JPH05119565A - Image forming device - Google Patents

Abstract

PURPOSE:To provide the image forming device where an appropriate image can be constantly formed by compensating variation in surface potential of a photosensitive drum. CONSTITUTION:The device is provided with an electrifying device 11 electrifying the surface of the photosensitive drum to a set potential, a surface potential detection means 30 detecting the surface potential of the electrified photosensitive drum, a discriminating means 31 discriminating whether the minimum value of the detected surface potential of the photosensitive drum is below the set potential or not, an electrification control means 31 increasing impressed voltage to an electrifying device when the minimum value of the detected surface potential is below the set potential, an electric charge erasing means 12 erasing the electric charge of the photosensitive drum, a level variation means 32 varying the level of electric charge erasing by the electric charge erasing means, a potential difference calculating means 31 calculating the difference between the surface potential of the photosensitive drum where the surface potential is raised and the above mentioned set potential, and a level variation control means 31 setting the level of the electric charge erasing by the level variation means.

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, and more particularly to controlling the surface potential of a photosensitive drum.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, the surface of a photosensitive drum is uniformly charged by a charging device, and then an original image scanned by an optical system is guided to the photosensitive drum. An electrostatic latent image is formed on the surface.

In such a device, the high voltage transformer for applying a high voltage to the charging device has a surface of the photosensitive drum of, for example, 700.
A high voltage is generated so as to be charged to a set potential of V.

[0004]

However, the surface potential of the photosensitive drum may vary due to dirt on the charging device, fatigue of the photosensitive drum, or the like.

As described above, the above-mentioned conventional image forming apparatus has a problem that it is impossible to properly form an image when the surface potential of the photosensitive drum varies.

The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of always forming an appropriate image by correcting the variation of the surface potential of the photosensitive drum. To do.

[0007]

In order to achieve the above object, the present invention provides a charging device to which a predetermined voltage is applied to charge the surface of a rotating photosensitive drum to a set potential, and the charged photosensitive member. Surface potential detecting means for detecting the surface potential of the body drum in the axial direction of the drum; determining means for determining whether the minimum value of the detected surface potential of the photosensitive drum is less than or equal to the set potential; When the minimum value of the surface potential of the photosensitive drum is less than or equal to the set potential, the charging control means for increasing the voltage applied to the charging device so as to raise the minimum value of the surface potential to the set potential, and the photosensitive drum. A plurality of charge erasing means arranged in the axial direction of the photosensitive drum for erasing the electric charges, level changing means for changing each charge erasing level by the charge erasing means, and surface potential subtraction. Potential difference calculating means for calculating the difference between the raised surface potential of the photosensitive drum and the set potential in the axial direction of the drum, and to reduce the surface potential of the photosensitive drum by the calculated potential difference. A level change control means for setting the charge erasing level by the level change means is provided (claim 1).

The level changing means outputs a pulse signal to the charge erasing means, and the duty of the pulse is changed based on the control signal from the level changing control means to change the charge erasing level. (Claim 2).

[0009]

According to the present invention having the above-described structure, the surface potential of the photosensitive drum charged by the charging device is detected by the surface potential detecting means, and the minimum value of the surface potential of the photosensitive drum is determined by the discriminating means. It is determined whether or not As a result, when the minimum value of the surface potential of the photosensitive drum is less than or equal to the set potential, the voltage applied to the charging device is increased by the charging control means, and the minimum value of the surface potential is raised to the set potential. Then, the difference between the surface potential of the photosensitive drum whose surface potential has been raised by the potential difference calculation means and the set potential is calculated in the axial direction of the drum, and the charge erasing level set by the level change control means, By the charge erasing means changed by the level changing means, the surface potential of the photosensitive drum is reduced by the calculated potential difference and made uniform.

According to the second aspect of the present invention, the duty of the pulse signal output to the charge erasing means is changed based on the control signal from the level change control means to change the charge erasing level.

[0011]

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to the present invention. The image forming apparatus has a contact glass 1 and a document retainer 2 on the upper surface thereof, and is provided with components such as an optical system L, an image forming unit P, and a transfer paper conveying system inside.

The optical system L is composed of an exposure lamp 3 and a reflection plate 4, and includes a light source section that reciprocates to scan an original document, and reflecting mirrors 5, 6 and 7 that reflect light reflected from the original document to form an optical path. It is composed of a lens unit 8 for adjusting the magnification of a formed image and a fixed mirror 9 for reflecting the reflected light toward a photosensitive drum 10 described later.

Further, the image forming means P includes a photoconductor drum 10 on which an electrostatic latent image is formed, a charging device 11 for charging the photoconductor drum 10 to a set potential of, for example, 700 V, and a charging device 11 having a high voltage. A high-voltage transformer 29 that supplies a voltage, a blank lamp 12 that erases electric charges in unnecessary areas on the photoconductor drum 10, a surface potential sensor 30 that detects the surface potential of the photoconductor drum 10, and an electrostatic latent image by charging toner. A developing device 13 for adhering and developing, a transfer device 14 for transferring a toner image onto a transfer paper, a separating device 15 for separating the transfer paper from the photoconductor drum 10, and toner remaining on the surface of the photoconductor drum 10 after transfer. Cleaning device 16 for cleaning
Etc.

