
This also results in a complicated structure and an increase in cost.

(B) In both of the contact AC charging and the contact DC charging, if the photosensitive member is scraped by the durable paper passing and the thickness is reduced, the following problems will occur.

The amount of charge Q required to charge the surface of the photoconductor to a constant potential V _D is determined by the electrostatic capacitance C of the photoconductor, and this amount of charge is inversely proportional to the thickness d of the photoconductor.

Therefore, the scraped photosensitive drum is set to the same potential V _D.
More charge than the initial charge (charging current)
Will be necessary.

However, when the charging current becomes large, the voltage drop due to the impedance of the contact charging member becomes remarkable.

Generally, the charging roller has a resistance layer in order to prevent the charging current from concentrating in the case where a pinhole is generated on the photosensitive member, and the roller resistance is 10 ⁵ to 1 1.
It has an impedance value of 0 ⁶ Ω. Further, if the roller resistance is further increased when the durable paper is passed in a low temperature and low humidity environment and the charging current is increased due to the abrasion of the photoconductor, the drop amount of the potential V _D becomes 100 to 200 V. May cause fog.

From the above, in order to obtain a good image, the thickness of the photosensitive member is required to be about 15 μm or more, and if the abrasion is more than this, a stable image cannot be guaranteed, and the photosensitive material cannot be guaranteed. It can be considered to have exceeded the life of the body.

However, conventionally, there are few effective means for directly knowing the thickness of the photoconductor, and there is no good method other than counting the total number of rotations of the photoconductor drum and indirectly calculating the abrasion amount. However, the amount of abrasion changes depending on the usage environment, the state of the cleaning device, etc., and therefore reliability was poor.

(C) Further, a method of detecting the condition of the photoconductor (photoconductor film thickness, exposure history, etc.) from the DC current flowing when the photoconductor is charged by the corona charger is also disclosed.
As disclosed in Japanese Patent No. 68, etc., these measure a current flowing from the photoconductor to the ground because a corona charger is used as a charging device. In this case, the current flowing from the photoconductor to the ground is charged. However, it has a drawback that the shield current and the current flowing into the photoconductor from the developing means, the transfer means, etc. are measured at the same time.

Further, when the toner on the photoconductor is cleaned, the electric current corresponding to the electric charge of the toner held by the conductive layer of the photoconductor also escapes to the ground, so an error due to this current cannot be avoided. Met.

In order to solve these problems with the corona charger, it is necessary to remove the current component other than the charging current in order to accurately detect only the DC current actually applied to the charging. Since the current obtained by subtracting the shield current, grid current, etc. from the current must be measured, there are problems that errors are likely to occur and the configuration becomes complicated.

An object of the present invention is to solve the above problems (A) to (C).

[0024]

The present invention is an image forming apparatus having the following configuration.

(1) In an image forming apparatus that outputs an image formed product by applying an image forming process including a charging process to a charged body as an image carrier, the charged body whose surface is charged to a potential V _D The direct current I _DC flowing from the power supply to the contact charging member when the exposed portion potential _VL obtained by exposing the substrate to the contact is charged to the potential V1 by contact charging, and the potential _VL is measured based on this. An image forming apparatus characterized by detecting a.

(2) The image forming apparatus described in (1) is characterized in that the current I _DC is measured by a current which directly flows in or out of a power supply which supplies power to the contact charging member.

(3) The image forming apparatus according to claim 1, wherein the condition of the exposing means is controlled based on the detected exposure portion potential V _L.

(4) The image forming apparatus according to (2), wherein the control target of the exposure means is a light amount (light intensity).

(5) The film thickness d of the member to be charged is detected by previously measuring the direct current I _DC ′ flowing when the surface potential of the member to be charged is changed from the potential V2 to the potential V3 by the contact charging member. Based on this, the exposed portion potential V
The image forming apparatus according to (1), which detects _L.

(6) The voltage applied to the contact charging member has a direct current component corresponding to the desired potential of the member to be charged and an AC component having a peak-to-peak voltage that is at least twice the charging start voltage V _th of the member to be charged. 2. It is a superposed one.
The image forming apparatus according to item 1.

(7) The image forming apparatus according to (5), further comprising means for switching the DC component of the voltage applied to the contact charging member between the voltage V2 and the voltage V3.

(8) The image forming apparatus according to claim 1, wherein the voltage V1 = 0.

(9) The image forming apparatus described in (1), wherein the contact charging member has a roller shape.

(10) In an image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image carrier, the charged body whose surface is charged to potential V _D The exposed portion potential V _L obtained by exposing the substrate to the light is applied to the potential V ₁ by contact charging.
Current I flowing through the contact charging member when charging up to 10
An image forming apparatus characterized by detecting _DC and changing an image forming process condition according to the current I _DC value.

(11) The image forming apparatus described in (10) is characterized in that the current I _DC is measured with a current which directly flows in or out of a power supply which supplies power to the contact charging member.

(12) The image forming apparatus according to (10), characterized in that the target of change in the image forming process condition is the developing bias condition.

(13) The image forming apparatus according to (10), wherein the target of change in the image forming process condition is a charging bias.

(14) The image forming apparatus described in (10), characterized in that the potential V1 = 0.

(15) In an image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image carrier, the charged body whose surface is charged to potential V _D The exposed portion potential _VL obtained by exposing the substrate to light is applied to the potential V1 by contact charging.
Current I flowing through the contact charging member when charging up to 10
It has a means for measuring _DC and detecting the potential _VL based on this, and a transfer means for transferring the image formed on the member to be charged onto a transfer material. When measuring the direct current I _DC , The potential fluctuation of the exposed portion potential V _L of the charged body before and after passing through the transfer portion is approximately 0 V.
The image forming apparatus is characterized in that the transfer means is controlled as described above.

(16) The image forming apparatus described in (15) is characterized in that the current I _DC is measured with a current flowing in or out of a direct current with respect to a power supply for supplying power to the contact charging member.

(17) The image forming apparatus according to (15), wherein the transfer member of the transfer means is in contact with the member to be charged.

(18) When the potential V _{L of the} exposed portion is detected, the voltage applied to the transfer means is controlled between the surface potential V _{D of the} charged body to be charged and 0 V. Image forming apparatus.

(19) The image forming apparatus according to (17), wherein the transfer member is electrically floated on the electric circuit when the exposed portion potential V _{L is} detected.

(20) The image forming apparatus as described in (17), wherein the transfer member is physically separated from the surface of the member to be charged and is not in contact when the potential V _{L of the} exposed portion is detected.

(21) The image forming apparatus described in (15), wherein the transfer means is a means utilizing corona discharge.

(22) The image forming apparatus according to (17), wherein the transfer bias is set to 0 V when the exposed portion potential V _{L is} detected.

(23) In an image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image carrier, a charging means for charging the charged body, A direct current component corresponding to a desired potential of the charged body is superimposed on the contact charging member brought into contact with the charged body, and an AC component having a peak-to-peak voltage that is at least twice the charging start voltage V _th of the charged body is superimposed. Is a contact charging means for applying a predetermined voltage to charge the charged body, and is a direct current supplied to the contact charging member when the charged body potential is charged or discharged from a predetermined first potential V2 to a predetermined second potential V3. current I _DC 'means for sensing the thickness d of the member to be charged by measuring, and a transfer means for transferring to a transfer material the image formed on the member to be charged, the direct current I _DC' a When detecting, mark on the transfer means. The image forming apparatus is a voltage, wherein the member to be charged potential transfer portion passes through the front and rear of the potential change of V2 is controlled so as to be substantially 0V.

(24) The image forming apparatus according to (23), wherein the current I _DC ′ is measured with a current which directly flows in or out of a power supply which supplies power to the contact charging member.

(25) In the transfer means, the transfer member is in contact with the body to be charged, and the voltage V _tr applied to the contact transfer member when the direct current I _DC ′ is detected is the voltage V _tr and the body to be charged. (23) The image forming apparatus according to (23), wherein the absolute value of the difference in the body potential V2 is controlled so as to be equal to or lower than the voltage Va at which the contact transfer member starts charging the charged body.

(26) When detecting the direct current I _DC ′, the voltage V _tr applied to the contact transfer member is controlled to the same voltage as the charged body potential V2. Forming equipment.

(27) The transfer means is a corona transfer charger, and when detecting the DC current I _DC , the voltage V _tr applied to the corona transfer charger is controlled to be equal to or lower than the corona discharge start voltage Vb. The image forming apparatus according to (23), which is characterized.

(28) In an image forming apparatus for applying an image forming process including a charging process to an object to be charged as an image bearing member to output an image formed object, a charging means for charging the object to be charged comes into contact. The charging means is a means for measuring the current I _M flowing in the contact charging means by charging or discharging the body to be charged from the potential before the charging processing to the potential after the charging processing, and the voltage applied to the contact charging means, an image forming apparatus comprising: the voltage applied at the time of image formation, a means for switching between the constant voltage V _M to be applied during the current I _M measurements.

(29) The surface potential V _L obtained by exposing a photosensitive member whose surface is to be charged is a photosensitive member whose surface potential has been charged, and the surface charge V _L is applied by contact charging to which the constant voltage V _M is applied. The image forming apparatus as described in (28), characterized in that the electric current I _M flowing through the contact charging member is measured and the potential V _L is detected based on the measured current I _M when the charging is performed.

(30) Constant voltage V when measuring the current I _M
It has two values of _M1 and V _M2 and is obtained when a constant voltage V _M2 is applied to the contact charging device from the charged potential of the charged member obtained when the constant voltage V _M1 is applied to the contact charging device. The image forming apparatus as described in (28), wherein the film thickness of the charged body is measured by measuring the current I _M flowing through the contact charging member when the charged body is charged to the charging potential.

(31) A DC component whose voltage applied to the contact charging member corresponds to the desired potential of the member to be charged and an AC component having a peak-to-peak voltage which is more than twice the charging start voltage V _th of the member to be charged. Characterized by being superposed (28)
The image forming apparatus according to any one of (30) to (30).

(32) The image forming apparatus as described in (29) or (30), characterized in that the current I _M is measured with a current flowing directly into or out of the voltage applying device.

(33) The image forming apparatus described in (30), wherein V _M1 or V _M2 = 0.

(34) The image forming apparatus as described in (28), wherein the contact charging member has a roller shape.

(35) In an image forming apparatus for applying an image forming process including a charging process to an object to be charged as an image bearing member to output an image formed article, a contact charging device for charging the object to be charged, A means for measuring the direct current flowing in the contact charging device by charging or removing the charged object from the potential before the charging process to the potential after the charging process, and the direct current voltage applied to the contact charging device during the direct current measurement. An image forming apparatus comprising:

(36) The direct current flowing through the contact charging device when the contact charging device charges the exposed portion potential obtained by exposing the charged photosensitive member to light. A means for calculating the exposed portion potential by measuring a current, detecting a direct current voltage applied to the contact charging device, and calculating the exposed portion potential using the direct current voltage value. The image forming apparatus according to claim 35, which is characterized in that.

(37) Means for calculating the film thickness of the charged body by measuring the direct current flowing through the contact charging apparatus when charging or discharging the charged body is applied to the contact charging apparatus. The image forming apparatus described in (35) is characterized in that the film thickness of the member to be charged is calculated using the DC voltage value detected.

(38) A direct current component whose voltage applied to the contact charging member corresponds to a desired potential of the charged body and an alternating current component having a peak-to-peak voltage which is more than twice the charging start voltage V _th of the charged body. Characterized by being superimposed (35)
The image forming apparatus described in any one of (37) to (37).

