JPH096099A - Image forming device - Google Patents

Abstract

(57) [Summary] [Purpose] To appropriately apply a voltage according to changes in the resistance value of a contact type charging member and the film thickness of a photoconductor in an image forming apparatus over time. In an image forming apparatus that forms an image using an electrophotographic process, a charging member 2 that contacts the surface of the photosensitive member to obtain a desired potential of the photosensitive member 1, and the photosensitive member that contacts the charging member. A means for changing the area of the photosensitive member, and a voltage adapted to a desired photosensitive member potential according to the resistance value of the charging member and the film thickness of the photosensitive member obtained by changing the contact area of the photosensitive member by the means. Is applied to the charging member, the life of the charging means is extended, and the charging potential of the surface of the photoconductor is optimized.

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 an electrophotographic apparatus which charges a surface to be charged of a photosensitive member by bringing a charging member into contact therewith.

[0002]

2. Description of the Related Art In an electrophotographic apparatus such as a copying machine or a laser beam printer, or an image forming apparatus such as an electrostatic recording apparatus, as a means for charging the surface of an image bearing member such as a photoreceptor or a dielectric member to be charged. In the past, corona discharge devices have been widely used. However, the corona discharge device requires a high-voltage power source, and is also required as a recent environmental problem such as generation of ozone due to corona discharge.

On the other hand, the method of contacting a surface to be charged with a semi-conductive roller, blade, brush or the like for charging has advantages such as lowering the voltage of the power source and generating less ozone. Therefore, it is being put to practical use as a charging unit of an image forming apparatus.

[0004]

However, the resistance value of these semi-conductive charging means becomes higher as they are used, and there arises a problem that a desired charging potential cannot be obtained on the surface to be charged. In particular, it is remarkable in the semiconductive charging means by ion conduction.

As a voltage to be applied to the charging means, there is a method in which a direct current voltage is superimposed on an alternating current voltage, or only a direct current voltage is applied, but the latter method is preferable because the amount of ozone generated is small. . However, in this case, as the use progresses, the photoconductor and the like are scraped off, and in a system in which only a certain DC voltage is applied, the charging potential gradually increases, and the bright part potential also increases, and for example, the normal portion potential increases. In the developing system, background fog has occurred.

The object of the present application is to detect both the resistance of the charging means and the abrasion of the photoconductor to prolong the life of the charging means and to charge the surface of the photoconductor to a desired potential.

[0007]

In order to achieve the above object, the invention according to the present application is as set forth in the appended claims, and charging by changing the area of the photoconductor in contact with the charging member. The resistance value of the member and the film thickness of the photoconductor are calculated so that a desired photoconductor potential can be obtained.

[0008]

【Example】

<First Embodiment> FIG. 8 is a schematic view of a copying machine embodying the present invention.

The operation will be briefly described. The photosensitive member 1 rotates in the direction of the arrow and is uniformly discharged by the exposure 3 from the pre-exposure light source 4, and thereafter, the photosensitive member 1 is appropriately supplied from the power source 11 via the semiconductive charging roller 2. Different voltages are applied and charged to a desired potential. Next, a latent image is formed by image exposure 5, the latent image is developed by developing means 6, and the image is transferred to transfer paper 10 by transfer means 7. The transfer sheet 10 is destaticized by the destaticizing unit 8 and is conveyed to a fixing unit (not shown). The semi-conductivity is, for example, a resistance value of 10
⁴ to 10 ⁸ Ω is preferable.

On the other hand, the photosensitive member is cleaned by the cleaning means 9 to remove the residual developer, and then the pre-exposure 3 again removes the electric charge to prepare for the next image formation.

The first embodiment will be described below.

