JPH10115646A - Surface potential sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface potential sensor in which a circuit is simplified and miniaturized and which can perform a measurement at a linear output characteristic by a method wherein a positive high voltage and a negative high voltage by a transformer are divided continuously and divided voltages are input to an output circuit as measuring voltages so as to be fed back to a common ground at a chopper, a chopper drive circuit and a conversion circuit. SOLUTION: On the basis of a DC voltage from an integrating circuit 9, the continuity degree of a transistor T is changed, and also a voltage drop due to a resistance R is changed accordingly. Consequently, the voltage VH generated by a high-voltage control circuit 11 is a voltage generated by continuously dividing a positive/negative high voltage (+100V or -500V) by a high- voltage power supply 13 on the basis of the DC voltage from the integrating circuit 9, and the relationship between a control voltage in the control circuit 11 and the generated voltage VH becomes completely linear. The generated voltage VH is input to an output circuit as a measuring voltage, and it is level- converted so as to be output as a measuring signal Vs . In addition, the voltage VH is fed back to a common ground at a sensor circuit as a feedback voltage Vf .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface potential sensor for measuring a surface potential of a charging drum of a copying machine, a printer, or the like, or a semiconductor wafer or the like.

[0002]

2. Description of the Related Art Conventionally, as a surface potential sensor of this type, an intermittent means for interrupting an electric field between a detection electrode and a surface to be measured in order to extract a surface potential of the object to be measured as an AC signal, A conversion circuit that converts a generated AC signal into a DC voltage is widely used. In such a surface potential sensor, when the distance from the detection electrode or the intermittent means to the surface to be measured fluctuates, the detection output fluctuates, and vibration of a device including the surface potential sensor leads to a fluctuation in the detection output, Also, high accuracy has been required for mounting the surface potential sensor. In order to solve such a problem, a surface potential sensor as disclosed in Japanese Patent Publication No. 3-6467 has been proposed.

In the surface potential sensor disclosed in Japanese Patent Publication No. 3-64767, a DC voltage from a conversion circuit is reduced to zero in order to reduce the potential difference between the measured object and the detection electrode to zero. Is returned to the intermittent means or the like, and a voltage corresponding to the returned DC voltage is output as the surface potential of the device under test, thereby solving the above-mentioned problem. However, in the configuration of this conventional surface potential sensor, in order to measure the bipolar potential, by combining voltage generators of opposite polarities, for example, by combining two transformers that generate bipolar voltages,
A feedback voltage corresponding to the output of the conversion circuit is generated.

A circuit having two transformers is effective for measuring a potential to be measured in both polarities, but it is necessary to construct a feedback voltage generating circuit by combining voltage sources having opposite polarities. Therefore, there is a problem that the cost is increased, the circuit is complicated, and the size is increased.

As a structure of a surface potential sensor for solving such a problem, a surface potential sensor having a structure schematically shown in FIG. 3 of the accompanying drawings has been proposed.
As shown in FIG. 3, this conventional surface potential sensor includes a detection electrode 4 which is opposed to a measured object through an opening of a shield (not shown), and a tuning fork 3 to which a piezoelectric element 2 is attached. A chopper, a preamplifier circuit 5 for impedance-converting an AC signal from the detection electrode 4, an amplifier circuit 6 for amplifying an output signal of the preamplifier circuit 5, a tuning fork driving circuit 7 for driving the tuning fork 3, and a tuning fork driving circuit 7, a synchronous detection circuit 8 for synchronously detecting the signal from the detection electrode 4 with the signal from the detection electrode 7, an integration circuit 9 for integrating the output of the synchronous detection circuit 8, and a transformer for boosting the output of the integration circuit 9 to a high voltage. There a high pressure amplifying circuit 13A has an output circuit 12 for transmitting a feedback voltage V _f dividing the (VH) to a low voltage, and low impedance to the output signal V _s of the high-voltage amplifier circuit 13A , And a power supply for supplying power to each circuit element.

[0006]

However, in such a conventional surface potential sensor, the output from the integrating circuit 9 is amplified and output by a transformer as a high voltage amplifier circuit 13A. The characteristics are not linear, especially
In low-level detection, it was unstable and inaccurate, and the response was low, causing a time lag.

[0007] In addition, in order to feed back the output to the sensor section, there is no other way than to feed back to the common ground or the same polarity point. In the case of a sensor having the opposite polarity, the polarities of the transformer and the inverter are changed and this output is returned. It was necessary to reconnect to the opposite polarity side of the output terminal of the power supply circuit.

On the other hand, the demand for miniaturization of this type of surface potential sensor also tends to increase year by year, and it has to be able to sufficiently meet such a demand.

An object of the present invention is to provide a surface potential sensor which can solve the above-mentioned problems of the prior art.

