JPH0614077B2 - Surface potential detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for detecting the surface potential of an object in a non-contact manner, and particularly to an output caused by a change in a set distance between a surface to be measured and a detection device. The present invention relates to a surface potential detecting device having a structure for reducing fluctuation.

[Prior Art] As a device for non-contactly detecting the potential of the surface to be measured, a chopper type device or a vibration capacitance type device is well known. In any type of detection device, the number of electric lines of force formed between the surface to be measured and the detection electrode is changed, and the surface potential is detected based on the fluctuation of the electric charge induced on the detection electrode. Is. Therefore, when the distance between the surface to be measured and the detection device changes, the number of lines of electric force changes,
As a result, it was unavoidable that the output of the detector changed.

Therefore, conventionally, various correction means have been proposed in order to correct the output change based on the change in the distance from the surface to be measured.

Japanese Unexamined Patent Publication No. 56-4062 discloses one example.
That is, as shown in FIG. 7, in a chopper type surface potential detecting device having a chopper 3 for periodically chopping the lines of electric force formed between the surface to be measured 1 and the detection electrode 2, FIG. As shown in FIG. 5, a configuration is shown in which a high voltage proportional to the measurement output is fed back to the chopper 3 itself to reduce the distance dependency.

Further, in JP-A-60-152959, as shown in FIG. 9, first and second detection electrodes 6 and 7 having different distances from the surface to be measured 1 are provided, and each detection electrode 6, A configuration is disclosed in which the difference between the outputs of 7 is taken and the measurement output is corrected based on the difference of the outputs.

[Problems to be Solved by the Invention] However, in the configuration disclosed in Japanese Patent Laid-Open No. 56-4062, since it is necessary to feed back a high voltage to the chopper, a high voltage generating means and an insulating structure of the chopper are required. However, there has been a problem that the configuration of the entire apparatus becomes extremely complicated and it is difficult to reduce the size.

Further, as disclosed in Japanese Patent Laid-Open No. 60-152959, the structure in which two types of detection electrodes 6 and 7 having different facing distances to the surface to be measured are arranged has the following problems.

As shown in FIG. 9, here, in order to guide the lines of electric force X from the surface to be measured 1 to the case 8, the window 8 having a constant shape is used.
a is formed. That is, although a plurality of detection electrodes are provided, the window portion 8a is single. Therefore, as schematically shown in FIG. 10, the lines of electric force X are applied to the detection electrodes 6 and 7 through the same window portion 8a. Will be reached.

A similar configuration is also possible in a vibration capacitance type surface potential detecting device. For example, as schematically shown in FIG. 11, the first and second devices are arranged so that the distance to the measured surface 1 is different. It is considered that the detection output can be corrected based on the output difference between the detection electrodes 11 and 12 by providing the detection electrodes 11 and 12.

However, in reality, in the surface potential detecting device including the sensing electrodes 6, 7 or 11, 12 having different facing distances from the surface to be measured, the difference between the outputs obtained from the two sensing electrodes is still a function of the distance. Therefore, it is obvious that the distance-corrected output cannot be obtained by the method of taking the difference between the two sensing electrodes. That is, as shown in FIG. 12, the output difference between the detection electrode 11 and the detection electrode 12 is not constant.

On the other hand, taking the ratio of the outputs of the two sensing electrodes 6, 7 or 11, 12 and correcting the one of the outputs of the two electrodes by utilizing the fact that the value of this ratio is a function of the distance, A method has been filed for obtaining a detection output that does not have a.

However, even in this method, the sensing electrodes 6, 7 or 1 having different facing distances from the surface to be measured are actually used.
It has been found that in the surface potential detecting device provided with Nos. 1 and 12, the amount of change in the ratio of the outputs obtained from the two detection electrodes is extremely small, and therefore it is difficult to obtain the data necessary for distance correction. That is, taking the vibration capacitance type surface potential detecting device as shown in the schematic view of FIG. 11 as an example, as shown in FIG. 12, if the distance between each sensing electrode and the surface 1 to be measured is different. Even if it did, it was found that the ratio of the outputs obtained from the detection electrodes 11 and 12 hardly changed. Note that FIG. 13 shows data on the structure used for the measurement of FIG. 12 in which the distance between each sensing electrode and the surface to be measured is made equal. By comparing the results of FIGS. 12 and 13, the values of the output ratios of the detection electrodes 11 and 12 are different, but even if the distance between the surface to be measured and the detection device is changed, the output ratio is changed. It can be seen that the value of is almost the same in each figure. That is, it can be seen that the effect of arranging the two detection electrodes 11 and 12 at different distances from the surface to be measured hardly appears.

