JP2000089624A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and accurately detect the thickness of a photosensitive layer on an image carrier with respect to the image forming device capable of charging the image carrier by non-contact type charging means in a state of being held in non-contact therewith. SOLUTION: This image forming device accurately and stably detects the thickness of the photosensitive layer on a photoreceptor 1 by simple device/ circuit structure by detecting the current value conducted from the scolo thoron type corona charger 2 to the photoreceptor 1, and a voltage applied from a power source 9 to the scolo thoron type corona charger 2 by the layer thickness detecting circuit 10, when applying charge bias from a power source 9 to the scolo thoron type corona charger 2, and predetermining the thickness of the photosensitive layer on the photoreceptor 1 by the controlling device 11 based on the detection information of the above current value and the voltage detected by the layer thickness detecting circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system, and more particularly to an image carrier (electrophotographic photosensitive member, electrostatic recording derivative, etc.) which is a member to be charged. The present invention relates to an image forming apparatus provided with a non-contact type charging member for charging a surface of the image forming apparatus in a non-contact manner.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an image carrier as an object to be charged such as an electrophotographic photosensitive member or an electrostatic recording dielectric is subjected to a charging process (including a charge removing process). Conventionally, a non-contact corona charger, a contact roller charger, and a blade charger have been used as the charging means.

As the contact type charging means, a charging member (conductive member) such as a roller type (charging roller) or a blade type (charging blade) is used as an image bearing member (electrophotographic photosensitive member, electrostatic member). (For example, JP-A-63-167380).
Has been put to practical use.

Further, in a transfer type image forming apparatus in which an image bearing member (electrophotographic photosensitive member, electrostatic recording derivative, etc.) as a member to be charged is repeatedly used, the image bearing member is subjected to a charging process and a durable paper passing. The surface is gradually scraped, and the thickness (film thickness) of the surface of the image carrier gradually decreases. Due to this decrease in film thickness, the charging stability of the image carrier is impaired,
The reason is based on the following principle.

The amount of charge Q required to charge the image carrier to a constant potential Vd is determined by the capacitance C of the image carrier, and the amount of charge is the capacitance of the dielectric layer of the image carrier. C
The charge amount is inversely proportional to the thickness d of the dielectric layer.

Therefore, in order to charge the image carrier whose surface has been shaved to a constant potential Vd, more charge (current in the direction of the image carrier) is required than in the initial stage. That is, in a state where a constant image carrier direction current Id is flowing through the image carrier, the potential gradually changes in accordance with the decrease in the thickness of the dielectric layer of the image carrier, and as a result, the density is low, or Problems such as darkening and fogging occur, and an appropriate image cannot be obtained.

[0007] Regarding this phenomenon, the charging method is a contact type,
Occurs regardless of the non-contact type. In order to solve this problem, it is necessary to measure the surface potential of the image carrier with a potential sensor or the like and control the potential. In this case, the use of a potential sensor increases the initial cost of the apparatus, and a cartridge-type copying machine or printer has a relatively inexpensive copying machine because there is no space for mounting the potential sensor in the apparatus. And printers have no method to cope with fluctuations in the thickness of the image carrier.

In order to maintain a constant charge stability against such a change in film thickness without having a means for measuring the surface potential of the image bearing member such as a potential sensor, the contact charging method employs an image bearing member. There are means for detecting the thickness of the body (for example, JP-A-5-223513).

The principle of the means for detecting the thickness of the image carrier in this contact charging system will be briefly described. The change in the capacitance C due to the decrease in the thickness d of the dielectric layer of the image carrier as the object to be charged is described. Is detected by an image carrier direction current Id flowing from the charging member to the image carrier, and at the same time, a voltage applied to the charging member (the sum of the surface potential of the image carrier and the discharge starting voltage) and a preset image carrier This is achieved by collating with the slope data of the VI characteristic regarding the thickness of the dielectric layer.