Further, the transfer paper transport system includes, in order from the upstream side in the transport direction, paper feed cassettes 17 and 18 capable of accommodating transfer papers of different sizes, and a paper feed roller 19 for transporting the transfer papers.
20, conveying roller pairs 21, 22 and registration roller pair 2
3 are provided. Further, downstream of the transfer sheet after the transfer in the conveying direction, a conveyor belt 24 for conveying the transfer sheet, a fixing device 25 for fixing the toner image on the transfer sheet, a discharge roller 26 for discharging the transfer sheet to a discharge tray 27, and the like are arranged. It is set up.

On the upper surface of the image forming apparatus, the original document,
An operation panel 28 for setting the size of the transfer paper, the enlargement / reduction mode, or the like is provided.

FIG. 1 is a block diagram showing a control system of an image forming apparatus according to the present invention. Blank lamp 12
Is composed of a series circuit of a light emitting element and a resistor.
As the light emitting element, an element that lights up with a constant light amount is normally adopted regardless of the input power source. The series circuits of the resistors R1 to Rn and the light emitting elements D1 to Dn and D11 to D1n are connected to the voltage generation circuit 32 via terminals T1 to Tn, respectively.
These light emitting elements are arranged side by side along the axial direction on the upper surface of the photosensitive drum 10, and the light emitting elements D1 and D11 and the light emitting elements Dn and D1n are arranged at both ends. ..

The control device 31 controls the operation of the image forming apparatus and is composed of a microcomputer. It controls the high voltage transformer 29 to supply a high voltage to the charging device 11 to charge the photosensitive drum 10 to a set potential. A storage unit 310 that stores the measurement data from the surface potential sensor 30 and the control data of the voltage generation circuit 32 described later is provided, and the terminals T1 to T of the voltage generation circuit 32 are based on the measurement data.
This is to instruct the voltage to be output to n. The high voltage transformer 29 is configured so that the output voltage can be continuously or stepwise increased.

The surface potential sensor 30 is the photosensitive drum 10.
It is designed to be movable in the axial direction. It should be noted that a plurality may be arranged in the axial direction so as to have the same dimension as the axial length.

The control device 31 is charged by the charging device 11 based on the transfer paper size set by the operation panel 28 or the transfer paper size calculated from the set or automatically detected original size and the set magnification. The unnecessary area (other than the transfer area) is obtained from the surface of the photosensitive drum 10, and the blank lamp 12 removes the unnecessary area, that is, erases the electric charge, and controls the charging potential described later.

The voltage generation circuit 32 outputs'H ',' L 'or a pulsed voltage of about 100 Hz, for example, from the terminals T1 to Tn based on an instruction from the control device 31. For example, when “H” is generated at the terminal T1, the light emitting elements D1 and D11 are not lit, and when “L” is generated, a current flows from the power supply circuit 33 toward the terminal T1. D1 and D11 are lit up.

The operation of the image forming apparatus configured as described above will be described with reference to FIGS. FIG. 2A is a diagram showing the initial surface potential of the photoconductor drum 10.
2B is a diagram showing the surface potential raised to at least 700 V or more, and FIG. 2C is a diagram showing the surface potential of the photosensitive drum 10 obtained based on the voltage output from the voltage generating circuit 32. Is. FIG. 3 is a diagram showing voltage waveforms output to the terminals T1 to Tn of the voltage generation circuit 32.

FIG. 4 is a flow chart showing the control operation of the image forming apparatus. When the operation of the image forming apparatus is started, the surface of the photoconductor drum 10 is uniformly charged by the charging device 11 (step S1). Next, the surface potential sensor 30 is moved in the axial direction of the photoconductor drum 10, the surface potential is measured at appropriate intervals (step S2), and the data is stored in the storage unit 310 (step S3).
Now, as shown in FIG. 2A, the potential of the central portion corresponding to the arrangement of the light emitting elements D3 to Dn-2 of the photosensitive drum 10 is 7
It is assumed that it is less than 00V.

Next, the minimum value of the measurement data is extracted (step S4), and it is determined whether or not the minimum value is less than the set potential, for example, 700 V (step S5). If it is less than 700 V, the difference, that is, the minimum value is at least 70.
The output voltage of the high-voltage transformer 29 is increased so as to be 0 V or higher (step S6), and the process returns to step S1.
As shown in (b), the minimum value of the surface potential data is 700.
When it becomes V or more (NO in step S5), the difference between each surface potential data and 700V is calculated (step S7), and the process proceeds to step S8.