(39) The image forming apparatus as described in (36) or (37), characterized in that the direct current is measured with a current flowing directly into or out of the voltage applying device.

(40) The image forming apparatus as described in (35), wherein the contact charging member has a roller shape.

[0065]

[Operation] In the contact charging method, unlike the corona charger, all the current flowing through the contact charging member is supplied to the photoconductor as the charged body.Therefore, by detecting this current, the condition of the photoconductor is detected, for example, the thickness of the photoconductor is detected. , The exposed portion potential V of the photoconductor
_L can be detected.

This is the charging DC that flows when the surface potential of the photosensitive member is changed by Vcontrast by the contact charging member.
This is a method of detecting the film thickness of the photoconductor that is in inverse proportion to the current I _DC by measuring the current I _DC . As described above, when the contact AC charging is used, the photoconductor surface potential is always the desired potential V. _Since it can be converged to _D , Vcontrast
Is especially advantageous because it can be kept constant regardless of the environment.

To explain this a little now, the measurement principle for detecting the state of the photoconductor is to measure the potential of the photoconductor by a certain amount.
It can be obtained by measuring the amount of direct current flowing through the contact charging member when changing only (Vcontrast).

The DC current required when changing the surface potential of the photosensitive member by Vcontrast is logically calculated as follows.

When the thickness of the photoconductor is d, the relative dielectric constant is ε, the dielectric constant in vacuum is ε0, the effective charging width of the contact charging member is L, the process speed is Vp, and the surface potential of the photoconductor is changed by Vcontrast, The following relations are derived. Here, C represents the electrostatic capacity of the photoconductor that is subjected to the charging process.

Charge amount: Q = ∫I · dt = C · Vcontrast → Charging current: I = d / dt (Vcontrast) Here, since dC / dt = ε · ε0 · L · Vp / d, charging Current: I = ε · ε0 · L · Vp · Vcontrast / d (1) From this, the charging current I is inversely proportional to d, and Vcont
It turns out that it is proportional to rast.

For example, from the electric potential 0 V after static elimination to the charging potential V
_The film thickness d can be detected when the charging potential V _D is known from the DC current I that flows when charging to _D.

Further, when the film thickness d is known, the exposed portion potential V _L
To the charging potential V _D , the exposed portion potential _VL can be detected from the DC current I flowing when charged.

.. In the present invention, the uniformly charged photosensitive member is exposed to light, and after the exposed portion potential _VL is applied, contact charging is performed to change the potential to a known potential V1, and the potential of the photosensitive member is fixed by Vcontrast ( | V _L -V1 |) DC current flowing through the contact charging member when brought into only the change (charging DC current) was measured I _DC, and detecting the exposed portion potential V _L from this relationship. With this, it is possible to detect the environment of the photoconductor, the usage state, and the sensitivity variation during manufacturing.

Then, when the exposed portion potential V _L is different from the desired value, the exposure means is controlled. The exposure means can be controlled by feeding back the potential V _L to a desired value, or can be intentionally converged to different values.

Further, since the charging DC current I _DC changes not only by the function of Vcontrast but also by the thickness d of the photoconductor, it is possible to detect the thickness d of the photoconductor in advance and improve the measurement accuracy. ..

In the present invention, since the contact charging member is used as the charging member, the current flowing from the power source into the contact charging member is the DC current that actually contributes to the charging, and the load including the photoconductor, which is difficult in the conventional method, is applied. Upstream charging DC current I _DC
Can be measured.

By adopting such a constitution, it becomes possible to easily remove the error current generated by the cleaning of the developing means, the transfer means and the toner, which has been a problem in the conventional method using the corona charger. It has become possible to accurately detect the photoconductor condition such as the exposed portion potential _VL and the photoconductor film thickness d.

.. The present invention is characterized in that the image forming process conditions are adjusted (changed) based on the detected charging DC current I _DC , whereby problems such as image defects can be reduced or eliminated.

.. The present invention relates to an image forming apparatus having a transfer means for transferring an image formed on a photoconductor to a transfer material, from the detected charging DC current I _DC to the exposed portion potential V _DC.
By comprising means for detecting _L, and the said DC current during the measurement, characterized in that the transfer unit before and after passing through the potential variation with respect to the exposed portion potential V _L of the photosensitive member to control the transfer means such that substantially 0V With this, it is possible to detect the environment of the photoconductor, the usage state, and the sensitivity variation during manufacturing.

Then, when the exposure portion potential V _L is different from the desired value, the exposure means is controlled. The control of the exposure means can be performed by feeding back the potential V _L to a desired value, or can be intentionally converged to different values.

[0081] Further, since the current I _DC to change the thickness of the photosensitive member rather than the function only of Vcontrast, it leaves detecting the thickness d of the pre photoreceptor can be improved the accuracy of the measurement.

.. According to the present invention, in an image forming apparatus having a transfer unit for transferring an image formed on a photoconductor to a transfer material, the photoconductor charging processing unit is contact AC charging, and the photoconductor potential is charged by a constant amount of potential Vcontrast. Or a means for measuring the charging DC current I _DC flowing through the contact charging member when the charge is removed, and at least the voltage applied to the transfer means at the time of measuring the current is a voltage that does not change the potential of the photoconductor before and after passing through the transfer portion. are characterized to be, thereby the film thickness d of the photosensitive member than the DC current I _DC flowing through the contact charging member can see exactly, it is possible to know the life of accurately photoreceptor.

.. As described above, the contact charging can be used to easily measure the film thickness d of the photoconductor as the member to be charged and the exposed portion potential V _L of the photoconductor, and at low cost without using a special device. However, when this is applied to electrophotography, some problems occur due to the process configuration of electrophotography.

The electrophotographic apparatus is provided with a density volume (hereinafter, the density level is abbreviated as “F value”) so that the user can adjust the image density and the image line width. As means for this, in the case of reversal development, the exposed portion potential V
There is a method of changing the development contrast given by the difference between _L and the development bias voltage V _DC . If this development contrast is made large, the image density will be high and the image line width will be thick, and conversely, if it is small, the image density will be light and the image line will be thin.

Further, the developing bias voltage V _DC and the charging potential V
_In order to prevent reversal fog and uneven charging due to a change in reversal contrast given by the difference from _D , control is performed so that when the developing bias voltage V _DC is changed depending on the F value, the charging potential V _D is also changed.

Generally, as shown in FIG. 22, the set values of the developing bias voltage V _DC and the charging potential V _D are changed.
For example, as typical values, F1 (maximum concentration): V _DC1 = -600 V, V _D1 = -75
0V F1 (central density): V _DC5 = -500V, V _D5 = -70
0V F1 (minimum concentration): V _DC9 = -400 V, V _D9 = -65
It is 0 V, and takes an arbitrary value in the range of V _D = −650 to −750 V and V _DC = −400 to −600 V corresponding to the F value.

When the condition of the photosensitive member is detected by the contact charging member, since the charging potential V _D changes corresponding to the F value, Vcontrast in the above formula (1) changes, and the charging current I is measured. However, there is a problem in that the film thickness d of the photoconductor and the exposed portion potential _VL cannot be calculated correctly just by doing so.

According to the present invention, the DC voltage applied to the contact charging member is detected at the time of measuring the charging current, so that the situation of the photosensitive member can be correctly detected by using the contact charging, and the above-mentioned problem can be solved.

.. On the other hand, with respect to the above, when the condition of the photoconductor is detected by the contact charging member, the charging potential V _D changes in accordance with the F value, so Vcontra in the formula (1) above is changed.
st changes, not only the circuit that measures the charging current I but also F
A circuit for measuring the charging potential V _D that changes depending on the value is also required. Therefore, there is a very disadvantageous aspect that the measuring device becomes complicated and the cost becomes high.

According to the present invention, the voltage applied to the contact charging member is switched between the voltage applied during image formation and the constant voltage V _M applied during measurement of the charging DC current, so that the state of the photoreceptor using contact charging is changed. The detection can be performed regardless of the settings of the electrophotographic process, and the above-mentioned problem can be solved.

[0091]

EXAMPLES [I] The following first to third examples are examples of the invention described in claims 1 to 8 of the claims.

<First Embodiment> (FIGS. 1 to 3) (1) Example of Image Forming Apparatus (FIG. 1) FIG. 1 is a schematic configuration diagram of an image forming apparatus of the present embodiment. The image forming apparatus of this embodiment is a laser beam printer using an electrophotographic process.

Reference numeral 2 denotes a rotary drum type electrophotographic photosensitive member (also referred to as a charged member or a drum) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined process speed (peripheral speed).

Reference numeral 1 denotes a charging roller as a contact charging member, which is arranged in parallel with the photosensitive member 2 and is pressed against it with a predetermined pressing force by a pressing means (not shown). In the case of this embodiment, the photosensitive member is rotated. Followed by the rotation. By applying a predetermined charging bias from the high-voltage power supply 1A to the charging roller 1, the peripheral surface of the rotating photoconductor 2 is charged by contact charging to a predetermined polarity and potential. High-voltage power supply 1A is charging roller 1
It is possible to change the applied voltage to.

Reference numeral 3 denotes a laser scanner, which outputs a laser beam L modulated in accordance with a time-series electric digital pixel signal of the target image information and which has been subjected to the above charging-processed rotating photosensitive member 2.
The surface is scanned to image-expose the two surfaces of the photoconductor. As a result, the image-exposed portion of the surface of the photoconductor is neutralized and an electrostatic latent image corresponding to the target image information is formed on the surface of the photoconductor 2.

Then, the electrostatic latent image is reversely developed by the toner developing device 4 and the toner is visualized as a toner image by adhering the toner to the image exposure portion on the surface of the photosensitive member 2. 41
Is a developing roller or a developing sleeve. 4A is a high voltage power source for applying a developing bias to the developing roller 41.

At the transfer portion, which is the pressure contact portion between the photoreceptor 2 and the transfer roller 5 as the transfer device, the toner image is transferred to the transfer portion 11 at a predetermined timing from a paper feed mechanism portion (not shown). Are sequentially transferred to. 5A is a high voltage power source for applying a predetermined transfer bias to the transfer roller 5.

The transfer material 11, which has received the toner image transfer through the transfer portion, is separated from the surface of the rotary photoconductor 2 and introduced into the heat fixing roller pair 7 to undergo the fixing process of the transferred toner image to form an image formed product (printed product). ) Is discharged out of the machine.

After the toner image is transferred onto the transfer material 11, the surface of the rotary photosensitive member 2 is cleaned by the urethane counter blade 61 of the cleaning device 6 to scrape off the residual adhered substances such as transfer residual toner and the next image. It is repeatedly subjected to formation.

In the printer of this example, four process devices including the photoconductor 2, the charging roller 1, the developing device 4, and the cleaning device 6 are arranged in a common cartridge housing in a predetermined manner and are collectively attached to and detached from the printer body. The process cartridge 8 is replaceable. By mounting the cartridge 8 on the printer body in a predetermined manner, the printer body side and the cartridge 8 side are mechanically and predeterminedly coupled in a predetermined state, and an image forming executable state is set.

The photosensitive layer 2a of the photosensitive member 2 is a negatively charged OPC (organic photoconductor) in this example, and a charge transfer layer (Carrier Transfer Layer: d = 25 μm) is formed on the charge generation layer.
A CT layer is abbreviated below) and is applied on the aluminum drum 2b having a diameter of 30 mm. In this example, the CT layer is made of a polycarbonate resin in which a hizorazone-based CT agent is used as a binder, and is gradually scraped due to durable paper passing.

