JPH045148B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a surface electrometer, and more particularly to an AC conversion type non-contact surface electrometer that can directly measure using a digital signal generated by a central control circuit. .

[Conventional technology]

Conventionally, when surface potential is measured, stored, and processed, and when each copying process is controlled based on that value, the state of each process measured as an analog value is converted into a digital value using an A/D converter. After converting and processing in the central control circuit, each process condition is processed by converting it back to an analog value using a D/A converter, but this type of method requires an A/D converter, etc. However, it has the drawbacks that the circuit configuration becomes complicated and the whole becomes expensive.

[Purpose of the invention]

This invention eliminates the drawbacks of the conventional ones as described above, and enables A
The surface potential can be stored and arithmetic processed without using a D converter, simplifying the circuit configuration, making the entire structure inexpensive, and controlling, for example, each copying process condition based on the surface potential. The purpose is to provide a

[Structure of the invention]

The present invention is an AC conversion type non-contact surface electrometer, which generates a voltage that changes stepwise in response to a digital signal, and includes a voltage applying means for applying the voltage to a chopper, a chopper drive signal, and a measuring electrode. a detection means for detecting a phase difference between the detection signal and the detection signal induced by the detection signal, and when the detection means detects and outputs the phase difference, the digital signal of the voltage application means at the time of output is converted into a surface potential detection signal It has a configuration that allows it to be taken out.

[Embodiments of the invention]

Embodiments of the invention shown in the drawings will be described below.

First, the principle of this invention will be explained. Third
Figures A, B, and C are conceptual diagrams showing the phase relationship between the chopper position and the electrometer output.

Figure 3A shows that the surface potential Vs of the object to be measured and the probe aperture plate and chopper potential Vg are Vs>
This shows the state when the probe is placed opposite the object to be measured when Vg.

The moment the probes are placed opposite each other, a charge with a polarity opposite to that of the object to be measured is generated on the measurement electrode, but because the input impedance of the electrometer amplifier is small, the induced charge disappears instantly.

However, since the electric field between the object to be measured and the measurement electrode is continuously interrupted by the chopper, charges are continuously induced in the measurement electrode in response to changes in the lines of electric force reaching the measurement electrode.

In other words, in the potential relationship described above, when the chopper is moving in the closing direction (in the direction of arrow a in the figure), an induced current i flows through the external circuit in the direction of arrow a in the figure through the resistor R, and the chopper opens. When moving in the direction (direction of arrow b in the figure), an induced current i flows in the direction of arrow b in the figure.

The above is the principle of the AC conversion type surface electrometer.
FIG. 3B shows the situation when the potential relationship is reversed, that is, Vs<Vg'.

In this case, the relationship between the direction of the chopper and the direction of the induced current is exactly opposite to the case where Vs>Vg.

Now, if the opposing area of the electrode and the object to be measured changes over time as shown in Figure 3C, the voltage waveforms of outputs 1 and 2 shown in Figure 3A and B will be as shown in Figure 3C. Become. In other words, when Vs>Vg and when Vs<
The phase of the output voltage will be 180° different from the case of Vg.

For example, if Vg is changed over time as shown in Figure 4A, a constant surface potential
With respect to Vs, the output phase shifts by 180° between the time domain _t1 and the time domain _T2 .

In this case, at the moment t ₀ when the output phase shifts,
This shows that it is possible to measure the surface potential by detecting Vg (t ₀ ).

The principle of the present invention is as described above, but in order to detect a phase shift, a reference signal whose phase is fixed at least within the measurement time is required.

Here, the most easily usable reference signal would be to detect the position of the chopper and convert it into an electrical signal.

For example, if the chopper is vibrated using a piezoelectric element, the position of the chopper can be accurately detected from the vibration signal, which is a well-known and widely used technique.

By using the above-mentioned technical means, it is possible to obtain a synchronizing signal (the reference signal obtained by shaping the chopper drive signal) having the phase relationship shown in Figure 4B with an extremely simple circuit configuration. can.

The present invention is characterized in that a staircase wave is generated as a digital value from the central control circuit 1, and the value is converted into an analog value by the D/A converter 2 and boosted.

The output for creating a class wave from the central control circuit 1 is input to a D/A converter 2, and the output of this D/A converter 2 is input to a booster 3 and a differential amplifier 4.
The output of the booster 3 is input to the aperture plate 5 and chopper 6 of the probe, as well as the voltage divider 7, and the output of the voltage divider 7 is input to the other input terminal of the operational amplifier 4. is input to the input terminal of. The output of the differential amplifier 4 is input to one input terminal of the comparator 8, and the reference value 9 of the allowable error is input to the other input terminal of the comparator 8. is input to the central control circuit 1.

On the other hand, the measurement electrode 11 of the measurement probe 10 is connected to a preamplifier 12 provided in the measurement probe 10, and the output of the preamplifier 12 is input to a bandpass filter 13, and the output of the bandpass filter 13 is phase-shifted. The output of the phase shifter 14 is input to a signal waveform shaping circuit 15, and the output of the signal waveform shaping circuit 15 is inputted to one input terminal of a phase difference detection circuit 16.

Further, the output of one piezoelectric element 17 provided in the chopper 6 of the measurement probe 10 is input to the sensor drive oscillation circuit 18, and the output of the sensor drive oscillation circuit 18 is input to the synchronization signal waveform shaping circuit 19, The output of the other piezoelectric element 20 provided in the synchronous signal waveform shaping circuit 1
9, the synchronizing signal waveform shaping circuit 19
The output of this phase difference detection circuit 19 is input to the other input terminal of the phase difference detection circuit 16, and the output of this phase difference detection circuit 19 is input to the central control circuit 1.