As described above, the contact charging device has a great advantage of being able to detect the film thickness of the image carrier as compared with the corona charger, and also has a corona discharge generation such as ozone which can lower the power supply voltage. It has advantages such as less generation of objects.

However, on the other hand, the surface layer of the image bearing member is largely scraped by the narrow-area discharge in the vicinity of the contact portion, and since the contact type is used, the surface layer of the charging member is soiled and image abnormalities are likely to occur.

Further, since the charging member is made of a conductive resin or rubber, there is a disadvantage that the life of the charging member itself is shorter than that of the corona charger due to deterioration of the material due to discharge and fluctuation of resistance. I have.

In particular, in recent years, in order to respond to environmental problems such as dust generated by discarding a cartridge and to a strong demand for cost reduction, it is necessary to extend the life of the photosensitive member as an image bearing member. The corona charger with a small amount of shaving has been reviewed again.

[0014]

However, in an electrophotographic apparatus provided with a corona charger as a means for charging an image carrier having no potential sensor, the above-described film thickness detecting means for the image carrier cannot be used. .

The reason is that, in order to detect the film thickness of the image carrier, it is necessary to know the VI characteristic which is the relationship between the current flowing through the image carrier and the applied voltage at that time.
The scorotron type corona charger includes a current stabilizing member called a shield or a grid in addition to a discharge wire. For this reason, the current flowing from the discharge wire flows not only to the image carrier, but also to the conductive member such as the above-mentioned shield or grid, so that the current flowing to the charging member and the applied voltage at that time are determined by the current flowing in the image carrier and the image carrier. (The value obtained by subtracting the firing voltage from the applied voltage). Therefore, the capacitance of the image carrier cannot be derived, and the thickness of the image carrier cannot be calculated.

Further, in a static elimination step (generally, static elimination by exposure irradiation of a fuse lamp, an LED, or the like) performed before charging the photosensitive member to lower the surface potential, a surface potential Vsl (Voltage supply) of the photosensitive member after the static elimination is applied.
er light) does not drop to 0V, FIG.
As shown in (2), the ratio (surface potential / current) between the surface potential of the photoconductor and the current flowing through the photoconductor shifts by the surface potential (potential after static elimination) Vsl of the photoconductor after static elimination.

The potential Vsl after static elimination gradually increases in accordance with the endurance state and use time of the photoreceptor, so that the ratio between the surface potential of the photoreceptor and the current shifts, and as a result, the photosensitive The body thickness will also deviate from the actual value.

For this reason, in an electrophotographic apparatus provided with a corona charger as a charging means, in general, the means for detecting the thickness of the photoreceptor is indirect by counting the number of durable sheets passed or the total number of rotations of the photoreceptor. For example, a method of calculating the shaving amount of the photoconductor, that is, the life of the photoconductor is used.
However, in this method as well, the thickness of the photoreceptor fluctuates depending on the use environment, the state of the cleaning device, and the like, so that the thickness of the photoreceptor cannot be accurately and stably detected.

Accordingly, an object of the present invention is to provide an image forming apparatus using a non-contact type charging means, which can accurately and stably detect the thickness of an image carrier.

[0020]

In order to achieve the above object, the present invention provides an image carrier having a photosensitive layer on its surface, and an image carrier provided close to the surface of the image carrier to charge the image carrier. In an image forming apparatus provided with a non-contact charging unit and a power supply for applying a voltage to the non-contact charging unit, when a voltage is applied from the power supply to the non-contact charging unit, the non-contact charging unit switches the image bearing device from the non-contact charging unit. Current / voltage detecting means for detecting a current value flowing through the body and a voltage value applied to the non-contact charging means from the power supply; and detecting the current value and the voltage value detected by the current / voltage detecting means. Calculating means for inputting information and calculating the thickness of the photosensitive layer based on the input detection information of the current value and the voltage value.

