JP6593986B2 - Surface potential measuring device - Google Patents

Description

  The present invention relates to a surface potential measuring device for measuring the surface potential of a charged object in a non-contact manner.

The surface potential measuring device measures the surface potential of a charged object by using an induced current corresponding to the charge induced in a detection electrode opposed to the charged object. In such an apparatus, it is impossible to measure the surface potential by bringing the detection electrode into contact with the surface of the charged object, and the detection electrode must keep a predetermined distance from the charged object.
This is because if the detection electrode is brought into contact with the surface of the charged object, the charge of the charged object flows to the detection electrode, and if the surface potential of the charged object is high, the detection electrode is discharged only by bringing it too close. I will. As described above, if the surface charge flows to the detection electrode, the charged state of the surface of the charged object changes, and the measurement device may be damaged by discharge, so that accurate potential measurement cannot be performed. End up.
Therefore, a non-contact surface potential measuring device is required.

However, if the charged object and the detection electrode are separated from each other, a change in capacitance between the charged object and the detection electrode affects the value of the measurement potential. Since the capacitance depends on the distance between the detection electrode and the charged object, the measurement result changes if the measurement distance is different even for the same charged object.
Therefore, in order to obtain an accurate measurement result, the measurement distance must be kept at a predetermined reference distance, or correction according to the measurement distance has to be performed.

For example, there is a surface potential measuring device disclosed in Patent Document 1 that corrects according to the measurement distance.
This conventional surface potential measurement device is a device that includes a distance sensor that measures a measurement distance L together with a detection electrode, and an arithmetic processing unit.
The distance sensor measures the measurement distance L at the time of measuring the potential, and the arithmetic processing unit obtains a correction coefficient corresponding to the measurement distance L by substituting the measurement distance L into a calculation formula stored in advance. Then, the detection potential by the detection electrode is corrected with this correction coefficient.
The calculation formula of the correction coefficient is a linear function of the measurement distance L, that is, correction coefficient α = a · distance L + b. The a and b are constants that are set in advance by measuring a reference sample whose surface potential is known.
By using such a correction coefficient, the above-described conventional surface potential measuring apparatus can cope with potential measurement at various measurement distances.

JP 2013-007694 A

As described above, in the conventional surface potential measuring apparatus, the constants a and b in the calculation formula for the correction coefficient α are determined using a specific reference sample, and the influence of the measurement distance when measuring the surface potential of the same charged object. Was to eliminate. However, this correction coefficient does not consider the area of the charged object.
On the other hand, the capacitance between the detection electrode and the detection electrode varies depending on the area of the charged object. This is because the capacitance between the counter electrodes is proportional to the area of the counter electrodes. Therefore, if the area of the charged object is different, the measurement result will be different even if the surface potential is the same.
FIG. 4 is a graph showing the results when the surface potentials of charged plates having different areas are measured by a conventional surface potential measuring device. The conventional measuring apparatus used here uses a 30 [cm] square charging plate as a reference sample, sets the constants a and b in the above calculation formula, and calculates the correction coefficient α by the calculation formula. is there.

Using such a measuring apparatus, the measurement results for the 20 [cm] square, the 30 [cm] square, and the 45 [cm] square charged plate at different measurement distances are shown in FIG. As shown in
In FIG. 4, the solid line indicates the measurement result of the reference sample, the circle and broken line indicate 20 [cm] square charged plates, and the triangle and dashed line indicate 45 [ cm] is a measurement result of a charged plate on all sides.
As a result, the measurement potential of the 30 [cm] square charged plate does not depend on the measurement distance, but the measurement potential varies depending on the measurement distance between the 20 [cm] square charged plate and the 45 [cm] square charged plate. I confirmed that it changed. In particular, the difference from the reference sample increases as the measurement distance increases.

