JPH02170175A - Image forming device - Google Patents

Abstract

PURPOSE:To optimize each image forming condition such as electrification, exposure and development, etc., based on detected potential by providing a detecting means for detecting the potential on a photosensitive body by coming into contact with the surface of the photosensitive body. CONSTITUTION:By turning on an electrifying high voltage power source 9 and a grid high voltage power source 10, electrifying high voltage VP is applied on an electrifying wire 3 and grid voltage VG is applied on a grid electrode 4 respectively, and all the surface of the photosensitive body 1 is exposed by an exposing means 17. When a discharging part(transfer means) 19 is connected to a current detection resistance 15 by switching a switching means 16, the current in accordance with the surface potential VL of the photosensitive body 1 flows in the resistance 15 and voltage VO is generated. A control part 21 calculates the surface potential VL with the voltage VO and judges whether or not it is a specified value. In the case that the detected potential VL is deviated from the specified value, the command of the alteration of the voltage VG is outputted to the power source 10 so as to repeat the above actions. When the detected potential VL is the specified one, the voltage VG is decided as a present condition and the formation of an image is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image forming apparatus using electrostatic photographic processes such as charging, exposure, development, and transfer.

(Prior art) In electrostatic photography, after a photoreceptor is primarily charged by a charging means, it is exposed to light by an exposure means to generate different potentials on the photoreceptor in exposed and non-exposed areas, thereby increasing the electrostatic potential. An image is formed and the latent image is developed with toner, but the potential of the exposed area changes greatly due to variations in the photoreceptor itself and changes over time.

Therefore, in general, the potential on the photoreceptor is detected by a detection means,
A method is used in which charging, exposure, development, and other conditions are optimized based on the detected potential to obtain a stable image.

(Problems to be Solved by the Invention) However, since conventional detection means employ a potential sensor such as a non-contact type FET for the photoconductor, they are susceptible to noise, and it is difficult to accurately detect the surface potential of the photoconductor. I couldn't do it. Therefore, electrostatic charge.

Conditions such as exposure and development could not be sufficiently optimized, and stable images could not be obtained. Further, the potential sensor itself is expensive, and as a result of providing special detection means near the photoreceptor, the structure becomes complicated and costs increase.

This invention is intended to solve the above-mentioned problems, and it is possible to accurately detect the surface potential of a photoreceptor and optimize charging, exposure, development, etc. conditions based on the detection results, thereby obtaining stable images. The object of the present invention is to provide an image forming apparatus that can perform the following operations. Another object of the present invention is to provide an image forming apparatus equipped with a potential detection means that is inexpensive and has a simple structure.

(Means for Solving the Problems) In order to achieve the above object, the present invention projects an image of an original onto a uniformly charged photoreceptor to form an electrostatic latent image, and An image forming apparatus that visualizes an image and then transfers it to a recording paper is provided with a detection means that detects the potential on the photoreceptor by contacting the surface of the photoreceptor.

(Function) The function of the present invention based on the above configuration is that the surface potential can be accurately measured by the detection means in contact with the surface of the photoreceptor.

(Example) Next, the present invention will be described based on an example shown in the accompanying drawings.

In the figure, l is a photoreceptor consisting of a photoconductive layer 2a and a conductive layer 2b, 3 is a charging wire, 4 is a grid electrode, 5 is a developer, and 6
The toner 7 contained in the developing device 5 forms a thin toner film on the surface of the developing sleeve to which a high developing pressure is applied. 8
10 is a developing high voltage power source that applies voltage to the developing sleeve 7; 9 is a charging high voltage power source that applies voltage to the charging wire 3; and 10 is a grid high voltage power source that applies voltage to the grid electrode 4.

13 is a cleaner, 14 is a static elimination lamp, and 17 is an exposure means such as a laser scanner.

Reference numeral 18 denotes a detection means in contact with the surface of the photoreceptor 1, and the detection means 18 includes a discharge section 19 that discharges charges on the surface of the photoreceptor 1, and a detection section 2 that detects the current discharged from the discharge section 19.
It is composed of 0.

In the illustrated embodiment, the discharge section 19 also serves as a transfer means, and can be applied with a voltage from the transfer high-voltage power source 11.

Furthermore, the detection section 20 includes a current detection resistor 15 and a control section 21.
It is composed of. In addition, the discharge section 19 and the detection section 20
A switching means 16 is provided between the discharging section 19 and the discharging section 19. There is. The control unit 21 includes a charging high voltage power source 9. Grid high voltage power supply 10. Exposure means 17. Developing high voltage power supply 8. The potential V of the surface of the photoreceptor 1 is determined from the discharge current value detected by the current detection resistor 15, which is connected to the transfer high voltage power source 11.

and the calculated surface potential V.

