Surface potential measuring apparatus

Abstract

To provide a surface potential measuring apparatus capable of accurately measuring the surface potential of a measurement target even when a noise generation source that generates electrical noise exists near a measurement target.SOLUTION: A surface potential measuring apparatus that detects the surface potential of a measurement target surface 2a provided near a noise generation source 3 that generates electrical noise comprises: a detection electrode 6 that faces the measurement target surface 2a and detects the surface potential of the measurement target surface; and a noise reduction electrode 5 that inputs electric line force with the reverse polarity to the electric line force input to the detection electrode 6 from the noise generation source 3 to the detection electrode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a surface potential measuring device for measuring the surface potential of a charged object. [Background technology]

[0002] As a device for non-contact measurement of the surface potential of a measurement object, a surface potential measuring device is known that chops the electric field between the measurement object and a detection electrode with a vibrator, converts it into an AC voltage, and detects the surface potential of the object from the voltage. Specifically, a chopper that periodically opens and closes is provided near the detection electrode, and the strength of the electric field entering the detection electrode is periodically changed by opening and closing this chopper, and the displacement current flowing from the detection electrode to the earth is detected as a surface potential signal (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-192414 A [Patent Document 2] JP 2017-015575 A [Patent Document 3] JP 2017-167011 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a surface potential measuring device such as that described above, if there is a noise source that generates electrical noise near the detection electrode, the detection electrode will detect the electric field due to the noise source, i.e., the electric field lines generated from the noise source, simultaneously with the electric field lines due to the object to be measured. If the electric field generated by the noise source is strong, the signal due to the surface potential of the measurement object may be buried in the noise from the noise source and may not be detected accurately. Furthermore, when the surface potential of the object to be measured is relatively small, it is possible to increase the detection sensitivity of the detection electrodes. However, in that case, the electrical noise detected by the detection electrodes may become too large, exceeding the measurement limit of the surface potential measuring device and making it impossible to perform the measurement at all.

[0005] An object of the present invention is to provide a surface potential measuring device that can accurately measure the surface potential of a measurement object even if a noise source that generates electrical noise is present near the measurement object. [Means for solving the problem]

[0006] A first invention is a surface potential measuring device that detects the surface potential of a surface to be measured, and includes a detection electrode that faces the surface to be measured and detects the surface potential of the surface to be measured, and a noise reduction electrode that inputs electric field lines of opposite polarity to electric field lines input to the detection electrode from a noise generating source that generates electrical noise in the vicinity of the surface to be measured.

[0007] In a second aspect of the present invention, the distance between the detection electrode and the noise reduction electrode is set to be smaller than the distance between the noise reduction electrode and the measurement object surface.

[0008] In a third aspect of the present invention, the noise reduction electrode includes an electrode body connected to a power source, and the electrode body has a surface shape in which a surface on the detection electrode side is covered with a curved surface.

[0009] A fourth invention includes an ion irradiation electrode that irradiates ions onto the surface to be measured, the ion irradiation electrode being the noise source, and the detection electrode detecting the surface potential of the ion irradiation portion during ion irradiation by the ion irradiation electrode. Effect of the Invention

[0010] In the first invention, the electric field lines entering the detection electrode from the noise reduction electrode cancel the electric field lines entering the detection electrode from the noise source, thereby reducing the electric noise from the noise source detected by the detection electrode. Therefore, the surface potential of the measurement target surface can be accurately measured by distinguishing it from the electric noise.

[0011] According to the second aspect of the present invention, the electric field lines of the noise reduction electrode easily enter the detection electrode and are less likely to affect the surface of the object to be measured, so that the potential of the surface of the object to be measured can be measured while reducing electrical noise.

[0012] According to the third aspect of the present invention, discharge is unlikely to occur on the surface of the electrode body of the noise reduction electrode, and electric field lines from the noise reduction electrode can be stably input to the detection electrode, thereby making it possible to continuously reduce electrical noise.