This also applies to the chopper type surface potential detecting device shown in FIG.
In which the first and second sensing electrodes 6,7 or 11,1
Even if 2 is arranged in a staggered manner, it is not possible to correct the output fluctuation based on the fluctuation of the set distance between the surface to be measured and the surface potential detecting device based on the outputs of the plurality of sensing electrodes. Recognize.

Therefore, an object of the present invention is to provide a surface potential detecting device having a structure capable of effectively reducing output fluctuations due to fluctuations in the set distance from the surface to be measured without requiring a complicated structure. It is in.

[Means for Solving Problems] The surface potential detecting device of the present invention is a device for detecting the surface potential of an object in a non-contact manner, and is applied to both a chopper type and a vibration capacitance type. is there.

Also in the present invention, the first and second detection electrodes that are arranged at a predetermined distance from the surface to be measured and that are configured to induce charges on the surface according to the potential of the surface to be measured are provided. ing. Further, a conductive case for accommodating the first and second detection electrodes is provided, and in this case, the first and second electrically conductive lines for causing the lines of electric force from the surface to be measured to enter each detection electrode. Windows are formed corresponding to the respective detection electrodes. Further, the first and second windows are formed so as to be displaced so that the distance to the surface to be measured is different. Then, even if the first and second detection electrodes are installed on the same plane, no inconvenience occurs.

Furthermore, first and second detection means for extracting the charges induced on the first and second detection electrodes as a voltage signal,
Compensation means for taking a ratio of the outputs of the first and second detection means and compensating the output of the first or second detection means based on the ratio.

[Principle of Correction in Surface Potential Detection Device of the Present Invention] As described above, in both the vibrating capacitance type and the chopper type surface potential detection device, two distances from the surface to be measured are different in the conductive case. It was not possible to arrange the detection electrodes and correct the output variation based on the variation in the set distance between the detection device and the surface to be measured based on the output difference or the output ratio of the detection electrodes.

Therefore, considering the results of FIGS. 12 and 13 again, it can be seen that the output ratios of both detection electrodes are substantially constant even if the distance between the surface potential detecting device and the surface to be measured changes. (Even if both sensing electrodes are arranged in a staggered manner),
This means that even if the detection electrode is installed behind the case window, that is, away from the case window, the output of the detection electrode is hardly affected.

On the other hand, in the present invention, the number of lines of electric force formed between the surface to be measured and the detection electrode, that is, incident on the detection electrode through the window portion of the case, is determined by the number of the surface to be measured and the window portion of the case. In consideration of the influence of the positional relationship between the first and second detection electrodes, a window is provided for each of the first and second sensing electrodes, and the window between the first and second windows and the surface to be measured is provided. It is formed by shifting the windows so that the distances are different.

Since the first and second windows are arranged so as to be displaced as described above, the magnitudes of the outputs obtained by the first and second sensing electrodes are different in the present invention, and the measured surface and the surface are different. The rate of change in the output of both detection electrodes due to the change in the set distance from the potential detecting device also becomes different. Therefore, by taking the ratio of the outputs of the first and second detection electrodes, it is possible to obtain the distance correction output according to the distance variation between the surface to be measured and the surface potential detecting device.

That is, in the conventional example, the line of electric force incident on the detection electrode is
While it was considered that it was determined by the distance between the surface to be measured and the surface of the detection electrode, in the present invention, the light is incident on the detection electrode due to the positional relationship between the surface to be measured and the window provided on the case. It is based on the idea that the number of lines of electric force is determined.

[Description of Embodiments] FIG. 1 is a sectional view showing an embodiment of the present invention with respect to a vibration capacitance type surface potential detecting device. Conductive case 21
A first detection electrode 23 and a second detection electrode 24 are housed inside. Each of the detection electrodes 23 and 24 is formed on a flexible substrate 25, as shown in FIG.
The flexible substrate 25 is adhered to one leg of a piezoelectric tuning fork 26 as a vibrating means by, for example, silicon adhesive. The piezoelectric tuning fork 26 is fixed to an insulating substrate 28 via a support member 27.

On the other hand, the conductive case 21 is formed with a first window portion 31 and a second window portion 32 corresponding to the detection electrodes 23 and 24. The windows 31 and 32 are formed so as to be displaced by a distance g, as is apparent from FIG. 2 and FIG. 2 which is an enlarged view of the main parts of FIG. Therefore, the distances d ₁ and d _{2 from the} surface to be measured 1 are also | d ₁ −
There is a relationship of d ₂ | = g. This distance g is
If 32 has a size of, for example, about 3.4 × 3.5 mm, it is selected to be about 1.0 mm.

