JP2730361B2 - Surface potential detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface potential detecting device (hereinafter, referred to as a potential sensor) for detecting the surface potential of an object in a non-contact state, and more particularly to a potential sensor called a vibration capacitance type.

[0002]

2. Description of the Related Art Conventionally, among potential sensors used for detecting a surface potential of a photoreceptor drum of a copying machine or a printer, a vibration capacitance type sensor configured as shown in FIGS. There is something to be done. That is, this potential sensor of the vibration capacitance type includes a piezoelectric tuning fork 1, a circuit board 2, and a conductive case 3 for housing them. The tuning fork driving circuit 5 and the various signal processing circuits (not shown), which are configured as described above and are called a single power supply type, are assembled.

An opening window 3a is formed in a predetermined portion of the conductive case 3 facing the surface S to be detected, and the piezoelectric tuning fork 1 facing the surface S to be detected through the opening window 3a. A detection electrode 7 is adhered via a flexible substrate 6 to an outer surface on the free end side of the leg 1a located on the outside. Therefore, the lines of electric force radiated from the detection surface S enter the detection electrode 7 after passing through the opening window 3a.

[0004] Further, piezoelectric ceramic vibrators 8, 9 for opening and closing the legs 1a, 1b of the piezoelectric tuning fork 1 are respectively attached to the base end side inner surfaces thereof, and are located outside thereof. The driving electrode 5a of the tuning fork drive circuit 5 is connected to the piezoelectric ceramic vibrator 8 attached to the leg 1a, while the piezoelectric ceramic vibrator 9 attached to the leg 1b located inside the piezoelectric tuning fork 1. Is connected to the feedback electrode 5b of the same tuning fork drive circuit 5. In addition,
The drive electrode 5a outputs an output voltage having a waveform as shown in FIG.

Accordingly, when the piezoelectric tuning fork 1 is driven by the output from the tuning fork driving circuit 5, the detection electrode 7 attached to the leg 1a located outside the tuning fork 1 faces the surface S to be detected while its normal direction. Therefore, a vibration capacitance capacitor is formed between the detection surface S having the surface potential and the detection electrode 7. At this time, the detected surface S
The electric field generated by the surface potential of the electrode 7 induces a charge in the detection electrode 7 in accordance with the capacitance of the capacitor and the surface potential. As a result, an alternating current flows in the detection electrode 7 in proportion to the surface potential. The surface potential of the surface S is detected as the detected voltage.

[0006]

The relationship between the sensor output voltage and the voltage to be detected when the surface potential of the surface to be detected S is detected using the potential sensor having the conventional structure will be examined in detail. As shown in FIG. 5, the linearity (linearity) of the detected voltage rapidly deteriorates near the origin of the diagram showing the correlation between the two voltages, and the detection error increases as the detected voltage becomes lower. It is clear that appears greatly. The inventor of the present invention has conducted various studies on the cause of such deterioration of the linearity. The linearity of the tuning fork drive circuit 5, particularly, the electromagnetic noise generated at the drive electrode 5 a is mixed with the detection electrode 7. It has been found that the higher the output voltage of the drive electrode 5a, the more electromagnetic noise is generated.

According to a further investigation by the inventor, in the conventional potential sensor, when the output voltage of the drive electrode 5a is high, the piezoelectric tuning fork 1 is displaced so as to close,
In addition, it was found that the piezoelectric ceramic vibrators 8 and 9 which are displaced so as to open the piezoelectric tuning fork 1 when the output voltage of the drive electrode 5a is low may be attached to the legs 1a and 1b of the piezoelectric tuning fork 1. . That is, if it looks like this,
As the output voltage of the drive electrode 5a increases, the leg 1a located outside the piezoelectric tuning fork 1 approaches the drive electrode 5a, and electromagnetic noise is mixed into the detection electrode 7 attached to the leg 1a. As a result, the deterioration of linearity is further increased.

The present invention has been made based on such knowledge, and has as its object to provide a potential sensor capable of improving the linearity of a detected voltage and reducing a detection error. And

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a support base having a base end which vibrates in parallel with a circuit board and along a normal direction of a surface to be detected. Through
And the same polarity as the piezoelectric tuning fork fixed to the circuit board .
A tuning fork drive circuit for driving the piezoelectric tuning fork by alternately outputting a high voltage and a low voltage, and one of the piezoelectric ceramic vibrators attached to each of the legs of the piezoelectric tuning fork has a drive of the tuning fork drive circuit. The electrode is connected , and the drive electrode and the detected
The distance between the surface and the surface along the normal direction is
Set longer than the distance along the normal direction from the detection surface.
In the constant surface potential detector, the piezoelectric ceramic vibrator is characterized in that the higher output voltage of the driving electrodes to open the piezoelectric tuning fork, also those to be displaced so as to close the piezoelectric tuning fork A low .

