JP3673597B2 - Surface electrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface potential meter that measures the surface potential of an object in a non-contact manner, and relates to a surface potential meter used to detect the surface potential of a photoreceptor in an electrophotographic apparatus such as a copying machine.
[0002]
[Prior art]
As surface electrometers for measuring the surface potential of a photoconductor of an electrophotographic apparatus in a non-contact manner, so-called chopper type electrometers and capacitance variation type electrometers are mainly known.
[0003]
A chopper-type electrometer measures the electric field strength of a measurement object by placing a conductive vibrating object between the measurement object and the measurement electrode, and increasing or decreasing the amount of electric field lines incident on the measurement electrode by the vibration object. The capacitance variation type electrometer measures the electric field strength by physically vibrating the measurement electrode itself and changing the electric field distribution between the measurement object and the measurement electrode. Both types have the same contents regarding signal reception processing.
[0004]
FIG. 2 is a diagram showing a schematic configuration of a conventional chopper type surface potential meter. In the figure, reference numeral 1 is a measurement electrode that receives electric lines of force from the measurement object 8, and 2 is a tuning fork vibrator that vibrates and chops electric lines of force incident on the measurement electrode 1 from the measurement object 8 in the A direction. Reference numeral 3 denotes an amplifying element for amplifying the minute alternating current signal induced in the measurement electrode 1 by impedance conversion, and 4 denotes a piezoelectric element for applying vibration to the tuning fork vibrator 2.
[0005]
In addition, 5 is a circuit board, 6 is a drive signal to the piezoelectric element 4, a received signal from the measurement electrode 1, and a connector for inputting / outputting a power source, and 7 is a measurement object 8 to the measurement electrode 1 in the B direction. An incident electric field line 9 is a shield case for housing the circuit board 5.
[0006]
FIG. 3 is a diagram showing an outline of an impedance conversion circuit configured on the circuit board 5. Here, impedance conversion is performed by a source follower circuit in which the input side resistor 11 is set to 100 MΩ, for example, and an FET is used as the amplifying element 3. Further, the resistors 12 and 13 on the output side are, for example, 100Ω and 20KΩ, respectively. These components such as resistors are printed on the circuit board 5 or soldered with discrete chip components.
[0007]
FIG. 4 is a perspective view showing the outer shape of the electrometer having the above configuration. As shown in the figure, the circuit board 5 is housed in a shield case 9, a connector 6 is disposed on the side of the case, and a small window (opening) for measurement is provided on the front.
[0008]
Next, the operation of the electrometer having the above configuration will be described. First, the piezoelectric element 4 and the tuning fork type vibrator 2 are brought into a resonance state by a piezoelectric element driving signal supplied from the outside, and mechanical vibration is generated. As a result, the amount of electric lines of force that pass from the measurement object 8 through the measurement window of the shield case 9 and enter the measurement electrode 1 increases or decreases in accordance with the vibration of the tuning fork vibrator 2. Thereby, 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 which is the amplifying element 3.
[0009]
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 measurement object 8.
[0010]
Here, 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 measuring object 8, the first stage amplified signal having a high S / N ratio is post-processed. Whether it can be transferred to the circuit determines the basic performance of the surface electrometer.
[0011]
[Problems to be solved by the invention]
Incidentally, in recent years, as the demand for downsizing of the apparatus has increased, for example, surface electrometers mounted on copying machines are required to be further downsized and thinned due to the installation space. Conventionally, in response to such demands for miniaturization and thinning, the measurement electrode is downsized (height direction), the vibrator is downsized, and the vibration direction of the vibrator is transverse to the measurement object. It was handled by such means. Furthermore, in order to compensate for the deterioration of the S / N ratio accompanying the downsizing of the measurement electrode, the measurement electrode is arranged as close as possible to the measurement object.
[0012]
However, in the conventional surface electrometer as described above, as shown in FIG. 5, the detection surface area decreases as the measurement electrode becomes smaller, and the measurement object passes through the measurement window of the shield case. The ratio of the electric lines of force that jump directly into the tuning fork type vibrator with respect to the incident total electric lines of force was large.
