JPH07333949A - Electrification controlling method - Google Patents

Abstract

PURPOSE:To stably obtain an image whose density is constant even though the film thickness of a photoreceptor is reduced by controlling the potential by electrification of the photoreceptor, and keeping the charge density of the surface of the photoreceptor based on the potential difference between the potential by electrification of the photoreceptor and the potential of a developing bias constant. CONSTITUTION:A specified voltage is impressed on an electrode wire 4, and a specified grid voltage is impressed on a grid 6 from a controller 8 for the potential by electrification, so that the photoreceptor 2 is electrified to nearly the same potential as the grid voltage in a state where an electrostatic latent image carrier 1 rotates in a direction shown by an arrow. The potential by electrification of the photoreceptor, that is, the grid voltage is adjusted so that the surface charge density of the photoreceptor 2 based on the potential difference between the potential by electrification of the photoreceptor and the voltage of the developing bias is constant in the case of the electrification control of an electric charge imparting device 3. Consequently, the surface charge density of the photoreceptor 2 based on the potential difference between the potential by electrification of the photoreceptor and the developing bias potential is kept constant even though the light quantity of an exposing device 11 is kept constant. Furthermore, the surface charge density found from the potential by the electrification of the photoreceptor rises as shaving amount increases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of charging a photoconductor on the surface of an electrostatic latent image bearing member in a copying machine or a printer using an electrophotographic method, and particularly to reduction of the film thickness of the photoconductor due to printing. The present invention relates to a method of controlling so that an image having a constant density can be obtained.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as an electrophotographic copying machine, an electrostatic latent image carrier comprises a conductive substrate and a photoconductor formed on the conductive substrate. Thus, a toner image is formed on the surface of this photoconductor. In this type of image forming apparatus, in order to remove toner that has not been transferred to a transfer material such as paper, a plate-shaped blade, a rotary brush roller, or the like is brought into contact with the photoconductor to remove residual toner. I am trying. However, due to the presence of these blades and brush rollers, there is a problem in that the film thickness of the photoconductor is reduced along with the printing durability, which reduces the sensitivity of the photoconductor and changes the developing characteristics.

Therefore, conventionally, two methods have been adopted in order to compensate for the decrease in the sensitivity of the photoconductor due to the decrease in the film thickness of the photoconductor. First, the first method is a method used in a corotron in which an electrode wire is arranged in parallel with the photoconductor and a voltage is applied to the wire to charge the photoconductor. In this method, as shown in FIG. 5, since the charge amount Q _V0 supplied to the photoconductor is constant, (a) the abrasion amount Δd increases, that is, (b) as the sensitivity decreases (c) of the photoconductor Since the charged potential V ₀ is reduced, the (d) light amount of the exposure lamp is reduced, which reduces the (e) surface charge density Q _{V0 -VB of the} photoreceptor based on the charged potential V ₀ -V _B.

The second method is applied to not only the above scorotron but also other charging devices.
As shown in FIG. 6, (a) the amount of abrasion is increased, (b) regardless of the decrease in sensitivity, (c) the charged potential V ₀ of the photoconductor is kept constant, while (d) the amount of light of the exposure lamp is reduced. The surface charge density Q _V0-VB of the photoconductor (e) is increased according to the amount.

[0005]

However, according to the first method, (a) the amount of abrasion of the photoconductor is increased and (d) the toner adhesion amount TD on the photoconductor is decreased, and (g) the image density I is reduced.
There is a problem in that D is reduced, and thus reproducibility of fine lines is reduced. On the other hand, in the second method, conversely, (a) the amount of abrasion of the photoconductor increases and (d) the toner adhesion amount TD increases, and the line becomes thick, or the toner that cannot be scraped off by the blade appears on the image. There is a problem that they adhere to each other and deteriorate the image quality. Further, there is a problem that the life of the exposure lamp is shortened and the lamp must be replaced early.