[0010]

According to the above construction, when the output voltage of the drive electrode is high, the legs of the piezoelectric tuning fork are opened, and the detection electrode is moved away from the drive electrode together with the leg to which it is attached. Electromagnetic noise generated at the drive electrode is less likely to be mixed into the detection electrode. When the output voltage of the drive electrode is low, the detection electrode approaches the drive electrode by closing the legs of the piezoelectric tuning fork. In this case, however, the electromagnetic noise itself generated at the drive electrode is small. Therefore, even if this electromagnetic noise enters the detection electrode, no serious adverse effect occurs.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway plan view showing a simplified structure of a potential sensor according to the present embodiment, FIG. 2 is an enlarged sectional view showing an essential structure thereof, and FIG. 3 is a tuning fork driving circuit thereof. FIG. 4 is an equivalent circuit diagram showing the configuration of FIG. Note that the basic structure of the potential sensor according to the present embodiment is not different from that of the conventional example, and only the displacement direction of the piezoelectric ceramic vibrator constituting the same is different from that of the conventional example. The present embodiment will be described based on this.

[0013] electric potential sensor according to the present embodiment is what is referred to as the vibration displacement, the potential sensor, the circuit board 2
A piezoelectric tuning fork 1 that vibrates along the normal direction of the surface S to be detected and a single power supply type tuning fork driving circuit 5 for driving the piezoelectric tuning fork 1 and various signal processing circuits (not shown) are assembled. Provided, and a box-shaped conductive case 3 made of aluminum or the like. Each of the piezoelectric tuning fork 1 and the circuit board 2 is positioned and housed in the conductive case 3. The signal processing circuit disposed on the circuit board 2 includes a tuning fork driving circuit 5 for driving the piezoelectric tuning fork 1, a source follower circuit, a band-pass filter / amplifying circuit, a rectifying circuit, a power supply circuit, and an amplifying circuit. / include offset adjustment circuit, a waveform as shown in FIG. 4 from the driving electrodes 5a of the tuning fork drive circuit 5, i.e., the same polarity
Tei Rukoto output voltage waveform and a high voltage H and low voltage L are alternately repeated is outputted to drive the piezoelectric tuning fork 1 is the same as the conventional example.

At a predetermined position of the circuit board 2, substantially U
The base end of the piezoelectric tuning fork 1 in the shape of a letter is fixed via a support base 15, and the legs 1 a and 1 b of the piezoelectric tuning fork 1, that is, the legs located on the detection surface S side. 1a
A detection electrode 7 is adhered to the outer surface on the free end side via a flexible substrate 6. The detection electrode 7 is connected to a gate electrode 11 of a source follower circuit (not shown).
It is connected to the. Further, an opening window 3a facing the detection surface S is formed at a predetermined portion of the conductive case 3 facing the detection electrode 7. Therefore, the lines of electric force from the detection surface S enter the detection electrode 7 that faces the detection surface S through the opening window 3a through the opening window 3a. In this case, the drive power
The distance between the pole 5a and the surface S to be detected along the normal direction
Is along the normal direction between the detection electrode 7 and the detection surface S.
Is set longer than the specified interval.

Further, the legs 1a and 1b of the piezoelectric tuning fork 1
A piezoelectric ceramic vibrator 8,
The piezoelectric ceramic vibrator 8 is connected to the drive electrode 5a of the tuning fork drive circuit 5, while the piezoelectric ceramic vibrator 9 is connected to the feedback electrode 5b of the same tuning fork drive circuit 5. . Here, it is needless to say that the same is true even when the feedback electrode 5b is connected to the piezoelectric ceramic vibrator 8 and the drive electrode 5a is connected to the piezoelectric ceramic vibrator 9.
The piezoelectric ceramic vibrators 8 and 9 are displaced so as to open the piezoelectric tuning fork 1 when the output voltage of the driving electrode 5a is high, and to close the piezoelectric tuning fork 1 when the output voltage of the driving electrode 5a is low. The polarization direction and the like are adjusted in advance.