The rotational peripheral speed of the photosensitive member 2, that is, the process speed is 95 mm / sec.

As the charging roller 1, a roller having a conductive rubber layer 1b formed concentrically with a core metal 1c and having a high resistance surface layer 1a formed on the outer periphery thereof was used. The high-resistivity surface layer 1a is used when a low withstand voltage defect portion such as a pinhole occurs in the photoconductor 2.
This is to prevent the charging current from concentrating on this portion and the potential on the surface of the charging roller to drop, resulting in poor charging of the horizontal stripes.

The laser light source of the laser scanner 3 is 7
An 80 nm semiconductor laser is used.

The developing device 4 is of a jumping developing type using a one-component magnetic toner.

A transfer bias of 3 KV is applied to the transfer roller 5.

The above printer configuration is common to all printers of the second to eighteenth embodiments shown below, except for all or some of them.

(2) Method of detecting exposed portion potential V _L of photoconductor 1 (FIGS. 2 and 3) The theoretical calculation of the charging DC current (charging current) required when the surface potential of the photoconductor is changed by Vcontrast is as described above. It is as the formula (1) described in the section of the action.

In the above equation (1), ε, ε0, L, V
Since p and d can be regarded as constants, it can be seen that the charging current I is inversely proportional to d and proportional to Vcontrast.

In this embodiment, ε = 3, ε0 = 8.85 ×
10 ^-12 [F / m], L = 230 mm, Vp = 95 mm / s
The value of ec is used. Further, for simplicity, K = ε · ε0 · L · Vp I = K · Vcontrast / d.

Therefore, in this embodiment, when the surface potential of the photosensitive member is set to V _D by the contact AC charging and the exposed portion potential V _L obtained by performing image exposure on this is charged to V _D again (here In the V1 = V _D), i.e. Vcontrast = potential | V _L -V _D | by measuring the flow by changing the charging DC current I _DC, to detect the exposed portion potential V _L.

In particular, since the potential V _L is stably and instantly converged to the potential V _D by performing the contact AC charging, the present method can perform the measurement with a small error.

In this embodiment, using this value, the potential V _L
Feedback is applied to the exposure amount to keep it constant.

An example of actually outputting an image will be shown below.

The electrophotographic printer shown above is
Although the initial potential setting values are V _D = -700 V and V _L = -150 V, the mobility of the CT layer becomes low in a low temperature and low humidity environment (hereinafter, abbreviated as L / L environment) of 15 ° C x 10% RH. Since it decreases, the sensitivity deteriorates and the voltage increases to _VL = -190V.

As a result, the line width (two-dot line at 300 dpi) set to 190 μm under normal environment became as thin as 170 μm. For this reason, the characters are thinned, and the printed font looks different from the original font, and the image quality is degraded.

Therefore, in the present embodiment, the potential V _{L is} detected during the pre-rotation of printing for non-image formation, and this is corrected.

A concrete sequence is shown in FIG. First,
The surface of the photoconductor is charged to a potential V _D as usual, and the image is exposed to this. As a result, the exposed portion is removed to the potential V _L , but this portion is charged to the potential V _D by passing through the charging section again. At this time, the charging DC current I _DC flowing through the charging roller 1 is a contact charging member is a current for charging the photosensitive member surface to the potential V _L → potential V _D (in FIG. 2, A portion of the current), the If the photoconductor film thickness d is known as shown in the equation (1), it can be obtained.

This value is the potential V that is originally required.
If it is different from the value of _L , the exposure amount is changed, and the control shown in the flowchart of FIG. 3 is performed so that the exposure amount is kept constant regardless of the environment, variations in sensitivity during manufacturing, and the like.

Specifically, for measuring the charging DC current I _DC ,
The DC voltage across the protective resistance (10 kΩ) of the high voltage circuit 1A is measured and a signal is sent to the DC controller. In order to reduce the error in the present embodiment, the measurement in synchronization with the sequence of the printer main body, the drum one rotation of the signal after increasing the exposed portion potential V _L of the photosensitive member subjected to laser exposure to the potential V _D The averaged value is used.

Since the current I _DC needs to be measured upstream of the load for the reason described above, the current is calculated from the voltage across the resistor in the high voltage circuit 1A in this embodiment.

First, in a normal environment (25 ° C. × 65% RH:
Hereinafter, when the above control is performed under the N / N environment), the charging DC current I _DC for setting the potential V _L to the potential V _D is 12.
8 μA flowed. From the equation (1), I _DC = K · Vcontrast
/ D, where d = 25 μm and Vcontrast = | V
_{If L} −V _D | = | _VL − (− 700) |, then _VL = −
Since it can be calculated as 150 V, no special control is performed on the exposure amount.

However, in the L / L environment, when the same measurement was performed, I _DC = 11.8 μA and V _L = -190 V calculated from this. The feedback control of the exposure amount is performed based on the flowchart of FIG.
As a result of changing from 3 μJ / cm ² to 0.2 μJ / cm ² , the exposure amount is 2.6 μJ / cm ^2, which is the same as the N / N environment.
It became possible to obtain a _VL value of 150V. Therefore, when the subsequent image formation is performed by changing the exposure amount to 2.6 μJ / cm ² , the line width can be set to the target value, and the image quality is not deteriorated as in the case where this control is not performed. I was able to prevent it.

Even if the sensitivity is varied during the manufacture of the photoconductor 2, the potential V _L can be kept constant by performing the same control. Therefore, if the present invention is applied to an electrophotographic apparatus, exposure can be performed. The amount of maintenance-free can be realized, and in the case of the cartridge system, the sensitivity frame can be eliminated, and a great effect can be obtained in stabilizing the printing quality and reducing the manufacturing cost.

In addition to the method of continuously changing the exposed portion potential V _L and performing the feedback as described above, several levels of variable levels are provided in advance and the measured potential V _L is lower than the target value. In the case of (for example, when it is lower than 10V), the light amount is increased by 10%, and on the contrary, when it is too high (for example, 10V or more), the light amount is reduced by 10%. It is possible.

<Second Embodiment> (FIGS. 4 to 6) In this embodiment, the same control as in the first embodiment is performed, but V1 = V _D is not the same as in the previous embodiment. V1 = 0V
The purpose is to improve the accuracy of measurement.

Even in the configuration of the first embodiment, it is possible to carry out the measurement without any problem under the normal use condition.
The photoconductor 2 may have pinholes during manufacture or use. As described above, by giving the contact charging member 1 a resistance value, the effect of the pinhole on the image is minimized. However, as shown in FIG. It is unavoidable that a leak current flows into 21 to some extent.

Since it is difficult to separate this leak current from the charging DC current measured to detect the exposed portion potential V _L , there is a possibility of causing a measurement error.

Therefore, in this embodiment, as in the first embodiment, not the current flowing when the surface potential of the photoconductor 2 is charged from V _L to V _D , but the potential V by the charging roller 1 as a contact charging member. The potential when the charge is removed from _L to 0 V is measured ((b) of FIG. 4). In this case, since the potentials of the contact charging member 1 and the pinhole portion 21 are 0V in terms of DC voltage, essentially no leak current flows.

The sequence of measurement in this embodiment will be described below.

The device configuration, conditions, etc. used for the experiment are the same as those in the first embodiment, but the measurement sequence and flow chart are changed as shown in FIGS. 5 and 6, respectively.

The photoconductor 2 is first uniformly charged to the potential V _D by the contact charging member 1 (contact AC charging), and then discharged to the potential V _L by performing image exposure. However, since this potential V _L changes depending on the sensitivity of the photoconductor, the environment, etc., the exposure amount is controlled to correct this.

In the present control, the DC voltage applied to the contact charging member 1 is set to 0V after the photoconductor potential is set to V _L, and the charge is removed to 0V. At this time, the contact charging member 1 is charged with a charging DC current for discharging the photoconductor 2 from the potential V _{L to} 0 V.
It flows for the time corresponding to one lap (B portion in FIG. 5). The current value Vconsrast = in (1) | V _L -0V | because it is a value when a can be determined as now V _L = I _DC / K.

The photoconductor 2 in which the pinhole 21 is actually opened
(Photoreceptor having a sensitivity of _VL = -150V) N /
When measured under N environment, in the first embodiment,
Although the charging DC current includes a leak current flowing into the pinhole and erroneously measured as V _L = −75 V (I _DC = 14.5 μA in the measurement of the first embodiment), this embodiment does. When controlled by the following, I _DC = 3.5 μA (V _L = −1)
It was found that it was possible to prevent erroneous measurement due to a leak current, and a correct value could be measured even if the pinhole 21 was present.

Since the charging DC current that is actually measured is as small as several μA as described above, the influence of the leak current on the measurement is large, and it is possible to perform more accurate measurement by using the method of this embodiment. became.

<Third Embodiment> (FIG. 7) In this embodiment, in order to prevent a factor of an error on the measurement when the photoconductor 1 is scraped by a durable paper feed, the film thickness of the photoconductor 1 is previously set. Is detected, and the potential V _L is corrected according to the detected value.

As in the first and second embodiments, the present invention makes it possible to detect the exposed portion potential V _L irrespective of factors such as the environment, sensitivity fluctuation of the photoconductor during manufacturing, pinholes and the like. Although it has been shown that it is possible to control the exposure amount and correct the potential V _L to a desired value based on this, as can be seen from the above-mentioned formula (1), it is measured in the present invention. Since the charging DC current used for is only I _DC = K · Vcontrast / d, Vcontrast and the film thickness d cannot be separated from the current I _DC . That is, in the previous embodiment, a measurement error occurs when the photoconductor film thickness d changes due to durable paper passing or the like.

Therefore, the film thickness d of the photoconductor 1 is detected in advance. As shown in the flowchart of FIG. 7, first, while applying the AC voltage to the contact charging member 1, the DC voltage is set to V2 and the surface potential of the photoconductor is converged to V2. Next, the DC voltage is changed to V3, and the charging D flowing at this time
Measure the C-current _IDC '. While it is preferred generally to V2 = 0, V3 = V _D because it can simplify the measurement, it is also possible to use different values.

Therefore, this charging DC is calculated by the equation (1).
The current is I _DC ′ = K · Vcontrast / d (Vconyrast = V2-V
3), it is possible to detect the photoconductor film thickness d from here.

Here, in order to eliminate the possibility of erroneous measurement due to the pinhole 21 (FIG. 4) shown in the second embodiment, V _D → 0 V instead of 0 V → V _D when charging. It is also possible to use the current during static elimination, which is preferable in terms of measurement accuracy, as described above.

After the photoconductor film thickness d is measured as described above, the exposure portion potential V _L is detected in the same manner as in the first or second embodiment. However, when calculating the potential V _L from the charging DC current I _DC at this time, correction is performed using the value of the photosensitive layer thickness d obtained in the film thickness detection step. This may be calculated by substituting d for I _DC = K · Vcontrast / d in the equation (1).

An example in which this control is specifically performed by using the method of this embodiment will be shown. An image was output after 8,000 sheets of durable paper were passed. First, it was subjected to sequence of the photoconductor film thickness detector, I _DC to charge from 0V to the V _D '
= 27.0 μA of current flowed. Substituting this into the equation (1), Vcontrast = -700V, so d = 15
It was calculated to be μm, and the correct film thickness could be measured.

