JPH09292426A - Surface electrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the measuring performance by enhancing the S/N ratio of a measuring signal in a chopper-type noncontact surface electrometer using a tuning-fork type vibrator. SOLUTION: Both tip parts 10c of fork parts 10b of a tuning-fork type vibrator 10 are bent, so that the tip parts approach each other and separate from a measuring electrode 1 receiving electric lines of force from an object to be measured, and chevron-shape is formed. Furthermore, the tip parts 10c are vibrated in the direction A by piezoelectric elements 4, and the amount of the electric lines of force 7 entering the measuring electrode 1 through the space between both tip parts 10C from the object to be measured is changed in time. Then, the minute AC current induced in the measuring electrode 1 is amplified and taken out by an amplifier element 3. The surface potential of the object to be measured 8 is calculated, based on this signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface electrometer for measuring the surface potential of an object in a non-contact manner. For example, a surface potential used for detecting the surface potential of a photoconductor in an electrophotographic apparatus such as a copying machine. It is about the total.

[0002]

2. Description of the Related Art As a surface electrometer for measuring the surface potential of a photoconductor of an electrophotographic apparatus in a non-contact manner, a so-called chopper type electrometer and a capacitance variation type electrometer are mainly known.

In the chopper type electrometer, a conductive vibrating object is arranged between the object to be measured and the measuring electrode, and the amount of incidence of electric force lines on the measuring electrode by the vibrating object is increased or decreased to measure the object to be measured. The electric field strength is measured, and a capacitance variation type electrometer physically vibrates the measurement electrode itself,
The electric field intensity is measured by changing the electric field distribution between the object to be measured and this measurement electrode, and both systems have the same contents regarding the signal reception processing.

FIG. 2 is a diagram showing a schematic configuration of a conventional chopper type surface electrometer. In the figure, 1 is a measuring electrode that receives an electric force line from the measuring object 8, and 2 is a tuning fork type vibrator that oscillates and chops the electric force line incident from the measuring object 8 to the measuring electrode 1 in the A direction. Reference numeral 3 is an amplifying element for impedance-converting and amplifying a minute AC signal induced in the measurement electrode 1, and 4 is a piezoelectric element for vibrating the tuning fork type vibrator 2.

Reference numeral 5 is a circuit board, 6 is a connector for inputting and outputting a drive signal to the piezoelectric element 4, a reception signal from the measuring electrode 1, and a power source, and 7 is a measuring object 8 to the measuring electrode 1. A line of electric force that is incident in the B direction, and 9 is a shield case that houses the circuit board 5 described above.

FIG. 3 is a schematic view of an impedance conversion circuit formed on the circuit board 5. here,
The amplifying element 3 has a resistance 11 on the input side of 100 MΩ, for example.
Impedance conversion is performed by a source follower circuit using an FET. Also, the resistors 12 and 13 on the output side
Are, for example, 100Ω and 20 KΩ, respectively. It should be noted that these components such as resistors are printed on the circuit board 5 or soldered with discrete chip components.

FIG. 4 is a perspective view showing the outer shape of the electrometer having the above structure. As shown, the circuit board 5 is housed in a shield case 9, a connector 6 is arranged on the side surface of the case, and a small window (opening) for measurement is provided on the front surface.

Next, the operation of the electrometer having the above structure will be described. First, the piezoelectric element 4 and the tuning fork type vibrator 2 are brought into a resonance state by the piezoelectric element drive signal supplied from the outside,
Mechanical vibration occurs. As a result, the amount of electric force lines that pass through the measurement window of the shield case 9 and enter the measurement electrode 1 from the measurement object 8 increases or decreases in accordance with the vibration of the tuning fork vibrator 2. As a result, a weak AC induced current is generated in the measurement electrode 1 and the input-side resistor 10 shown in FIG. 3, and this is applied as a voltage signal to the gate of the FET that is the amplification element 3.

At this time, since the FET circuit is a source follower circuit as described above, impedance conversion with an amplification factor of 1 is performed and a voltage signal is output from the source of the FET. Then, this signal is transferred to an external signal processing circuit (not shown) via the connector 6, and the subsequent processing is performed to detect the surface potential of the measuring object 8.

Since the magnitude of the output signal of the impedance conversion circuit having the amplifying element 3 is proportional to the magnitude of the surface potential of the object 8 to be measured, the amplified signal of this first stage having a high S / N ratio is obtained. Can be transferred to the post-processing circuit, which determines the basic performance of the surface electrometer.

