JPH0145873B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface potential detection device for non-contact measurement of the surface potential of a photoreceptor, etc. in an electrophotographic copying device.

Conventionally, in order to measure the surface potential without contact, a method is often used in which lines of electric force from the surface to be detected are stopped and output is extracted from the stopped lines of electric force. Specifically, as shown in JP-A-55-144556, for example, a window is provided in the case through which the lines of electric force from the surface to be detected pass, and a detection electrode is placed opposite the window to receive the lines of electric force. A chopper electrode is provided between the window and the detection electrode, and by vibrating the chopper electrode with a piezoelectric tuning fork, the lines of electric force directed toward the detection electrode are intermittently interrupted, and an alternating current signal is generated from the detection electrode. It is designed to extract the output.

However, the conventional surface potential detection device described above is
Since it is designed to tip the electric lines of force, it requires a window through which the lines of electric force can pass, and it has the disadvantage that it cannot be made into a sealed structure.When used in an electrophotographic copying device, toner etc. can easily enter the case.
A problem arises in that it adversely affects the detection electrode and piezoelectric tuning fork. Therefore, great care must be taken when attaching it to a copying machine.

In addition, if the mounting position of the detection electrode or tipper electrode is misaligned with respect to the window through which electric lines of force pass, the output level will change from the predetermined value, making it impossible to accurately measure the surface potential. It also had the disadvantage that it required careful positioning, resulting in poor work efficiency.

Furthermore, since the detection voltage is directly obtained from the amount of electric lines of force received by the detection electrode, there is a problem in that if leakage occurs to the detection electrode, it directly affects the subsequent circuit.

All of the above-mentioned drawbacks occur because the lines of electric force are chopped and the detected voltage is directly obtained from the chopped lines of electric force. Therefore, the present invention does not detect the surface potential by chopping electric lines of force, but rather detects the surface potential by detecting a capacitor C ₁ formed between the surface to be detected and the collecting electrode.
A capacitor C ₂ whose capacitance can be varied by the vibration of the piezoelectric device is installed in series with the capacitor C ₁ ,
It is a capacitor divided type using _C2 , and the voltage applied to the capacitor _C2 is extracted by vibration of a piezoelectric device and used as a detection voltage.

Specifically, a metal case is provided, a collector electrode is provided in the opening of the case facing the surface to be detected, and a variable capacitor is electrically coupled to the collector electrode.
The piezoelectric device is housed in a case, and at least one electrode of a variable capacitor is vibrated by the piezoelectric device to change the distance between the electrodes, and an electric signal based on the capacitance change of the capacitor due to this distance change is used to detect the surface to be detected. It is designed to detect electric potential.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1a is a diagram for explaining the principle of the present invention, in which 1 is a surface to be detected such as a photoreceptor of an electrophotographic copying device, and a collector electrode 2 is attached opposite to this surface to be detected 1. There is. 3 and 4 are capacitor electrodes, which are provided on insulating plates 5 and 6, respectively.The insulating plates 5 and 6 are attached to the leg tips of the piezoelectric tuning fork 7, and one capacitor electrode 3 is connected to the collector electrode 2, and the other is connected to the collector electrode 2. The capacitor electrode 4 is grounded through the resistor R and the field effect transistor FET
connected to the gate.

Next, the operating principle will be explained. Detected surface 1
When a high voltage is applied to the capacitor electrode 1, electric lines of force from the high potential surface 1 are applied to the collector electrode 2, and a charge equal to that generated on the collector electrode 2 is accumulated between the capacitor electrodes 3 and 4. Then, when the piezoelectric tuning fork 7 is driven to vibrate the capacitor electrodes 3 and 4 to change the distance between the electrodes 3 and 4, that is, the capacitance, the capacitance change causes charges to be charged and discharged, and an electric signal based on this is transmitted to the field effect transistor FET. In addition to this, a detection voltage is extracted from this field effect transistor FET. Figure b is an equivalent circuit diagram.

Next, specific examples will be described. In FIG. 2, an insulating plate (for example, an alumina porcelain plate) 12 on which a collector electrode 11 is formed is attached to one opening of a cylindrical metal case 10 with the collector electrode 11 on the outside. The piezoelectric tuning fork 13 and the circuit member 14 are fixed to a substrate 15, and this substrate 15 is attached to the other opening of the case 10. Piezoelectric tuning fork 13
Capacitor electrodes 16, 17 are installed at the tips of the two legs.
Insulating plates 18 and 19 are attached with electrodes facing each other, and an air capacitor C ₂ is formed between these electrodes 16 and 17. The circuit member 14 includes a signal processing circuit shown in d of the same figure and a piezoelectric tuning fork 1 shown in e of the same figure.
3 oscillation circuit is built-in. One capacitor electrode 16 is a through-hole electrode 11 that is provided on the insulating plate 12 and is electrically connected to the collector electrode 11.
It is connected to a with a lead wire. The other capacitor electrode 17 is connected to a predetermined terminal of the circuit member 14, that is, an input terminal 20 of the signal processing circuit. The piezoelectric film and tuning fork body of the piezoelectric tuning fork 13 are connected to predetermined terminals of the circuit member 14, that is, the terminals 21 of the oscillation circuit,
22 and 23.