[0010]

According to the present invention, there is provided a surface potential sensor for detecting a surface potential of an object to be measured, comprising: a detection electrode opposed to the surface of the object to be measured; A chopper disposed between the object to be measured and the detection electrode in order to interrupt the electric field between the object to be measured and the detection electrode at a predetermined cycle so as to be detected by the detection electrode as an AC voltage. A chopper drive circuit for driving the chopper, a conversion circuit for converting an AC signal generated at the detection electrode into a DC voltage representing the surface potential, and a measurement corresponding to the DC voltage from the conversion circuit. An output circuit for receiving a voltage and outputting a signal indicating the surface potential, wherein at least the detection electrode and the chopper have an operating point floating from a ground potential, and A high-voltage power supply and a high-voltage control circuit are disposed between the circuit and the output circuit. The high-voltage power supply includes a transformer as a constant-voltage power supply. The voltage is simply received as a control signal, and the positive or negative high voltage by the transformer is continuously divided based on the control signal.The generated voltage is input to the output circuit as the measurement voltage, and the chopper, The signal is fed back to a common ground of the chopper drive circuit and the conversion circuit.

According to a specific embodiment of the present invention, the chopper includes a tuning fork, and the chopper driving circuit is a tuning fork driving circuit, and the tuning fork driving circuit is disposed outside a probe of the sensor. I have.

According to another particular embodiment of the invention,
The high-voltage power supply is arranged outside the substrate of the sensor.

According to still another specific embodiment of the present invention, the high voltage power supply is provided by utilizing an existing voltage source provided for a device including the device under test.

[0014]

1 and 2 of the accompanying drawings.
The present invention will be described in more detail with reference to Examples of the present invention.

FIG. 1 schematically shows the structure of a surface potential sensor as one embodiment of the present invention. As shown in FIG. 1, the surface potential sensor of this embodiment has a sensing electrode 4 that is opposed to a measured object through an opening of a shield (not shown) and a tuning fork to which a piezoelectric element 2 is attached. 3, a preamplifier circuit 5 for amplifying an AC signal generated on the detection electrode 4, an amplifying circuit 6 for amplifying an output signal of the preamplifier circuit 5, and a tuning fork for driving the piezoelectric element 2 attached to the tuning fork 3. A drive circuit 7, a synchronous detection circuit 8 for synchronously detecting a signal from the detection electrode 4 with a signal from the tuning fork drive circuit 7, an integration circuit 9 for integrating the output of the synchronous detection circuit 8, and a constant voltage source A high-voltage power supply 13 having a transformer, a high-voltage control circuit 11, an output circuit 12, and an external power supply are electrically insulated so that a preamplifier circuit 5, an amplification circuit 6, a synchronous detection circuit 8, an integration circuit 9, and a tuning fork driver are provided. And a power supply circuit 14 supplies power to the circuit 7. As is clear from the electrical connection in FIG. 1, the tuning fork 3 and the sensing electrode 4 have operating points floating from the ground potential.

In this embodiment, the transformer serving as the high-voltage power supply 13 electrically insulates the external power supply, and connects the primary winding energized by the external power supply, the intermediate tap to ground, and one end, for example, + 1000V. A secondary winding configured to output a constant voltage of (V1) and to output a constant voltage of, for example, -500 V (V2) is provided on the other end side. The high-voltage control circuit 11 includes a photocoupler PC, a resistor R, and a transistor T.

The high-voltage control circuit 11 in this embodiment comprises:
The two ends of the secondary winding of the transformer of the high-voltage power supply 13 are connected to both ends of the resistor R and the transistor T connected in series, and the DC voltage from the integrating circuit 9 is applied to the photocoupler P.
It is configured to be added to the transistor T simply as a control signal via C. Photocoupler PC
This is to completely separate the integrating circuit 9 and the high voltage control circuit 11 electrically. The DC voltage from the integrating circuit 9 is once converted into an optical signal and then converted again into an electric signal. Acts to control the conductivity of the transistor T.

Since the degree of conduction of the transistor changes based on the DC voltage from the integrating circuit 9, the current flowing through the resistor R changes accordingly, and the voltage drop due to the resistance changes accordingly. Therefore, the generated voltage VH of the high-voltage control circuit 11 is based on the DC voltage from the integration circuit 9 as a control signal, and based on the positive or negative high-voltage (+1000 V or-
(500 V). FIG. 2 illustrates the relationship between the control voltage and the generated voltage VH in the high-voltage control circuit 11. As is clear from the graph of FIG. 2, the relationship between the control voltage and the generated voltage VH is completely linear.

As described above, the voltage VH generated by the high voltage control circuit 11 is input to the output circuit 12 as a measurement voltage, and is fed back to the common ground of the sensor circuit as the feedback voltage _Vf . That is, in this embodiment, the feedback voltage _Vf is fed back to the common ground of the tuning fork 3, the amplification circuit 6, the tuning fork drive circuit 7, the synchronous detection circuit 8, and the integration circuit 9. On the other hand, the generated voltage VH that has been allowed to enter the high-voltage control circuit 11 to the output circuit 12 is output to the outside as a measurement signal V _s is level converted by the output circuit 12.