As shown in FIG. 4, the insulating substrate 28 has appropriate electronic components mounted on both surfaces thereof, and a detection unit for extracting charges generated on the detection electrodes 23, 24 on the substrate 28 and each of them. A correction unit is configured to correct the output fluctuation based on the set distance between the surface to be measured and the surface potential detection device based on the ratio of the detection outputs of the detection electrodes 23 and 24.

FIG. 5 is a schematic block diagram of the surface potential detecting device of the embodiment shown in FIG. First sensing electrode 23 and second
Each of the detection electrodes 24 has a current-voltage conversion resistor 4 between it and the reference potential (the ground potential in this embodiment).
1, 42 are connected. The resistors 41 and 42 form part of the first and second detecting means for taking out the charges induced on the surfaces of the detection electrodes 23 and 24 as a voltage. On the first detection electrode 23 side, this detection means includes, in addition to the resistor 41, an impedance conversion circuit 43, a bandpass filter / amplification circuit 45, and a rectification / smoothing / amplification circuit 47 connected to the subsequent stage. Similarly, also on the second detection electrode 24 side, the impedance conversion circuit 44, the bandpass filter / amplification circuit 46, and the rectification / smoothing / amplification circuit 48 are sequentially provided in the subsequent stage of the resistor 42.
Are connected.

Further, in this embodiment, an amplifying circuit 49 is connected to the output side of one of the rectifying / smoothing / amplifying circuits 47 in order to use the output based on the first detection electrode 23 as the measurement output. Further, as correction means for performing correction based on the above-described correction principle, the division / multiplication circuit 51 and the subtraction / amplification circuit 52 are connected to the subsequent stages of the rectification / smoothing / amplification circuits 47 and 48. That is, one rectifying / smoothing / amplifying circuit 4
The output V ₁ of 7 is divided and applied to not only the amplifier circuit 49 but also the division / multiplication circuit 51.

The output V ₂ of the other rectifying / smoothing / amplifying circuit 48, that is, the output from the second detection electrode 24 is given to the division / multiplication circuit 51. The division / multiplication circuit 51 outputs the output V ₁ given by the rectification / smoothing / amplification circuits 47 and 48.
The ratio of V ₂ is calculated, and the output V ₃ given from the amplifier circuit 49 is multiplied to output V ₄ = (1-V ₁ / V ₂ ) × V ₃ . Then, the corrected output V ₄ is given to the subtraction / amplification circuit 52. The subtraction / amplification circuit 52 is also supplied with the output V ₃ of the amplification circuit 49. This subtraction / amplification circuit 52
Subtracts and amplifies the correction output V ₄ from the measurement output V ₃ and gives the output terminal 53 a measurement output that does not depend on the variation in the distance between the surface to be measured and the surface potential detecting device.

Note that the first detection electrode 23 and the second detection electrode 24
Is fixed to the piezoelectric tuning fork 26 as shown in FIG. 1, and the piezoelectric tuning fork oscillation circuit 61 of FIG.
6 is provided for exciting.

As described above, since the case windows 31 and 32 are arranged so as to be displaced from each other, the first and second detection electrodes 23 and 2 are
4, the magnitude of the output obtained is different, and the value of the fluctuation of the detected output caused by the fluctuation of the set distance between the surface to be measured and the surface potential detecting device is also different. Therefore, by taking the ratio of the outputs of the detection electrodes 23 and 24, it is possible to obtain the output for distance correction according to the distance variation.

Next, specific experimental results will be described. The signal obtained from each detection electrode is a sine wave of about 0.5 mV _rms per 100 V of surface potential when the distance between the surface to be measured and the first window portion 32 is 3.0 mm. Frequency is piezoelectric tuning fork 2
It is equal to the vibration frequency of 6, which is 800 Hz in this example.
FIG. 6 shows the value of the amplified detection signal per surface potential of 100 V and the value of the output for distance correction obtained by each rectified detection signal.

As is apparent from FIG. 6, the output ratio greatly changes when the distance between the surface to be measured and the surface potential detecting device (here, the second window 32 is used as a reference) is 2 to 4 mm. I understand. Therefore, multiply the obtained distance correction output appropriately,
It can be seen that by adding or subtracting to one of the outputs derived from either one of the detection electrodes 23 and 24, an output that does not depend on the variation in the set distance between the surface to be measured and the surface potential detecting device can be obtained.