Next, when the sequence for detecting the potential V _L of the first embodiment was performed, a current of I _DC = 19 μA flowed. When this value was calculated assuming that the film thickness was 25 μm and the potential V _L was calculated, it was V _L = + 120 V, which was difficult to consider as negatively charged OPC.

However, in this example, when the potential V _L was calculated using the value of the film thickness d = 15 μm which was measured in advance, V _{L was} −200 V.

When an electric potential was actually measured with a measuring instrument in this state, V _L = −200 V, which proved that correct measurement can be performed by this method.

As described above, by using the method of this embodiment, it is possible to accurately detect the exposed portion potential V _L even when the photoconductor film thickness d changes due to durable paper passing or the like. ..

As described above in the first to third embodiments, in the present invention, the contact DC charging is applied to the photoconductor exposed portion potential V _L , and the charging DC flowing when the charging or discharging is performed. It has become possible to detect the potential V _L by measuring the current. Then, it becomes possible to control the exposure means in order to prevent the deterioration of the image quality caused by the fluctuation of the potential V _L due to various factors, and keep the potential V _L constant under any conditions.

This is because the present invention can be realized only by measuring the charging DC current without providing a special means such as a potential measuring device for measuring the potential V _L as in the prior art. It is possible to obtain a highly reliable effect at low cost. Specifically, the maintenance of exposure amount adjustment that was performed when installing the main body of the electrophotographic device becomes unnecessary, and in the cartridge type process unit, it was conventionally provided to convey the sensitivity of each photoconductor to the main body of the device.
It became possible to abolish the so-called "sensitivity frame".

[II] The following fourth to sixth examples are examples of the invention described in claims 9 to 12 of the claims.

<Fourth Embodiment> (FIG. 8) In this embodiment, the charging DC current I _DC and the exposure portion potential V _{L are used.}
The measurement / detection procedure of is the same as that of the first to third embodiments.

[0151] It is possible to know the charging DC current I _DC from the exposed portion potential V _L as described above, the potential V _D instantly stable from the potential V _L by particular make contact AC charging
Since this method converges to, this method can perform measurement with a small error.

Further, since the contact charging method is used, all the current output from the contact charging member becomes the charge amount for charging (eliminating) the photoconductor, and therefore the charging current (eliminating current) can be obtained by simply measuring this current. It is possible to directly detect, and it is not necessary to separate the shield current like a corona charger or to measure the inflow current to the photoconductor that separates the transfer of development etc., and the charging current can be measured very easily. it can.

[0153] Depending on the value of the sensed charging DC current I _DC, in the present embodiment is characterized by changing the DC component Vdev. Of the developing bias applied to the developing roller 41. That is, the DC component Vdev. Is controlled so that the development contrast becomes constant.

The electrophotographic printer described above uses the jumping developing system as described above, and the developing bias is AC component, peak-to-peak voltage 1600 V _PP , frequency 180.
0H _Z DC component Vdev = -. A 500V, initial potential setting value _{V D = -700V, V L =} -
Although it is 150 V, in the L / L environment, the mobility of the CT layer is lowered and the sensitivity is deteriorated, and the V _L is increased to −190 V. As a result, the line width (2 dot line at 300 dpi), which was set to 190 microns under normal environment, became as thin as 170 microns. For this reason, the characters are thinned, and the printed font looks different from the original font, and the image quality is degraded.

Therefore, in this embodiment, the charging DC current I _{DC is} measured during the pre-rotation of printing, and the detected current I
And to adjusting the DC component Vdev. Of the developing bias according to _DC.

The measurement / detection sequence of the charging DC current V _D is the same as that of the first embodiment shown in FIG.

[0157] The detected because it is possible to know the exposed portion potential V _L by the charging DC current I _DC, DC component Vdev of the developing bias in accordance with the value of the sensed current I _DC.
Is controlled so that the contrast for image formation becomes constant, as shown in the flowchart of FIG.

Specifically, to measure the charging DC current I _DC , as described above, the DC voltage across the protective resistance (10 KΩ) of the high voltage circuit 1A is measured and a signal is sent to the controller. In the present embodiment, in order to reduce the error, the measurement is performed in synchronization with the sequence of the main body, and the value obtained by averaging the signals for one rotation of the drum after performing the laser exposure and raising V _L to V _D is used. ..

First, when the above control is performed in the N / N environment, the charging DC current I _DC for setting the potential V _L to the potential V _D
Flowed at 12.8 μA. From the above formula (1), I _DC = K · V _contrast / d, where d = 25 μm, and V _contrast = V _L −V _D = V _L − (− 700 V), V _D = −150 V Development bias DC component Vde
v. remains the default value.

However, in the L / L environment, when the same measurement was performed, I _DC = 11.8 μA, and from this, the exposed portion potential V _L = -190 V. Therefore, V _dev. Is set to −540 V by calculation based on the flowchart of FIG. 8 so that the contrast for image formation is 350 V, similar to the N / N environment. Therefore, as a result of the subsequent image formation, the line width can be set to a target value, and it is possible to prevent the image quality from being deteriorated as in the case where this control is not performed.

The same control can be performed to maintain a constant contrast for image formation even when variations in sensitivity occur during the manufacture of the photoconductor.

<Fifth Embodiment> (FIG. 9) This embodiment is similar to the fourth embodiment in that the charging DC current I _DC
Performs measurements in accordance with the value of the sensed current I _DC, the AC component of the developing bias of the jumping development frequency Vdev.
f is changed. The change in the charging DC current I _DC , that is, the change in the line width due to the change in the exposed portion V _L is represented by the frequency V
It is corrected by adjusting dev.f.

The printer as the image forming apparatus is the same as the printer of the first embodiment (FIG. 1), and N / N
The initial potential setting value under the environment is V _D = -700 V, V _L =
-150V, but under the L / L environment, _VL = -190
Rise to V.

[0164] Therefore performs detection of the charging DC current I _DC before the time of rotation of the print in the present embodiment, the detected I _DC
The frequency Vdev.f is adjusted according to the value.
The method of measuring the charging DC current I _DC is the same as in the fourth embodiment.

Specifically, the control shown in the flow chart of FIG. 9 is performed. Actual current I _DC under N / N environment
As a result of detection, I _DC = 12.8 μA (V _L = −150 V), so the AC component Vdev.f (= 1 of the developing bias).
800H _Z) adjustment is not made to.

However, in the L / L environment, I _DC = 11.8 μ
Because it became A (V _L = -190V), and adjust the Vdev.f reference to a flowchart of FIG. 9, 1 from 1800H _Z
It was changed to 700H _Z. This is derived from a table showing the relationship between the I _DC value and Vdev.f, which has been obtained through experiments in advance.

Therefore, Vdev.f is set to 1 for the subsequent image formation.
Was carried out by changing the 700H _Z, can be a line width value of the target, it was possible to prevent deterioration of image quality.

<Sixth Embodiment> (FIG. 10) In this embodiment, the DC voltage of the charging bias applied to the contact charging member 1 according to the value of the detected charging DC current I _DC (hereinafter, V _{C · DC} ). It is characterized by controlling. That is, V _{C · DC} is controlled according to the detected current I _DC , and the result V _D
To be fed back to the desired current I _DC .

The printer used in this embodiment is the same as the printer used in the first embodiment (FIG. 1), and the initial potential setting values under N / N environment are V _D = -700 V and V _L =-.
It is 150V, but under the L / L environment, _VL = -190V
Rise to.

Therefore, in this embodiment, the current I _{DC is} detected during the pre-rotation of printing, and V _{C · DC} is adjusted according to the detected current I _DC .

The method of measuring the current I _DC is different from that in the fourth embodiment, and the charging DC current I _DC flowing when the charge is removed from the potential V _L to 0 V is determined.

Specifically, the portion B of the sequence is measured in the same manner as the sequence of FIG. 5 described in the second embodiment.

This current value is Vcontrast = Equation (1)
Since it is a value when | _VL- 0 |, _VL = d.I _DC
/ K can be obtained.

When the value of the current I _DC thus detected is different from the desired value of I _DC , V _{C · DC} is changed according to the value of the detected I _DC , and thus V _D Is changed and the control as shown in the flowchart of FIG. 10 is performed so that the desired I _DC is obtained.

When the current I _DC was actually detected in the N / N environment, I _DC = 3.5 μA (V _L = −150 V) was obtained. Therefore, a special value for V _{C · DC} (= −700 V) was obtained. No adjustment is made.

However, in the L / L environment, I _DC = 4.5 μA
Since ( _VL = -190V), feedback control of VC _{/ DC} was performed based on the flowchart of FIG. As a result of changing the initial value of −700 V (= V _D ) by 10 V, the same value as −600 V in the normal environment I _DC = 3.5 μA
(V _L = −150 V) can be obtained.

Therefore, in the subsequent image formation, V _{C · DC is set} to −6.
When the line width was changed to 00V, the line width could be set to a target value and the deterioration of image quality could be prevented.

In the above fourth to sixth embodiments, the DC voltage of the developing bias, the AC component frequency of the developing bias, and the charging bias are set as the electrophotographic process conditions which are changed according to the value of the detected current I _DC. However, the peak-to-peak voltage V _PP of the AC component of the developing bias may be used. A combination of the above is also possible. Further, the developing conditions such as the speed of the developing roller against the photosensitive drum, the gap between the photosensitive drum and the developing roller, and the setting of the developing blade can be selected as other conditions.

As in the above fourth to sixth embodiments, in the present invention, contact charging is performed with respect to the photoconductor exposed portion potential V _L , and charging (discharging) that flows when charging or discharging is performed. By measuring the DC current I _DC and changing various image forming process conditions (electrophotographic process conditions) according to the value of the detected charging DC current (static elimination), the exposed portion potential V due to various factors. _It is now possible to easily prevent deterioration of image quality caused by _L fluctuations at low cost.

[III] The following seventh to tenth examples are examples of the invention described in claims 13 to 19 of the appended claims.

<Seventh Embodiment> (FIG. 11) The configuration of the printer as the image forming apparatus in this embodiment is the same as that of FIG. 1 of the first embodiment. However, in this embodiment, the thickness d of the charge transport layer (CT layer) of the photosensitive layer 2a of the photoconductor 2 is 23 μm, and the process speed is 47.7 mm / sec. The transfer roller 5
The transfer bias with respect to is set to 2 kV.

The method of detecting the exposed portion potential V _L of the photosensitive member is the same as that described in the first embodiment. However, in this embodiment, the effective charging width L of the contact charging member (charging roller) 1 is 270 mm, and the process speed V _P is 47.7 mm / sec as described above.

In this embodiment, in contact AC charging, a DC voltage of -600V was applied to the surface of the photoconductor to set the surface potential V _{1 of the} photoconductor to -600V. Then, image exposure was performed to set the surface potential (exposed portion potential) _VL of the photoconductor to -120V. Furthermore,
And direct current voltage -600V applied to the photoreceptor surface to detect a V _L by measuring the charging DC current I _DC flowing when the surface potential of the photosensitive member was changed from V _L to V _1.

At this time, it is necessary to prevent the charging roller 5 as a transfer member from affecting the photosensitive member surface potential V _L.

The effect of the transfer roller 5 on the potential V _L will be described with reference to FIG.

A switch 101 is connected to the first contact 102 of the transfer roller 5 at the time of image formation, and a transfer bias of 2 kV is applied from the first transfer bias power source 5A. Even when the potential _{VL is} detected, if the same transfer bias of 2 kV as that used in image formation is applied, the surface potential of the photoconductor is charged (charge elimination), and the influence on the exposed portion potential _VL cannot be ignored.

