JP2017003397A - Flat surface vibration measurement device and flat surface vibration measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat surface vibration measurement device that can determine the distributions of the two-dimensional frequency, phase, and amplitude of a vibration surface all together of a large-sized measurement object, using an optical interferometer having such an imaging element as an existing CCD camera.SOLUTION: The flat surface vibration measurement device includes: a light source 1 emitting a light; a measurement object 4, which vibrates at a first frequency; a reference mirror 6, which vibrates at a second frequency; a light receiving element 9; a controller 12; a division part 3, which divides the light emitted from the light source 1 into plural lights and emits the lights to the directions of the measurement object 4 and of the reference mirror 6; and integration parts 3 and 8 integrating lights reflected from the measurement object 4 and from the reference mirror 6 and emitting the lights to the light receiving element 9, the difference of the first and second frequencies being smaller than a frame rate of the light receiving element 9, the light receiving element 9 generating an interference image based on the integrated light obtained by the integration parts 3 and 8, and the controller 12 determining a frequency distribution, a phase distribution, and an amplitude distribution on a flat surface of the measurement object 4 based on the interference image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a planar vibration measuring apparatus and a planar vibration measuring method capable of simultaneously measuring a two-dimensional distribution of vibration frequency, phase, and amplitude of a surface of an oscillating object or an internal stepped surface.

  Conventionally, a laser Doppler vibration measuring device has been used to measure weak and high-speed vibration of a vehicle body, an industrial product, or a biological sample (see, for example, Patent Document 1). These laser Doppler vibration measurement devices are applied to optical coherence tomography measurement (Doppler OCT) in combination with an optical interferometer (see, for example, Patent Document 2). These Doppler OCTs are attracting a great deal of attention as the need for optical non-contact measurement techniques in living body measurement has increased in recent years.

JP2013-33014A JP 2014-178338 A

  The conventional laser Doppler vibration measuring apparatus and Doppler OCT measure the displacement, flow velocity, and vibration of a single measurement point, so that it is difficult to simultaneously measure a measurement surface having a large area. Spatial probe scanning is indispensable for measuring vibrations of large objects, but a photodetector is required to receive high-speed vibrations of several kHz to several hundred kHz, and the object plane distribution can be acquired in a batch. This is because it is difficult to use an image sensor such as a CCD camera.

  The present invention has been developed in view of the above-described situation, and a measurement object (object plane) having a large area does not require spatial scanning, and uses an optical interferometer including an image sensor such as a CCD camera. It is an object of the present invention to provide a plane vibration measuring apparatus and a plane vibration measuring method capable of obtaining a two-dimensional frequency, phase, and amplitude distribution of a vibrating surface in a lump.

  In order to achieve the above object, a planar vibration measuring apparatus of the present invention is provided with a light source that emits light, a measurement object that vibrates at a first frequency, and a vibrating part, and vibrates at a second frequency by the vibrating part. A reference mirror, a light receiving element, a control unit, a light branched from the light source, and a light beam reflected from the measurement object, a branching unit that emits light in the direction of the measurement object, and the direction of the reference mirror, respectively. And an integration unit that integrates the light reflected from the reference mirror and emits the light to the light receiving element, and a difference between the first frequency and the second frequency is smaller than a frame rate of the light receiving element. The light receiving element generates an interference image based on the light integrated by the integration unit, and the control unit generates a frequency distribution, a phase distribution, and an amplitude distribution on the plane of the measurement object based on the interference image. Ask for And wherein the door.

  In order to achieve the above object, the planar vibration measuring method of the present invention includes a light source that emits light, a measurement object that vibrates at a first frequency, and a vibration unit that is attached and vibrates at a second frequency by the vibration unit. A reference mirror, a light receiving element, a control unit, a branching unit that branches the light emitted from the light source and emits the light in the direction of the measurement object and the reference mirror, and the light reflected from the measurement object, A plane vibration measurement method in a plane vibration measurement apparatus comprising: an integration unit that integrates light reflected from the reference mirror and emits the light to the light receiving element, wherein the difference between the first frequency and the second frequency Is made smaller than the frame rate of the light receiving element, the light receiving element generates an interference image based on the light integrated by the integrating unit, and the control unit adds the interference image to the interference image. Zui, the frequency distribution on the plane of the measurement object, characterized in that it comprises determining a phase distribution, and amplitude distribution, the.