In this example, the area of the collector electrode 11 is 4 cm ² ,
2cm apart from the surface to be detected, capacitor electrode 1
When the area of electrodes 6 and 17 is 0.2 cm ² , the distance between electrodes 16 and 17 is 3 mm, and Vcc = 15 V, the detected voltage (voltage at output terminal 24 in d in the same figure) with respect to the potential on the detected surface is as shown in FIG. It became like that. As is clear from the figure, since the detected voltage with respect to the detected potential changes linearly, the detected voltage can be directly read from the obtained detected voltage.

According to the above-mentioned embodiment, since it can be configured to have a sealed structure, toner and the like will not enter the case, and no special consideration is required when incorporating it into a copying apparatus. In addition, a collector electrode 11, a capacitor electrode 16, 1
Since the positional relationship between the parts 7 and 7 is not a particular problem, assembly of the detection device becomes very easy. Furthermore, the collector electrode 11
Even if a leak occurs, capacitor _C2 acts as a buffer, reducing the effect on subsequent circuits.

Next, other embodiments will be described with reference to the schematic diagrams of FIGS. 3 to 7. Note that for convenience of explanation, only the differences from the previous embodiment will be described.

First, FIGS. 3 to 5 show one capacitor electrode fixedly attached, and FIG. 3 shows another capacitor electrode 25 attached to capacitor electrodes 16, 17.
fixedly attached to the insulator 40 with an intervening
The electrode 25 is connected to the collector electrode 11 with a lead wire, and the electrodes 16 and 17 vibrating with the piezoelectric tuning fork 13 are connected together.
It is connected to FET. According to this embodiment, capacitor C ₂ is the capacitance between electrodes 16 and 25.
It is expressed as a parallel capacitance between C ₂ ′ and the capacitance C ₂ ″ between the electrodes 17 and 25, and the capacitance can be made relatively large. Therefore, the charge appearing on the electrode of the capacitor C ₂ becomes large, increasing the detection voltage. be able to.

In FIG. 4, capacitor electrodes 16 and 17 are attached facing outward, and other capacitors 26 and 27 facing each electrode 16 and 17 are integrally formed in a U-shape and fixedly attached to an insulator 40. Electrode 26,2
7 is connected to the collector electrode 11 with a lead wire, and the electrodes 16, 1
7 are connected to the FET all at once. In this embodiment as well, the detection voltage can be increased as in the embodiment shown in FIG.

In FIG. 5, a piezoelectric vibrating piece 28 is used as a piezoelectric device, an insulating plate 18 having a capacitor electrode 16 formed thereon is attached to its tip, and another capacitor electrode 2 is placed opposite the capacitor electrode 16.
9 is fixedly attached to an insulator 40.

FIG. 6 shows an example in which the collector electrode and one of the capacitor electrodes are combined. In the embodiment of FIG. 5, the other capacitor electrode 29 is removed, the collector electrode 11 and the capacitor electrode 16 are directly opposed, and the capacitor ₂ . According to this embodiment, the lead wire connection between the collector electrode 11 and the capacitor electrode can be omitted, making assembly simple and improving reliability.

FIG. 7 shows another capacitor electrode 34 formed by extending the capacitor electrode 16 in the embodiment shown in FIG _. ′ is formed,
The equivalent circuit is as shown in figure b. Also in this embodiment, the lead connection between the collector electrode and the capacitor electrode can be omitted.

As explained in detail above, according to the present invention,
It is now possible to construct a sealed structure, allowing it to be freely incorporated into copying machines, etc., improving characteristics such as changes over time, simplifying assembly, and creating a structure that is resistant to leakage characteristics. .

[Brief explanation of drawings]

FIG. 1a is a diagram for explaining the principle of the detection device according to the present invention, FIG. 1b is an equivalent circuit diagram of the main parts,
Figure 2 shows a specific example, where a is a front view and b is a front view.
is a cross-sectional view along B-B, c is a cross-sectional view along line C-C, and d is a cross-sectional view along line C-C.
is a signal processing circuit diagram, e is an oscillation circuit diagram, and FIGS. 3 to 7 are schematic diagrams showing main parts of modified examples.
FIG. 8 is a detection voltage characteristic diagram according to the embodiment of FIG. 2. In the figure, 1 is the detection surface, 2 and 11 are collector electrodes,
3, 4, 16, 17 are capacitor electrodes, 5, 6,
18 and 19 are insulating plates, 7 and 13 are piezoelectric tuning forks, and 10
is the case.

Claims (1)

[Claims] 1. A metal case is provided, a collector electrode facing the surface to be detected is provided in the opening of the case, a variable capacitor and a piezoelectric device electrically coupled to the collector electrode are housed in the case, and the variable capacitor is The method is characterized in that the distance between the electrodes is changed by vibrating at least one of the electrodes using a piezoelectric device, and the potential on the surface to be detected is detected by an electric signal based on a change in capacitance of the capacitor due to the change in distance. Surface potential detection device.