JP3325670B2 - Film thickness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the thickness of a coating film formed on the surface of a substrate.

[0002]

2. Description of the Related Art Heretofore, an eddy current type measuring device has been mainly used as a measuring device for a coating film thickness when the coating state is dry, and a gauge when the coating state is wet.

[0003]

However, since all of them are of the contact type, there is a possibility that the coating film surface will be damaged or other adverse effects. There was the inconvenience of having to use a measuring instrument.

[0004]

SUMMARY OF THE INVENTION A coating thickness measuring apparatus of the present invention has been completed in view of the above points, and is intermittently arranged at a constant frequency toward a coating surface of an object to be coated. Irradiating means for irradiating laser light, detecting means for detecting an acoustic signal generated from the coating film surface by a photoacoustic effect accompanying the irradiation of the laser light, and the intensity of the acoustic signal detected by the detecting means,
Analysis means for analyzing the phase difference between the acoustic signal and the laser beam, and reference data indicating the correspondence between the intensity and phase difference of the acoustic signal due to the photoacoustic effect and the coating film thickness are stored in advance for each type of paint. The storage unit is provided with a comparison unit for comparing the analytic signal obtained by the analysis unit with reference data called from the storage unit in accordance with the type of the paint to determine the coating film thickness.

[0005]

The present invention is an application of the photoacoustic effect,
This means that when a substance absorbs light that is intermittent at a certain frequency, the surrounding gas will produce a sound of the same frequency.

An acoustic signal generated by irradiating the surface of a coating film with intermittent laser light generally shows a tendency that the intensity increases as the weight of the coating film increases, that is, as the film thickness increases. In addition, there is a time lag between the irradiation of the laser beam and the generation of the acoustic signal, that is, there is a phase difference between the acoustic signal and the laser beam. Since the surface approaches the light source, the delay of sound generation is reduced, that is, the phase difference tends to be reduced. However, these tendencies differ depending on the type of paint and also on the color even with the same type.

Therefore, for one paint, the thickness of the coating film is sequentially changed, and each time the thickness of the coating film is measured with a ready-made measuring device such as an eddy current type, the photoacoustic effect caused by each film thickness is caused. The intensity of the acoustic signal and the phase difference between the acoustic signal and the laser light are measured, and reference data indicating the correspondence between the intensity and the phase difference of the acoustic signal and the coating film thickness for the paint is created.

This is similarly performed for other paints, and reference data is created for each kind of paint including a color difference, and these are stored in the storage means in advance.

When measuring the coating thickness, reference data corresponding to the type of the coated paint is called from the storage means to the comparing means, and the object to be coated is set at a predetermined measurement position.

Subsequently, when the irradiating means is operated, the coating film surface is irradiated with laser light intermittently at a constant frequency. Then, an acoustic signal is generated from the coating film by the photoacoustic effect and detected by the detecting means. The detected acoustic signal is sent to the analyzing means, and the phase difference between the intensity and the laser light is analyzed.

[0011] The analysis signal is sent to the comparing means and compared with the called reference data, and the coating film thickness is determined according to the value of the analysis signal. The determined value is displayed by a display means or the like as a measured value of the coating film thickness.

[0012]

As described above, according to the present invention, since the non-contact method utilizing the photoacoustic effect is used, there is no possibility that the coating film surface is damaged or the like, and the measurement can be performed with high accuracy. Can be. In addition, there is an effect that it can be used for both dry and wet application states.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. The present invention utilizes the photoacoustic effect as described above, and its basic principle is as described in the section of operation.

In FIG. 1, reference numeral 1 denotes a cell installed at a predetermined coating film thickness measuring place, and a test piece of an object a having a coating film b formed on the surface is placed on the bottom surface thereof. The ceiling 2 of the cell 1 is formed of a translucent material, and a detection window 3 is opened on a side surface.

Irradiation means 5 is provided above the cell 1 and receives an oscillation signal from an oscillator 6 to direct a pulsed semiconductor laser beam x having a constant period toward the surface of the coating film b. Irradiation.

In the detection window 3 of the cell 1, the laser light x
Is provided with a microphone 7 (corresponding to the detecting means of the present invention) for detecting an acoustic signal y generated from the coating film b by the photoacoustic effect accompanying the irradiation.