Further, the non-contact type charging means is a scorotron type corona charger having a discharge wire and a grid in a shield, and the current / voltage detecting means is applied from the power source to the scorotron type corona charger. And a current value flowing from the power supply to the discharge wire, the shield, and the grid, and the current / voltage detecting means further detects the image from the scorotron-type corona charger based on the detected current values. A charging current value flowing to the carrier is detected, and the calculation unit calculates the thickness of the photosensitive layer based on the detection information of the voltage value and the charging current value input from the current / voltage detection unit. And

Further, the non-contact type charging means is a corona charger having a discharge needle and a grid in a shield, and the current / voltage detecting means is provided with a voltage value applied from the power supply to the corona charger. Detecting the respective current values flowing from the power supply to the discharge needle, the shield, and the grid, and furthermore, the current / voltage detecting means detects the charging current flowing from the corona charger to the image carrier according to the detected current values. The value is detected, and the calculating means calculates the thickness of the photosensitive layer based on the detection information of the voltage value and the charging current value input from the current / voltage detecting means.

[0023] The image processing apparatus further includes storage means for storing characteristic values of a surface potential and a charging current of the image carrier in accordance with the thickness of the photosensitive layer. It is characterized in that the thickness of the photosensitive layer is calculated from characteristic value information of the surface potential of the carrier and charging current and detection information of the current value and the voltage value input from the current / voltage detection means.

A charge removing means for removing charge from the surface of the image bearing member; and a surface potential of the image bearing member corresponding to the thickness of the photosensitive layer after removing the charge on the surface of the image bearing member by the charge removing means. A storage unit storing a characteristic value of the charging current; and the calculating unit, characteristic value information of a surface potential and a charging current of the image carrier input from the storage unit,
The thickness of the photosensitive layer is calculated from the detection information of the current value and the voltage value input from the current / voltage detection means.

If the thickness of the photosensitive layer detected by the calculating means is equal to or less than a preset value, the display means is notified that the thickness of the photosensitive layer has reached the lower limit thickness. Alternatively, the image forming operation is stopped.

(Operation) According to the structure of the present invention, the image carrying means is calculated by the calculating means based on the current value flowing from the non-contact charging means to the image carrier and the voltage value applied from the power supply to the non-contact charging means. The thickness of the photosensitive layer of the body can be accurately and stably detected.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a schematic configuration diagram showing a main part of an image forming apparatus (a copying machine using a transfer type electrophotographic process in this embodiment) according to the present embodiment. It is.

This image forming apparatus includes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive member) 1 serving as an image carrier.
And a scorotron type corona charger 2 as a non-contact type charging member (primary charger), a developing device 3, a transfer roller 5, a cleaning device 6, and a static eliminator 8 around the photoreceptor 1.

The photoconductor 1 is a negatively charged organic photoconductor in the present embodiment. An OPC photoconductor layer (dielectric layer) (not shown) as a surface layer is formed on an aluminum drum (conductive drum substrate) having a diameter of 30 mm. It is formed by coating, and is rotationally driven in a direction of an arrow R1 at a predetermined process speed (for example, a rotational peripheral speed of 150 mm / sec).

The thickness of the OPC photosensitive layer (hereinafter referred to as dielectric layer) of the photosensitive member 1 is d = 25 μm in the initial state. In addition, a charge transport layer (not shown) for forming an OPC photoreceptor layer (Carrier Transfer Layer)
As the binder of r), a polycarbonate resin is used, and the charge transport layer is gradually scraped by durable paper passing to reduce the thickness.

The scorotron-type corona charger 2 includes a discharge wire 2a, a shield 2b which is a conductive plate for covering the outer periphery of the side of the discharge wire 2a,
Is provided with a grid 2c for controlling the surface potential.

A power supply 9 is connected between the discharge wire 2a and the shield 2b, and a charging bias is applied to the discharge wire 2a at one end of the discharge wire 2a via an electrode (not shown). You.

A power supply 9 supplies a scorotron type corona charger 2
The values of the current and the voltage applied to are detected by the film thickness detection circuit 10. The values of the current and the voltage detected by the film thickness detection circuit 10 are input to the control device 11,
Calculates the thickness of the dielectric layer of the photoconductor 1 based on the input information of the current and voltage values (details will be described later).