[0013] According to the fourth invention, while ions are being irradiated from the ion irradiation electrode to the measurement target surface, even if there is electrical noise from the ion irradiation electrode, the surface potential of the ion irradiation portion can be accurately measured. For example, the volume resistance of a coating film during the curing process can be detected. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram of a measurement device according to an embodiment. [Diagram 2] FIG. [Diagram 3] 13 is a graph of measurements when the noise reduction electrodes are not activated. [Figure 4] 13 is a graph of measurements when the noise reduction electrodes are activated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Embodiment] An embodiment of the present invention will be described below. In this embodiment, the surface potential measuring device of the present invention is applied to a device for detecting volume resistance that depends on the degree of hardening of a coating film in order to estimate the degree of hardening (dryness) of the coating film. The principle of measuring the volume resistivity of a coating film is described in, for example, Patent Document 3.

[0016] In this embodiment, the surface to be measured is a coating film 2 formed on a grounded conductor base 1. While ions are irradiated onto the surface of this coating film 2 from an ion irradiation electrode 3, the surface potential of an ion irradiation portion 2a is measured. The surface potential measuring device of the embodiment shown in FIG. 1 includes a potential detection unit 4 facing a coating film 2 and a noise reduction electrode 5 adjacent to the potential detection unit 4.

[0017] The potential detection section 4 has a configuration similar to that of the conventional surface potential measurement device described above, and is provided with a detection electrode 6 that faces the ion irradiation section 2a of the coating film 2 and has an electric charge induced therein in response to the surface potential of the ion irradiation section 2a. Although not shown, the potential detection section 4 is provided with an oscillator that chops the electric field between the coating film 2 and the detection electrode 6 and converts it into an AC voltage, and a data processing section that processes the detected current, and detects the displacement current flowing from the detection electrode 6 to earth as a surface potential signal.

[0018] On the other hand, the noise reduction electrode 5 is made of a metal electrode body, and is connected to a power source 7. This power source 7 is a power source that applies a voltage of the opposite polarity to the ion irradiation electrode 3 to the noise reduction electrode 5.

[0019] The noise reduction electrode 5 is disposed on the substantially opposite side of the potential detection unit 4 from the ion irradiation electrode 3, and is composed of a tip 5a located on the potential detection unit 4 side and a support 5b connected to a power source 7. The tip 5a has a curved surface, and the entire surface is free of sharp edges and corners. For example, the tip 5a may be a sphere or a cylinder with curved both end faces. The shape of the tip 5a is the surface shape of the electrode body on the detection electrode 6 side. The tip of the round rod support 5b is fixed to the surface of the tip 5a, and the base end of the support 5b is connected to the power source 7. By applying a predetermined voltage to such noise reduction electrode 5, electric field lines E' are generated from the surface of the tip portion 5a (see FIG. 2).

[0020] The ion irradiation electrode 3 is a needle-shaped discharge electrode, and is surrounded by a grounded cylindrical electrode 8 as shown in FIG. 1, so that the tip of the ion irradiation electrode 3 does not protrude from the cylindrical electrode 8. The cylindrical electrode 8 suppresses the spread of the electric charge generated at the ion irradiation electrode 3, and reduces the number of electric field lines that directly enter the detection electrode 6 from the ion irradiation electrode 3.

[0021] [Actions and Effects] When the surface potential of the ion irradiation portion 2a of the coating film 2 is measured with the above-mentioned surface potential measuring device, a negative voltage is applied to the ion irradiation electrode 3 to generate a discharge and irradiate a negative charge onto the ion irradiation portion 2a on the surface of the coating film 2. At this time, the ion irradiation portion 2a and the detection electrode 6 are set so as to face each other directly. The potential detection unit 4 detects the surface potential of the ion irradiation unit 2a by detecting charges induced in the detection electrode 6 in accordance with the surface potential of the ion irradiation unit 2a.

[0022] In addition, the volume resistivity of the coating film 2 is sufficiently low when the paint is in a semi-dried state, so the value of the surface potential at the ion-irradiated portion 2a of the coating film 2 should be small. 2, in reality, the detection electrode 6 is not only subjected to electric field lines from the ion irradiation portion 2a, shown by thin solid lines, but also to negative electric field lines E, shown by dashed lines, which are generated directly from the ion irradiation electrode 3 and from negative charges that do not reach the ion irradiation portion 2a of the coating film 2 from the ion irradiation electrode 3. Therefore, the potential detection unit 4 detects both the electric field due to the surface potential of the ion irradiation portion 2a and the electric field lines E generated from the ion irradiation electrode 3 or the negative charges. These dashed electric field lines E are electrical noise.