When the fluctuation of the exposed portion potential V _L due to the mounting via the transfer roller 5 is actually examined, the exposed portion potential V _L before reaching the transfer roller is −12 which is substantially the set value.
While it was 0.2 V, the exposed portion potential V _L after passing through the transfer roller was −102.6, which was a measurement error of 17.6 V.

Therefore, in this embodiment, in order to avoid the influence of the transfer roller 5 on the exposed portion potential V _L , when the charging DC current I _DC is measured, the switch 101 of FIG.
It was decided to switch to the contact 103 and apply a transfer bias equivalent to the exposure part potential _VL (-120 V in this embodiment) by the second power supply 5B.

In order to distinguish the transfer bias by the second power source 5B applied to the transfer roller 5 at the time of measuring the potential V _L from the transfer bias by the first power source 5A applied to the transfer roller 5 at the time of image formation, It will be referred to as "transfer bias at the time of detecting V _L ".

[0190] As a result, the transfer current Itr the V _L detected during the transfer bias when the exposed portion potential V _L (-120 V set value) that becomes substantially 0 (.mu.A) was confirmed.

[0191] Desirably, as in the present embodiment, even if it is to the I _DC measurement transfer bias to the same potential as the set value of the exposed portion potential V _L, a V _L detected during the transfer bias to 0V, and measuring Since the transferred transfer current Itr was about 0 μA, it was at a level that had almost no influence on the measurement error for the detection of the photoconductor film thickness d or the detection of the exposed portion potential _VL .

[0192] Indeed, V by measuring the charging DC current I _DC measurement method using I _DC measurement transfer bias to the exposed portion potential V _{L L}
I asked. After the durability test of 6000 sheets, V contrast (=
| Measured) to flow charging DC current I _DC, | V _L -V1
When V1 was calculated based on Vcontrast calculated from the above formula (1), it was -140.9V, and the photoreceptor surface potential at _VL measured by a surface potential meter was -139.9V.

[0193] Therefore, measurement was performed similar to the case of 2.2μJ / cm ² by gradually changing the exposure amount from 2.0μJ / cm ^2, was determined from V contrast of the (1) formula V
_L is for -120.3V, V _L was measured with a surface potential meter
Was 120.6 V, which was almost the same.

Further, the exposure amount is controlled in the same manner as the sensitivity frame, and if the error is within ± 15 V with respect to the set exposure portion potential V _L , the exposure amount is 2.0 μJ / cm which is the initial setting value.
Leave ^{2, 2.2μJ} / cm ² exposure amount in case of error is -15 to-30 V, even by the exposure to 1.8μJ / cm ² in the case of error is +. 15 to + 30 V, conventional It became possible to maintain the same image quality, and it became a simple control method.

[0195] Thus, by measuring the I _DC measured transfer bias and equal to the exposed portion potential V _L charging DC current I _DC, the exposed portion potential V _L can be accurately obtained, the surface potential is stabilized It is now possible to always maintain a stable potential V _L without requiring a large device for controlling the exposure amount to obtain it.

As a result, the line width can always be set to the target value, and it is possible to prevent the deterioration of the image quality which would occur when this control is not performed.

If sensitivity variations occur during the manufacture of the photosensitive member, the same control is performed to make the exposed portion potential V _L
Therefore, if the present invention is applied to an electrophotographic apparatus, maintenance-free exposure can be realized.
In the case of the cartridge system, the sensitivity frame can be eliminated, and a great effect can be obtained in stabilizing the print quality and reducing the manufacturing cost.

<Eighth Embodiment> (FIG. 12) This embodiment performs the same control as that of the seventh embodiment, but in this embodiment, a countermeasure is taken on the electric circuit so that the transfer current Itr does not flow. Is taken.

That is, in FIG. 12, only when the charging DC current I _DC is measured, the circuit in which the switch 101 is connected to the contact 104 on the float side is used to stop the flow of electric charge, and to prevent the transfer roller 5 and the photosensitive member. By making the two surfaces have the same potential, the transfer current Itr is prevented from flowing.

This method is easy to handle because it is only switched on the circuit. Also, as in the case of the seventh embodiment, I
_{Since the DC} measurement transfer bias is not required, it has a feature that the configuration is simple.

In this method, the charging DC current I _DC after the durability test of 6000 sheets was actually measured, and V contras of the above formula (1) was measured.
When the exposed portion potential V _L was calculated from t, the exposure amount was 2.0
.mu.J / cm Under ² is -141.2V, when V _L measured at surface potentiometer photosensitive member surface potential -139.9V
It was possible to measure within an error range of 1% or less.

After that, when the exposure amount was controlled in the same sequence as in the seventh embodiment, the same result was obtained. Therefore, even when the method of this embodiment is used, the exposure portion potential V
It is possible to detect _L accurately and maintain a stable exposed portion potential _VL .

<Ninth Embodiment> (FIG. 13) This embodiment is characterized in that the charging DC current I _DC is measured when the transfer roller 5 is separated from the surface of the photosensitive member 2.

The structure is as shown in FIGS. 13 (a) and 13 (b). At the time of transfer, as shown in (a), the transfer roller bearing member 14 of the transfer roller 5 is pushed in the direction of arrow a due to the electric field effect of the solenoid 12, and contacts the surface of the photoconductor 2 for transfer. At the time of measuring the partial potential V _{L, the} electric field by the solenoid 12 is stopped as shown in (b), and the transfer roller 5 is pulled in the direction of arrow b by the spring 13 and separated from the surface of the photoconductor 2.

The transfer roller 5 is measured for the charging DC current I _DC.
Is carried out when the transfer roller 5 is separated from the surface of the photosensitive member 2, and when the transfer roller 5 is separated from the surface of the photosensitive member 2, the transfer roller 5 can completely prevent the surface potential change of the photosensitive member 2. The advantage is that it can be incorporated into the current sequence.

V contrast (= | V _L − in the above equation (1)
Potential V _L based on the DC current I _DC flowing according to V ₁ |)
Is detected, and a sufficient flow for controlling the exposure amount to correct the electric potential V _L to the set value is satisfied, so that a sufficient time for controlling the sheet interval cannot be obtained. However, the charging DC current I _DC was measured during the previous rotation because the exposure amount cannot be controlled.

Actually, during the pre-rotation, the exposed portion potential V _L is detected, the transfer roller 5 is separated from the surface of the photosensitive drum 2, the charging DC current I _DC is measured, and the potential V _L is calculated based on the equation (1). Calculated. The exposure amount was 2.0 μm when measured with a cartridge that was durable for passing 6,000 sheets as in the eighth embodiment.
V _L calculated at J / cm ² was -140.3 V, and the surface potential of the photosensitive member at V _L measured by a surface potential meter was −
Only a slight difference with 139.9V was observed. Further, when the exposure amount was controlled in the same manner as in the seventh embodiment, the exposure portion potential V _{L according} to the set value could be obtained.

Therefore, when the charging DC current I _DC is measured, the transfer roller 5 is separated from the surface 5 of the photoconductor, so that the measurement can be performed accurately without being affected by the transfer roller 5, and the exposure portion potential V It has become possible to detect _L and further maintain this potential V _L stably.

<Tenth Embodiment> In this embodiment, in order to accurately measure the charging DC current I _DC even when corona transfer is used as the transfer member 5 in FIG.
This is a method in which the transfer bias is always turned off when the charging DC current I _{DC is} measured.

At present, corona transfer is shifting to roller transfer due to the same problem of ozone generation as corona charging, but it is desired to maintain stable transfer on high speed machines, large machines, etc.
Alternatively, in the case of corona transfer in which a voltage of 5 to 7 kV is applied, but in the case of positive discharge, corona transfer may be performed because ozone is not generated as much as in the case of negative discharge corona transfer in which a voltage of the same level is applied. There were many.

In the case of corona transfer, the surface potential of the photoconductor 2 changes due to discharge during transfer, and V c
This will cause an erroneous measurement in the ontrast (= V _L ) measurement. In order to avoid this erroneous measurement, the transfer bias is always turned off when the exposed portion potential _VL is detected, thereby preventing the positive charge of corona transfer from affecting the negative charge on the surface of the photosensitive drum.

When actually detecting the potential V _L , Vcontrast (= | V _L when the transfer bias is on and when the transfer bias is off)
−V ₁ |) is obtained from the equation (1), and the potential V
Was calculated _L, and the contrast is measured by the cartridge at the time of the unused V _L in a state of turn on the transfer bias in the original exposure 2.0μJ / cm ² was -101.7V, V _L in the state where the transfer bias was turned off was -120.2 V, which was a value as set.

If V _L is detected while the transfer bias is turned on, it will be read if the exposure amount is too large, and the exposure amount will be 1.84 μm in order to reach the set value of −120 V.
Although it has to be changed to J / cm ² , the true V _L is −143.2 V under the exposure amount, and the line quality of the resulting image is confirmed to be thin.

However, when the transfer bias is turned off, the true exposed portion potential V _L can always be detected stably, and therefore deterioration of image quality such as line thinning is not recognized, and V _L detection is not possible. It was confirmed to be an extremely effective means.

As described in the seventh to tenth embodiments, in the present invention, the contact AC charging is applied to the photosensitive member exposure portion potential V _L , and the DC current flowing when charging this is measured. In addition, it is possible to prevent the influence of erroneous measurement due to the transfer member. As a result, V _L due to various factors
It has become possible to control the exposure means in order to prevent the deterioration of the image quality caused by the fluctuation, and to keep V _L more accurately and constant under any conditions.

This is the same as the conventional one, such as the potential measuring device V _L.
It is possible to obtain a highly reliable effect only by measuring the charging DC current without providing any special means for measuring. Specifically, the maintenance of the exposure amount adjustment, which was performed when the electrophotographic apparatus main body was installed, becomes unnecessary, and in the cartridge type process unit, the so-called conventionally provided so as to convey the photoconductor sensitivity to the apparatus main body. It became possible to abolish "sensitivity frame".

[IV] The following eleventh and twelfth examples are examples of the invention described in claims 20 to 23 of the claims.

<Eleventh Embodiment> (FIGS. 14 to 18) The construction of the printer as the image forming apparatus is the same as that of the first embodiment shown in FIG.

Next, the method of detecting the photoconductor film thickness in this embodiment will be described.

To carry out contact AC charging of the photosensitive member 2, the AC voltage is superimposed on the DC offset voltage on the charging roller 1. As the DC voltage, V3 = -700V corresponding to the desired dark portion potential of the photoconductor is used.

As the AC voltage, a constant peak-to-peak voltage of 1800V is used in this embodiment because a peak-to-peak voltage that is at least twice the discharge start voltage Vth is required to converge the potential. With respect to this voltage, it is also possible to perform AC constant current control in order to eliminate the influence of the impedance change of the charging member 1.

In the electrophotographic process, as a pretreatment for forming an image, it is general to remove the charge during the pre-rotation in order to remove the potential history of the photoconductor 2. As the charge eliminating means, pre-exposure can be performed, but contact A
When C charging is performed, the potential of the photoconductor can be set to 0V by utilizing the convergence property of the potential and setting the DC voltage to V2 = 0 and superimposing the AC voltage.

Next, in order to form an image, the DC offset voltage is set to V3 = V3 = in this embodiment as shown in the sequence of FIG.
The charging is performed at -700. At this time, the DC charging current required to raise the surface potential of the photoconductor by Vcontrast flows for one revolution of the photoconductor as shown in FIG.
After being charged to −700 V, the charging DC current does not flow unless there is a change in the surface potential of the photoconductor (ignoring dark decay and the like without performing image exposure).