The shield 2b and the grid 2c are electrically connected by an end electrode (not shown), and a charging bias is applied from the power supply 9 via the electrode (not shown), similarly to the discharge wire 2a. Therefore, the shield 2b and the grid 2c
Have the same potential and the same current during the charging process.

In the present embodiment, the developing device 3 is a one-component jumping developing device, and a rotatable developing sleeve 4.
It has a magnet roller (not shown) fixedly arranged inside.

Next, an image forming operation of the above-described image forming apparatus will be described.

During image formation, the photosensitive member 1 is driven to rotate at a predetermined process speed (for example, 150 mm / sec) in the direction of arrow R1 by a driving means (not shown). At this time, a charging bias is applied from the power supply 9 to the scorotron corona charger 2 to charge the surface of the photoconductor 1 to a negative polarity.

The photoreceptor 1 charged by the scorotron corona charger 2 receives a laser beam L output from an exposure device (not shown) according to a time-series electric digital pixel signal of target image information. The exposed portion of the photoreceptor 1 is subjected to scanning exposure by the laser beam irradiated by the laser beam irradiation, thereby forming an electrostatic latent image of image information on the surface of the photoreceptor 1.

Then, the electrostatic latent image is reversely developed by a one-component magnetic toner by a developing device 3 of a jumping development system, and the exposed portion of the surface of the photoconductor 1 is visualized as a toner image by the adhesion of the toner.

When the toner image formed on the surface of the photosensitive member 1 reaches the transfer nip portion between the transfer roller 4 and the photosensitive member 1, transfer of a sheet or the like from a paper feeding mechanism (not shown) is performed in accordance with this timing. The material P is transported to the transfer nip. Then, the transfer roller 5 to which a transfer bias (for example, about 3 KV) is applied gives a charge having a polarity opposite to that of the toner to the back side of the transfer material P, and the toner image on the surface of the photoconductor 1 is transferred to the front side. The transfer material P on which the toner image has been transferred is conveyed to a fixing device (not shown), and the transferred toner image is fixed as a permanently fixed image on the surface of the transfer material P by heating and pressing by a fixing device (not shown) and output. You.

The surface of the photoconductor 1 after the transfer of the toner image is
The cleaning blade (counter blade made of urethane rubber) 7 of the cleaning device 6 scrapes and removes adhered contaminants such as transfer residual toner and paper dust to make the surface clean, and further, the charge is removed and initialized by the charge removing device 8. ,
It is repeatedly provided for image formation.

Next, detection of the thickness of the dielectric layer of the photosensitive member 1 will be described.

The thickness d (μm) of the dielectric layer of the photosensitive member 1 is
The increase in the surface potential of the photoconductor 1 due to the charging process of the scorotron type corona charger 2 is Vp (V), the photoconductor current flowing through the photoconductor 1 is Id (μA), and the relative permittivity of the dielectric layer of the photoconductor 1 Is ε, the dielectric constant in vacuum is ε0, the effective charging width of the scorotron corona charger 2 is L (mm), and the process speed is PS (mm / sec). C is calculated, and the following relational expression is derived.

Charged charge amount Q = ∫Id · dt = C · Vp (1) From equation (1), charging current Id = d / dt (C · Vp) (2) is obtained. Here, since dC / dt = ε · ε0 · L · PS / d, the charging current Id = ε · ε0 · L · PS · Vp / d (3) From equation (3), The thickness d = ε ・ ε0 ・ L ・ PS ・ Vp / d (4) is obtained.

In the equation (4), ε, ε0, L, PS
Is a constant determined by the characteristics of the image forming apparatus and the dielectric, so that the thickness d of the dielectric layer can be seen as a function of Vp and Id. That is, by obtaining the relationship between Vp and Id, the thickness d of the dielectric layer of the photoconductor 1 can be detected.

