JP2000147036A - Surface electrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface electrometer which has a simple constitution and can reduce the variation of the measured surface potential value of a charged body caused by the variation of the distances between the charged body and detection electrodes. SOLUTION: Amplifier circuits 4 and 5 respectively amplify potential signals induced in a detection electrode 1, which is a fixed electrode and another detection electrode 2 which is an oscillating electrode. A detection circuit 6 detects a output signal Vb of the amplifier circuit 5. A subtraction circuit 7 outputs the signal of the level Vs, corresponding to the surface potential of a charged body by subtracting an output level Va of the amplifier circuit 4 from an output level Vc of the detection circuit 6. Since the influence of distance variation appears in both the electrodes 1 and 2, the influence can be eliminated, when the output level Va is subtracted from the output level Vc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface voltmeter, and more particularly to a surface voltmeter for measuring the surface potential of a drum-shaped or belt-shaped charged body.

[0002]

2. Description of the Related Art Conventionally, a surface voltmeter has been used to measure a charged potential of a drum-shaped or belt-shaped photosensitive member used in a copying machine or a printer.

As shown in FIG. 4, a sensor 30a of the surface voltmeter 30 is disposed at a predetermined distance L, for example, facing the surface of the photosensitive drum 31. Photoconductor drum 31
Is charged by a charging device (not shown) while being rotated at a constant speed in one direction. The charged potential of the photosensitive drum 31 is measured by the surface voltmeter 30 via the sensor 30a. The measured value is, for example, the photosensitive drum 31
Is used to test if is normal.

FIG. 5 is a circuit block diagram illustrating a specific configuration of the surface voltmeter shown in FIG. Such a surface voltmeter is disclosed, for example, in Japanese Patent Application Laid-Open No. 54-18882. In FIG. 5, this surface voltmeter is of a so-called chopper type, and has shield plates 41 and 42, detection electrodes 43 and 44, amplification circuits 45 and 46, and a subtraction circuit 4.
7 is provided. Among these, the shield plates 41 and 42, the detection electrodes 43 and 44, and the amplifier circuits 45 and 46 are provided in the sensor.

[0005] The shield plates 41 and 42 are arranged to face the surface of the photosensitive drum. A vibration device (not shown) applies a certain period of vibration to the one shield plate 41 in a horizontal direction (the direction of the arrow in the figure) with respect to the surface of the photosensitive drum. The other shield plate 42 is fixed.
The detection electrodes 43 and 44 are respectively connected to the shield plates 41 and 42.
Are arranged at a predetermined distance from each other so as to face the back surface (surface opposite to the photosensitive drum).

The amplifier circuits 45 and 46 amplify the potential signals induced on the detection electrodes 43 and 44, respectively. The subtraction circuit 47 includes an operational amplifier 48 and resistance elements 49 to 52, and subtracts the output level Vb of the amplifier 46 from the output level Va of the amplifier 45 to obtain a level Vs according to the surface potential.
The signal of is output.

Next, the operation of the surface voltmeter will be described. When the shield plate 41 vibrates like a shutter at a predetermined cycle, a potential signal of a level corresponding to the charged potential of the photosensitive drum is induced in the detection electrode 43, and the potential signal is amplified by the amplifier circuit 45. However, the output level Va of the amplifier circuit 45 also varies depending on the temperature and humidity around the detection electrode 43. On the other hand, since the shield plate 42 is fixed, a potential signal of a level corresponding to the charged potential of the photosensitive drum is not induced in the detection electrode 44, but the amplification circuit 4
6, the output level Vb fluctuates due to fluctuations in temperature and humidity, similarly to the output level Va of the amplifier circuit 45.

The subtraction circuit 47 subtracts the output level Vb of the amplifier 46 from the output level Va of the amplifier 45, and outputs a signal of a level Vs corresponding to the charged potential of the photosensitive drum. At this time, since Vb is subtracted from Va, the variation of Vs due to the variation of temperature and humidity is eliminated. A display device (not shown) operates according to the output level Vs of the subtraction circuit 47.
The measured value Vs' of the surface potential is displayed.

