JPH0625877B2 - Surface potential detector - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a surface potential detecting device in an electrophotographic copying machine or the like, and more particularly to a surface potential detecting device capable of easily detecting the surface potential of a photosensitive surface or the like by using an impedance element. Regarding

[Prior art]

An electrophotographic copying apparatus uses, for example, a photoconductor drum as an image carrier, an optical device is provided above the photoconductor drum, and a charger, a developing device, a transfer device, a cleaning device, etc. are provided near the peripheral surface of the photoconductor drum. ing.

An electrostatic latent image of the original is formed on the photosensitive surface of the photosensitive drum by the exposure containing the information of the original by the optical device, and the electrostatic latent image of the original is formed by the toner contained in the developer in the developing device by the developing device as the photosensitive drum rotates. The latent image is visualized. The toner image on the photosensitive surface is transferred onto a transfer paper by a transfer device, and the transfer paper is carried out of the device via a fixing device. In addition, the toner not completely transferred by the transfer device is cleaned by the cleaning device,
A uniform charge is charged on the photosensitive surface by the charger to prepare for the next exposure.

In the electrophotographic copying machine in such a process, the voltage charged on the photosensitive surface by the charger is controlled within a certain range, so it is necessary to measure the surface potential of the photosensitive surface and feed it back to the high voltage generator.

The conventional device for measuring the surface potential of the photosensitive surface is to directly measure the surface potential of the photosensitive surface by providing a surface electrometer using a capacitor or the like near the photosensitive surface.

[Problems of conventional technology]

However, the conventional surface electrometer for measuring the charged potential of the photosensitive surface is very expensive and leads to an increase in the cost of the apparatus. Further, during the detection of the dark portion potential of the photosensitive surface, the dark portion potential is developed at a high density when passing through the developing portion, and there is a drawback that the toner consumption increases.

[Object of the Invention]

In view of the above-mentioned conventional drawbacks, the present invention connects a high-impedance element to a developing sleeve that rubs against a photosensitive surface, and grounds the other end of the high-impedance element so that the potential according to the surface potential of the photosensitive surface is increased. It is an object of the present invention to provide a surface potential detecting device capable of measuring the surface potential of a photosensitive surface by utilizing the induction of light.

[Main points of the invention]

In order to achieve the above object, the present invention provides a surface potential detecting device for an image carrier having a photosensitive surface on a grounded conductive base layer, wherein a developer is held on the peripheral surface and an electrostatic latent image on the image carrier is held. It is characterized in that it includes a sleeve of a developing machine for developing the toner and an impedance element connected between the sleeve and the ground, and detects a voltage applied to the impedance element.

Example of Invention

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a principle block diagram of a surface potential measuring device according to the present invention.

In the figure, a charger 2 and a developing sleeve 3 are provided near the peripheral surface of the photosensitive drum 1, and exposure 5 is performed on the photosensitive surface 4 of the photosensitive drum 1 between the charger 2 and the developing sleeve 3.
A high impedance element 6 is connected to the developing sleeve 3, and the other end of the high impedance element 6 is grounded.

FIG. 2 is an equivalent circuit of the photosensitive drum 1, the developing sleeve 3, and the high impedance element 6 of FIG. In the figure, a varistor 7 is the equivalent resistance of the magnetic brush that is in contact with the photosensitive surface 4, and a parallel circuit of the resistor 8 and the capacitor 9 is an equivalent circuit of the conventionally known photosensitive drum 1. The resistance of the varistor 7 is generally a so-called non-linear load that does not exhibit an eigenvalue and changes depending on the voltage, and exhibits a value of several hundreds KΩ to several tens of MΩ at a practical voltage.

The parallel circuit of the resistor 8 and the capacitor 9, the varistor 7, and the high impedance element 6 form a closed circuit, and the connection point of the parallel circuit of the resistor 8 and the capacitor 9 and the high impedance element 6 is grounded.

Letting R be the impedance of the high impedance element 6 and R _D be the impedance of the magnetic brush when the surface potential V _s of the photosensitive surface 4 is in contact with the magnetic brush, the potential V _i induced in the developing sleeve 3 is the surface potential V _s . It is a value obtained by dividing the pressure by R and R _D and is represented by the following formula.

V _i = {R / (R + R _D )} · V _s Therefore, when the impedance R is set large and the high impedance element 6 having a value that can ignore the impedance R _D is selected, the induced potential V _i and the surface potential V _s are almost equal. Then, the surface potential V _s is induced in the developing sleeve 3. Actually, when the induced potential V _i approaches the surface potential V _s , the impedance R _{D of the} magnetic brush becomes infinite, so the induced potential V _i
i converges near the potential of 0.9 × V _s . Thus the bias potential setting suitable for the surface potential V _s by performing look strained was corrected decrement from the surface potential V _s is obtained.

An actual measurement example measured by this embodiment is shown in FIG. This figure is a characteristic diagram showing the relationship between the surface potential V _s and the induced potential V _i when the resistance value of the high impedance element 6 is 200 MΩ.

The surface potential V _s and the induced potential V _i of the photosensitive surface form a curve indicated by a solid line A in the figure. The solid line A is substantially equal to the straight line in which the potential V _i and the potential V _s are completely proportional, which is indicated by the dotted line B in FIG.