FIG. 1 is a view showing the positional relationship between the photoconductor 1 and the charging roller 2 as seen from the direction A in FIG.
The area of the photoconductor 1 in contact with is S. The current characteristic of the charging roller 2 with respect to the DC applied voltage V _p is described by the following equation using Paschen's law. Assuming that the charging roller resistance value R, the roller applied voltage are V _p , the roller surface potential is V _s , and the current value is I, the charging roller resistance value R is R≡ (V _p −V
_s ) / I

[0013]

[Equation 1]

The following relational expression is obtained. If the current value I is changed from the formula and the characteristic of V _p is measured, the slope of the formula (dT / εS + R) can be obtained. Slope (dT / εS +
R) includes two quantities, the film thickness d of the photoconductor to be obtained and the resistance value R of the roller. Next, as shown in FIG. 2, the charging roller 2 and the photoconductor 1 are moved by shifting the charging roller 2 with respect to the photoconductor 1 in the longitudinal direction or the axial direction by an appropriate means.
If the contact area of is changed from S to S ', the slope will also be (dT
/ ΕS + R) to (dT / εS ′ + R). Since the dielectric constant ε of the photoconductor 1 and the rotation period T of the photoconductor 1 are known, the desired photoconductor film thickness d and the roller resistance value R can be obtained by detecting the change in the inclination.

Since the potential V on the surface of the photoconductor is expressed by V = ITd / εS ..., Substituting the film thickness d of the photoconductor obtained from the equation for the current value to be passed in order to obtain a desired photoconductor surface potential. Determined by.

From the above, at the time of image formation during the copying operation,
If a constant current control is performed with the current value I obtained from the equation, a desired photoreceptor surface potential can be obtained.

A specific example will be shown.

A semi-conductive charging roller having a diameter of 12 mm is used as the charging means, and a diameter of the photosensitive member is 30 mm as the image bearing member.
The organic photoconductor of was used and rotated at a peripheral speed of 30 π mm / s. In FIG. 1, the surface area S of the photosensitive member that contacts the charging roller 2 is 30π × 220 mm ² . When a constant current of −20 μA was controlled during the pre-multi revolution before forming an image during the copying operation, the applied voltage V _p at that time was −1300 V. Further, the applied voltage V _p when the constant current control of 25 μA is performed is −1.
It was 540 [V]. From the formula, the slope (dT / εS +
R) is

[0019]

[Equation 2]

Can be expressed as

Next, when the charging roller is moved 20 mm in the longitudinal direction of the photosensitive member as shown in FIG. 2, the surface area S'of the photosensitive member which is in contact with the charging roller 2 is 30π × (220-20) mm.
It becomes ² . In this state, the applied voltage under the constant current control of -20 μA was -1350 [V], and the applied voltage under the constant current control of -25 μA was -1610 [V]. Therefore, similarly from the formula

[0022]

(Equation 3)

## EQU2 ## , And T = 1 [1 /
S], ε = 3.0 × 8.854 × 10 ⁻¹² [F / m], the photosensitive member film thickness d = 25 μm and the charging roller resistance value R =
2.0 × 10 ⁶ [Ω] can be calculated.

Here, the surface potential V of the photoreceptor is -700 [V].
If you try to

[0025]

(Equation 4)

## EQU1 ## From the above, at the time of image formation 14 [μ
If the constant current is controlled in A], the desired surface potential of the photosensitive member is -700
[V] could be obtained.

FIG. 3 shows an example of the surface potential of the photoconductor obtained when the resistance value of the charging roller changes while the photoconductor film thickness is kept constant at 25 μm. The mark ○ indicates that the control of the present invention is used, and the resistance value of the charging roller is up to about 10 ⁸ Ω.
It shows that 700 [V] can be maintained.

On the other hand, when the voltage applied to the charging roller was kept constant at 1.4 kV without using the present invention, the surface potential of the photosensitive member gradually decreased as the roller resistance increased, and the potential could not be rapidly removed at 10 ⁷ Ω or more. .

FIG. 4 shows a resistance value of the charging roller of up to 5 × 10.
It is an example of the surface potential of the photoconductor obtained when the film thickness of the photoconductor CT layer is changed while keeping it constant at ⁵ Ω.

The mark ○ indicates that the target potential of −700 V can be maintained up to a thickness of 10 to 30 μm in the CT layer while the control of the present invention is used, whereas the uncontrolled one is about 200 V.
I made a difference.

FIG. 5 shows the results of durability test using a photoreceptor CT layer having a film thickness of 35 μm and a charging roller having a resistance value of 5 × 10 ⁵ Ω.

After 100,000 sheets of durability, the CT layer film thickness decreased to 16 μm and the roller resistance value increased to 3 × 10 ⁷ Ω.

The mark ◯ indicates the present invention, and the target potential of 700 V could be maintained up to the durability of 100,000 sheets.

On the other hand, the mark X is uncontrolled, and the decrease of the film thickness of the photoconductor has a greater effect than the increase of the roller resistance up to the endurance of 60,000 sheets, and the surface potential of the photoconductor at the initial time is 60%. It increased from -700V to -800V. Endurance 6
The effect of the increase in roller resistance was large after about 10,000 sheets, and the surface potential suddenly decreased.

As described above, the desired photoconductor surface potential could be obtained by obtaining the photoconductor film thickness and the charging roller resistance value.

<Second Embodiment> In the present embodiment, the means for changing the area of the photosensitive member in contact with the charging member is constructed as follows. As shown in FIG. 6, the charging roller 2 is set to 2a and 2b.
2a and 2b are connected by an insulating member 12. A switch 13 is provided between the charging roller 2b and the high voltage power source 11. When the surface area of the photoconductor in contact with the charging roller 2a is S _a and the surface area of the photoconductor in contact with the charging roller 2b is S _b , when the switch 13 is turned on,
Photoconductor surface area in contact with the charging roller 2 for turning off the S _a + S _b, the switch 13, the photosensitive member surface area in contact with the charging roller 2 becomes S _a.

With the above construction, the surface of the photoconductor in contact with the charging roller can be changed, so that the control described in the first embodiment can be performed and a desired photoconductor surface potential can be obtained. <Third Embodiment> As shown in FIG.
It is divided into two parts, b and the switch 1 between the photoconductor 1a and the ground.
4 is provided. The surface area of the photosensitive member 1a in contact with the charging roller 2 S _a, when the surface area of the photosensitive member 1b which is in contact with the charging roller 2 and S _b, the photosensitive member surface area in contact with the case the charging roller 2 which turns on the switch 14 S _a + S _b , switch 1
When 4 is turned off, the surface area of the photosensitive member in contact with the charging roller 2 becomes _Sa.

Since the surface area of the photosensitive member in contact with the charging roller can be changed by the above structure, the control described in the first embodiment can be performed and the desired photosensitive member surface potential can be obtained.

In each of the above embodiments, the roller was used as the charging member, but the present invention can of course be implemented by other blades or brushes.

[0040]

As described above, according to the present invention,
By changing the area of the photoconductor in contact with the charging roller and obtaining the film thickness of the photoconductor and the resistance value of the charging member, the current value for obtaining the desired photoconductor surface potential is obtained, and the photoconductor surface potential is maintained for a long time. We were able to.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a positional relationship between a photoconductor and a charging roller according to a first exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating that the positional relationship between the photoconductor and the charging roller has changed in the above-described embodiment.

FIG. 3 is a diagram showing a relationship between a resistance value of a charging roller and a photosensitive member surface potential in the above embodiment.

FIG. 4 is a diagram showing a relationship between a photoreceptor film thickness and a photoreceptor surface potential when the present invention is carried out and not carried out.

FIG. 5 is a diagram showing the number of used photoconductors and the surface potential after control when the present invention is carried out and not carried out.

FIG. 6 is a schematic diagram showing a second embodiment of the present invention.

FIG. 7 is a schematic diagram showing a third embodiment of the present invention.

FIG. 8 is a schematic diagram of a device configuration for explaining a first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photoconductor 2 ... Charging roller 11 ... High-voltage power supply 12 ... Insulator 13 ... Switch 14 ... Switch

Claims (5)

[Claims] 1. An image forming apparatus for forming an image using an electrophotographic process, comprising: a charging member that contacts a surface of a photosensitive member to obtain a desired photosensitive member potential; and a photosensitive member that contacts the charging member. A voltage adapted to a desired photoconductor potential is provided in accordance with the resistance value of the charging member and the film thickness of the photoconductor, which is obtained by changing the contact area of the photoconductor with the device. An image forming apparatus characterized by being applied to a charging member. 2. The image forming apparatus according to claim 1, wherein the voltage applied to the contact charging member is a DC voltage. 3. The image forming apparatus according to claim 1, wherein the contact charging member is a semiconductive roller. 4. The image forming apparatus according to claim 1, wherein the contact charging member is a semiconductive blade. 5. The image forming apparatus according to claim 1, wherein the contact charging member is a semiconductive brush.