[0023] Therefore, the surface potential measuring device cannot accurately measure the surface potential of the ion irradiation portion 2a, which is the measurement target surface. In particular, if the surface potential measuring device increases the detection sensitivity of the potential detection portion 4 in an attempt to detect a small value of the surface potential, the measured value will go off the scale due to the electrical noise.

[0024] Therefore, a positive voltage is applied to the noise reduction electrode 5, and the positive electric field lines E' generated from this positive noise reduction electrode 5 are input to the detection electrode 6. The positive electric field lines E' from this noise reduction electrode 5 cancel the electric field lines E generated from the ion irradiation electrode 3 or the negative charge, and the negative electric noise generated from the ion irradiation electrode 3 can be canceled. Therefore, the surface potential measuring device can measure the surface potential of the ion irradiation portion 2a even during ion irradiation.

[0025] It should be noted that the cancellation of electrical noise does not mean that the electrical noise is completely cancelled, but rather includes that the electrical noise is reduced to a level that allows the measured values ​​to be distinguished. Moreover, the electric field lines from the negative electrode toward the detection electrode 6 are referred to as negative electric field lines E, and the electric field lines from the positive electrode toward the detection electrode are referred to as positive electric field lines E'.

[0026] [Confirmatory experiment] An experiment for confirming the effect of the noise reduction electrode 5 will be described. The experimental apparatus is as shown in FIG. 3, in which a negative voltage (−2.1 kV) is applied to the ion irradiation electrode 3 and a positive voltage (+2.1 kV) is applied to the noise reduction electrode 5 . The potential detection unit 4 calibrates the output value by measuring a calibration sample whose surface potential is known in advance while a voltage is applied to the noise reduction electrode 5. The following experiment is carried out using the potential detection unit 4 calibrated in this manner.

[0027] In the confirmation experiment, three types of samples (A, B, C) in which zinc-rich paint was applied to a zinc-plated plate were used as the low-resistance coating film 2, which was the surface to be treated, and the surface potential of the ion irradiation section 2a was measured with and without the noise reduction electrode 5 operating. The above samples A, B, and C are samples that have been adjusted to have different volume resistivities depending on the density of zinc particles. Therefore, each sample A, B, and C should have a different surface potential.

[0028] Specifically, 10 seconds after the start of measurement by the potential detection unit 4, a voltage is applied to the ion irradiation electrode 3. Then, the ion irradiation unit 2a is corona-charged for 20 seconds, and the voltage application is stopped after 20 seconds, after which the measurement of the charging potential is continued for 30 seconds. The noise reduction electrode 5 has a height h from the surface of the coating film 2 and a distance d from the center of the detection electrode 6 of h = 2 [mm] and d = 7 [mm], respectively. These values ​​were experimentally determined as positions where the positive electric field lines E' input from the noise reduction electrode 5 to the detection electrode 6 are approximately equal to the electric field lines E of the noise, thereby enabling effective noise reduction.

[0029] It has been confirmed that by setting the distance between the noise reduction electrode 5 and the detection electrode 6 to be smaller than the distance between the noise reduction electrode 5 and the ion irradiation section 2a, which is the surface to be measured, noise can be reduced even if the voltage applied to the noise reduction electrode 5 is low. Furthermore, by setting the tip 5a of the noise reduction electrode 5 so that it does not protrude into the measurable area of ​​the detection electrode 6, the tip 5a is prevented from interfering with the detection of the electric field lines from the surface of the object to be measured.

[0030] [Experimental Results] In the above confirmation experiment, when the noise reduction electrode 5 was not operated, the measurement result of the surface potential was as shown in Figure 3, which exceeded the detection limit (OR) of the potential detection unit 4. Therefore, the surface potential of the coating film 2 during corona charging could not be read at all. In this case, the volume resistivity of the coating film 2 must be estimated from the slight change in the surface potential after the corona charging is stopped. However, from Figure 3, no difference between samples A, B, and C could be detected.