Here, in order to determine the charging current Id flowing from the scorotron type corona charger 2 to the photosensitive member 1, the power supply 9
A discharge wire current Ipr flowing from the discharge wire 2a to the discharge wire 2a;
The current Igs flowing to the grid 2c and the shield 2b is detected by the film thickness detecting circuit 10, and the photoreceptor current Id is obtained by subtracting the grid shield current Igs from the discharge wire current Ipr. That is, Id = Ipr-Igs (5).

Here, the grid shield current flowing through the grid 2b and the shield 2c is represented by Igs.
This is because, in the present embodiment, the grid 2b and the shield 2c are conductive, and the current is supplied from the same power supply 9.

The surface potential of the photoconductor 1 is sufficiently larger than the charging current (photoconductor current) Id of the discharge wire current Ipr flowing through the discharge wire 2a of the scorotron corona charger 2 (photoconductor current). (Generally about 7 to 8 times or more), it can be detected by using the characteristic that it becomes equal to the grid shield voltage Vgs. That is, Vd = Vp (6).

Therefore, as in the present embodiment, the photosensitive member 1
In the image forming apparatus using the scorotron type corona charger 2 as the non-contact type charging member, the discharge wire current l
charging current Id determined from p and grid shield current Igs, and surface potential V determined from grid voltage Vgs
Using p, the thickness of the dielectric layer of the photoconductor 1 can be detected.

The condition for detecting the thickness of the dielectric layer of the photosensitive member 1 is the potential Vs after the static elimination at the time of detection.
If l is not near OV, the charge flowing to the photoconductor 1 is reduced by the potential Vsl after static elimination. For this reason, the VI characteristic, which is the characteristic between the surface potential V of the photoconductor 1 and the charging current I, is different from each other and causes an error.
Of the photosensitive member 1 is performed by the charge removing device 8 so that the value of the photoreceptor 1 becomes approximately OV.

The time for applying each voltage is as follows:
At least one photoconductor 1 should be used to remove the effects of noise.
The rotation is equal to or more than one rotation (one rotation in this embodiment), and the current measured during this period is averaged. Further, the detection of the thickness of the dielectric layer of the photoconductor 1 is performed during the pre-rotation of the photoconductor 1, so that the sequence is such that the image formation is not adversely affected.

In order to detect the thickness of the dielectric layer of the photoreceptor 1, the inclination of the VI characteristic of the photoreceptor 1 must be determined in advance.
It is necessary to measure the relationship of the thickness (thickness) d of the dielectric layer. Therefore, the measurement was performed using the photoconductor 1 in which the thickness d of the dielectric layer of the photoconductor 1 was 15 μm, 18 μm, 21 μm, and 25 μm, respectively.

FIG. 2 shows that the thickness d of the dielectric layer of the photosensitive member 1 is 1
It is a figure which shows each VI characteristic in case of 5 micrometers, 21 micrometers, and 25 micrometers, and a horizontal axis | shaft is surface potential V (KV) and a vertical axis | shaft is charging current I. FIG. As is clear from the VI characteristics shown in this figure, ε, ε0, L, PS / d, which are the intercepts of the VI characteristics.
However, it has been experimentally proved that this depends on the thickness d of the dielectric layer of the photoreceptor 1.

Based on the relationship between the VI characteristics at 15 to 25 μm, as shown in FIG. 3, the thickness (μm) d of the dielectric layer of the photosensitive member 1 and the gradient (V / The correlation of I) can be obtained. Here, the slope of the VI characteristic (V /
I) is a value obtained by dividing the charging current Id by the surface potential (voltage) Vp. In the present embodiment, the charging current Id was 36 μA, and the grid and shield voltage Vgs were 700 V.

In the present embodiment, the above-described FIG.
The relationship between the thickness d of the dielectric layer of the photoreceptor 1 and the gradient (V / I) of the VI characteristic shown in FIG. The thickness d of the dielectric layer of the photoconductor 1 can be calculated from the surface potential Vp and the charging current Id.