As described above, the measurement potential changes depending on the area of the charging plate because the electrostatic capacitance between the charging plate and the detection electrode depends on the area.
That is, in the conventional measuring apparatus, if the area of the charged object to be measured is different from the area of the reference sample when determining the calculation formula of the correction coefficient α, the measurement is performed even if the correction coefficient α is used. There was a problem that accurate measurement was not possible without the influence of distance.
An object of the present invention is to provide a surface potential measuring apparatus capable of performing an accurate potential measurement independent of a measurement distance to a charged object and an area of the charged object.

The present invention includes a potential detection unit that detects a surface potential of a charged object, a distance sensor that measures a measurement distance that is a distance from the potential detection unit to the surface of the charged object, and an arithmetic processing unit. based on the measured value the potential detecting section detects at least three measured distances which the distance sensor is measured to identify the approximate function representing the relationship between the measured distance and the potential, the measurement distance of the approximate function By substituting zero, a potential when the measurement distance is zero or almost zero is calculated, and the calculated potential is output as a measured potential of the charged object.
The above measurement distance is almost zero, although it is not strictly zero, it is a distance that can be regarded as zero, and is a distance in which an error from the measurement potential when the measurement distance is zero falls within an allowable range.

According to this invention, the measurement potential when the measurement distance is zero can be specified by an approximate function obtained from three or more actually measured values. The case where the measurement distance is zero or almost zero corresponds to the case where measurement is performed by bringing the potential detection unit into contact with the surface of the charged object.
Therefore, by using the surface potential measuring apparatus of the present invention, the surface potential of the charged object can be measured regardless of the measurement distance and the area of the charged object.

It is a lineblock diagram of the surface potential measuring device of an embodiment of this invention. It is the graph which showed the measured potential according to the measurement distance, and the approximate function calculated based on the measured potential. It is the graph which showed the result of the confirmation experiment in the surface potential measuring device of an embodiment. It is the graph which showed the relationship between the measurement distance and the measurement potential in the conventional surface potential measurement apparatus by using the area of the charging plate as a parameter.

FIG. 1 is a configuration diagram of a surface potential measuring apparatus according to an embodiment of the present invention.
The surface potential measuring apparatus according to this embodiment includes an arithmetic processing unit 2, a potential detecting unit 3 connected thereto, a distance sensor 4, and an output unit 5 in the apparatus main body 1.
Similar to the conventional measuring apparatus, the potential detection unit 3 converts a detection electrode 6 facing the charged object P to be measured, and an induced current caused by the charge induced in the detection electrode 6 into a voltage using a resistance, and measures the voltage. The measuring unit 7 is input to the arithmetic processing unit 2 as the potential Vm.

The distance sensor 4 is a sensor that measures the distance from the surface of the charged object P to the detection electrode 6 and inputs the measurement result as the measurement distance L to the arithmetic processing unit 2.
The measurement principle of the distance sensor 4 may be anything, for example, using ultrasonic reflection or optical. However, when the charged object P is an object that transmits light like a transparent film, an optical object is not suitable.
Further, the output unit 5 is a display or the like for outputting the measurement potential calculated by the arithmetic processing unit 2. The output unit 5 may be connected to an external printer or display, and the measured values may be displayed on these external devices.

The arithmetic processing unit 2 is input with the actual measurement potential Vm output from the potential detection unit 3 and the distance L output from the distance sensor 4. The arithmetic processing unit 2 has a function of associating the input actual measurement potential Vm with the measurement distance L when the measurement potential Vm is measured and storing the set as one actual measurement point.
Specifically, the potential detection unit 3 and the distance sensor 4 operate in synchronization, and each actual measurement value is input to the arithmetic processing unit 2 while maintaining the corresponding relationship.

  On the other hand, when a plurality of the actual measurement points for one charged object P are input, the arithmetic processing unit 2 approximates the function f () indicating the relationship between the measurement distance and the potential based on the input plurality of actual measurement points. A function of specifying L), a function of calculating a potential value when the measurement distance is zero from the calculated approximate function f (L), and outputting the value to the output unit 5 as a surface potential of the charged object P; It has.

Next, the approximate function f (L) calculated by the arithmetic processing unit 2 will be described with reference to FIG.
In FIG. 2, a plurality of actually measured points are indicated by black circles, and an approximate function f (L) specified based on these actually measured points is indicated by a broken line.
Each of the actual measurement points is a point of the actual measurement potential Vm output from the potential detection unit 3 corresponding to each measurement distance L when the 30 [cm] square charged plate P is measured at a plurality of measurement distances L. It is. That is, one actual measurement potential Vm corresponds to one measurement distance L. The calculated approximate function f (L) based on the plurality of actual measurement points is a curve that approximates the relationship between the measurement distance L and the potential that decreases as the distance L increases.

If the approximate function f (L) is obtained, the potential V0 when the measurement distance L is zero can be calculated by substituting L = 0 into the approximate function f (L).
When the measurement distance L is zero, this corresponds to the contact between the potential detection unit 3 and the charged object P. That is, in this approximate function f (L), the value of the potential V0 when the measurement distance L is zero is constant regardless of the measurement distance and the area of the charged object. Therefore, by setting the value as the measurement potential of the charged object P, a measurement potential that is not affected by the measurement distance or area can be obtained.

Therefore, the arithmetic processing unit 2 of this embodiment specifies the approximate function f (L) as described above for each measurement of one charged object P, and the measurement distance L is zero by the approximate function f (L). The potential V0 at this time is calculated to enable accurate surface potential measurement.
The approximate function f (L) represents the relationship between the measurement distance L and the actual measurement potential Vm, and is a function that decreases the actual measurement potential Vm as the measurement distance L increases. In this embodiment, the approximate function is assumed to be a quadratic function of the measurement distance L of f (L) = A · L ² + B · L + C. Note that A, B, and C are constants, and these values are specified by the calculation processing unit 2 based on a plurality of actually measured values.

The arithmetic processing unit 2 specifies the approximation function f (L) by an approximation method, and the constants A, B, and C in the approximation function f (L) measure the surface potential of one charged object P. It is a value calculated every time. The constant C corresponds to the potential V0 when the measurement distance L is zero.
Note that a general approximation method can be used as a method by which the arithmetic processing unit 2 calculates the approximate function f (L). In this embodiment, the least square method is used, but the approximation method is not limited to this.
Further, the function assumed as the approximate function f (L) is not limited to a quadratic function. As long as the relationship between the measurement distance L and the potential can be approximated, various curve functions such as a quartic function, a sixth function, and a hyperbolic function can be used. However, if a low-order function such as a quadratic function is used, the arithmetic processing in the arithmetic processing unit 2 can be simplified.

In this embodiment in which the approximate function f (L) is assumed to be a quadratic function, an experiment for confirming the accuracy of the approximate function f (L) was performed. The experiment will be described.
<Confirmation experiment>
Measurement was performed with the surface potential measuring apparatus of this embodiment, using a charged plate charged by applying a voltage as a measurement target. There are four types of charging plates, 15 [cm] square, 20 [cm] square, 30 [cm] square, and 45 [cm] square, and the charging potential is between 2 [kV] and 10 [kV], respectively. It was changed at intervals of 2 [kV].
For each charging plate, the measured potential Vm at a plurality of measurement distances L for each charging potential is input from the potential detection unit 3 to the arithmetic processing unit 2, and the potential V0 output from the arithmetic processing unit 2 is used as the measurement potential. did.

The result of this confirmation experiment is shown in the graph of FIG.
In this graph, the charging potential of the charging plate controlled by applying a voltage is plotted on the horizontal axis, and the measured potential calculated by the arithmetic processing unit 2 is plotted on the vertical axis. This measured potential is the potential V0 when the measurement distance L calculated by the arithmetic processing unit 2 using the approximate function f (L) is zero.
In the graph of FIG. 3, a circle and a solid line indicate a 15 [cm] square charged plate, a square and a broken line indicate a 20 [cm] square charged plate, and a triangle and a thin line indicate 30 [cm]. The measurement results for the 45 cm square charging plate are indicated by the cm] square charging plate, the cross mark and the thin broken line.