  According to the present invention, a measurement object having a large area does not require spatial scanning, and an optical interferometer including an imaging device such as a CCD camera is used to measure the two-dimensional frequency, phase, and amplitude of the vibration surface. Distribution can be obtained in a lump.

It is a figure which shows the structural example of the plane vibration measuring device figure which concerns on one Embodiment of this invention. (A) 0th-order intensity distribution image, (b) 2-dimensional FFT image of 0th-order intensity distribution, (c) FFT-filtered 0th-order intensity distribution FFT image obtained from the temporal waveform of the interference image, (d) It is a figure which shows the 0th-order intensity distribution image after image processing. (A) a primary intensity distribution image, (b) a two-dimensional FFT image of the primary intensity distribution, (c) an FFT image of the frequency-filtered primary intensity distribution obtained from the temporal waveform of the interference image, (d) It is a figure which shows the primary intensity distribution image after image processing. It shows a plot of R _01. It is a figure which shows (a) amplitude distribution, (b) frequency distribution, and (c) phase distribution in the measurement object obtained by experiment.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the planar vibration measuring apparatus 100 according to the present embodiment includes an optical interferometer configured by a spatial system, and includes a light source 1, a collimator 2, a beam splitter 3, a measurement object 4, 1 piezo element 5, reference mirror 6, second piezo element 7, lens system 8, light receiving element 9, and computer 10. In addition, the computer 10 includes a frame acquisition unit 11, a control unit 12, and a D / A conversion unit 13.

  In this example, the light source 1 is configured by a semiconductor laser that emits coherent light having a peak wavelength of 650 nm. The collimator 2 emits light incident from the light source 1 as parallel light rays. The beam splitter 3 functions as a branching portion that splits the light incident from the collimator 2, transmits part of the light, emits it in the direction of the measurement object 4, reflects the rest, and emits it in the direction of the reference mirror 6.

  In this example, the measurement object (measurement surface) 4 is constituted by a flat mirror having a diameter of 15 mm as a sample. In actual measurement, a measurement object to be measured is attached. The measurement object 4 reflects light incident from the beam splitter 3 on the surface.

  In this example, a first piezo element 5 is attached to the plane mirror 4. In response to the voltage signal transmitted from the D / A conversion unit 13 by the signal from the control unit 12, the first piezo element 5 causes the flat mirror 4 to vibrate at a predetermined frequency, in this example, a sine wave vibration of 1 kHz. generate. Since this example is a verification experiment, the first piezo element 5 is used to reproduce the vibration of the measurement object 4. However, when the vibration object is used as the measurement object 4, the first piezo element 5 is not necessary. It is.

  The reference mirror 6 reflects the light incident from the beam splitter 3. A second piezo element 7 is attached to the reference mirror 6. The second piezo element 7 has a vibration with a frequency slightly different from the vibration of the measurement object 4 according to the voltage signal transmitted from the D / A conversion unit 13 by the signal from the control unit 12, 1.0044 kHz in this example. It functions as a vibration part that generates the sine wave-like vibration of the reference mirror 6.

  The light reflected from the measurement object 4 and the light reflected from the reference mirror 6 enter the beam splitter 3 again and are emitted in the direction of the lens system 8 together.

  The lens system 8 is for collecting the light incident from the beam splitter 3 and emitting it to the light receiving element 9, and is composed of a plurality of lenses. FIG. 1 shows two lenses, but the number is not limited to two. As described above, the beam splitter 3 and the lens system 8 as a whole function as an integration unit that integrates the light reflected from the measurement object 4 and the light reflected from the reference mirror 6 and emits the light to the light receiving element 9.