Next, the operation of the above-mentioned device will be explained.

The central control circuit 1 is configured to generate a step wave of digital values, and when the step wave of the digital value generated by the central control circuit 1 is input to the D/A converter 2, the step wave of the digital value is converted into a step wave of the digital value. The wave is converted into an analog value and then input to the booster 3, so that the booster 3 outputs a high-voltage staircase wave, which is applied to the aperture plate 5 and chopper 6 of the measurement probe 10.

The current induced in the measurement electrode 11 of the one-side constant probe 10 is transferred to the preamplifier 12 in the measurement probe 10.
After being converted into a voltage by and input to the phase shifter 14. Then, the phase is adjusted by the phase shifter 14 so that a phase difference with a synchronization signal, which will be described later, can be detected (the phase difference in the reference state is set to 0), and then input to the signal waveform shaping circuit 15. The signal waveform shaping circuit 15 converts the signal into a rectangular wave, which is input to the phase difference detection circuit 16.

Furthermore, the synchronization signal, which is a reference signal for detecting the phase shift with the output signal of the measurement electrode 11, can be obtained by detecting the position of the chopper 6 and converting it into an electrical signal. For example, the vibration of the chopper 6 can be detected by a thick electric element, and the position of the chopper 6 can be accurately detected based on the signal. Therefore, the synchronization signal is the output of one piezoelectric element 17 in the measurement probe 10.
8, the output of this sensor drive oscillation circuit 18 and the output of the other piezoelectric element 20 are input to the synchronization signal waveform shaping circuit 19, whereby the drive signal from the sensor drive oscillation circuit 18 is The synchronizing signal is shaped by a synchronizing signal waveform shaping circuit 19, and the synchronizing signal output from the synchronizing signal waveform shaping circuit 19 is input to the other input terminal of the phase difference detection circuit 16.

The phase difference detection circuit 16 is, for example, Exclusive.
- Consisting of an OR circuit, when the synchronization signal based on the output of the sensor drive oscillation circuit and the output signal of the measurement electrode 11 are in phase, the phase difference detection circuit 1
6 output is L, but when the phase is reversed, it changes to H output, so the digital value of the staircase wave at that point is determined by the central control circuit 1 based on the output to the D/A converter 2 at that point. and stored in the memory of the central control circuit 1 as shown in FIG. 2b. The state of each sampling is shown in FIGS. 2a and 2b. If the step wave potential 21 from the central control circuit 1 is sampled at the rising edge of the output of the phase detection circuit 16, the step wave potential 21 from the central control circuit 1 becomes the surface potential. The potential of the staircase wave at the time when it exceeds 22 is sampled, and that potential becomes the output 23 of the electrometer and is stored in the memory as a surface potential. Of course, if you have a step wave, you can make it finer and closer to a triangular wave.

Furthermore, although the voltages applied to the aperture plate 5 and chopper 6 of the measurement probe 10 cannot be directly read, a monitoring circuit prevents the accuracy from decreasing due to changes in the surrounding environment. That is, the high-voltage step wave that is the output of the booster 3 applied to the measurement probe 10 is divided by the voltage divider 7 to a level equal to the voltage before being boosted by the booster 3, and is then applied to one input terminal of the differential amplifier 4. Since the output of the D/A converter 2 is input to the other input terminal of the differential amplifier 4, the difference between the output value from the central control circuit 1 and the voltage actually applied is the difference. The signal is amplified by the dynamic amplifier 4 and input to one input terminal of the comparator 8. Therefore, in the present invention, since the reference value of the allowable error is input to the other input terminal of the comparator 8, when the error exceeds the reference value, an abnormality signal is input from the comparator 8 to the central control circuit 1. Therefore, the central control circuit 1 can sense when an abnormality occurs in surface potential measurement.

In the above embodiment, a D/A converter was provided to convert the digital value from the central control circuit 1 into an analog value, but the D/A converter used when the central control circuit performs process control may be repurposed. It is possible to do so.

〔Effect of the invention〕

By configuring this invention as described above,
The surface potential can be digitally processed, and since expensive components such as A/D converters are not used, the overall circuit structure can be made simple and inexpensive, and it can also be used under adverse conditions such as high temperature and high humidity. However, it has excellent effects such as preventing runaway of process control due to erroneous detection of surface potential and ensuring reliable control.

[Brief explanation of drawings]

Figure 1 is a circuit diagram, Figure 2a is a diagram showing the relationship between the surface potential and the staircase wave potential, Figure 2b is a diagram showing the electrometer output, Figures A, B, C, and 4. Figure A,
B is a diagram for explaining the principle of this invention. 1...Central control circuit, 2...D/A converter, 3
...Booster, 4...Differential amplifier, 5...Aperture plate, 6...Chipper, 7...Voltage divider, 8...
Comparator, 9...Reference value, 10...Measurement probe,
11...Measurement electrode, 12...Preamplifier, 13...
...Band pass filter, 14... Phase shifter, 15...
...Signal waveform shaping circuit, 16...Phase difference detection circuit,
17, 20...Piezoelectric element, 18...Sensor drive oscillation circuit, 19...Synchronizing signal waveform shaping circuit, 21
...Staircase wave, 22...Surface potential, 23...Electrometer output.

Claims (1)

[Claims] 1 Voltage application means that generates a voltage that changes stepwise according to a digital signal and applies the voltage to the chopper, and detection means that detects the phase difference between the chopper drive signal and the detection signal induced in the measurement electrode. An AC conversion type non-contact surface potential meter, characterized in that a digital signal from the voltage application means when the detection means detects and outputs a phase difference is used as a surface potential detection signal.