[0009]

However, in the surface voltmeter of FIG. 5, the distance L between the surface of the photosensitive drum 31 and the sensor 30a is reduced due to the eccentricity of the photosensitive drum 31, as shown in FIG. If it fluctuates, the level of the potential signal induced on the detection electrode 43 also fluctuates, and the measured value Vs' of the surface potential fluctuates. At this time, as shown in FIG. 6, the surface potential Vs' fluctuates at the same cycle T as the rotation period of the photosensitive drum 31, and the fluctuation amount ΔVs' of the surface potential Vs' depends on the fluctuation amount ΔL of the distance L. Increase.

As a countermeasure against this, two shield plates 43,
There is also a method of oscillating both of them 44 to cancel the variation ΔVs ′ of the surface potential Vs ′ due to the variation of the distance L. However, two devices for oscillating the shield plates 43 and 44 are required, and the device becomes complicated. There was a problem.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a surface voltmeter which has a simple structure and which can reduce the variation of the measured value of the surface potential due to the variation of the distance between the charged body and the detection electrode. To provide.

[0012]

The invention according to claim 1 is
A surface potentiometer for measuring the surface potential of a drum-shaped or belt-shaped charged body, comprising a vibrating electrode, a fixed electrode, a detecting means, and a subtracting means. The vibrating electrode is arranged to face the surface of the charged body, and receives vibration of a predetermined frequency in a direction perpendicular to the surface of the charged body. The fixed electrode is arranged near the surface of the charged body in the vicinity of the vibration electrode. The detecting means extracts an electric signal of a level corresponding to the surface potential of the charged body from the electric signal induced by the vibrating electrode.
The subtraction means subtracts the level of the electric signal induced at the fixed electrode from the level of the electric signal extracted by the detection means,
The fluctuation of the measured value of the surface potential of the charged body due to the fluctuation of the distance between the surface of the charged body and the vibrating electrode is eliminated.

According to the second aspect of the present invention, a storage means is further provided in the first aspect of the present invention. The storage means samples the level of the electric signal induced at the fixed electrode at a predetermined sampling frequency and stores a waveform for at least one cycle. The subtracting means subtracts the level of the electric signal read from the storage means in synchronization with the rotation of the charged body from the level of the electric signal extracted by the detecting means.

[0014]

[First Embodiment] FIG. 1 is a block diagram showing a configuration of a surface voltmeter according to a first embodiment of the present invention. In FIG. 1, the surface voltmeter is of a so-called vibration capacitance type, and includes detection electrodes 1 and 2, a tuning fork 3, amplification circuits 4 and 5, a detection circuit 6 and a subtraction circuit 7. Among these, the detection electrodes 1 and 2, the tuning fork 3 and the amplification circuits 4 and 5
Is provided in the sensor.

The detection electrodes 1 and 2 are arranged opposite to the surface of the photoreceptor belt 10 at a predetermined distance. One detection electrode 1 is fixed. To the other detection electrode 2, a vibration of a fixed period is given by the tuning fork 3 in a direction perpendicular to the surface of the photoreceptor belt 10. The tuning fork 3 is driven by, for example, a piezoelectric element and its drive circuit (not shown).

The amplifier circuits 4 and 5 are respectively provided with detection electrodes 1 and
2 is amplified. The detection circuit 6 detects the output signal Vb of the amplification circuit 5. Subtraction circuit 7
Is obtained by subtracting the output level Va of the amplifier circuit 4 from the output level Vc of the detection circuit 6 and obtaining a level Vs = V corresponding to the surface potential.
The signal of c-Va is output.

Next, the operation of the surface voltmeter will be described. The photoreceptor belt 10 is charged by a charging device (not shown) while being rotated at a constant speed in one direction via rollers 11 and 12. At this time, the rollers 11, 12
The distance between the surface of the photoreceptor belt 10 and the detection electrodes 1 and 2 fluctuates due to the eccentricity.

A fixed detection electrode 1 and a photoreceptor belt 10
The distance from the surface changes at a constant period T according to the eccentricity of the rollers 11 and 12, and a potential signal of a level corresponding to the change is guided to the detection electrode 1. Therefore, the amplifier 4
Output level Va fluctuates at a constant period T according to the eccentricity of the rollers 11 and 12, as shown in FIG.