[0031] On the other hand, the measurement results when the noise reduction electrode 5 was operated simultaneously with the ion irradiation electrode 3 are shown in Fig. 4. That is, the measured value of the surface potential during corona charging was within the detectable range of the potential detection unit 4, and the surface potential of each of the coating films (samples A, B, and C) with different volume resistivities could be measured. As described above, by generating electric field lines E' input from the noise reduction electrode 5 to the detection electrode 6, the electric field lines E of the electric noise from the ion irradiation electrode 3 can be canceled, making it easier to detect the potential of the surface to be measured. In addition, in Figure 4, a spike appears in the measured potential immediately after the applied voltage to the ion irradiation electrode 3 and the noise reduction electrode 5 is turned off. This is due to the discharge of the charge induced in the detection electrode 6 and does not affect the measurement.

[0032] In the above embodiment, the ion irradiation electrode 3 for irradiating the measurement target surface with ions is the noise source, but the noise source is not limited to this. Anything that forms an electric field around it, such as an electrode, a power line, or a signal line, can be a noise source that generates electrical noise. Regardless of the noise source, the electrical noise can be reduced by inputting an electric field of the opposite polarity to the electric field line from the noise source toward the detection electrode 6 to the detection electrode 6 using the noise reduction electrode 5 as described above.

[0033] In this case, if the electric field lines detected by the detection electrode 6 from the noise source and the electric field lines detected by the detection electrode 6 from the noise reduction electrode 5 are equal in magnitude, the electric noise can be completely canceled. However, even if these electric field lines are not equal in magnitude, measurement is possible as long as the electric noise can be sufficiently reduced.

[0034] In addition, the tip of the noise reduction electrode 5 is curved to prevent discharge from the surface, thereby enhancing the noise reduction effect. If the surface of the noise reduction electrode 5 has a sharp tip, this will become a discharge point and cause a discharge. If a discharge occurs, the electric field lines E' entering the detection electrode 6 will become unstable.

[0035] The position of the tip 5a of the noise reduction electrode 5 is preferably set so that the electric field lines E' from the tip 5a do not affect the surface to be measured. If the noise reduction electrode 5 is too close to the surface to be measured, the electric field lines from the surface to be measured will be directed toward the noise reduction electrode 5 instead of the detection electrode 6. However, as described above, by placing the noise reduction electrode 5 closer to the detection electrode 6 than the surface to be measured, the positive electric field lines E' generated from the noise reduction electrode 5 can more easily enter the detection electrode 6 and the effect on the surface to be measured can be reduced. Furthermore, even if the positive electric field lines E' from the noise reduction electrode 5 may affect the surface potential of the surface being measured and thus the measured value, the effect on the measured value can be reduced by calibrating the potential detection unit 4 with the noise reduction electrode activated. [Industrial Applicability]

[0036] The surface potential of various charged objects can be measured without being affected by electrical noise. [Explanation of symbols]

[0037] 2. (Measurement object) Coating 2a (measurement surface) Ion irradiation part 3. (Noise source) Ion irradiation electrode 4. Potential detection section 5 Noise reduction electrodes 5a (detection electrode side of electrode body) tip 5b (electrode body) support part 6 Detection electrode

Claims

1. A surface potential measuring device for detecting a surface potential of a measurement target surface, comprising: a detection electrode facing the measurement target surface and detecting a surface potential of the measurement target surface; a noise reduction electrode for inputting to the detection electrode an electric field line of opposite polarity to an electric field line input to the detection electrode from a noise generation source that generates electric noise in the vicinity of the measurement target surface; A surface potential measuring device comprising:

2. The distance between the detection electrode and the noise reduction electrode is: set smaller than the distance between the noise reduction electrode and the measurement target surface The surface potential measuring device according to claim 1 .

3. The noise reduction electrode is An electrode body connected to a power source, The electrode body has a surface shape in which the surface on the detection electrode side is covered with a curved surface.

3. The surface potential measuring device according to claim 1 or 2.

4. An ion irradiation electrode that irradiates the measurement target surface with ions; The ion irradiation electrode is the noise source, The detection electrode detects a surface potential of an ion irradiation portion during ion irradiation by the ion irradiation electrode. The surface potential measuring device according to claim 1 .

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