However, since the transfer roller 5 is in contact with the photoconductor 2, the voltage applied to the transfer roller 5 charges or discharges the photoconductor drum 2, thus changing the surface potential of the photoconductor.

Therefore, it is necessary to control the voltage applied to the transfer roller 5 only for one round of the photosensitive member when the charging DC current is detected. Here, in order to prevent the transfer roller 5 from charging or discharging the photoconductor 2, the voltage V applied to the transfer roller 5
The difference between tr and the surface potential V2 of the photoconductor 2 may be set to be equal to or lower than the voltage Va at which the transfer roller 5 starts charging the photoconductor 2.

When the transfer roller 5 is made of a medium resistance material having a specific resistance of 10 ⁸ to 10 ¹⁰ Ωcm, Va is about 800 V, and therefore | Vtr−V ₁ | ≦ 800.
Since V2 = 0V, −800 ≦ Vtr ≦ + 800.

In the above description, V2 = 0V is changed to V3 = -80.
Although the case of detecting the DC current flowing at the time of charging to 0V has been performed, the same detection can be performed in the case of discharging V2 = -700V to V3 = 0V. In that case V
Since 2 = −700V, −1500 ≦ Vtr ≦ + 100.

Since any of the above values of Vtr is considerably different from the actual transfer voltage (about +4 kV), it is necessary to set another voltage value for the detection of the present invention. In particular,
If Vtr = 0V, it is not necessary to separately set the applied voltage value, and the output may be simply turned off or floated.

The above description will be described with reference to the sequence diagram of FIG. 14. V2 = 0, V3 = -700
In the case of charging, Vtr is applied to the transfer roller 5 for one round of the photoconductor earlier than the start of the DC current detection by the time T1. Here, T1 is the time required for a certain position on the drum to move from the transfer position to the charging position. V2 = -70
The same can be considered for static elimination at 0 and V3 = 0.

Up to now, only the transfer roller 5 has been described as a means for changing the photoconductor potential.
When a separation charger for separating the paper is provided, it is necessary to perform the same control for this as well.

Regarding the above equation (1), in this embodiment, ε =
3, ε0 = 8.85 × 10 ⁻¹² [F / m], L = 230 mm,
Since Vp = 95 mm / sec and V _D = 700 [V], d =
When 25 μm, I = 16 μA.

Actually, by using the photoconductors 2 having different film thicknesses,
H / H environment), N / N environment, L / L environment d-
The result of measuring the relationship of I is shown in FIG. Even if this is seen, it turns out that the relationship of d-I does not depend on environment according to theory.

On the basis of this result, means for warning the drum life is provided when the current amount corresponding to the CT film thickness of 15 μm, which is considered to be the life of the photoconductor 2, is exceeded.

In FIG. 17, since the current amount I required for charging is 27 μA when the film thickness is 15 μm in each environment, the voltage V generated across the resistor R1 of 10 kΩ is 27 μA due to I as shown in FIG. When the corresponding voltage exceeds 0.27V, the warning light on the front of the printer body linked to this will be turned on.

Specifically, the protection resistor (10 k
Ω) The voltage V across R1 is the reference voltage Vref = 0.2
Compared with 7V, D when the output of comparator 15
A drum life signal is sent to the C controller 16.

In this embodiment, the voltage V is synchronized with the sequence of the main body, and the DC offset voltage is changed from 0V to V _D.
The value obtained by averaging the signals for one rotation of the photoconductor after being raised to 1 is used (see FIG. 15).

When an endurance test was actually carried out, V rose due to endurance paper passing, 10,000 sheets were passed in each environment,
A warning is issued when the CT layer is scraped by 10 μm and the remaining 15 μm, and it is possible to prevent the occurrence of image defects due to excessive scraping.

In addition, since the present embodiment is of the contact charging type, all the current flowing through the charging member 1 becomes the amount of charge for charging (eliminating) the photoconductor 2. Therefore, the charging current (eliminating charge) can be measured only by measuring this current. Current) can be detected directly,
There is no need to separate the shield current as in a corona charger or to measure the inflow current to the photoconductor in which development and transfer are separated, which is very simple.

Although the transfer roller 5 is described as the transfer device in this embodiment, the same applies to the case where a block-shaped transfer device or a belt-shaped transfer device is used.

<Twelfth Embodiment> (FIG. 19) The contact transfer method was described in the eleventh embodiment. In this embodiment, a corona transfer charger 51 was used as a transfer device as shown in FIG. Describe the case.

Also in this embodiment, the method of detecting the film thickness of the photoconductor is carried out in substantially the same manner as in the eleventh embodiment.
The difference from the above embodiment is that the voltage Vtr applied to the corona transfer charger 51 only when the charging DC current is detected is set to the corona discharge starting voltage Vb or less. The sequence is the same as that shown in FIG. Further, similarly to the eleventh embodiment, the current may be detected during charging or static elimination.

Further, the voltage Vtr may be 0V, and in this case, it is not necessary to set another voltage for the detection of the present invention, and the applied voltage may be simply turned off.

In this embodiment, only the corona transfer charger 51 has been described as a means for changing the photosensitive member potential, but when the separation charger for separating the paper from the photosensitive member 2 is provided, It is necessary to perform the same control for this as well. In that case, the voltage V _SP applied to the separation charger is applied.
Is equal to or lower than the corona discharge starting voltage Vb, or when the grid is provided, the grid voltage Va is preferably equal to the surface potential V2 of the photoconductor 2.

As described in the eleventh and twelfth embodiments above, in the present invention, in the image forming apparatus having the transfer device to which the contact AC charging is performed and the voltage is applied, the charging potential of the member to be charged is kept constant. Vcontrast amount Vcontrast Measures the DC current flowing through the contact charging member at the time of charging or discharging, and by controlling the transfer voltage at the time of measuring this DC current, the charging potential of the photoconductor is not changed, so that the charged object is accurate. It was possible to measure the film thickness of. By giving a warning when the film thickness is below a certain value, it becomes possible to prevent the occurrence of image defects in electrophotography.

This method is different from the conventional method of measuring the DC current flowing to the ground side of the photoconductor, and since the DC current flowing to the charging member is measured, only the current contributing to charging can be measured with high accuracy. .. Further, since it is not necessary to provide any special means for measuring the film thickness, it is possible to obtain a reliable and high effect at low cost.

[V] The thirteenth to fifteenth embodiments below are the embodiments of the invention described in claims 24 to 30 of the claims.

<Thirteenth Embodiment> (FIG. 20) FIG. 20 is a schematic view of the essential portions of the printer of this embodiment.
In this embodiment, a high voltage power source 1A ₁ applied to the charging roller 1 in the primary bias high voltage circuit 1A during image formation is applied.
And a high-voltage power supply A ₂ that is applied at the time of current detection.

At the time of image formation, the switch S in the high-voltage circuit 1A for the primary bias is in the A side, and the high-voltage circuit 1A ₁ on the A side works in conjunction with the developing bias and changes the density volume to change the charging voltage V _D = It changes in the range of -650 to -750V.

On the other hand, at the time of current measurement, the switch S in the primary bias high-voltage circuit 1A is switched to the B side to set the voltage applied to the charging roller 1 to a constant DC voltage V _M , regardless of the change of the density volume. The charging DC current I _DC can be measured.

Specifically, for measuring the charging DC current I _DC ,
D at both ends of the protection resistor R2 of the primary bias high voltage circuit 1A
Measure the C current. In order to reduce the error in the present embodiment, the measurement in synchronization with the sequence of the main body, when raising the exposed portion potential V _L after laser exposure to the potential at the constant DC voltage V _M applied, the photosensitive member rotation min The value obtained by averaging the signals of is used.

When the charging DC current was actually measured, I _DC = 11.6 to 13.9 by changing the density volume when measured with the applied voltage during image formation.
The charging DC current, which had fluctuated to μA, was I _DC = 12.8 μA by switching to the DC constant voltage, and it was possible to measure regardless of the F value.

From now on, by performing this control,
It has become possible to realize a simple measuring device that is not affected by changes in the F value, and it has been possible to eliminate the complexity and cost of the measuring device for changing the concentration volume.

<Fourteenth Embodiment> (FIGS. 21 to 23) FIG. 21 is a conceptual diagram of a density volume which is an essential part of the printer of this embodiment, and FIG. 22 is a developing bias voltage when the density volume is changed. It is a conceptual diagram of control of V _DC and charging potential V _D.

First, when the user changes the density volume 60, the amount of change is converted by the A / D converter 61. Next, the CPU 62 calculates the developing bias voltage and the charging voltage according to the change amount, and the control signal is sent to the respective high voltage power supplies 1A and 4A through the D / A converter 63. Then, a voltage in which the development contrast and the reverse contrast are adjusted is applied, and the image density and the image line width desired by the user are obtained.

On the other hand, in order to measure the charging current, the voltage applied during image formation and the voltage applied during measurement are measured by the CPU 6
Use the control signal from 2 to switch.

Specifically, according to the density volume set by the user at the time of image formation, 1 at the time of measuring the charging DC current.
The CPU is controlled so that the charging voltage of the next bias power source 1A becomes a constant DC voltage V _M.

FIG. 23 shows a current measurement sequence. As shown, the V _D combined primary DC bias on the concentration volume when coming out of the image signal, in the non-image-forming to a constant charging voltage V _M. During the detection period of the charging DC current, the charging voltage V _M
The accuracy is improved by taking one rotation of the photosensitive member after the start of applying the voltage and averaging the measured values during that period.

When the charging current was actually measured, the charging DC current was fluctuated as I _DC = 15.1 to 17.4 μA by changing the density volume when measured with the applied voltage during image formation. By switching to DC constant voltage, I _DC = 16.2 μA, which was measurable regardless of F value.

By performing this control from this, F
It is possible to realize a measuring device that is not affected by changes in values,
It was possible to eliminate the complexity and cost increase of the measuring device for changing the concentration volume.

<Fifteenth Embodiment> (FIG. 24) In this embodiment, the film thickness of the photosensitive member is detected by utilizing the contact transfer member (transfer roller) 5, and FIG. ..

This printer transfers a toner image onto a transfer material by applying a bias to the roller-shaped conductive contact transfer member 5 and applying pressure thereto. Since the transfer roller 5 is in contact with the photoconductor 2 when the transfer material is not present, it is possible to detect the film thickness d of the photoconductor 2 using this.

In the printer of this embodiment, in order to transfer a toner image well regardless of various kinds of transfer materials, the back surface of the transfer material is given a certain charge or more. As the method, the bias condition applied to the transfer roller 5 is constant current control. Further, the transfer voltage is positive because it is reversal development, and since the OPC photoconductor 2 used in this embodiment is negative and has positive carriers, the photoconductor 2 has a low resistance to the positive voltage.

Therefore, since the applied bias changes depending on the resistance of the transfer roller 5 and the transfer material, Vco in the equation (1) is changed.
Since ntrast is not determined and the positive bias does not satisfy the relation of I = K · Vcontrast / d in the equation (1),
It was impossible to detect the film thickness with the current transfer bias.

Therefore, in the present embodiment, at the time of measuring the current for detecting the photoconductor film thickness, the voltage applied to the transfer roller 5 is switched from the positive current control at the time of image formation to the negative constant voltage to enable the measurement.