If it is a specified value, the state is maintained as it is, and if the calculated surface potential VL deviates from the specified value, the voltage etc. is applied to each connection site so that the surface potential VL becomes equal to the specified value. It also has a control function that outputs a signal that changes the

Note that a specific method of calculating the surface potential vL of the photoreceptor 1 by the control unit 21 will be described later.

Next, the image forming operation will be described assuming that the potential of the grid electrode 4 is vG, the potential of the charging line 3 is VP, the potential of the exposed portion on the photoreceptor I is VL, and the potential of the developing sleeve 7 is VD.

First, a negative high voltage (
Several gyropol)) Vp is applied, and the grid electrode 4
is a negative voltage VG of several hundred ports due to the grid high voltage power supply 10.
is applied. Then, corona discharge occurs, so that the surface of the photoreceptor 1 has a potential approximately equal to VC. Next, the photoreceptor l is exposed to light by the exposure means 17, and the potential of the exposed portion rises to a potential VL higher than vG, and a potential difference is created between the exposed and non-exposed areas, resulting in an electrostatic latent image that is the same as the original image. is formed. In this poem, a thin film of toner 6 is formed on the surface of the developing sleeve 7, and the developing high-voltage power supply 8 generates a high voltage.
When (Vc<Vo<Lc) is applied, toner 6
Due to its characteristics, it is negatively charged and adheres to the Vl portion, that is, the exposed portion of the photoreceptor 1, so that the electrostatic latent image becomes visible. The adhered toner 6 is transferred to the photoreceptor 1 by a transfer means (discharge section) 19 to which a positive voltage is applied by a transfer high-voltage power source 11.
The image is then transferred onto the recording paper 12. The toner 6 remaining on the surface of the photoreceptor 1 without being transferred onto the recording paper 12 is scraped off by the cleaner 13. Finally, the photoreceptor 1 is uniformly irradiated with light by the static elimination lamp 14, and the surface potential is returned to 0 port in preparation for the next image formation.

Here, a method for detecting the surface potential of the photoreceptor 1 will be explained based on FIG. 2. Negative ions adhere to the surface of the photoreceptor 1 due to corona discharge from the charging wire 3 to which the negative high voltage VP is applied, and the potential becomes approximately equal to the potential VG of the grid electrode 4.

Since the photoconductive layer 2a of the photoreceptor 1 is an insulator unless exposed to light, a certain electrostatic capacitance C (F/m2) exists on the surfaces of the conductive layer 2b and the photoconductive layer 2a. Now, since the potential difference between the surfaces of the conductor layer 2b and the photoconductive layer is Vc, the photoconductive layer 2
The charge density on the surface of a is C*VG (07m2). Similarly, the surface charge density of a portion of the surface of the photoreceptor l that is exposed to light and has a surface potential of V[ is C-vL (07m2). Here, when the transfer means (discharge section) 19 is dropped to GND through the resistor 15, the charges on the surface of the photoreceptor l are discharged through the transfer means 19.

The current flowing through the resistor 15 at this time is: I=r・ω・,Q, C・■s Where, r is the radius of the photoconductor, ω is the angular velocity of the photoconductor, C is the length of the photoconductor, and C is The unit area capacitance between the conductive layer and the photoconductive layer surface, VS, is the surface potential of the photoreceptor. Therefore, resistance 1
If the voltage generated across the R2 resistor 13 is VO, the surface potential Vs of the photoconductive layer is expressed by the following equation.

Vs= I ÷ (r・ω・1−C) = Vo÷(R−r
・ω・Tachi・C) The surface potential of the photoconductive layer 2a can be detected in the above manner.

When measuring the surface potential of the photoconductive layer 2a, the recording paper must not be passed, and the developing high voltage Vo is 0FFL.

I have to keep it. It goes without saying that the switching means 16 connects the discharge section 19 to the current detection resistor 15.

FIG. 3 is a graph diagram showing potential changes on the photoreceptor 1 during image formation, and FIG. 4 is a graph diagram showing changes in vL due to changes in the characteristics of the photoreceptor l. In this way, photoreceptor 1
When the potential V1 of the exposed part of the surface changes, the developing high voltage V
Since D is constant, the development characteristics change greatly, i.e.
This has a significant effect on the image transferred to the recording paper.

Next, a method for stabilizing the potential V on the exposed photoreceptor will be specifically described.

As shown in FIG. 5(a), the surface potential vL of the exposed photoreceptor 1 tends to deviate from the target value.

Now, if ■[ is higher than the target value, vL -V.

Since the (development high pressure) increases, a large amount of toner 6 tends to adhere to the surface of the photoreceptor 1. Therefore, the image formed on the transfer paper 12 will be darker than usual. Therefore, the voltage v of the grid high voltage power supply 10 is controlled via the control unit 1o.
When G is lowered, vL shifts toward the target value. Therefore, if VG is changed while detecting vL- using the above-described method, vL becomes close to the specified value as shown in FIG. 5(b), and good development characteristics are obtained.

FIG. 6 is a flowchart for determining the grid voltage VG while measuring the surface potential VL on the photoreceptor 1.

First, the charging high voltage power supply 9 is ONL, and the charging wire 3 is charged with the high voltage V
P is applied, the grid high-voltage power source lo is turned on, and the grid voltage VG is applied to the grid electrode 4, and the exposure means 17
The entire surface of the photoreceptor 1 is exposed to light. Further, the switching means 16 is switched to connect the discharge section 19 to the current detection resistor 15 (STEPl). Then, the surface potential of photoreceptor l (
A current corresponding to the potential (potential of the exposed portion) VL flows through the current detection resistor 15, and a voltage Vo is generated. The control unit 21 calculates the surface potential V[ from the Vo (STEP 2), and determines whether it is a specified value (STEP 3). If the detected potential V[ deviates from the specified value, a command to change the voltage vG is output to the grid high voltage power supply 10 (
STEP4) L, repeat the operation of 5TEP2 again.

When the detected potential V is the specified value in 5TEP3, the grid voltage vG is determined to be the current value (5TEP5)
L: Subsequent image formation will be performed.

(Second Example) In the above example, the grid potential VG was changed, but the graphs in FIGS. 7(a) and (b) show that the developing sleeve 7
This is to change the voltage Vo applied to. Photoreceptor 1
Even if the surface potential V changes, the voltage V applied to the developing sleeve 7 changes accordingly.

By changing (1) [-VD can be maintained at an appropriate value, development characteristics can be maintained favorably. However, since the potential ■L on the photoreceptor 1 changes, it may be necessary to change the transfer voltage applied to the transfer means 19.

(Third Embodiment) In the embodiment shown in FIGS. 8(a) and 8(b), the surface potential VL of the photoreceptor 1 is stabilized by changing the exposure amount.

The surface potential V[ is low when the exposure amount is small, and becomes high when the exposure amount is large. Therefore, the exposure means 17 while detecting ■[
An appropriate surface potential V[ can be obtained by adjusting the amount of exposure light. However, since the pixel diameter also changes when the exposure light amount is changed, an appropriate laser light amount must be set depending on the relationship between the pixel diameter and the surface potential vL.

(Effects of the Invention) Since the present invention is configured as described above, it is possible to accurately detect the surface potential of the photoreceptor, and each image forming condition such as charging, exposure, and development can be determined based on the detected potential. can be maintained at its optimum level.

Therefore, it is possible to obtain a high-quality image forming apparatus in which images transferred to recording paper are stable and of high quality. Further, since the discharge means also serves as the transfer means, there is another effect that the structure is simple and can be manufactured at low cost.

[Brief explanation of the drawing]

1 to 8 show examples of the present invention, FIG. 1 is an explanatory diagram showing the overall schematic configuration, FIG. 2 is an explanatory diagram showing the principle of the invention, and FIG. Graphs showing the surface potential of the photoreceptor; FIG. 4 is a graph showing the surface potential due to changes in the characteristics of the photoreceptor; FIGS. 5(a), (b); FIGS. 7(a), (b); Figure 8(a). (b) is a graph showing stabilization of the surface potential due to changes in grid voltage, stabilization of development characteristics due to changes in development voltage, and stabilization of surface potential due to changes in exposure amount. It is a flowchart figure shown. Explanation of symbols 1...Photoconductor 12...Recording paper 16,...
-Switching means 18...Detection means 19...Discharge section (transfer means) 20...Detection section

Claims (5)

[Claims] (1) An image forming device that projects an image of a document onto a uniformly charged photoreceptor to form an electrostatic latent image, visualizes the electrostatic latent image, and then transfers it to recording paper. An image forming apparatus according to the present invention, further comprising a detection means for detecting a potential on the photoreceptor by contacting the surface of the photoreceptor. (2) The detection means is charged based on the detected potential;
The image forming apparatus according to claim 1, further comprising means for changing image forming conditions such as exposure and development. (3) The image forming apparatus according to claim 1, wherein the detection means includes a discharge section that discharges charges on the surface of the photoreceptor, and a detection section that detects the current discharged from the discharge section. (4) The image forming apparatus according to claim 3, wherein the discharge section also serves as a transfer means for transferring the visible image on the photoreceptor to recording paper. (5) The image forming apparatus according to claim 4, wherein the discharge section has a switching means that can be switched between discharge and transfer.