In the present embodiment, the film thickness d of the dielectric layer of the photosensitive member 1 is V−V corresponding to the lower limit of 15 μm.
When the slope (V / I) of the I characteristic is lower than 19.5 V / μA, a warning indicator (not shown) provided on a display panel (not shown) of the image forming apparatus is turned on or the photosensitive member 1 is turned on. The user is notified by, for example, displaying that the thickness of the dielectric layer has reached the lower limit thickness. Further, the control device 11 may stop the image forming operation together with the warning display or the like.

As a result, the user can recognize that the thickness of the dielectric layer of the photosensitive member 1 has reached the end of its service life and can replace the photosensitive member 1, so that the photosensitive member 1 reaches the limit of use. Despite this, it is possible to prevent the occurrence of charging failure and image failure due to use.

In the first embodiment, the scorotron type corona charger is used as the non-contact charging means. However, the present invention is similarly applied to a corona charger having a discharge needle, a shield and a grid. be able to.

<Embodiment 2> In the present embodiment, when detecting the film thickness of the dielectric layer of the photosensitive member 1 described in the first embodiment, the fluctuation of the potential VsI after static elimination is further taken into consideration. This is to accurately detect the film thickness. Note that, also in the present embodiment, an explanation will be given using an image forming apparatus having the same configuration as that of Embodiment 1 shown in FIG. 1 and using the image forming apparatus shown in FIG.

As in the first embodiment, when the potential of the photosensitive member 1 after the charge elimination does not become about 0 V, the surface potential Vp of the photosensitive member 1 actually includes the potential Vsl after the charge elimination. Is reduced by the amount of charge corresponding to the potential Vsl after static elimination. For this reason, as shown in FIG.
The ratio V / I of the surface potential V to the current I becomes lower than the actual value, which causes erroneous detection of the film thickness.

That is, the surface potential of the photosensitive member 1 after the charging process is Vd (V), and the surface potential of the photosensitive member 1 after the charge is removed is Vsl.
Assuming that (V), the rise Vp (V) of the surface potential of the photoconductor 1 due to the charging process is as follows: Vp = Vd−Vsl (7)

Here, as described above, the potential Vs after static elimination is used.
1 varies depending on the durability of the photoconductor 1. In the present embodiment, the integrated value N of the number of durable sheets passed through the photoconductor 1 and the potential Vsl after static elimination are obtained in advance by actual durable sheet passing using the image forming apparatus shown in FIG. The relationship between N (sheets) and the potential Vsl after static elimination is stored in the ROM 12 in the controller 11 as a potential table after static elimination, and the surface potential Vp of the photoconductor 1 after the charging process is calculated using the potential table after static elimination. I did it.

FIG. 4 is a graph showing the relationship between the number of durable sheets and the potential Vsl after static elimination in a normal environment (N / N environment) at a room temperature of 25 ° C. and a humidity of 60% RH.

The potential Vsl after static elimination is obtained by removing the developing device 3 of the image forming apparatus of FIG. 1 and mounting a potential sensor at a position where the developing device 3 and the photosensitive member 1 are opposed to each other every 5,000 sheets of paper passing durability. It was measured.

As described above, in the present embodiment, as shown in FIG. 5, the relationship between the integrated sheet passing value N measured in advance and the potential Vsl after static elimination of the photosensitive member 1 is stored in the ROM 12 in the control device 11. In advance, a potential Vsl after static elimination at the time of film thickness detection is derived from the integrated sheet passing value N stacked in a counter (not shown) in the controller 11 to obtain Vp, which is a substantial rise in surface potential. , Vsl can be detected more accurately without depending on the variation of Vsl.

[0066]

As described above, according to the present invention, when the charging bias is applied to the non-contact charging means from the power supply, the current and voltage values applied to the image carrier from the non-contact charging means are determined. Since the thickness of the photosensitive layer of the image carrier can be detected, the thickness of the photosensitive layer of the image carrier can be accurately and stably detected with a simple device and circuit configuration without using a special device such as a potential measuring device. can do.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a charging current and a surface potential of the photoconductor when the thickness of the photoconductor is changed.