[0013]
Further, the distance between the tuning fork vibrator and the measurement surface of the measurement electrode is shortened, and the coupling capacitance between the two is increased, so that a minute AC signal once induced on the measurement electrode escapes from the tuning fork. Here, there is also a proposal that the tuning fork vibrator is positioned in the direction of the measurement object as well as the direction of the measurement electrode. However, the tip of the tuning fork vibrator jumps out of the shield case, and the surface potentiometer Cannot meet the demands for downsizing.
[0014]
In addition, if an insulator (impurity) such as dust adheres to the tip of the tuning fork vibrator, the potential at the tip of the tuning fork vibrator must be GND due to the influence. It was charged and this was mixed in the measurement electrode as noise.
[0015]
As a result, the S / N signal component (S) becomes small or the noise component (N) becomes large, and the basic performance as a surface electrometer tends to deteriorate. was there.
[0016]
The present invention has been made paying attention to the above problems, and has as its object to provide a non-contact type surface electrometer with a high S / N ratio of measurement signals and improved basic performance. .
[0017]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention , a surface electrometer is configured as described in (1) and (2) below.
(1) A measurement electrode that receives a line of electric force from a measurement object, and the measurement electrode is located inside the fork portion and in a position close to the tip portion of the fork portion, and the measurement is performed from the tip portion of the fork portion. A surface potentiometer including a tuning fork vibrator that temporally changes the amount of electric lines of force entering an electrode,
The tuning fork vibrator is a surface electrometer in which most of the fork portions face each other in parallel, and a tip portion of the fork portion is formed in a C-shape.
(2) In the surface electrometer according to (1),
A surface electrometer having a conversion element for impedance-converting a minute signal induced in the measurement electrode into a voltage signal.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 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 denote the same components.
[0020]
In FIG. 1, reference numeral 1 denotes an electric field of a measurement object 8 such as a photoconductor whose surface potential is to be measured. It is a tuning fork type vibrator of a chopper part that changes the amount of the electric force line 7 that chops the electric force line 7 and enters the measuring electrode 1 with time, and both end portions 10c of the fork part 10b opposite to the fixed part 10a It is formed so as to be bent in such a way as to be close to each other and away from the measurement electrode 1 so as to have a square shape.
[0021]
Reference numeral 3 denotes an amplifying element (converting element) for impedance-converting a minute alternating current signal induced in the measurement electrode 1 into a voltage signal, and 4 is a piezoelectric element that applies vibration to the tuning-fork vibrator 2. A circuit board on which the impedance conversion circuit or the like is configured, 6 is a connection signal for inputting / outputting a drive signal to the piezoelectric element 4, a reception signal from the measurement electrode 1, and a power supply, and 9 is a circuit board that houses the circuit board 5. Shield case.
[0022]
The impedance conversion circuit having the amplifying element 3 is the same as that shown in FIG. The appearance of the entire case covered with the 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.
[0023]
In the surface potentiometer having the above-described configuration, both the tip portions 10c of the C-shaped shape of the tuning fork vibrator 10 are the amount of electric force lines 7 incident in the B direction from the measuring object 8 along the center line of the tuning fork. Is physically vibrated in the horizontal direction (A direction) as viewed from the measuring object 8 so as to change with time. The tuning fork vibrator 10 has a fixed portion 10a side opposite to the tip portion 10c of the tuning fork vibrator 10 and opposite to the incident direction (B direction) of the electric force lines 7. Is provided with a measuring electrode 1, which absorbs electric lines of force 7 passing between both tip portions 10 c of the fork portion 10 b and generates a surface potential of the measuring object 8 from a minute AC signal induced in the measuring electrode 1. Is measured.
[0024]
Here, in the present embodiment, the tip shape of the tuning fork vibrator 10 is formed in a C shape, so that the vibration amplitude amount of the tuning fork vibrator 10 remains almost the same as in the past, and from the measurement object 8. The amount of electric force lines 7 that escape (jump into) the tuning fork vibrator 10 is drastically reduced. Further, since the coupling capacitance is reduced by increasing the distance between the tip of the tuning fork vibrator 10 and the measurement electrode 1, the amount of the minute AC signal induced in the measurement electrode 1 escaping from the tuning fork vibrator 10 is drastically reduced. .
[0025]
Furthermore, even when the tip of the tuning fork vibrator 10 is charged to a certain potential due to adhesion of an insulator or the like, the distance between the tuning fork vibrator 10 and the measurement electrode 1 is far away, so that the noise component mixed in the measurement electrode 1 can be reduced. Also decreases.
[0026]
Therefore, the signal component (S) in the S / N ratio can be increased and the noise component (N) can be decreased, and the basic performance as a surface electrometer can be greatly improved.
[0027]
Conventionally, the measurement electrode is miniaturized in order to cope with the miniaturization of the apparatus, so that the detection surface area of the measurement electrode is reduced, and the total electric force lines incident from the measurement window of the surface potential meter from the measurement object are reduced. The ratio of the lines of electric force that jump directly into the tuning fork type vibrator was large.
[0028]
Furthermore, the distance between the tuning fork vibrator and the measurement electrode measurement surface is shortened, and the coupling capacitance between the two is increased, so that a minute AC signal once induced in the measurement electrode escapes to the tuning fork vibrator.
[0029]
In addition, if an insulator (impurity) such as dust adheres to the tip of the tuning fork vibrator, the electric potential at the tip of the tuning fork vibrator must be GND, which is charged to a certain potential. As a result, noise was mixed in the measurement electrode.
[0030]
Therefore, as a result, the signal component (S) of the S / N ratio becomes small or the noise component (N) becomes large, and the basic performance of the surface electrometer tends to deteriorate.
[0031]
However, in this embodiment, since the tip of the tuning fork vibrator 10 is formed in a C shape as described above, the opening of the tuning fork vibrator 10 can be widened, The amount of the electric force lines 7 that escape to the tuning fork vibrator 10 can be drastically reduced, and since the distance between the tuning fork vibrator 10 and the measurement electrode surface is increased, the coupling capacity between the two can be reduced, It is possible to drastically reduce the amount of the minute AC signal induced in the measurement electrode 1 that escapes to the tuning fork vibrator 10.
[0032]
Therefore, the S / N ratio of the measurement signal can be increased, and the basic performance as a surface electrometer can be improved.
[0033]
【The invention's effect】
As described above, according to the present invention, since both tip portions of the tuning fork vibrator are formed so as to be close to each other and away from the measurement electrode, the electric lines of force that jump from the measurement object to the tuning fork vibrator As the amount of noise decreases, the coupling capacitance between the tuning fork vibrator and the measurement electrode decreases, the amount of noise mixed into the measurement electrode also decreases, the S / N ratio of the measurement signal increases, and the basicity is reduced. There is an effect of improving.
[Brief description of the 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. 5 is a perspective view showing an enlarged view of the measurement unit.
1 Measuring electrode 3 Amplifying element (conversion element)
4 Piezoelectric element 5 Circuit board 7 Line of electric force 8 Measurement object 10 Tuning fork type vibrator 10a Fixing part 10b Fork part 10c Tip part

Claims (2)

A measurement electrode that receives electric lines of force from a measurement object, and the measurement electrode is located inside the fork portion and in a position close to the tip portion of the fork portion, and enters the measurement electrode from the tip portion of the fork portion. a surface potential meter and a tuning fork resonator which temporally changing the amount of electrical power lines,
In the tuning fork vibrator, most of the fork portions face each other in parallel, and a tip portion of the fork portion is formed in a C-shaped shape . The surface potential meter according to claim 1,
Front surface electrometer characterized and Turkey that having a conversion element for impedance conversion of the induced small signal to the measuring electrode to a voltage signal.

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