On the other hand, the distance between the detection electrode 2 vibrated by the tuning fork 3 and the surface of the photosensitive belt 10 fluctuates according to the vibration of the tuning fork 3 and the eccentricity of the rollers 11 and 12. Therefore, the output level Vb of the amplifier 5 is as shown in FIG.
As shown in FIG. 5, the high frequency component based on the vibration of the tuning fork 3 and the low frequency component based on the eccentricity of the rollers 11 and 12 are included.

The detection circuit 6 detects the output level Vb of the amplifier 5
Are converted to direct current. Therefore, the output level Vc of the detection circuit 6 includes a DC component and a low-frequency component based on the eccentricity of the rollers 11 and 12, as shown in FIG.

The subtraction circuit 7 outputs the output level V of the detection circuit 6.
The output level Va of the amplifier 4 is subtracted from c, and a signal of a level Vs = Vc−Va according to the surface potential of the photoreceptor belt 10 is output. The output level Vs of the subtraction circuit 7 is shown in FIG.
As shown in (d), the photosensitive belt 10 has only a DC component at a level corresponding to the surface potential of the photosensitive belt 10. The display device (not shown) displays the measured value Vs' of the surface potential digitally or analogly according to the output level Vs of the subtraction circuit 7.

In this embodiment, a detection electrode 1 functioning as a fixed electrode and a detection electrode 2 functioning as a vibrating electrode are provided opposite to a photoreceptor belt 10 which is a charged body, and a potential signal induced by the detection electrode 2 is provided. The surface potential detected based on the potential signal induced on the detection electrode 1 is subtracted from the surface potential detected on the basis of the above, so that the fluctuation of the measured value of the surface potential due to the eccentricity of the photoreceptor belt 10 can be reduced with a simple configuration. Can be canceled. Further, similarly to the surface electrode of FIG. 5, the fluctuation of the measured value Vs' of the surface potential caused by the fluctuation of the temperature and humidity around the detection electrodes 1 and 2 can be canceled.

Second Embodiment The first embodiment is effective when the surface of the photosensitive belt 10 is uniformly charged, but is effective when the surface of the photosensitive belt 10 is not uniformly charged. Surface potential cannot be detected accurately. Because
When the surface of the photoconductor belt 10 is not uniformly charged, the output level Va of the amplifier circuit 4 is
This is because not only the fluctuation of the distance between 0 and the detection electrode 1 but also the fluctuation of the surface potential of the photoreceptor belt 10 can not cancel only the fluctuation of the measured value of the surface potential due to the distance fluctuation. . This embodiment aims to solve this problem.

FIG. 3 is a block diagram showing a main part of a surface voltmeter according to a second embodiment of the present invention. In FIG. 3, this surface voltmeter is different from the surface voltmeter of FIG.
The difference is that the subtraction circuit 7 is replaced by the A / D converters 21 and 22 and the computer 23. Computer 2
3 includes a storage unit 24 and an arithmetic processing unit 25.

The A / D converters 21 and 22 sample the output level Va of the amplifier 4 and the output level Vc of the detection circuit 6 at a predetermined sampling frequency and convert them into digital signals. Storage unit 2 of computer 23
Reference numeral 4 stores the output of the A / D converter 21 when the photoreceptor belt 10 is uniformly charged for a plurality of cycles. The arithmetic processing unit 25 averages data for a plurality of cycles read from the storage unit 24 to generate correction data for one cycle, and stores the correction data in the storage unit 24. The arithmetic processing unit 25
Reads the correction data from the storage unit 24 in synchronization with the rotation of the photoreceptor belt 10 at the time of the actual measurement, subtracts the correction data corresponding to the data from the output data of the A / D converter 22, and responds to the surface potential. And outputs a signal having the level Vs.

Next, the operation of the surface voltmeter will be described. First, the photosensitive belt 10 is uniformly charged by the charging device while rotating at a constant speed, and the output data of the A / D converter 21 is stored in the storage unit 24 for a plurality of cycles. The arithmetic processing unit 25 averages data for a plurality of cycles read from the storage unit 24 to generate correction data for one cycle, and stores the correction data in the storage unit 24.

