JPS5919871A - Potential sensor - Google Patents

Abstract

PURPOSE:To measure and control contactlessly the charged potential of a photosensitive drum of a dry type copying machine, by constituting a titled sensor of an oscillating circuit whose frequency deviation value is varied by the charged potential of a housing, and an FM demodulating circuit for demodulating a frequency deviation portion. CONSTITUTION:As for a Colpitts oscillating circuit 21, the oscillation frequency is varied by electrostatic capacity by which a variable capacity diode 4 is varied through a capacitor 5. A low frequency signal generated by a low frequency oscillating circuit 20 is applied to the variable capacity diode 4, and the frequency deviation is obtained. Charged potential of a housing 1 is applied to an electrode plate 3 through electrostatic capacity 2 of air, and the frequency deviation value is varied by the charged potential of the housing 1. A low frequency component of the frequency deviation is fetched by an FM demodulating circuit 18 through a limiting circuit 17 for eliminating an AM component which exerts bad influence on FM demodulation, and it is displayed by a display part 19. Since this sensor is not a mechanical vibration system, it can be made small- sized, light and inexpensive.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a potential sensor used for purposes such as improving copy quality by measuring the charged potential of a photosensitive drum of a dry type copying machine without contact and controlling the charged potential. . In other words, it detects and prevents deterioration in copy image quality and uneven shading due to the potential drop caused by drum material quality, leakage current due to humidity, and potential drop caused by variations in high voltage generation circuits. The purpose is to

Further, the potential sensor of the present invention is used not only for dry copying machines but also for non-contact detection of electrostatic potential in powder electrostatic coating machines and semiconductor devices.

Conventionally, there have been many methods for measuring charged potential, but all of them have advantages and disadvantages. One is a foil detector that uses two pieces of metal foil to detect the opening angle of the two pieces, but this method has low reproducibility and is unsuitable for applications that require precision. The other method is to use a high impedance voltmeter in contact with the object to be measured, but this method cannot be used for long periods of time due to deterioration of the contact surface due to friction. Furthermore, it is difficult to accurately measure the potential due to noise generated from the surroundings of the measuring instrument itself due to the high impedance.

There is a vibrating capacitance type electrometer that converts DC voltage into AC voltage, but the method of generating vibration is generally done mechanically.

Therefore, although this method has excellent noise resistance, it has problems such as mechanical reliability, precision, and variations, and is difficult to put into practical use.

The present invention has been made to eliminate the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to the drawings.

First, it is composed of a resistor 6.11 for supplying bias, a resistor 16 for positive feedback, capacitors 12 and 13 for feedback 16, a coil 8 for tuning, a capacitor 7, and a transistor 14 for amplifying and oscillating. The oscillation frequency of the Colpitts oscillation circuit changes due to the changing capacitance of the diode 4 via the capacitor 5.Then, the low frequency signal generated in the low frequency oscillation circuit 20 is Capacitor 9 and noise h for low impedance
The configuration is such that the frequency shift is applied to the variable capacitance diode 4 through the resistor 1o. However, the charged potential of the viewing body 1 is applied to the electrode plate 3 through the static air quantity 2, and this electrode plate 3t/'i and the variable capacitance diode 40
Since it is connected to the cathode side, the frequency deviation value changes depending on the charged potential of the housing 1.

A limiter circuit 17 that sufficiently amplifies all of the oscillation signals with frequency deviation and removes AM components that adversely affect FM demodulation.
After that, the jM demodulation circuit 18 extracts the low frequency component of the frequency shift and displays it on the display section 19 in analog or digital form.

The present invention is configured as described above, and can solve problems such as the reproducibility problem of the foil tester and contact failure due to the contact method, which can be considered in the conventional example. Furthermore, since it is not a mechanical vibration method, it can be made smaller, lighter, and less expensive, and can be a practical potential sensor that can be expected to have a long life and high accuracy.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an embodiment of a potential sensor according to the present invention. 1... Housing, 2... Air capacitance,
3... Electrode plate, 4... Variable capacitance diode, 17... Limiter circuit, 18...
FM demodulation circuit, 19...display section.

Claims (1)

[Claims] The charged potential of the casing is applied to the electrode plate via an air capacitor, this potential is applied to a variable capacitance diode, and an oscillation output is obtained using the capacitance of the variable capacitance diode as part of the tuning capacitance. An oscillator circuit whose frequency deviation value changes depending on the case band potential by inputting a low frequency signal in series to the variable capacitance diode to shift the frequency, and a limiter circuit which limits the oscillation level of the oscillation circuit. A potential sensor comprising: an FM demodulation circuit that demodulates frequency deviation; and a display section that displays the output of the FM demodulation circuit with a meter or digitally.