The following table shows the results of actual measurement of the surface potential V _s and the developing sleeve potential V _i when a developer having a volume resistance of 10 ⁸ Ω · cm is used and the impedance R is set to 50 MΩ, 100 MΩ, and 200 MΩ.

As described above, according to the present embodiment, the potential proportional to the surface potential of the photosensitive surface appears at both ends of the high impedance element, and this potential is measured, and the measured potential is multiplied by a constant value. The surface potential of the surface can be measured.

FIG. 4 is a diagram showing a specific embodiment of the present invention.

A high impedance element 6 is provided between the developing sleeve 3 and the ground.
The resistor 10 is connected in series to divide the potential applied to the developing sleeve 3, and the divided potential is input to the plus input of the differential amplifier 13 via the resistor 12 in the amplifier circuit 11. The negative input of the differential amplifier 13 is grounded via the resistor 14, and the comparison reference potential is the ground potential. Further, the differential amplifier 13 is provided with a negative feedback circuit using the resistor 15. The output of the amplifier circuit 11 is converted into a digital signal by the analog / digital converter 16 and input to the arithmetic control circuit 17.

A hold circuit is incorporated in the arithmetic and control unit 17 to temporarily hold a digital input signal. Arithmetic control circuit 17
The output of is input to the digital-analog converter 18, and the signal converted into the analog signal by the digital-analog converter 18 is input to the high voltage generator 19. The high voltage generator 19 applies an appropriate bias voltage according to the input analog signal to the developing sleeve 3 via the diode 20.

The operation of the surface potential measuring device having the above configuration will be described with reference to the timing chart of FIG.

First, the photosensitive surface 4 is subjected to uniform charging and exposure including original information to form a bright portion potential V _L on the photosensitive surface 4.

Next, when this bright portion potential comes into contact with the developing sleeve 3, an induced potential V _i corresponding to the bright portion potential is induced from the photosensitive surface 4 to the developing sleeve 3, and this induced potential V _i is sampled for a certain period of time, High impedance element 9 and resistor 10
The potential V _i is divided by the
To enter. The amplifier circuit 11 compares the ground potential input to the negative input of the differential amplifier 13 with the divided induced potential input to the positive input, amplifies the comparison potential, and outputs the output to the analog-digital converter 16. input. The signal input to the analog / digital converter 16 is converted into a digital signal by the analog / digital converter 16 and input to the arithmetic control circuit 17. Arithmetic control circuit 1
At 7, the surface potential is calculated according to the input signal, the bias voltage according to the surface potential is determined, and the output thereof is input to the digital / analog converter 18. A signal analogized by the digital-analog converter 18 is sent to the high voltage generator 19, and the high voltage generator 19 applies a proper developing bias potential to the developing sleeve 3 via the diode 20 according to the input analog signal.

In this embodiment, the potential of the photosensitive surface 4 is applied to the developing sleeve 3 by using a magnetic brush that can be used as the developing sleeve 3, and the potential applied to the developing sleeve 3 is divided by the high impedance element 6 and the resistor 10 to divide the photosensitive surface. The device also includes detecting the surface potential of No. 4 and controlling the sleeve potential to an appropriate value.

As the high impedance element 6 used in the present invention, a commercially available resistance element can be used, and it is very inexpensive as compared with the conventional surface electrometer.

Further, the present invention is effective not only for measuring the light potential but also for measuring the dark potential. In that case, the developing sleeve potential V _i and the dark portion potential V _D are substantially equal to each other, and the potential difference from the surface potential is small, so that development during sampling is not performed and wasteful toner consumption can be suppressed, and the surface potential is efficiently increased. Can be measured.

〔The invention's effect〕

As described in detail above, according to the present invention, the surface potential of the photosensitive surface or the like can be easily measured by connecting a high impedance element to the developing sleeve without using a dedicated surface electrometer for measuring the surface potential of the photosensitive surface or the like. Can be measured. Further, the high impedance element is inexpensive, and the cost of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of the present invention, and FIG.
FIG. 3 is an equivalent circuit diagram of the figure, FIG. 3 is a characteristic diagram showing the relationship between the surface potential and the induced potential, FIG. 4 is a configuration diagram for explaining a concrete example of the present invention, and FIG. 5 is a timing chart diagram. . 3 ... Development sleeve, 6 ... High impedance element, 1
1 ... Amplifying circuit, 13 ... Differential amplifier, 17 ... Arithmetic control circuit, 19 ... High-voltage generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-37805 (JP, A) JP-A-58-224355 (JP, A) JP-A-58-153951 (JP, A) Actual development Sho-55- 140750 (JP, U) Actual public 61-147050 (JP, Y2) Actual public 62-39399 (JP, Y2)

Claims (1)

[Claims] 1. A surface potential detecting device for an image carrier having a photosensitive surface on a grounded conductive base layer, comprising: a developing device which holds a developer on a peripheral surface and develops an electrostatic latent image on the image carrier. A surface potential detecting device comprising a sleeve and an impedance element connected between the sleeve and the ground, and detecting a voltage applied to the impedance element.