[0011]

By the way, in recent years, with the increasing demand for downsizing of the apparatus, for example, even in a surface electrometer mounted on a copying machine, further downsizing and thinning are required due to the installation space. Has been. In the past, in response to such demands for downsizing and thinning, downsizing of the measurement electrode (in the height direction), downsizing of the vibrator, and the vibration direction of the vibrator are lateral to the object to be measured. I was dealing with such means. Further, in order to compensate for the deterioration of the S / N ratio due to the miniaturization of the measurement electrode, the measurement electrode is arranged as close as possible to the measurement object.

However, in the conventional surface electrometer as described above, as shown in FIG. 5, the detection surface area becomes smaller as the measuring electrode becomes smaller, and the measuring window of the shield case from the object to be measured is reduced. The ratio of the lines of electric force that jumped directly into the tuning-fork vibrator was larger than the total lines of electric force that entered through.

Further, the distance between the tuning fork type vibrator and the measurement surface of the measurement electrode is shortened, and the coupling capacitance between the two is increased, so that the minute AC signal once induced in the measurement electrode escapes from the tuning fork. . Here, there is a plan to position the tuning fork vibrator in the direction of the measurement object as well as the position of the measurement electrode, but this causes the tip of the tuning fork vibrator to fly out of the shield case, causing We cannot meet the demand for miniaturization.

Further, when an insulator (impurity) such as dust is attached to the tip of the tuning fork type vibrator, the potential of the tip of the tuning fork type vibrator should be GND by its influence. It was charged to a certain potential, and this was mixed in the measurement electrode as noise.

Therefore, as a result, the S / N signal component (S)
Has become small, or the noise component (N) has become large, and there has been a problem that the basic performance of the surface electrometer tends to deteriorate.

The present invention has been made in view of the above problems, and provides a non-contact type surface electrometer having a high S / N ratio of a measurement signal and improved basic performance. Has an aim.

[0017]

SUMMARY OF THE INVENTION A surface electrometer according to the present invention is a tuning fork type which has a measuring electrode for receiving a line of electric force from an object to be measured and a time-varying amount of the line of electric force entering the measuring electrode. The tuning fork type vibrator is formed such that both tip portions of the fork portion on the side opposite to the fixed portion are close to each other and apart from the measurement electrode, and the fork portion between both tip portions of the fork portion is provided. It is configured to measure the surface potential of the object to be measured from a minute signal induced in the measurement electrode upon receiving a line of electric force passing therethrough.

Further, in the above electrometer, both end portions of the fork portion of the tuning fork type vibrator are formed in a V shape, and the minute signal induced in the measuring electrode is further converted into a voltage signal. It has a conversion element for impedance conversion.

[0019]

1 is a schematic configuration diagram of a non-contact type surface electrometer according to the present invention, and the same reference numerals as those in FIG. 2 indicate the same components.

In FIG. 1, reference numeral 1 denotes a measuring electrode which receives an electric field of a measuring object 8 such as a photoconductor whose surface potential is to be measured, and a line of electric force 7 is incident on the measuring electrode 10. A tuning fork type vibrator of a chopper part for chopping the electric force lines 7 incident on the measuring electrode 1 and temporally changing the amount of the electric force lines 7 entering the measuring electrode 1. Both ends of the fork part 10b opposite to the fixed part 10a. The portions 10c are bent so that they come close to each other and away from the measurement electrode 1, and are formed in a V-shape.

Further, 3 is an amplifying element (conversion element) for impedance-converting and amplifying a minute AC signal induced in the measuring electrode 1 into a voltage signal, and 4 is a piezoelectric element for vibrating the tuning fork type vibrator 2. Reference numeral 5 is a circuit board on which the impedance conversion circuit and the like are configured, 6 is a connection connector for inputting and outputting a drive signal to the piezoelectric element 4, a reception signal from the measurement electrode 1, and a power source, and 9 is the circuit board described above. 5 is a shield case that accommodates 5.

The impedance conversion circuit having the amplification element 3 is the same as that shown in FIG. The external shape of the entire shield case 9 is the same as that of FIG. 4 except for the C-shaped tip portion 10c of the tuning fork vibrator 10, and a measurement window is provided on the front surface.

In the surface electrometer having the above-mentioned structure, both tip ends 10c of the tuning fork type vibrator 10 having the V-shape are electric lines of force incident in the direction B from the measuring object 8 along the center line of the tuning fork. Physically vibrates in the horizontal direction (direction A) when viewed from the measuring object 8 so that the amount of 7 changes with time. Then, the fixed portion 10 of the tuning fork vibrator 10 facing the position close to the tip portion 10c of the tuning fork vibrator 10 and opposite to the incident direction (B direction) of the electric force line 7 is located.
The measurement electrode 1 is provided on the a side, and the fork portion 1 is provided.
The surface potential of the measuring object 8 is measured from the minute AC signal induced in the measuring electrode 1 by absorbing the electric force line 7 passing between both tip portions 10c of 0b.