As is apparent from the graph of FIG. 3, it was confirmed that the value of the measured potential was almost equal regardless of the area of the charging plate at any charging potential.
That is, if the potential when the measurement distance L is zero is calculated by an approximate function f (L) composed of a quadratic function, the measurement potential corresponding to the charging potential is output regardless of the measurement distance and the size of the charging plate. It can be done.
Therefore, the potential V0 when the measurement distance L is zero can be used as the measurement potential of the charged object.

However, a value obtained by multiplying the value of the potential calculated as described above by a correction coefficient according to the characteristics of the measurement apparatus may be used as the measurement potential. The correction coefficient may be multiplied by the calculation unit 2 after specifying the potential when the measurement distance L is zero from the approximate function f (L), or multiplied by the correction coefficient in the measurement unit 7. The measured value may be input to the arithmetic processing unit 2 as the actually measured potential Vm.
In any case, according to the surface potential measuring apparatus of this embodiment, it is possible to measure an accurate surface potential regardless of the area of the charged object.
In this embodiment, the arithmetic processing unit 2 calculates the potential V0 by substituting the measurement distance L = 0 into the approximate function f (L). However, the approximate function f (L) is set to zero instead of zero. A potential calculated by substituting a close value and substantially zero may be used as the surface potential of the charged object. The almost zero measurement distance is a distance that can be considered that the potential detection unit 3 and the charged object P are in contact with each other, and is an distance in which an error with respect to the potential value calculated by the measurement distance L = 0 falls within an allowable range. .

Further, the apparatus main body 1 includes a control unit (not shown) for controlling each function, and the arithmetic processing unit 2 is triggered by the input of a preset number of actually measured points to the arithmetic processing unit 2. Control can be performed to calculate f (L).
Furthermore, when the apparatus main body 1 is provided with a moving mechanism and the charged object P is operated with the potential detection unit 3 facing the apparatus main body 1, the apparatus main body 1 may be moved to automatically change the measurement distance L. Then, while changing the measurement distance L, the distance sensor 4 and the potential detection unit 3 can be synchronized to input the respective actual measurement values to the arithmetic processing unit 2 as the actual measurement points.

The number of actually measured points required for the arithmetic processing unit 2 to specify the approximate function f (L) may be any number as long as it is plural, but it is considered that the accuracy of the approximate function increases as the number increases.
In particular, considering the fact that errors are included in the actual measurement values of the potential detector 3 and the distance sensor 4, the number of actual measurement points is required to some extent in order to increase the accuracy of the approximation function.
Further, the number of necessary actual measurement points varies depending on what curve function is assumed as the approximate function.
However, as the number of actual measurement points input to the arithmetic processing unit 2 increases, the measurement time by the potential detection unit 3 and the distance sensor 4 and the processing time of the arithmetic processing unit 2 become longer. In view of the above, it is preferable to set the type of function and the optimum number of actually measured points.

  The surface potential measuring apparatus of the present invention is useful when it is necessary to measure the surface potential of charged objects having various areas.

DESCRIPTION OF SYMBOLS 1 Apparatus main body 2 Arithmetic processing part 3 Potential detection part 4 Distance sensor 5 Output part 6 Detection electrode 7 Measurement part P Charged object L Measurement distance V Potential Vm Actual measurement potential V0 Potential f (L) approximation (when measurement distance is zero) function

Claims (1)

A potential detector for detecting the surface potential of the charged object;
A distance sensor that measures a measurement distance that is a distance from the potential detection unit to the surface of the charged object;
An arithmetic processing unit,
The arithmetic processing unit is based on an actual measurement value detected by the potential detection unit at three or more measurement distances measured by the distance sensor.
Specify an approximate function indicating the relationship between the measurement distance and the potential,
Substituting zero into the measurement distance of this approximate function to calculate the potential,
A surface potential measuring device for outputting the calculated potential as a measured potential of the charged object.

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