  The light receiving element 9 is composed of a commercially available conventional CCD camera (frame rate of about 30 Hz to about 60 Hz), and in this example, a CCD camera with a frame rate of 35.2 Hz. The light receiving element 9 converts the light incident from the lens system 8 into an electric signal and acquires it as an interference image. Here, the interference image obtained by the light receiving element 9 changes with a period equal to the frequency difference between the reference mirror 6 and the measurement object 4, that is, with a period of 4.4 Hz in this example. Note that the harmonic component of the time-varying image of the interference image is not observed because it is averaged by the action of the low-pass filter based on the CCD frame rate. The light receiving element 9 outputs the acquired interference image to the frame acquisition unit 11.

  The frame acquisition unit 11 acquires and stores an interference image received from the light receiving element 9.

  The control unit 12 includes a microcomputer having a nonvolatile storage unit and a processor that executes a control program stored in the nonvolatile storage unit, and controls the operation of each unit. Specifically, as described above, the control unit 12 outputs a signal for generating vibration of the measurement object 4 and the reference mirror 6 to the D / A conversion unit 13 and also the interference image acquired by the frame acquisition unit 11. The amplitude distribution, the frequency distribution, and the phase distribution of the measurement object 4 can be obtained by performing the processing described later.

When the reference mirror 6 and the measurement object 4 are vibrated at frequencies f _r and f _s and phase modulation amplitudes Z _r and Z _s , interference signals measured on the light receiving element 9 are expressed by the following (Equation 1). Given in.
Here, since the frequency difference (beat frequency) between the reference mirror 6 and the measurement object 4 is 4.4 Hz, which is smaller than 35.2 Hz, which is the frame rate of the light receiving element, the higher-order component of (Expression 1) is Almost no detection is made, and the zeroth-order component and the first-order component represented by the following (Equations 2 and 3) are detected.
(Expression 2) | A + BJ ₀ (Z _r ) J ₀ (Z _s ) cos (α ₀ ) |
(Formula 3) | BJ ₁ (Z _r ) J ₁ (Z _s ) cos (α ₀ ) | cos (2π | f _s −f _r | + | ψ _r −ψ _s |)
Here, J ₀ and J ₁ are Bessel functions of the first kind.

FIGS. 2A and 3A show a zeroth-order intensity distribution image and a first-order intensity distribution image obtained from the time waveform of the interference image obtained by the measurement by the planar vibration measuring apparatus 100 according to this embodiment. Respectively. Since these distributions include a spatial carrier component and a direct current component, a filtering process was performed after two-dimensional fast Fourier transform (FFT). FIG. 2B and FIG. 3B show a two-dimensional FFT image of the zeroth-order intensity distribution and a two-dimensional FFT image of the first-order intensity distribution, respectively. Among these frequency components, for the zeroth-order intensity distribution, a spatial carrier component (J ₀ (Z _s ) J ₀ (Z _r )) is extracted to obtain a distribution obtained by separating cos (α ₀ ), and the first-order intensity component With respect to, a distribution proportional to (J ₁ (Z _s ) J ₁ (Z _r )) is obtained by extracting only the DC component. The results are shown in FIGS. 2 (c) and 3 (c). The FFT image subjected to the image filtering in this way was restored by inverse FFT conversion. The restored zeroth-order and first-order intensity distribution images are shown in FIGS. 2 (d) and 3 (d), respectively. Since the restored distribution includes the common interference amplitude component B, the amplitude component can be removed by calculating the ratio between the two, and the _Zs distribution can also be known. At that time, Z _r needs to be known.

Here, FIG.
(Equation _{4) R 01 = J 0 (} Z s) J 0 (Z r) / J 1 (Z s) J 1 (Z r)
The plot line is shown. The ratio of the distributions of FIG. 2 (d) and FIG. 3 (d) obtained by the above processing was calculated, and the _Zs distribution was obtained by comparing with the plot line of FIG. Here, _Zr is a known value before the experiment.