Next, actual measurement is performed. in this case,
The photoreceptor belt 10 may be non-uniformly charged. The correction data is provided from the storage unit 24 to the arithmetic processing unit 25 in synchronization with the rotation of the photoreceptor belt 10, and the correction data is subtracted from the output data of the A / D converter 22. This allows
The fluctuation of the measured value of the surface potential due to the distance fluctuation is canceled. The arithmetic processing unit 25 outputs a signal of level Vs corresponding to data obtained by subtracting correction data from output data of the A / D converter 22.

In this embodiment, correction data is recorded by paying attention to the high periodicity and reproducibility of the distance fluctuation due to the eccentricity of the rollers 11 and 12, and the correction data is subtracted from the actual measurement data. . Therefore, even when the surface of the photoreceptor belt 10 is not uniformly charged, the fluctuation of the measured value of the surface potential due to the distance fluctuation can be canceled.

It should be noted that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0030]

As described above, according to the first aspect of the present invention, the vibrating electrode and the fixed electrode are provided so as to face the surface of the charged body, and the electric signal induced on the vibrating electrode is used in accordance with the surface potential of the charged body. The level of the electric signal induced at the fixed electrode from the level of the extracted electric signal to eliminate the fluctuation of the measured value of the surface potential due to the fluctuation of the distance between the charged body and the vibrating electrode. I do. Therefore, the fluctuation of the measured value of the surface potential due to the distance fluctuation can be eliminated with a simple configuration.

According to the second aspect of the present invention, the level of the electric signal induced at the fixed electrode according to the first aspect of the present invention is sampled and stored at a predetermined sampling frequency, and the storage means is synchronized with the rotation of the charged body. Is subtracted from the level of the extracted electric signal. In this case, if the charged body is uniformly charged in advance and the electric signal induced on the fixed electrode is stored, even if the charged body is unevenly charged during the actual measurement, the surface potential can be accurately measured. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a surface voltmeter according to Embodiment 1 of the present invention.

FIG. 2 is a time chart showing the operation of the surface voltmeter shown in FIG.

FIG. 3 is a block diagram showing a configuration of a surface voltmeter according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional surface voltmeter.

FIG. 5 is a circuit block diagram illustrating a specific configuration of the surface voltmeter shown in FIG. 4;

FIG. 6 is a diagram for explaining a problem of the surface voltmeter shown in FIG. 5;

[Explanation of symbols]

 1, 2, 43, 44 Detection electrode 3 Tuning fork 4, 5, 45, 46 Amplification circuit 6 Detection circuit 7, 47 Subtraction circuit 10 Photoreceptor belt 21, 22 A / D converter 23 Computer 24 Storage unit 25 Arithmetic processing unit 30 Surface Electrometer 30a Sensor 31 Photoconductor drum 41, 42 Shield plate

Claims (2)

[Claims] 1. A surface voltmeter for measuring a surface potential of a drum-shaped or belt-shaped charged body, wherein the surface voltmeter is arranged to face the surface of the charged body, and is arranged in a direction perpendicular to the surface of the charged body. A vibrating electrode to which a vibration of a predetermined frequency is applied; a fixed electrode disposed in the vicinity of the vibrating electrode so as to face the surface of the charged body; and a surface potential of the charged body from an electric signal induced on the vibrating electrode. Detection means for extracting an electric signal of a level corresponding to
And subtracting the level of the electric signal induced at the fixed electrode from the level of the electric signal extracted by the detection means, and changing the distance between the surface of the charged body and the vibrating electrode to change the level of the charged body. A surface voltmeter including a subtraction unit that eliminates a variation in a measured value of a surface potential. 2. The apparatus according to claim 1, further comprising a storage unit that samples a level of the electric signal induced at the fixed electrode at a predetermined sampling frequency and stores a waveform of at least one cycle. 2. The surface electrometer according to claim 1, wherein a level of the electric signal read from the storage unit is subtracted from a level of the electric signal extracted by the detection unit in synchronization with the rotation of the body.