Since the tuning fork drive circuit 7 tends to generate high frequency noise and adversely affect the measurement of the surface potential,
It is preferable that the sensor is not provided inside the probe but is provided outside. It is preferable to dispose the tuning fork driving circuit outside the probe in order to reduce the size of the probe.

In the above-described embodiment, the high-voltage power supply 13
Is provided inside the sensor unit. However, if it is arranged outside the substrate of the sensor unit, the sensor unit body can be downsized. Moreover, in the embodiment described above,
Although a special transformer is used to configure the high-voltage power supply 13, the high-voltage power supply can also be provided by using an existing voltage source provided for the device including the device under test. For example, in a copying machine or a printer having a charging drum, a high-voltage and constant-voltage power transformer for charging or the like is always provided in the apparatus. If such a power transformer is configured to be shared as a transformer for the high-voltage power supply 13, a special transformer for the surface potential sensor can be omitted.

[0022]

According to the configuration of the surface potential sensor of the present invention, a linear change in the output can be obtained over the entire region including the vicinity of the rising edge and the vicinity of the peak, and the measurement can be performed with linear output characteristics. In addition, stable and accurate measurement can be performed even in a low-level output region near 0 volt.

The response speed of the measurement output to the change in the charge amount of the object to be measured is increased, the response is improved, and the time lag is eliminated.

Since the output from the high-voltage control circuit can be fed back to the common ground of the sensor unit regardless of the polarity, the polarity of the transformer or inverter can be changed according to the polarity of the sensor, or the output terminal of the power supply circuit can be connected to the output terminal of the power supply circuit. There is no need to change the connection.

By disposing the tuning fork drive circuit outside the sensor probe instead of inside the probe, the probe can be miniaturized, and the adverse effect of noise from the tuning fork drive circuit can be eliminated. It is also possible to perform more advanced control.

By sharing the existing high-voltage power supply transformer with the device including the device to be measured as the high-voltage power supply, not only can the sensor be reduced in size, but also the cost can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a surface potential sensor as one embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a control voltage and a generated voltage in a high voltage control circuit in the surface potential sensor of FIG.

FIG. 3 is a diagram schematically illustrating a configuration of an example of a conventional surface potential sensor.

[Explanation of symbols]

 2 Piezoelectric element 3 Tuning fork 4 Detecting electrode 5 Preamplifier circuit 6 Amplifying circuit 7 Tuning fork driving circuit 8 Synchronous detection circuit 9 Integrating circuit 11 High voltage control circuit 12 Output circuit 13 High voltage power supply 14 Power supply circuit PC Photocoupler R Resistance T transistor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Naoki Sakurai 2-6-23 Shin-Yokohama, Kohoku-ku, Yokohama-shi, Kanagawa 8F Kaneko No. 2 Building Inside Hirose Cherry Precision Co., Ltd.

Claims (4)

[Claims] 1. A surface potential sensor for detecting a surface potential of an object to be measured, wherein the detection electrode is opposed to the surface of the object to be measured, and the surface electrode is detected by the detection electrode as an AC voltage. A chopper disposed between the object to be measured and the detection electrode for intermittently interrupting an electric field between the object to be measured and the detection electrode at a predetermined cycle, and a chopper drive for driving the chopper A circuit, a conversion circuit for converting an AC signal generated at the detection electrode into a DC voltage representing the surface potential, and receiving the measurement voltage corresponding to the DC voltage from the conversion circuit to indicate the surface potential. An output circuit that outputs a signal, at least the detection electrode and the chopper have an operating point floating from a ground potential, and are interposed between the conversion circuit and the output circuit. A high-voltage power supply and a high-voltage control circuit are arranged, the high-voltage power supply includes a transformer as a constant-voltage power supply, and the high-voltage control circuit receives the DC voltage from the conversion circuit as a control signal and performs the control. A positive or negative high voltage generated by the transformer is continuously divided based on the signal, and the generated voltage is input to the output circuit as the measurement voltage, and is applied to a common ground of the chopper, the chopper drive circuit and the conversion circuit. A surface potential sensor characterized in that it is fed back. 2. The sensor according to claim 1, wherein the chopper includes a tuning fork, and the chopper driving circuit is a tuning fork driving circuit, and the tuning fork driving circuit is disposed outside a probe of the sensor.
The surface potential sensor as described in the above. 3. The surface potential sensor according to claim 1, wherein the high-voltage power supply is disposed outside a substrate of the sensor. 4. The surface potential sensor according to claim 1, wherein the high-voltage power supply is provided by using an existing voltage source provided for an apparatus including the device under test.