Note that the addition / subtraction differs depending on which detection electrode output is used as the denominator when the output ratio of both detection electrodes 23, 24 is taken. In the example shown in FIG. 5, since the output of the second detection electrode 24 is used as the denominator, the first detection electrode 23
The correction output V ₄ is subtracted from the derived measurement output, but on the contrary, when the ratio is taken with the output V ₁ derived from the first detection electrode as the denominator, it is added.

Although the detection electrodes 23 and 24 are fixed to the same piezoelectric tuning fork 26 in the above-described embodiments, they may be fixed to separate piezoelectric tuning forks. In this case, the output ratio of the two electrodes is obtained after rectifying the respective outputs. The vibrating means for vibrating the detection electrode is not limited to the piezoelectric tuning fork, and an I-shaped or H-shaped piezoelectric tuning piece may be used.
Alternatively, an electromagnetic vibrator may be used.

Further, the present invention can be applied not only to the vibration capacitance type surface potential detecting device but also to a chopper type surface electrode detecting device using a chopper.

[Effect of the Invention] In the present invention, the first and second detection electrodes are provided in correspondence with each other.
A first window portion and a second window portion are formed in the case, and the first window portion and the second window portion are formed so that the distance from the surface to be measured is different. . Further, since the correction means for determining the output ratio of each detection electrode and correcting the measured output by the output ratio is provided, it is possible to obtain an output that is not affected by the variation in the set distance between the surface to be measured and the surface potential detecting device. It will be possible. Therefore, when using the surface potential detecting device, it is possible to eliminate a complicated positioning adjustment work for the surface to be measured. In addition, the surface potential detection device of the present invention does not require a complicated correction circuit connected to the detection electrode, so that the size of the surface potential detection device is
In particular, the size of the detection electrode portion is not increased. Therefore, it can be easily installed in a narrow space such as near the photosensitive drum of a copying machine.

[Brief description of drawings]

FIG. 1 is a sectional view showing a surface potential detecting device according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a main part of the surface potential detecting device of FIG. FIG. 3 is a plan view showing the arrangement of the detection electrodes used in the embodiment shown in FIG. FIG. 4 is a plan view showing an insulating substrate used in the embodiment shown in FIG. 1 and an electronic component mounted on the substrate. FIG. 5 is a schematic block diagram of a circuit portion of the embodiment shown in FIG. Figure 6 shows
It is a figure which shows the relationship between the output from each detection electrode in the surface potential detection apparatus comprised based on one Example of this invention, and the distance between the to-be-measured surface-surface potential detection apparatus. FIG. 7 is a sectional view showing an example of a conventional surface potential detecting device. FIG. 8 is a schematic block diagram showing an example of the correction means in the conventional surface potential detecting device. FIG. 9 is a cross-sectional view showing another example of the conventional surface potential detecting device. First
FIG. 0 is a cross-sectional view for explaining the shape of the lines of electric force formed between the surface to be measured and the detection electrode in the surface potential detecting device shown in FIG. FIG. 11 is a sectional view showing a correction means in still another example of the conventional surface potential detecting device. FIG. 12 is a diagram showing the relationship between the output of each sensing electrode and the set distance between the surface potential detecting device and the surface to be measured in the conventional example shown in FIG. Figure 13 shows
In the conventional example shown in FIG. 11, the relationship between the output of each detection electrode and the set distance between the surface to be measured and the surface potential detection device when the detection electrode is arranged at the same position with respect to the case window portion is shown. It is a figure. In the figure, 21 is a case, 23 is the first detection electrode, 2
Reference numeral 4 is a second detection electrode, 31 is a first window portion, and 32 is a second window portion.

Claims (1)

[Claims] 1. A device for detecting the surface potential of an object in a non-contact manner, the device being arranged at a predetermined distance from the surface to be measured so that electric charges are induced on the surface according to the potential of the surface to be measured. A first and a second sensing electrode configured as described above, and a first for accommodating the first and the second sensing electrode, and for causing the lines of electric force from the surface to be measured to enter each of the sensing electrodes. And a conductive case having a second window portion formed therein, wherein the first and second window portions are formed so as to be different from each other in distance from the surface to be measured. The ratio between the outputs of the first and second detecting means for extracting the electric charge induced on the second detecting electrode as a voltage signal and the output of the first and second detecting means is taken, and the first or the second based on the ratio. A surface further comprising a correction means for correcting the output of the second detection means. Position detection device.