JP4378503B2 - Vibration measuring method and measuring apparatus using electronic speckle interferometry - Google Patents

Description

  The present invention relates to a vibration measuring method using an electronic speckle interferometry capable of measuring vibration (amplitude, vibration frequency) of a vibration part such as a precision device or an in-vehicle device in a non-contact and real-time manner. And measuring device.

Precision equipment and in-vehicle equipment are in transit unless they are provided with adequate rigidity against the vibration that may occur during use or are not reinforced by a support structure. There is a possibility that the equipment may be damaged in a short period of time due to vibrations repeatedly received in the state of being mounted on a vehicle or the like, or a resonance phenomenon caused by the vibrations, or the bolts etc. that are attached may fall off. is there.
Furthermore, the desired performance itself of the precision instrument or the in-vehicle apparatus may be impaired or malfunctioned due to the vibration or resonance.

  For this reason, conventionally, vibration measurement (refer to Patent Document 1) is performed on a portion that vibrates in various devices including these precision devices and in-vehicle devices using a contact-type vibration measuring device (see Patent Document 1) for vibration measures and the like. It was useful.

However, in the case of the contact type, when the mass of the measurement portion is not so large as compared with the mass of the sensor or the like of the vibration measuring device, accurate vibration measurement cannot be performed.
In addition, the vibration changes slightly in an instant, but it is difficult to accurately measure the vibration that changes slightly in such an instantaneous instant, and a two-dimensional vibration pattern is measured in real time without contact. There was nothing I could do.
JP 2001-159562 A

  The present invention has been made in view of such a situation, and provides a vibration measurement method and apparatus capable of easily measuring vibration (amplitude, vibration frequency) of an arbitrary part in a non-contact manner in real time. With the goal.

  The object of the present invention can be solved by a vibration measuring method and apparatus having the following configuration.

The vibration measuring method according to the first aspect of the present invention uses a laser as a light source, separates the laser light, and irradiates the separated one to the measurement surface, and the separated other light. Superimposing reference light consisting of light to form an interference image on the imaging surface, and processing the interference image group accumulated in time series to obtain a vibration fringe image and measure the vibration of the object to be measured In electronic speckle interferometry,
The vibration on the measurement surface is measured by utilizing the maximum bright spot generated on the vibration fringe image by changing the wavelength of the laser beam.

The vibration measuring method according to the second aspect of the present invention uses a laser as a light source, separates the laser light, and irradiates the separated one on the measurement surface, and the separated other light. Superimposing reference light consisting of light to form an interference image on the imaging surface, and processing the interference image group accumulated in time series to obtain a vibration fringe image and measure the vibration of the object to be measured In electronic speckle interferometry,
Modulating the wavelength of the laser beam of the laser, and setting the state where the maximum bright spot in the vibration fringe image is located at an arbitrary position to be measured on the measurement surface,
Based on the amplitude value of the modulation signal of the wavelength of the laser light at the time of setting and the correlation between the amplitude value of the modulation signal obtained in advance and the vibration amplitude of the corresponding measurement surface, at the arbitrary position. The vibration amplitude is obtained.

Further, the vibration measuring method according to the third aspect of the present invention uses a laser as a light source, separates the laser light, irradiates the separated surface onto the measurement surface, and the separated light. The interference light is superimposed on the reference light consisting of one light to form an interference image on the image plane, and the interference fringe image is obtained by performing image processing on the interference image group accumulated in time series to vibrate the object to be measured. In electronic speckle interferometry to measure
The modulation frequency of the modulation signal that modulates the wavelength of the laser light is changed within a predetermined range until the maximum value of the brightness of the maximum bright spot in the vibration fringe image is obtained, and the above processing is repeated to obtain the maximum value. Then, the vibration frequency of the measurement surface is obtained using the modulation frequency of the modulation signal as the vibration frequency of the measurement surface.

The vibration measuring device according to the fourth invention is a vibration measuring device for carrying out the second invention, and the vibration measuring device comprises:
The laser capable of changing the wavelength of the laser beam;
Modulation signal changing means capable of changing the value of the amplitude of the modulation signal for changing the wavelength;
Separate the light emitted from the laser, irradiate one of the light on the measurement surface to obtain the reflected light, and use the other light as the reference light, superimposing the reflected light and the reference light, An optical system that forms an interference image on the imaging plane;
A TV camera that captures an interference image formed on the imaging surface;
An interference image group obtained by chronologically obtaining the interference image is subjected to image processing to obtain a vibration fringe image having the maximum bright spot, and the measurement signal is changed to an arbitrary position to be measured by changing the amplitude value of the modulation signal. When the maximum bright spot is located, the maximum bright spot on the measurement surface is generated based on the correlation between the amplitude value of the modulation signal and the vibration amplitude of the measurement surface, and the value of the modulation signal amplitude. And a control device for obtaining a vibration amplitude at a certain position.