Here, assuming that the transfer paper size is the arrangement size of the light emitting elements D2 to Dn-1, for example, FIG.
As shown in (c), the voltage generating circuit 32 has terminals T1 and T2.
n outputs “L” to erase the electric charge in the unnecessary area of the photosensitive drum 10, outputs “H” from the terminals T3 to Tn-2 to maintain 700 V, and from the terminals T2 and Tn−1, A pulsed voltage of about 100 Hz, which outputs "H" and "L" alternately, is output. This pulse voltage lowers the average voltage applied to the blank lamp 12,
The average luminous intensity of the light emitting devices D2, D12, Dn-1, D1n-1 is reduced. As a result, the surface potential of the transfer area of the photosensitive drum 10 is adjusted to a uniform potential of 700V. Then, the control data of the pulse voltage at this time is stored in the storage unit 310 for reference in future control (step S9).

After this, exposure is started (step S1).
0). That is, the light from the light source section is reflected by the document placed on the contact glass 1, and the reflected light is guided to the lens section 8 via the reflecting mirrors 5 to 7, and then passes through the fixed mirror 9. The transfer area of the photosensitive drum 10 is exposed to form an electrostatic latent image.

Next, from the developing device 13 to the photosensitive drum 1
Toner development is performed by attaching the charged toner supplied to 0 to the electrostatic latent image. Then, the toner image is transferred onto the transfer paper by the transfer device 14, and the transfer paper is separated from the photosensitive drum 10 by the separating device 15. Then, after the toner image is fixed on the transfer paper by the fixing device 25, the transfer paper is discharged to the discharge tray 27 by the discharge roller 26.

The average voltage can be changed by changing the duty of the pulse voltage.
The luminous intensity can be adjusted for each of the terminals T1 to Tn.

Further, in this embodiment, the light emitting element which is turned on at a constant luminous intensity when a predetermined voltage is applied is adopted, but the present invention is not limited to this, and a luminous element whose luminous intensity is changed according to the applied voltage is used. You can also In this case, the voltage control may change the voltage level itself instead of the pulse wave.

[0029]

As described above, according to the present invention, the charging device to which a predetermined voltage is applied to charge the surface of the rotating photoconductor drum to the set potential, and the surface potential of the charged photoconductor drum are set to the axis of the drum. Surface potential detection means for detecting the direction,
When the minimum value of the detected surface potential of the photoconductor drum is less than or equal to the set potential, and the minimum value of the surface potential of the photoconductor drum is less than or equal to the set potential, the surface potential Charge control means for increasing the voltage applied to the charging device so as to raise the minimum value to the set potential, and a plurality of charge erasing means arranged in the axial direction of the photoconductor drum for erasing the charge of the photoconductor drum. And level changing means for changing each charge erasing level by the charge erasing means, and a difference between the surface potential of the photosensitive drum whose surface potential is raised and the set potential in the axial direction of the drum. A potential difference calculating means and a level changing system for setting the charge erasing level by the level changing means to lower the surface potential of the photosensitive drum by the calculated potential difference. Since a unit, due to fatigue or the like of the dirt and the photosensitive drum of the charging device, even if there is variation in the surface potential of the photosensitive drum can be corrected always uniform set potential.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system of an image forming apparatus according to the present invention.

2A is a diagram showing the initial surface potential of the photosensitive drum 10, FIG. 2B is a diagram showing the surface potential raised to at least 700 V or more, and FIG. 2C is a voltage generation circuit. Photoreceptor drum 1 obtained based on voltage output from 32
It is a figure which shows the surface potential of 0.

FIG. 3 is a diagram showing voltage waveforms output to terminals T1 to Tn of a voltage generation circuit 32.

FIG. 4 is a flowchart showing a control operation of the image forming apparatus according to the present invention.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to the present invention.

[Explanation of symbols]

 10 Photoreceptor Drum 11 Charging Device 12 Blank Lamp 28 Operation Panel 29 High Voltage Transformer 30 Surface Potential Sensor 31 Control Device 32 Voltage Generation Circuit 33 Power Supply Circuit T1 to Tn Terminals

Claims (2)

[Claims] 1. A charging device to which a predetermined voltage is applied to charge a surface of a rotating photosensitive drum to a set potential, and a surface potential of the charged photosensitive drum is detected in the axial direction of the drum. Surface potential detecting means, determining means for determining whether or not the minimum value of the detected surface potential of the photosensitive drum is less than or equal to the set potential, and the minimum value of surface potential of the photosensitive drum is less than or equal to the set potential. A charging control means for increasing the voltage applied to the charging device so as to raise the minimum value of the surface potential to the set potential, and a plurality of charging control means arranged in the axial direction of the photosensitive drum so as to erase the charge of the photosensitive drum. The charge erasing means provided, level changing means for changing the respective charge erasing levels by the charge erasing means, the surface potential of the photosensitive drum whose surface potential is raised, and the set potential. Potential difference calculating means for calculating the difference in the axial direction of the drum, and level change control means for setting the charge erasing level by the level changing means for reducing the surface potential of the photosensitive drum by the calculated potential difference. An image forming apparatus comprising: 2. The level changing means outputs a pulse signal to the charge erasing means, and the duty of the pulse is changed based on a control signal from the level changing control means to change the charge erasing level. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as described above.