To specifically measure the transfer current, the bias of the transfer roller 5 is electrically switched to the constant voltage side (the high-voltage circuit 5A in FIG. 24 is the switch B side) during non-image formation. The bias of the transfer roller 5 is primary charging as well as _{AC = 1800v pp, 550H Z,} DC = -70
The DC current across the protection resistor R1 of the high-voltage circuit 5A was measured with AC + DC fixed bias of 0V.

When actually measured, the DC current, which could not be measured when the control of this embodiment was not performed (switch A side in FIG. 24), was caused by applying the above constant voltage. By controlling, I _DC = 16.2 μA, and the film thickness d = 25 μm was calculated from the equation (1). The film thickness of this photoconductor 1 was measured to be 25 μm, which proved that the measurement under the control of this embodiment was correct.

From this, the film thickness measurement at the transfer roller 5
It became possible by performing the control in this embodiment.

As described in the thirteenth to fifteenth embodiments, in the present invention, the contact charging member is used to measure the DC current flowing when the charging potential of the member to be charged is Vcontrast charged or discharged. In this case, by making the applied voltage constant regardless of the settings of the electrophotographic process, it is possible to suppress the complication of the measuring device for dealing with the difference in the process settings, and to expose the exposed portion potential _{VL of the} charged body and the film. It has become possible to measure the thickness d at low cost.

[VI] The sixteenth to eighteenth embodiments below are the embodiments of the invention described in claims 31 to 36 of the claims.

<Sixteenth Embodiment> (FIG. 25) FIG. 25 is a schematic view of a main part of a printer of this embodiment.
The present embodiment is characterized in that the primary bias high-voltage circuit 1A applied to the charging roller 1 has a circuit for measuring the DC voltage V _D , which is the charging potential, and a circuit for measuring the charging DC potential I _DC .

The voltage V _D, which is the DC component of the primary bias, changes in the range of V _D = -650 to -750 V with the change of the density volume in conjunction with the developing bias. Therefore, Vcontrast in the equation (1) is not determined, and the charge D
Only measures the C current I _DC, it was not possible to correctly detect the thickness d · exposed portion potential V _L of the photosensitive member.

Therefore, when measuring an image, the switch in the high voltage circuit of the primary bias is put on the A side to measure the DC voltage V _D, and when measuring the current, the switch is switched to the B side to protect the high voltage circuit of the primary bias. The DC voltage across the resistor R3 is measured to calculate the charging DC current I _DC . Using the thus measured V _D and the charging DC current I _DC , the film thickness d of the photosensitive member and the exposed portion potential V _L are detected from the above formula (1).

An example in which the film thickness d is detected is shown as an example of actual measurement.

The charging DC current I _DC when increasing the potential from 0 V after charge elimination to the potential when V _{D was} applied using a photoconductor having a known film thickness (d = 25 μm) was measured and found to be I according to the concentration volume. _DC = 15.1-17.4 μA is measured. Film thickness by the film thickness d = 23.3~26.9μm and the downside was calculated to a typical value of V _D = -700V does not know the value of V _D when you try to operations not detect the V _D has changed. Therefore, this control was performed, V _D was measured, and then the switch was switched to measure the charging current I _DC , and calculation was performed. As a result, the film thickness d = 25 μm was detected regardless of the lower value.

From this, by performing this control,
It has become possible to correctly detect the status of the photoconductor according to the difference in various settings of the electrophotographic process due to the change of the density volume.

<Seventeenth Embodiment> (FIGS. 26 and 27) FIG. 26 is a schematic view of a main part of a printer of this embodiment.
The printer of this embodiment uses contact AC charging.
The developing bias high voltage circuit 5A is characterized by having a circuit for measuring a DC voltage.

During image formation, the DC voltage V of the developing bias
_DC is linked to the DC voltage V _D of the primary bias high-voltage circuit 1A, and the developing voltage V _DC = −400 to −600 V and the primary bias DC voltage V _D = −650 to −750 V in the range shown in FIG. It changes like.

On the other hand, when measuring the current, the DC voltage V _DC of the developing bias applied to the developing roller 41 is measured with a voltmeter,
V _D is detected from the relationship between the measured value of the developing voltage V _DC and FIG. And at the same time calculates the charging DC current I _DC from the voltage across the protective resistor R3 of the primary bias measured by voltmeter, the I _DC and V _D of the used (1) the thickness d of the photosensitive member from the equation, the exposure The partial potential V _L is detected.

Specifically, in order to measure the charging DC current I _DC , as shown in FIG. 26, the DC voltage across the protection resistor R3 of the primary bias high voltage circuit 1A is measured and calculated. In addition, in this embodiment, in order to reduce the error, the measurement is performed in synchronization with the sequence of the main body by the photosensitive member when the potential V _L of the exposed portion after laser exposure or the potential 0 V after static elimination is increased to the potential when V _{D is} applied. A value obtained by averaging the signals for one rotation is used.

An example in which the exposure potential V _L is detected is shown as an example of actual measurement. It is measured and the charging DC current I _DC = 11.6~13.9μA accordingly by changing the concentration volume. The value of V _D was calculated in the remains of the representative value V _D = -700V, V _L has changed by V _L = -100~-200V and the F value.

Therefore, by carrying out this control, the developing voltage V _DC was measured at the same time as the charging current measurement, and V _D calculated from this was calculated, and V _L = −150 V, which was detected regardless of the F value.

As a result, by performing this control, it is possible to correctly detect the status of the photoconductor in accordance with the difference in various settings of the electrophotographic process due to the change of the density volume.

<Eighteenth Embodiment> (FIG. 28) FIG. 28 is a conceptual view of a density volume which is a main part of the printer of this embodiment.

First, when the user changes the density volume 60, the amount of change is converted by the A / D converter 61. Next, the CPU 62 calculates the developing bias voltage and the charging voltage according to the change amount, and the control signal is sent to the respective high voltage power supplies 1A and 4A through the D / A converter 63.
Then, a voltage in which the development contrast and the reverse contrast are adjusted is applied, and the image density and the image line width desired by the user are obtained.

Therefore, in the present embodiment, a signal for sending the change amount of the density volume from the A / D converter 61 to the CPU 62,
Alternatively, the control signal sent from the CPU 62 to the D / A converter 63 is read, and the DC voltage V _D applied during charging is detected from this value.

However, FIG. 28 shows an example in which a signal sent from the A / D converter 61 to the CPU 62 is read.

[0287] The thickness d of the photosensitive member from the charging DC current I _DC measured simultaneously using the value of the DC voltage V _D, to detect the exposed portion potential V _L.

By carrying out such control, as in the sixteenth and seventeenth embodiments, even if there are changes in various settings of the electrophotographic process due to changes in the density volume, the status of the photoconductor is correctly detected. It has become possible.

As in the sixteenth to eighteenth embodiments,
In the present invention, when measuring the DC current flowing when the charging potential of the member to be charged is charged by a constant amount Vcontrast by using the contact charging member, the DC voltage applied to the contact charging device corresponding to the charging potential is detected in advance. By providing a means for calculating the photoconductor film thickness and the exposed portion potential _VL by using the voltage value, the film thickness of the charged body and the exposed portion potential _VL are changed even if various settings of the electrophotographic process are changed. It became possible to measure _L correctly.

[0290]

According to the present invention, the charging DC current that flows when the contact AC charging is applied to the exposed portion potential V _L of the member to be charged (photosensitive member) as the image bearing member, and the charging or discharging is performed. It has become possible to detect the potential V _L by measuring. Then, it becomes possible to control the exposure means in order to prevent the deterioration of the image quality caused by the fluctuation of the potential V _L due to various factors, and keep the potential V _L constant under any conditions.

This is because the present invention can be realized only by measuring the charging DC current without providing a special means for measuring the potential V _L such as a potential measuring device as in the prior art. It is possible to obtain a highly reliable effect at low cost. Specifically, the maintenance of exposure amount adjustment that was performed when installing the main body of the electrophotographic device becomes unnecessary, and in the cartridge type process unit, it was conventionally provided to convey the sensitivity of each photoconductor to the main body of the device.
It became possible to abolish the so-called "sensitivity frame".

As described above, it is possible to know the exposed portion potential V _L from the charging DC current I _DC , and particularly by performing the contact AC charging, the potential V _D can be stably and instantaneously changed from the potential V _L.
Since this method converges to, this method can perform measurement with a small error.

Since the contact charging method is used, all the current output from the contact charging member is the amount of electric charge for charging (eliminating) the photosensitive member. Therefore, the charging current (eliminating current) can be obtained only by measuring this current. It is possible to directly detect, and it is not necessary to separate the shield current like a corona charger or to measure the inflow current to the photoconductor that separates the transfer of development etc., and the charging current can be measured very easily. it can.

In the present invention, the photoconductor exposed portion potential V _L
In contrast, by performing contact charging and measuring the charging (charging) DC current I _DC that flows when charging or discharging this, various images are formed according to the value of the detected charging DC current (charging). Process conditions (electrophotographic process conditions)
It is possible to easily prevent the deterioration of the image quality caused by the fluctuation of the exposed portion potential _VL due to various factors at a low cost by changing the value.

In the present invention, the photoconductor exposed portion potential V _L
It is possible to prevent the influence of erroneous measurement due to the transfer member when the contact AC charging is performed on the above and the DC current flowing when charging the same is measured. As a result, it becomes possible to control the exposure means in order to prevent the deterioration of the image quality caused by the fluctuation of V _L due to various factors, and to keep V _L constant more accurately under any conditions.

This is the same as in the prior art, such as the potential measuring device V _L
It is possible to obtain a highly reliable effect only by measuring the charging DC current without providing any special means for measuring. Specifically, the maintenance of the exposure amount adjustment, which was performed when the electrophotographic apparatus main body was installed, becomes unnecessary, and in the cartridge type process unit, the so-called conventionally provided so as to convey the photoconductor sensitivity to the apparatus main body. It became possible to abolish "sensitivity frame".

In the present invention, contact AC charging is performed,
In an image forming apparatus having a transfer device to which a voltage is applied, a DC current flowing through a contact charging member is measured when the charging potential of a member to be charged is Vcontrast charged or discharged, and the transfer voltage at the time of measuring the DC current is measured. Since the charging potential of the photoconductor is not changed by controlling the above, the film thickness of the charged body can be accurately measured. By giving a warning when the film thickness is below a certain value, it becomes possible to prevent the occurrence of image defects in electrophotography.

Unlike the conventional method of measuring the DC current flowing to the ground side of the photosensitive member, this method measures the DC current flowing to the charging member, so that only the current contributing to charging can be accurately measured. .. Further, since it is not necessary to provide any special means for measuring the film thickness, it is possible to obtain a reliable and high effect at low cost.

In the present invention, a contact charging member is used,
When measuring the DC current that flows when the charging potential of the body to be charged is charged by a constant amount of Vcontrast or discharged, the difference in the process settings can be dealt with by making the applied voltage constant regardless of the settings of the electrophotographic process. Therefore, it is possible to suppress the complication of the measuring device and measure the exposed portion potential _VL and the film thickness d of the charged body at a low cost.

In the present invention, when measuring the direct current flowing when the charging potential of the member to be charged is charged or discharged by Vcontrast using the contact charging member, it is applied to the contact charging device corresponding to the charging potential in advance. DC voltage is detected, and the voltage value is used to determine the photoconductor film thickness and the exposed portion potential _VL.
By providing a means for calculating, it becomes possible to correctly measure the film thickness of the member to be charged and the exposed portion potential _VL even if there are changes in various settings of the electrophotographic process.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus (laser beam printer) according to a first embodiment.