Furthermore, the vibration measuring device according to the fifth invention is a vibration measuring device for carrying out the third invention, and the vibration measuring device comprises:
The laser capable of modulating the wavelength by inputting a modulation signal;
Modulation signal changing means capable of changing the frequency of the modulation signal;
Separate the light emitted from the laser, irradiate one of the light on the measurement surface to obtain the reflected light, and use the other light as the reference light, superimposing the reflected light and the reference light, An optical system that forms an image on the imaging plane;
A TV camera that captures an image formed on the imaging surface;
A control device that obtains the maximum value of the brightness of the maximum bright spot in the vibration fringe image obtained by changing the modulation frequency of the modulation signal in an appropriate range, and uses the modulation frequency when the maximum value is obtained as the vibration frequency of the measurement surface It is characterized by comprising.

  According to the vibration measuring method according to the first invention having the above-described configuration, a vibration fringe image is obtained by performing image processing on the interference image group sequentially formed on the imaging surface in time series, Since the maximum bright spot generated on the vibration fringe image changes by changing the wavelength of the laser (for example, a semiconductor laser), the vibration (vibration amplitude, vibration frequency) can be measured. The vibration of the surface can be easily measured without contact and in real time.

  In the vibration measuring method according to the second aspect of the invention, the separated one of the laser beams is irradiated onto the measurement surface of the vibrating object to be measured whose vibration amplitude is to be measured. The reflected light reflected from the measurement surface and the reference light composed of the other separated light are superimposed to obtain an interference image group on the imaging surface, and the interference image group is image-processed to obtain the maximum While obtaining a vibration fringe image having a bright spot, and changing the amplitude of the modulation signal to the laser so that the maximum bright spot in the vibration fringe image is located at the position to be measured on the measurement surface, Using the amplitude value of the modulation signal at this time, the vibration amplitude of the portion to be measured on the measurement surface is determined in a non-contact and real-time manner from the correlation between the modulation amplitude value and the vibration amplitude obtained in advance. And you can ask for it. Moreover, since the amplitude is not measured by directly counting the number of fringes in the vibration fringe image, measurement is possible even when the vibration amplitude of the vibration is large.

  Further, according to the vibration measuring method of the third aspect of the invention, one of the separated laser beams is irradiated onto the measurement surface of the vibrating object to be measured for vibration frequency measurement. By superimposing the reflected light reflected from the measurement surface and the reference light composed of the other separated light, an interference image is sequentially obtained on the imaging surface, and the interference image group is subjected to image processing, whereby vibration fringes are obtained. Obtain an image, change the modulation frequency of the modulation signal to be input to the laser beam within the appropriate range, obtain an interference image group, and perform image processing on the interference image group to obtain a vibration fringe image. Until the maximum value of the brightness of the maximum bright spot in the image is obtained, a series of processes for changing the modulation frequency in the predetermined range of the modulation signal is repeated, and if only the modulation frequency at the maximum value is detected, the modulation frequency is On the measurement surface Becomes kicking vibration frequency, the vibration frequency of the thus measured surface, and in real time without contact, it can be obtained.

  The vibration measuring method according to the second invention can be executed by the vibration measuring apparatus according to the fourth invention.

  The vibration measuring method according to the third invention can be executed by the vibration measuring apparatus according to the fifth invention.

  In the vibration measuring method according to the second invention, the correlation between the amplitude value of the modulation signal obtained in advance and the vibration amplitude of the corresponding measurement surface is stored in the form of a table or function. If the vibration amplitude is determined from the stored table or function, a preferred embodiment is obtained.

  Furthermore, in the vibration measuring apparatus according to the fourth or fifth aspect of the invention, the optical system includes a first beam splitter that separates light emitted from a semiconductor laser into light toward the measurement surface and light as the reference light. And a convex lens that enlarges the reflected light reflected from the measurement surface and passes it to the imaging surface, and a second beam splitter that superimposes the reflected light and the reference light.

In the vibration measuring method according to the third aspect of the present invention, the brightness of the maximum bright spot in the vibration fringe image obtained without inputting a modulation signal to the laser is obtained in advance as a maximum value to be compared. ,
Next, the modulation frequency of the modulation signal input to the laser is changed within a predetermined range, and the brightness of the maximum bright spot in the obtained vibration fringe image is compared with whether or not the maximum value to be compared matches. When the modulation frequency is changed within the predetermined range and the process is repeated, and the modulation frequency of the modulation signal when matched is determined to be the vibration frequency of the measurement surface, the vibration frequency of the measurement surface is obtained. If the modulation frequency at that time is detected, the modulation frequency becomes the vibration frequency on the measurement surface, and thus the vibration frequency on the measurement surface can be obtained accurately in a non-contact manner in real time.