[0006]

SUMMARY OF THE INVENTION Therefore, according to the present invention, the electrostatic latent image formed on the photosensitive member is developed by using the charged position of the photosensitive member and a developer carrying member for applying toner to the photosensitive member. It was made paying attention to the point that it is made based on the potential difference from the applied developing bias potential, and it is obtained from the potential difference between the photoconductor charge level and the developing bias potential by predicting or actually measuring the amount of abrasion of the photosensitive body. The charge position of the photoconductor is controlled so that the surface charge density of the photoconductor is kept constant.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an electrophotographic image forming apparatus,
1 shows a configuration of a main part necessary for explaining the basic principle of the charging method according to the present invention, and the drum type electrostatic latent image carrier 1 is
The outer periphery is covered with a photoconductor 2 having a predetermined thickness, and is driven to rotate in the arrow direction (counterclockwise direction). The charge applying device 3 charges the photoconductor 2 and is provided in a holder 4 having an opening facing the photoconductor 2, an electrode wire 5 stretched in parallel with the photoconductor 2, and an opening in the holder 4. A scorotron made up of a mesh or grid 6 formed by the above is used, and the electrode wire 5 is connected to a power supply 7. The charging position control device 8 includes a grid 6
This is a device for controlling the charge level of the photoconductor 2 by adjusting the voltage applied to the. The scraped amount detecting device 9 is a device for detecting the scraped amount of the photoconductor 2, and in this embodiment, the scraped amount Δd is proportional to the number of copies X as shown in FIG.
The number of copies is counted at 0, and the abrasion amount is calculated from the counted value. The exposure device 11 is for exposing the photoconductor 2 charged by the charge applying device 3 with image light to form an electrostatic latent image. The toner carrier 12 makes toner visible on the electrostatic latent image formed on the photoconductor 2 by applying toner to the electrostatic latent image.
The developing bias V _B is applied from 3. The transfer device 14 is a device that transfers the toner attached to the photoconductor 2 to a transfer material 15 such as paper. The cleaning blade 16 scrapes off the toner remaining on the photoconductor 2 without being transferred to the transfer material 15.
The charge removing device 17 is a device that removes charges remaining on the photoconductor 2 after transfer.

In the image forming apparatus having the above-mentioned structure, a predetermined voltage is applied to the electrode wire 4 while the electrostatic latent image carrier 1 is rotating in the direction of the arrow, and the charge level controller 8 A predetermined grid voltage V _G is applied to the grid 6, whereby the photoconductor 2 is charged to a potential V ₀ (≈V _G ) which is substantially the same as the grid voltage V _G. The charge control here will be described in detail later. Next, the photoreceptor 2 is exposed to image light from the exposure device 11 to form an electrostatic latent image corresponding to the image to be reproduced. This electrostatic latent image is visualized by supplying toner from the toner carrier 12 based on the potential difference between the potential of the photoconductor 2 and the developing bias potential V _G. Next, the toner image is transferred to the transfer material 15 by the transfer device 14. However, all the toner on the photoconductor 2 is not transferred to the transfer material 15, and the residual toner is scraped off by the cleaning blade 16. Further, the electric charge remaining on the photoconductor 2 is removed by the electric charge removing device 17.

In the charge control of the charge applying device 3, the charge position of the photoconductor is set so that the surface charge density Q _{V0-VB of the} photoconductor based on the potential difference between the photoconductor charge position V ₀ and the developing bias voltage V _B becomes constant. V ₀ , that is, the grid voltage V _G is adjusted. Specifically, with reference to FIG. 3, in the abrasion amount detecting device 9, using the relational expression (Equation 1) (see FIG. 2) between the abrasion amount of the photoconductor and the number of copies, which is previously obtained from the experiment, From photoconductor 2
The film thickness d of is calculated.

[0010]

[Formula 1] α = Δd / ΔX Δd: Abrasion amount of photoconductor ΔX: Number of copies α: Abrasion ratio

[0011]

D _X = d ₀ − (X / α) d _X : photoconductor film thickness after copying X sheets d ₀ : initial photoconductor film thickness X: number of copies α: scraping ratio

Next, the grid voltage V _GX at the time of the number of copies X is obtained based on the equation 3.

[0013]

## _EQU3 ## V _GX = (V _G0 −V _B ) · (d _X / d ₀ ) + V _B = (V _G0 −V _B ) · [1−X / (α · d ₀ )] + V _B V _GX : Grid voltage at the time of the number of copies X V _G0 : Initial grid voltage V _B : Development bias voltage

This equation 3 is a number obtained by modifying the relational expression (equation 4) of the surface charge density Q of the photoconductor, the surface potential V, and the film thickness d of the photoconductor, and the relational expression of V _G ≈V _0. It is derived from the relationships of 5, 5, and 7.

[0015]

[Formula 4] V = Q · d / (ε ₀ · ε _r ) V: Photoconductor surface potential Q: Photoconductor surface charge density d: Photoconductor film thickness ε ₀ : Vacuum permittivity ε _r : Specific permittivity (OPC In the case of photoconductor, ε _r = 3)

[0016]

[ _Formula 5] V _G0- V _B = Q _G0-VB · d ₀ / (ε ₀ · ε _r )

[0017]

[ _Equation 6] V _GX- V _B = Q _GX-VB · d ₀ / (ε ₀ · ε _r )

[0018]

[ _Equation 7] Q _G0-VB = Q _GX-VB

[0019] Subsequently, the initial grid applied voltage (V _G)
Difference (ΔV) from the grid voltage (V _GX ) when copying X sheets
_G ) is obtained (see Eq. 8), and the grid voltage is lowered by this potential difference (ΔV _G ).

[0020]

[Formula 8] ΔV _G = V _G −V _GX = X / (α · d ₀ )

When the grid voltage V _G is adjusted for each predetermined number of sheets as described above, as shown in FIG.
(A) Increase in abrasion amount, (b) Sensitivity decrease, and
(C) The charged position V ₀ decreases. However, the exposure device 11
(D) Even if the amount of light is maintained constant, the (f) surface charge density Q _{V0 -VB of the} photoconductor 2 based on the potential difference V ₀ -V _B between the photoconductor charging position V ₀ and the developing bias potential V _B is Maintained constant. It should be noted that the surface charge density Q _V0 (e) obtained from the photoconductor charge potential V ₀ increases with an increase in the abrasion amount. However, the rate of increase is the surface charge density Q in the case of the second conventional method.
_It is smaller than _V0 [Fig. 6 (e)]. As a result, (h) the toner adhesion amount TD from the toner carrier 12 to the photoconductor 2 becomes constant regardless of the number of copies, and (g) the image density ID is kept constant.

In the above description, the abrasion amount of the photoconductor 2 is predicted from the number of copies, but the reduction of the film thickness is measured by the film thickness measuring device using a laser or the like, and the grid is calculated based on the result. The voltage V _G may be adjusted. According to this method, it is possible to properly adjust the photoconductor charge level in consideration of the difference in the amount of abrasion between the machines and the difference in the amount of abrasion based on the dimensional error and the setting error of the cleaning blade.

Further, when predicting the abrasion amount of the photoconductor, the abrasion amount can be estimated not only from the number of copies but also from the number of revolutions of the photoconductor, the copying time, the drive time or the number of revolutions of the motor for driving the photoconductor, and the like. Good.

Further, the charged potential of the photoconductor is measured by a surface electrometer 18
Alternatively, the grid voltage may be corrected using the measurement result (see FIG. 1). According to this method, the charged potential of the photoconductor 2 is accurately detected and controlled.

Furthermore, in the above embodiment, a scorotron is used as the charge applying device 3 and the grid voltage is changed to adjust the charging position of the photoconductor. However, charging is performed by adjusting the distance between the grid and the photoconductor. The position of the photoconductor may be adjusted by adjusting the voltage applied to the electrode wires in the case of a corotron without a grid, or the charging device using a charging member such as a blade or a brush. in the case of,
Contact pressure, contact length of each charging member to the photoreceptor,
Alternatively, the charging potential may be adjusted by adjusting the voltage applied to these charging members.

Further, the charge level of the photoconductor may be adjusted continuously in proportion to the decrease in the film thickness of the photoconductor, or may be adjusted stepwise for each predetermined abrasion amount.

According to the present invention, the photoconductor charge level is controlled,
The increase in the number of copies and the change in image density were examined. The experimental conditions are as shown below. The abrasion amount of the photoconductor was predicted from the number of copies based on known data. Further, the charged potential V _{0 of the} photoconductor was controlled by adjusting the grid voltage while measuring it with a surface electrometer.

Experimental conditions ・ Copier used: EP54 manufactured by Minolta Camera Co., Ltd.
00 ・ Developer EP5400 developer ・ Photoreceptor OPC photoreceptor

The results of the experiment are shown in FIG. In this figure, Q _V0-VB (C / cm ² ) is the following Formula 9 obtained by modifying Formula 4 based on the potential difference V ₀ -V _B between the charged potential V ₀ of the photoconductor and the developing bias potential V _B. The surface charge density of the photoconductor obtained from

[0030]

[ _Equation 9] Q _{V0 −VB} = (V ₀ −V _B ) · (ε ₀ · ε _r ) / d

As is apparent from FIG. 7, in the charging control method according to the present invention, the surface charge density Q of the photoconductor based on the potential difference between the photoconductor charging position V ₀ and the developing bias potential V _B.
As a result of controlling _V0-VB to be constant, both the reflection density ID and the toner adhesion amount TD were kept constant even if the film thickness of the photoconductor was reduced. Also, the number of copies 120K (photosensitive film thickness: 10μ
Up to m), an image of almost constant density without fog is obtained,
The photoconductor could be used until image noise (white spots, black spots, etc.) caused by deterioration of the photoconductor occurred.

As Comparative Example 1, FIG. 8 shows the result of charge control so that the surface charge density Q _V0 becomes constant based on the charged position V ₀ of the photoconductor. As Comparative Example 2, FIG. 9 shows the result of charge control in which the charge position V ₀ of the photoconductor is kept constant and the exposure amount is increased as the number of copies increases. The other conditions were set the same as the experimental conditions of the present invention.

As a result, in the case of Comparative Example 1, the reflection density I
D, the toner adhesion amount TD tended to decrease as the film thickness decreased. Further, when the number of copies was 50K, the image became unclear, and further copying was impossible. On the other hand, in the case of Comparative Example 2, the reflection density ID and the toner adhesion amount TD increase as the film thickness decreases.
increased. At the time when the number of copies was 80K, the exposure lamp exceeded the endurance limit and further copying was impossible.

[0034]

As is apparent from the above description, according to the charging control method of the present invention, the image is stable at a constant density even if the film thickness of the photoconductor used in the electrophotographic copying machine is reduced. Obtained. Further, the durable life of the photoconductor and the exposure lamp is extended, and the running cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic main configuration of a copying machine related to a charging control method according to the present invention.

FIG. 2 is a diagram showing the relationship between the number of copies and the amount of abrasion of the photoconductor.

FIG. 3 is an explanatory diagram of a charge control method according to the present invention.

FIG. 4 is a diagram showing changes in image density and the like when the charging control method according to the present invention is carried out.

FIG. 5 is a diagram showing changes in image density and the like when the first conventional charge control method is carried out.

FIG. 6 is a diagram showing changes in image density and the like when a second conventional charge control method is carried out.

FIG. 7 is a table showing experimental results of the charge control method according to the present invention.

FIG. 8 is a table showing experimental results of the first conventional charge control method.

FIG. 9 is a table showing experimental results of a second conventional charge control method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrostatic latent image carrier, 2 ... Photosensitive body, 3 ... Charge applying device,
6 ... Grid, 8 ... Charge level control device, 9 ... Scrap amount detecting device, 10 ... Copy number counter, 12 ... Toner carrier, 1
3 ... Development bias power supply.

Claims (1)

[Claims] 1. A photosensitive member charge position is controlled according to a decrease in the thickness of the photosensitive member, and a photosensitive member surface charge density based on a potential difference between the photosensitive member charge position and a developing bias potential is kept constant. Charge control method.