Here, in this embodiment, since the tip shape of the tuning fork type vibrator 10 is formed in a V shape, the amount of vibration amplitude of the tuning fork type vibrator 10 is almost the same as the conventional one, and the measurement target is The amount of the lines of electric force 7 that escapes (jumps) from the object 8 into the tuning fork type vibrator 10 is drastically reduced. Further, since the distance between the tip of the tuning fork vibrator 10 and the measurement electrode 1 is increased to reduce the coupling capacitance, the amount of the minute AC signal induced in the measurement electrode 1 escaping from the tuning fork vibrator 10 is drastically reduced. .

Further, even when the tip of the tuning fork type vibrator 10 is charged to a certain potential due to adhesion of an insulator or the like, the tuning fork type vibrator 10 and the measuring electrode 1 are distant from each other, so that they are mixed in the measuring electrode 1. The amount of noise generated is also reduced.

Therefore, the signal component (S) in the S / N ratio can be increased and the noise component (N) can be reduced, and the basic performance of the surface electrometer can be significantly improved.

Conventionally, since the measuring electrode is downsized in order to correspond to the downsizing of the device, the detection surface area of the measuring electrode is small, and the total electric force line incident from the measuring object through the measuring window of the surface electrometer. On the other hand, the ratio of the lines of electric force that directly jump into the tuning fork type vibrator and hit is large.

Further, the distance between the tuning fork type vibrator and the measuring surface of the measuring electrode is shortened, and the coupling capacitance between the two is increased, so that the minute AC signal once induced in the measuring electrode escapes to the tuning fork type vibrator. Was there.

Further, if an insulator (impurity) such as dust is attached to the tip of the tuning fork type vibrator, the potential of the tip of the tuning fork type vibrator should originally be GND due to the influence, and a certain potential. It was electrified and was mixed in the measurement electrode as noise.

Therefore, as a result, the signal component (S) of the S / N ratio is obtained.
Becomes smaller, or the noise component (N) becomes larger, and the basic performance of the surface electrometer tends to deteriorate.

However, in the present embodiment, since the tip of the tuning fork type vibrator 10 is formed in a V shape as described above,
The opening of the tuning fork vibrator 10 can be widened, the amount of electric force lines 7 escaping from the measurement object 8 to the tuning fork vibrator 10 can be drastically reduced, and the tuning fork vibrator 10 and the measurement electrode surface can be reduced. Since the distance is separated from each other, the coupling capacitance between the two can be reduced, and the amount of the minute AC signal induced in the measurement electrode 1 escaping into the tuning fork vibrator 10 can be drastically reduced.

Therefore, the S / N ratio of the measurement signal can be increased, and the basic performance of the surface electrometer can be improved.

[0033]

As described above, according to the present invention,
Since both tips of the tuning fork vibrator are formed so as to come close to each other and away from the measurement electrode, the amount of electric force line that jumps into the tuning fork vibrator from the object to be measured and hits the tuning fork vibrator is reduced. The coupling capacitance between the measurement electrodes is reduced, the amount of noise mixed in the measurement electrodes is reduced, the S / N ratio of the measurement signal is increased, and the basicity is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a surface electrometer according to the present invention.

FIG. 2 is a schematic configuration diagram showing a conventional example.

FIG. 3 is a circuit diagram showing an example of an impedance conversion circuit.

FIG. 4 is a perspective view showing the external shape of a surface electrometer.

FIG. 5 is an enlarged configuration diagram showing a measurement unit.

[Explanation of symbols]

 1 Measuring Electrode 3 Amplifying Element (Converting Element) 4 Piezoelectric Element 5 Circuit Board 7 Electric Force Line 8 Object to be Measured 10 Tuning Fork Vibrator 10a Fixing Part 10b Fork Part 10c Tip Part

Claims (3)

[Claims] 1. A measuring electrode for receiving a line of electric force from an object to be measured, and a tuning fork type vibrator for temporally changing the amount of the line of electric force entering the measuring electrode. The tuning fork type vibrator is fixed. Formed so that both tip portions of the fork portion on the opposite side of the fork portion are close to each other and apart from the measurement electrode, and are induced in the measurement electrode by receiving an electric force line passing between both tip portions of the fork portion. A surface electrometer, which measures the surface potential of the measurement object from a very small signal. 2. The surface electrometer according to claim 1, wherein both end portions of the fork portion of the tuning fork type vibrator are formed in a V shape. 3. The surface electrometer according to claim 1, further comprising a conversion element for impedance-converting a minute signal induced in the measurement electrode into a voltage signal.