FIG. 3 shows the relationship between the thickness of the photoconductor and the slope of the VI characteristic (surface potential V).
FIG. 6 is a graph showing a relationship between the charging current Id and the charging current Id.

FIG. 4 is a diagram showing the relationship between the number of sheets passed when endurance sheet passing is performed and the potential after static elimination of the photoconductor surface.

FIG. 5 is a diagram showing a relationship between a potential after static elimination on the surface of a photoconductor, a surface potential of the photoconductor, and a ratio of charging current (surface potential / charging current).

DESCRIPTION OF THE SYMBOLS 1 Photoconductor (image carrier) 2 Scorotron corona charger (non-contact charging means) 2a Discharge wire 2b Shield 2c Grid 3 Developing device 5 Transfer roller 6 Cleaning device 7 Cleaning blade 8 Static eliminator 9 Power supply 10 Film thickness detection circuit (current / voltage detection means) 11 Control device (calculation means) 12 ROM (storage means)

Claims (6)

[Claims] An image carrier having a photosensitive layer on a surface thereof; a non-contact charging means provided in proximity to the surface of the image carrier for charging the image carrier; and applying a voltage to the non-contact charging means. An image forming apparatus including a power supply, wherein when a voltage is applied from the power supply to the non-contact charging means, a current value flowing from the non-contact charging means to the image carrier, and Current / voltage detecting means for detecting a voltage value applied to the current and voltage information, and detecting information of the current value and the voltage value detected by the current / voltage detecting means, Calculating means for calculating the thickness of the photosensitive layer based on the detection information. 2. The non-contact type charging means is a scorotron type corona charger having a discharge wire and a grid in a shield, and the current / voltage detecting means is applied from the power source to the scorotron type corona charger. And a current value flowing from the power supply to the discharge wire, the shield, and the grid, and the current / voltage detecting means further detects the image from the scorotron-type corona charger based on the detected current values. The charging current value flowing to the carrier is detected, and the calculation unit calculates the thickness of the photosensitive layer based on the detection information of the voltage value and the charging current value input from the current / voltage detection unit. 2. The image forming apparatus according to 1. 3. The non-contact type charging means is a corona charger having a discharge needle and a grid in a shield, and the current / voltage detecting means is provided with a voltage value applied to the corona charger from the power supply. The discharge needle from the power supply,
The current / voltage detecting means detects a charging current value flowing from the corona charger to the image carrier based on the detected current values; and 2. The image forming apparatus according to claim 1, wherein the thickness of the photosensitive layer is calculated based on detection information of the voltage value and the charging current value input from the current / voltage detection unit. 3. 4. A storage unit for storing characteristic values of a surface potential and a charging current of the image carrier according to a thickness of the photosensitive layer, wherein the calculation unit is configured to input the image input from the storage unit. The thickness of the photosensitive layer is calculated from characteristic value information of a surface potential and a charging current of a carrier and detection information of the current value and the voltage value input from the current / voltage detection unit. 3. The image forming apparatus according to 3. 5. A charge removing means for removing charge on a surface of the image carrier, and a surface potential of the image carrier according to a thickness of the photosensitive layer after the charge on the surface of the image carrier is removed by the charge removing means. A storage unit for storing a characteristic value of a charging current; a calculating unit configured to store characteristic value information of a surface potential of the image carrier and a charging current input from the storage unit; 4. The image forming apparatus according to claim 1, wherein the thickness of the photosensitive layer is calculated based on the detection information of the current value and the voltage value input from a computer. 6. When the thickness of the photosensitive layer detected by the calculation means is a predetermined value or less, the display means is notified to the effect that the thickness of the photosensitive layer has reached the lower limit thickness. 6. The image forming apparatus according to claim 1, wherein the image forming operation is stopped.