[Fig. 2] Sequence diagram of detection of potential of exposed area and measurement of charging DC current

[Fig. 3] Control flowchart

FIG. 4A is an explanatory diagram of a leak current to a pinhole, and FIG. 4B is an explanatory diagram of a charging DC current measurement procedure in the device of the second embodiment.

[Figure 5] Measurement sequence diagram

FIG. 6 Flow chart of measurement

FIG. 7 is a flow chart for detecting the photoconductor film thickness of the third embodiment device.

FIG. 8 is a control flowchart of the fourth embodiment device.

FIG. 9 is a control flowchart of the fifth embodiment device.

FIG. 10 is a control flowchart of the sixth embodiment device.

FIG. 11 is a schematic view of a main part of a seventh embodiment device.

FIG. 12 is a schematic diagram of a main part of an eighth embodiment device.

13A and 13B are schematic views of a ninth main part.

FIG. 14 is a control sequence diagram of the eleventh embodiment device.

FIG. 15: Primary DC current waveform used for film thickness detection

FIG. 16: Voltage application procedure diagram

FIG. 17 is a graph showing the relationship between the photoconductor film thickness d and the charging DC current I.

FIG. 18 is a conceptual diagram of a primary DC current detection constituent circuit.

FIG. 19 is a schematic configuration diagram of a twelfth embodiment device.

FIG. 20 is a schematic view of a main part of a thirteenth embodiment device.

FIG. 21 is a block diagram of a control system of a fourteenth embodiment device.

FIG. 22 is a conceptual diagram of the control of the developing bias voltage and the charging potential when the density volume is changed.

FIG. 23 is a control sequence diagram.

FIG. 24 is a schematic view of the essential parts of the device according to the 15th embodiment.

FIG. 25 is a schematic view of a main part of the device according to the 16th embodiment.

FIG. 26 is a schematic view of the essential portions of the seventeenth embodiment device.

FIG. 27 is a conceptual diagram of the control of the developing bias and the charging voltage when the density volume is changed.

FIG. 28 is a block diagram of a control system of the eighteenth embodiment device.

[Explanation of symbols]

 1 Contact charging member (charging roller) 2 Charged object (photoconductor) 3 Laser scanner 4 Developing device 5 Transfer roller 6 Cleaning device 7 Fixing roller 8 Process cartridge 1A, 4A, 5A Bias application power supply

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Norio Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takashi Shibuya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Tadashi Furuya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (40)

[Claims] 1. An image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image carrier, wherein the charged body whose surface is charged to a potential V _D. measuring the DC current I _DC flowing through the contact charging member from the power source when the charging until the potential V1 by performing contact charging an exposed portion potential V _L obtained by giving exposure, the potential V _L to this based on An image forming apparatus characterized by detecting. 2. The image forming apparatus according to claim 1, wherein the current I _DC is measured by a current which directly flows in or out of a power supply which supplies power to the contact charging member. 3. The image forming apparatus according to claim 1, wherein the condition of the exposure unit is controlled based on the detected exposure portion potential V _L. 4. The image forming apparatus according to claim 3, wherein the control target of the exposure unit is a light amount (light intensity). 5. The film thickness d of the member to be charged is detected by previously measuring the direct current I _DC ′ flowing when the surface potential of the member to be charged is changed from the potential V2 to the potential V3 by the contact charging member. The image forming apparatus according to claim 1, wherein the potential V _L of the exposed portion is detected based on the above. 6. A voltage applied to the contact charging member comprises a direct current component corresponding to a desired potential of the member to be charged and an alternating current component having a peak-to-peak voltage twice or more the charging start voltage V _th of the member to be charged. The image forming apparatus according to claim 1, wherein the image forming apparatuses are superposed ones. 7. The image forming apparatus according to claim 5, further comprising means for switching a DC component of a voltage applied to the contact charging member between a voltage V2 and a voltage V3. 8. The image forming apparatus according to claim 1, wherein the voltage V1 = 0. 9. The image forming apparatus according to claim 1, wherein the contact charging member has a roller shape. 10. An image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image carrier, wherein the charged body whose surface is charged to potential V _D A direct current I _DC flowing through the contact charging member is detected when the exposed portion potential _VL obtained by exposing is charged to the potential V1 by performing contact charging, and the image forming process is performed according to the current I _DC value. An image forming apparatus characterized by changing conditions. 11. The image forming apparatus according to claim 10, wherein the current I _DC is measured by a current which directly flows in or out of a power supply which supplies power to the contact charging member. 12. The image forming apparatus according to claim 10, wherein the change target of the image forming process condition is a developing bias condition. 13. The image forming apparatus according to claim 10, wherein the target of change in the image forming process condition is a charging bias. 14. The image forming apparatus according to claim 10, wherein the potential V1 = 0. 15. An image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image bearing member, wherein the surface of the charged body is charged to potential V _D. the DC current I _DC flowing through the contact charging member when charging until the potential V1 by performing contact charging an exposed portion potential V _L obtained by providing the exposure was measured, which was based on sensing the potential V _L Means and a transfer means for transferring the image formed on the charged body to a transfer material, and during the measurement of the direct current I _DC , the potential fluctuation of the exposed portion potential _VL of the charged body before and after passing through the transfer portion. The image forming apparatus is characterized in that the transfer means is controlled so that the voltage is approximately 0V. 16. The image forming apparatus according to claim 15, wherein the current I _DC is measured with a current flowing in or out of a direct current with respect to a power supply which supplies electric power to the contact charging member. 17. The image forming apparatus according to claim 15, wherein the transfer member of the transfer unit is in contact with the member to be charged. 18. At the time of detecting the exposed portion potential V _L , the voltage applied to the transfer means is the charged target surface potential V _D and 0 V.
The image forming apparatus according to claim 15, wherein the image forming apparatus is controlled during the period. 19. The image forming apparatus according to claim 17, wherein the transfer member is electrically floated on the electric circuit when the exposed portion potential V _{L is} detected. 20. The image forming apparatus according to claim 17, wherein the transfer member is physically separated from the surface of the member to be charged and is not in contact when the potential V _{L of the} exposed portion is detected. 21. The image forming apparatus according to claim 15, wherein the transfer unit is a unit utilizing corona discharge. 22. The image forming apparatus according to claim 17, wherein the transfer bias is set to 0 V when the exposed portion potential V _{L is} detected. 23. In an image forming apparatus for applying an image forming process including a charging process to an object to be charged as an image bearing member to output an image formed article, a charging unit for charging the object to be charged is A direct-current component corresponding to a desired potential of the charged body and an alternating-current component having a peak-to-peak voltage that is at least twice the charging start voltage _Vth of the charged body are superimposed on the contact charging member brought into contact with the charged body. A contact charging unit that applies a voltage to charge the charged body, and is a direct current supplied to the contact charging member when charging or discharging the charged body potential from a predetermined first potential V2 to a predetermined second potential V3. It has means for detecting the thickness d of the charged body by measuring I _DC ′ and transfer means for transferring the image formed on the charged body to a transfer material, and detects the direct current I _DC ′. Is applied to the transfer means. That the voltage is the image forming apparatus, wherein said member to be charged potential transfer portion passes through the front and rear of the potential change of V2 is controlled so as to be substantially 0V. 24. The image forming apparatus according to claim 23, wherein the current I _DC ′ is measured by a current which directly flows in or out of a power source which supplies power to the contact charging member. 25. A transfer means is intended to transfer member contacts the member to be charged, the direct current voltage V _tr applied to the contact transfer member when detecting the I _DC 'is the voltage V _tr and the member to be charged 24. The image forming apparatus according to claim 23, wherein the absolute value of the difference between the potentials V2 is controlled so as to be equal to or lower than the voltage Va at which the contact transfer member starts charging the charged body. 26. The image forming method according to claim 25, wherein the voltage V _tr applied to the contact transfer member when the direct current I _DC ′ is detected is controlled to the same voltage as the charged object potential V2. apparatus. 27. The transfer means is a corona transfer charger,
24. The image forming apparatus according to claim 23, wherein the voltage V _tr applied to the corona transfer charger when the DC current I _DC ′ is detected is controlled to be equal to or lower than the corona discharge starting voltage Vb. 28. In an image forming apparatus for outputting an image forming object by applying an image forming process including a charging treatment step to a charged body as an image bearing member, a charging means for charging the charged body is contact charging. Means for measuring the current I _M flowing in the contact charging means by charging or discharging the charged body from the potential before the charging processing to the potential after the charging processing, and the voltage applied to the contact charging means an image forming apparatus comprising: the voltage applied at the time of formation, means for switching between the constant voltage V _M to be applied during the current I _M measurements. 29. The charged body is a photoconductor, and the surface potential V _L obtained by exposing the photoconductor whose surface is charged is determined by contact charging with the constant voltage V _M applied. The current I _M flowing through the contact charging member is measured when the charging is performed, and the potential V _L is measured based on the measured current I _M.
29. The image forming apparatus according to claim 28, wherein: 30. A constant voltage V _M at the time of the current I _M measured
₁ and V _{M 2} , and a constant voltage V _{M 2} is applied to the contact charging device from the charging potential of the charged member obtained when the constant voltage V _{M 1} is applied to the contact charging device. 29. The image forming according to claim 28, wherein the film thickness of the member to be charged is measured by measuring the current I _M flowing through the contact charging member when charging to the charged potential of the member to be charged obtained at the time. apparatus. 31. A direct current component corresponding to a desired potential of the charged body to which the voltage applied to the contact charging member is applied, and an alternating current component having a peak-to-peak voltage that is at least twice the charging start voltage V _th of the charged body. 31. The image forming apparatus according to claim 28, wherein the image forming apparatus is an image forming apparatus. 32. The image forming apparatus according to claim 29, wherein the current I _M is measured by a current flowing directly into or out of the voltage applying device. 33. The image forming apparatus according to claim 30, wherein V _{M 1} or V _{M 2} = 0. 34. The image forming apparatus according to claim 28, wherein the contact charging member has a roller shape. 35. An image forming apparatus for outputting an image formed product by applying an image forming process including a charging process to a charged body as an image bearing member, and a contact charging device for charging the charged body, Means for measuring a direct current flowing through the contact charging device by charging or discharging the charged body from a potential before the charging process to a potential after the charging process, and detecting a direct current voltage applied to the contact charging device during the direct current measurement. An image forming apparatus having means. 36. The direct current flowing through the contact charging device when the contact charging device charges the exposed portion potential obtained by exposing the charged photosensitive member to light, And a means for calculating the potential of the exposed portion by measuring the DC voltage applied to the contact charging device, and calculating the potential of the exposed portion using the DC voltage value. The image forming apparatus according to claim 35. 37. Means for calculating the film thickness of the charged body by measuring a direct current flowing through the contact charging apparatus when charging or discharging the charged body is applied to the contact charging apparatus. 36. The image forming apparatus according to claim 35, wherein a DC voltage is detected, and the film thickness of the charged body is calculated using the DC voltage value. 38. A direct current component corresponding to a desired potential of the charged body to which a voltage applied to the contact charging member is applied, and an alternating current component having a peak-to-peak voltage that is at least twice the charging start voltage _Vth of the charged body are superimposed. 38. The image forming apparatus according to claim 35, wherein the image forming apparatus is an image forming apparatus. 39. The image forming apparatus according to claim 36 or 37, wherein the direct current is measured by a current flowing directly into or out of the voltage applying device. 40. The image forming apparatus according to claim 35, wherein the contact charging member has a roller shape.