In the range where Z _s is 2.4 or less, Z _s is uniquely obtained by comparing R ₀₁ with the ratio of experimental values. The obtained Z _s distribution is shown in FIG. Further, the frequency distribution was obtained from the frequency values of the primary distribution, and the result shown in FIG. 5B was obtained. Further, the phase distribution is obtained from the phase value of the primary distribution, and the phase value can be calculated by the arc tangent of the ratio between the real value and the imaginary value of the primary distribution. The obtained phase distribution is shown in FIG.

  As described above, according to the planar vibration measuring apparatus 100 according to the present embodiment, a two-dimensional vibration surface is measured on a measurement object having a large area using an optical interferometer including an image sensor such as a conventional CCD camera. It is possible to obtain a uniform frequency, phase, and amplitude distribution all at once.

  Therefore, it is possible to perform full-field vibration measurement at a high speed collectively even for a large-scale measurement object that requires a spatial probe scan in the conventional laser Doppler meter. As a result, measurement time can be shortened and control devices such as synchronous control can be simplified. Furthermore, it is possible to expect a significant improvement in image resolution in the horizontal direction (x-axis-y-axis) in the efficiency improvement and visualization of planar vibration measurement. Further, the present invention can be easily introduced into a biological measuring instrument such as an optical tomographic imaging apparatus.

  Although the present invention has been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various changes and modifications based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each component can be rearranged so as not to be logically contradictory, and a plurality of components can be combined into one or divided.

1 Light source 2 Collimator 3 Beam splitter 4 Measurement object (plane mirror)
DESCRIPTION OF SYMBOLS 5 1st piezo element 6 Reference mirror 7 2nd piezo element 8 Lens system 9 Light receiving element 10 Computer 11 Frame acquisition part 12 Control part 13 D / A conversion part 100 Plane vibration measuring device

Claims (4)

A light source that emits light;
A measuring object that vibrates at a first frequency;
A reference mirror to which a vibration unit is attached and vibrates at a second frequency by the vibration unit;
A light receiving element;
A control unit;
Branching the light emitted from the light source, and branching portions respectively emitting in the direction of the measurement object and in the direction of the reference mirror;
An integration unit that integrates the light reflected from the measurement object and the light reflected from the reference mirror and emits the light to the light receiving element;
With
The difference between the first frequency and the second frequency is smaller than the frame rate of the light receiving element,
The light receiving element generates an interference image based on the light integrated by the integration unit,
The control unit obtains a frequency distribution, a phase distribution, and an amplitude distribution on a plane of the measurement object based on the interference image;
Plane vibration measuring device. The control unit, the ratio of the distribution of each image obtained based on the zero-order intensity distribution image and the first-order intensity distribution image obtained from the time waveform of the interference image,
Formula: R ₀₁ = J ₀ (Z _s ) J ₀ (Z _r ) / J ₁ (Z _s ) J ₁ (Z _r )
(Z _s is the phase modulation amplitude of the measurement object, Z _r is the phase modulation amplitude of the reference mirror, and J ₀ and J ₁ are first-type Bessel functions)
To obtain the frequency distribution, phase distribution, and amplitude distribution on the plane of the measurement object,
The planar vibration measuring device according to claim 1.   The planar vibration measuring device according to claim 1, wherein the light receiving element is a CCD camera. A light source that emits light, a measurement object that vibrates at a first frequency, a reference mirror that is attached with a vibration unit and vibrates at a second frequency by the vibration unit, a light receiving element, a control unit, and light emitted by the light source Branching part that emits light in the direction of the measurement object and the direction of the reference mirror, and the light reflected from the measurement object and the light reflected from the reference mirror are integrated and emitted to the light receiving element. A plane vibration measuring method in a plane vibration measuring apparatus comprising an integration unit,
Making a difference between the first frequency and the second frequency smaller than a frame rate of the light receiving element;
The light receiving element generating an interference image based on the light integrated by the integrating unit;
The control unit obtains a frequency distribution, a phase distribution, and an amplitude distribution on a plane of the measurement object based on the interference image;
A plane vibration measuring method including: