JP2001165643A - Resonance type photoacoustic measuring and inspection device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for measuring the finish dimension of a solid sample having a cylindrical structure or detecting a minute surface defect present on the inner surface of a tube. SOLUTION: The solid sample having the cylindrical structure is locally irradiated with optical beam, and its acoustic resonance is coupled with a photoacoustic effect, whereby the finish dimension of a tube part present in the solid sample is measured, or the minute surface detect present on the tube inner surface is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring a finished dimension of a cylindrical solid sample such as an inner surface of a pipe formed into a metal casting or the like, and a non-destructive measuring and inspecting device for a defect on the inner surface of the sample. .

[0002]

2. Description of the Related Art Conventionally, a method for non-destructively inspecting a defect generated on an inner surface of a solid sample such as an inner surface of a pipe formed into a metal casting has a problem that visual inspection becomes more difficult as its size becomes finer. Existed.

[0003]

Particularly, when inspecting the inside of a structure having a complicated structure, such as the inner surface of a nozzle for injecting fuel into an engine, there is a serious technical bottleneck. Had to be resolved.

[0004]

SUMMARY OF THE INVENTION The present invention provides a non-destructive and accurate measurement of the finished dimensions of a cylindrical structure existing inside a structure having a complicated structure, and a method for detecting surface defects existing on the inner surface of the cylindrical structure. For non-destructive inspection, the solid-state tube is irradiated with a light beam, such as a laser, that modulates the acoustic resonance of a straight tubular tube that is open at both ends, and the absorbed light energy is converted into heat. The object of the present invention is to solve the conventional problem by effectively achieving the above object by utilizing resonance of generated sound waves.

Generally, an acoustic system having boundary conditions such as open ends at one end or open ends (close at the other end) such as a pipe generally has a unique acoustic resonance condition determined by the boundary conditions. Therefore, even for a structure having a complicated structure, such as the inner surface of a nozzle that injects fuel into the engine, the local structure has the boundary conditions such as the above-mentioned open ends or open ends (closed ends). Therefore, if it is possible to locally excite the acoustic resonance condition, the present method can be applied.

[0006] In short, the resonant photoacoustic method of the present technique is:
Using a light beam such as a laser beam, a weak sound wave is generated on the inner surface of the solid cylindrical sample by the photoacoustic effect, and the modulation frequency is changed near the resonance frequency determined by the boundary conditions to obtain information on the inner surface of the solid cylindrical sample. This is a method of measuring with a resonance spectrum in the frequency domain by acoustic resonance, and effectively and with high sensitivity by a detection method such as a lock-in amplifier. The present invention employs a micro-optical system, so that the resolution determined by light irradiation, such as the diameter of a light beam, and the image whose resolution is determined by a large area determined by thermal diffusion to a sample within one cycle of modulation, are determined. This is a non-destructive inspection / evaluation device that also works as a device.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The nondestructive measurement / inspection apparatus according to the present invention will be described below with reference to an example of measuring the inner surface dimensions of a solid sample having a cylindrical structure or measuring surface defects existing on the inner surface of a tube. The principle of the present invention will be described with reference to the drawings.

First, as shown in FIG. 1, a light beam from a light source 1 such as a laser is modulated at a constant frequency by a modulator 2 such as an acousto-optic modulator, and is modulated into a solid sample having a cylindrical structure such as a metal pipe. 3 In this case, the sample is supported in a suitably designed photoacoustic cell 4 and the light beam is introduced into the cell via a window indicated by double lines. Periodic heat is generated in the solid sample that has absorbed the modulated light,
Therefore, a temperature rise occurs in the photoacoustic cell in the same cycle as the light beam, and as a result, a pressure wave (sound wave) is generated. This is detected by an acoustic sensor 5 such as a high-sensitivity microphone installed in the cell and converted into an electric signal. If necessary, it is further amplified by preamplifier 6 and locked in.
By performing synchronous detection using the same reference signal applied to the modulator 2 by the amplifier 7, high-sensitivity detection is realized. Signal output is displayed using a computer 8, recorder 9, etc.
Be recorded. In order to sweep the modulation frequency in the vicinity of the acoustic resonance frequency, the frequency for driving the modulator 2 is changed using the function generator 10, and the computer 8 and the GP-IB or the like are used to control this device. They are often connected via bus lines.

Next, a second embodiment of the present invention is shown in FIG.
FIG. 2 shows an embodiment in which the present invention is implemented in the embodiment of FIG. 1 to measure a finished dimension of an inner surface of a cylindrical nozzle for injecting fuel into an engine and as an inspection device for an inner surface of a nozzle tube. It is a conceptual diagram. The light beam is condensed by a lens, and is irradiated from a window to a cylindrical nozzle installed in the photoacoustic cell. Since the size of the cylindrical nozzle is as short as several millimeters in tube length, the resonance frequency is several tens of kHz to several hundreds of kHz.
Of the ultrasonic band. Therefore, it is characterized in that it becomes necessary to use an acoustic sensor such as an ultrasonic capacitance transducer 5 '.

[0010]

As described above, the present invention has the effect of solving the bottleneck that has been technically difficult in non-destructive measurement and inspection of surface defects existing on the inner surface of a solid sample having a conventional cylindrical structure. .

[Brief description of the drawings]

FIG. 1 shows an embodiment of a first embodiment of the present invention. FIG. 1 shows an apparatus for measuring the inner surface dimensions of a cylindrical solid sample and measuring surface defects existing on the inner surface of a tube.

[Explanation of symbols]

 Reference Signs List 1 light source 2 optical modulator 3 solid sample having cylindrical structure 4 photoacoustic cell 5 acoustic sensor (microphone) 6 preamplifier 7 lock-in amplifier 8 computer 9 recorder 10 function generator

FIG. 2 is a diagram illustrating an embodiment in which the present invention is implemented in the embodiment of FIG. 1 to measure a finished dimension of an inner surface of a cylindrical nozzle for injecting fuel into an engine and as an inspection device for an inner surface of a nozzle tube. It is a conceptual diagram showing a form.

[Explanation of symbols]

1 'Light source 2' Optical modulator 3 'Solid sample having cylindrical structure 4' Photoacoustic cell 5 'Acoustic sensor (ultrasonic capacitance transducer) 6' Preamplifier 7 'Lock-in amplifier 8' Computer 9 'Recorder 10' Function Generator

Claims (5)

[Claims] 1. A light beam (2) such as a modulated laser is irradiated so as to make contact with the inner surface of a cylindrical solid sample (1), and is contacted by a heat source generated on the inner surface of the tube by light absorption. A device that uses the so-called "photoacoustic effect" to detect weak sound waves generated in a gas by a pressure sensor such as a microphone (3), and determines the frequency at which light is modulated in the cylindrical sample. Finished dimensions of cylindrical solid sample (1) using a method that detects that the photoacoustic signal greatly changes both in amplitude and phase due to the resonance effect when it is changed near the resonance frequency of a sound wave oscillating as a standing wave Measurement and inspection equipment that non-destructively inspects for defects on the inner surface of the sample. 2. The measurement / inspection apparatus according to claim 1, wherein the microphone (3) is a capacitance / ultrasonic sensor (2a). 3. The measurement and inspection device according to claim 1, wherein the microphone is a non-acoustic sensor such as a light beam and a position sensor. 4. The measurement / inspection apparatus according to claim 1, wherein a micro optical system such as an objective lens of a microscope is used for irradiating the sample with light. 5. The measurement / inspection apparatus according to claim 1, wherein an optical fiber or the like is used for a waveguide system of light to the sample.