The above acoustic signal y is, as shown in FIG.
Although it is generated in the form of a pulse having the same cycle as the pulse of the laser beam x, the intensity of the acoustic signal y is larger when the coating b is present than when it is absent. A phase difference occurs with the laser beam x. In this case, generally, as the thickness of the coating film b increases, the intensity of the acoustic signal y increases, and the phase difference decreases on the contrary.

Therefore, the microphone 7 is connected to the analyzing means 9 via the amplifier 8. The analyzing means 9 analyzes the intensity of the acoustic signal y detected by the microphone 7, and generates a pulse of the acoustic signal y and a pulse of the laser beam x detected by the signal from the transmitter 6. Has a function of analyzing the shift of the phase difference, that is, the phase difference.

As described above, as the thickness of the coating film b increases, the intensity of the sound signal y generally increases, and the phase difference generally tends to decrease. ,
It depends on the type of paint, and even on the same type, depending on the color.

Therefore, for a certain paint, the coating film thickness is sequentially changed, and each time the coating film thickness is measured by an eddy current type measuring device, the intensity of the acoustic signal accompanying the photoacoustic effect generated at each film thickness is measured. And the phase difference between the laser beam and the laser beam, and creates reference data indicating the correspondence between the strength and phase difference of the acoustic signal and the coating film thickness for the paint. When the type of the paint is “melamine black”, reference data as shown in the graph of FIG. 3 is obtained.

This is similarly performed for other paints, and reference data is created for each paint type including a color difference, and the reference data is input from the input means 10 to the identification number indicating the paint type. At the same time, it is stored in the storage means 11 in advance.

The comparing means 12 is connected to the output side of the storing means 11 and the analyzing means 9. The input means 10 attached to the storage means 11 also has a function of, when an identification number is input thereto, calling the reference data of the corresponding paint stored in the storage means 11 to the comparison means 12. The comparing means 12 calculates the reference data thus called,
It has a function of comparing with an analysis signal output from the analysis means 9. Display means 13 is connected to the output side of the comparison means 12.

Next, the operation of this embodiment will be described. When measuring the coating film thickness, a test piece of the coating object a on which the coating film b is formed is set in the cell 1 and an identification number indicating the type of the coated coating material is input to the input means 10. Then, the corresponding reference data is stored in the comparing means 1 from the storage means 11.
Call 2

Subsequently, when the irradiating means 5 is operated, a pulsed semiconductor laser beam x is radiated to the coating film surface. Then, an acoustic signal y is generated from the coating film b by the photoacoustic effect, and is detected by the microphone 7. The detected acoustic signal y is sent to the analyzing means 9 and the phase difference between the intensity and the laser light x is analyzed.

The analysis signal is sent to the comparison means 12 and compared with the above-mentioned called reference data.
If the type of the paint is “melamine black”, the intensity of the acoustic signal y in the analysis signal is 24 mV, and the phase difference is 90 °, the coating thickness of 23 μm is determined from the reference data in FIG. The determined value is displayed by the display means 13 as a measured value of the coating film thickness.

When the type of the paint changes, the same operation may be performed by changing the reference data called to the comparing means 12.

As described above, according to this embodiment, the film thickness can be measured without coming into contact with the surface of the coating film.
It can be used for both dry and wet application.

Further, since the semiconductor laser is used, the size of the device can be reduced. Further, since the displacement from the laser irradiation position is not calculated as in the case of the triangulation method, the measurement is not affected even if the laser position slightly changes.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of waveforms of a laser beam and an acoustic signal.

FIG. 3 is an explanatory diagram of reference data.

[Explanation of symbols]

a: object to be coated b: coating film x: laser beam y: acoustic signal
5: Irradiation means 7: Microphone (detection means) 9:
Analysis means 11: Storage means 12: Comparison means

Claims (1)

(57) [Claims] An irradiation means for intermittently irradiating a laser beam at a constant frequency toward a coating surface of an object to be coated, and a sound generated from the coating surface by a photoacoustic effect accompanying the irradiation of the laser light. Detecting means for detecting a signal; analyzing means for analyzing the intensity of the acoustic signal detected by the detecting means, and the phase difference between the acoustic signal and the laser light; and the intensity and phase difference of the acoustic signal due to the photoacoustic effect And storage means for storing in advance reference data indicating the correspondence relationship with the coating film thickness for each type of paint; and a reference called from the storage means in accordance with the type of paint, the analysis signal obtained by the analysis means. And a comparing means for determining the coating thickness by comparing the data with the data.