Therefore, when the piezoelectric tuning fork 1 is driven by the output from the tuning fork driving circuit 5, the detecting electrode 7 attached to the leg 1a located outside the tuning fork 1 faces the surface S to be detected while its normal direction. As a result of oscillating along
The surface potential of the detected surface S is detected as a detected voltage. At this time, if the output voltage of the drive electrode 5a is high, each of the legs 1a and 1b of the piezoelectric tuning fork 1 is opened, and the detection electrode 7 moves away from the drive electrode 5a together with the leg 1a to which this is attached. Therefore, it is difficult for the detection electrode 7 to be mixed with the electromagnetic noise generated at the drive electrode 5a. When the output voltage of the driving electrode 5a is low, the detection electrode 7 approaches the driving electrode 5a by closing the legs 1a and 1b of the piezoelectric tuning fork 1. In this case, the driving electrode 5a Since the generated electromagnetic noise itself is small, even if this electromagnetic noise enters the detection electrode 7, no significant adverse effect occurs.

When the inventor of the present invention carried out a characteristic test of the potential sensor according to the present embodiment, it was confirmed that the linearity was improved by about 1% when the detected voltage was 50 V. I have. That is, even when the potential sensor according to the present embodiment is used, the same correlation as shown in FIG. 5 is observed between the sensor output voltage and the detected voltage. The linearity of the detected voltage in the vicinity of the origin of the diagram showing the relationship is improved as compared with the conventional example. Note that this linearity is represented by the formula (V ₁ −V ₀ ) / V ₀ × 100%, where V ₀ is the detected voltage 10 in FIG.
It shows a virtual output voltage value at a detected voltage of 50 V when a sensor output voltage a at 0 V and a sensor output voltage b at a detected voltage of 800 V are used to linearly approximate the characteristics of the sensor, V ₁ indicates a practical output voltage value when the detected voltage is 50 V.

[0018]

As described above, in the potential sensor according to the present invention, the piezoelectric ceramic vibrator attached to each leg of the piezoelectric tuning fork is opened so that the piezoelectric tuning fork is opened when the output voltage of the driving electrode is high. In addition, if it is low, the piezoelectric tuning fork is displaced so as to close. Therefore, if the output voltage of the drive electrode is high, the detection electrode attached to the leg portion of the piezoelectric tuning fork will move away from the drive electrode, and it is difficult for the detection electrode to receive the electromagnetic noise generated by the drive electrode. . When the output voltage of the drive electrode is low,
When the leg of the piezoelectric tuning fork closes, the detection electrode approaches the drive electrode.In this case, the electromagnetic noise itself generated at the drive electrode is small, and this electromagnetic noise is mixed into the detection electrode. No significant adverse effects will occur.

As a result, according to the potential sensor according to the present invention, it is possible to improve the linearity of the detected voltage indicating the surface potential of the detected object which is detected in a non-contact state. The effect is obtained that the detection error which appears largely when the potential is low can be reduced.

[Brief description of the drawings]

FIG. 1 is a partially cutaway plan view showing a simplified structure of a potential sensor according to the present embodiment and a conventional example.

FIG. 2 is an enlarged cross-sectional view showing a main structure of a potential sensor according to the present embodiment and a conventional example.

FIG. 3 is an equivalent circuit diagram illustrating a configuration of a tuning fork driving circuit according to the present embodiment and a conventional example.

FIG. 4 is a characteristic diagram showing a waveform of an output voltage from a drive electrode of the tuning fork drive circuit according to the present embodiment and a conventional example.

FIG. 5 is a characteristic diagram showing a relationship between an output voltage of a potential sensor according to the present embodiment and a conventional example and a detected voltage.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric tuning fork 1a leg 1b leg 5 tuning fork drive circuit 5a drive electrode 8 piezoelectric ceramic vibrator 9 piezoelectric ceramic vibrator S surface to be detected

Claims (1)

(57) [Claims] 1. A base having a base end which vibrates in parallel with a circuit board (2) and in a direction normal to a surface to be detected (S).
(15) The piezoelectric tuning fork (1) fixed to the circuit board (2) through the high voltage and the low voltage of the same polarity alternately.
Tuning fork drive circuit (5) that outputs and drives a piezoelectric tuning fork (1 )
And leg portions (1a, 1b) of the piezoelectric tuning fork (1).
Piezoelectric ceramic vibrators (8,
9) One of the driving electrodes (5a) of the tuning fork driving circuit (5)
Are connected , and the drive electrode (5a) and the surface to be detected (S)
The distance along the above-mentioned normal direction between the detection electrodes (7)
The distance along the above normal direction between the object and the surface to be detected (S)
In the surface potential detecting device set to be longer , the piezoelectric ceramic vibrators (8, 9)
A surface potential detecting device characterized in that the piezoelectric tuning fork (1) is displaced so as to open when the output voltage of (a) is high, and to close the piezoelectric tuning fork (1) when the output voltage is low.