Further, in the vibration measuring method according to the third aspect of the invention, when the interference image group is formed by changing the modulation frequency of the modulation signal within a predetermined range, it can be practically used if the amplitude of the modulation signal is reduced. The vibration frequency can be measured accurately in a short time. That is, the phase “θ (t)” of the interference light forming the interference image is

Dc + Lcos (2πft + φ)
θ (t) = 2πg ---------------... Formula (1)
λc + Mcos 2πfm t

However, if the value of “M” is reduced here, the amount of change in phase within the TV camera storage time becomes smaller. As a result, the maximum bright spot associated with the change in modulation frequency is reduced. Since the change in luminance becomes gentle as shown in FIG. 5, even if the modulation frequency and the vibration frequency are different, the modulation frequency (indicated by “Z” in FIG. 5) is the maximum luminance value of the maximum bright spot. The modulation frequency at the position) can be easily found without overlooking. In the equation (1), the term of the fractional numerator is an optical path difference between the reflected light from the measurement surface and the reference light, and the term of the fractional denominator indicates a wavelength that changes with time. “Dc” is the optical path difference when not vibrating, “λc” is the wavelength when not modulating, “L” is the oscillation amplitude, “M” is the modulation amplitude, “f” is the oscillation frequency, and “fm” is the modulation frequency. , “Φ” represents a phase difference between the vibration and the modulation signal, and “g” represents a constant.

  Embodiments of a vibration measuring method and a vibration measuring apparatus according to the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is an overall view schematically showing the overall configuration of a vibration measuring apparatus according to an embodiment of the present invention.

  In FIG. 1, 1 is a TV camera (CCD camera) having a shutter speed of 1/30 second in this embodiment, and 2 is a semiconductor laser (hereinafter referred to as modulation) whose wavelength amplitude or frequency of laser light changes according to an input modulation signal 3 is a function generator capable of changing the modulation amplitude or the modulation frequency of the modulation signal (injection current) input to the semiconductor laser 2. A control device (configured by a computer in this embodiment) for obtaining the vibration amplitude of the measurement surface based on the correlation between the value of the modulation amplitude of the modulation signal and the vibration amplitude of the measurement surface and the value of the modulation amplitude of the modulation signal; Reference numeral 5 denotes a first beam splitter that separates light emitted from the semiconductor laser, reference numeral 6 denotes an object to be measured, and reference numeral 7 denotes reflected light from the measurement surface 6A of the object to be measured 6. A convex lens 8 that passes through, an ND filter (Neutral Density filter) that passes one of the lights separated by the first beam splitter 5 and reduces the power of the passing light in accordance with the power of the reflected light, and 9 is the reflection A second beam splitter 10 for superimposing the one light and the one light is connected to the control device 4 via a control line L4, and is a video monitor for copying an image processed by the control device 4.

As shown in FIG. 1, the semiconductor laser 2 emits light so that laser light is diffused. The wavelength of the laser light is adjusted by operating an adjustment knob (not shown) of the function generator 3. By changing the value of the modulation amplitude of the modulation signal (injection current) i input to the laser 2, the modulation amplitude of the wavelength of the laser beam of the semiconductor laser can be changed. The function generator 3 operates the adjustment knob (not shown) different from the adjustment knob (not shown), and the modulation frequency of the modulation signal (injection current) i input to the semiconductor laser 2 The frequency of the wavelength of the laser light of the semiconductor laser can be changed by changing. For this reason, the semiconductor laser 2 and the function generator 3 are connected by a control line L1.
The function generator 3 is connected to the control device 4 via a control line L2, and the modulation amplitude value or the modulation frequency value of the modulation signal is transmitted from the function generator 3 to the control device 4. It is configured as follows.
In a memory (storage device) (not shown) of the control device 4, a table related to the correlation between the modulation amplitude value and the vibration amplitude L of the measurement surface 6A as shown in FIG. 4 is stored. . Further, the modulation frequency of the modulation signal is transmitted from the function generator 3 to the control device 4 via the signal line L2, and the wavelength of the light of the semiconductor laser 2 is changed by this modulation frequency. The control device 4 is configured so that the modulation frequency can be determined.

  Then, the laser light emitted from the semiconductor laser 2 is separated into two lights by the first beam splitter 5, and one of the separated lights is applied to the measurement surface 6A of the measurement object 6. The other separated light is applied to the second beam splitter 9. Then, the reflected light reflected from the measurement surface 6A and the reference light from the first beam splitter 5 are superimposed by the second beam splitter 9. In this embodiment, the ND filter 8 is interposed between the first beam splitter 5 and the second beam splitter 9 in order to reduce the power of the reference light so as to correspond to the power of the reflected light. It is disguised.

Then, a speckled interference image is formed on the image plane of the TV camera 1 by the light superimposed by the second beam splitter 9. The interference image is captured by the TV camera 1 and transmitted to the control device 4 via the control line L3. Then, the wavelength of the laser beam of the semiconductor laser 2 is changed, and an interference image at that wavelength is similarly captured by the TV camera 1 and transmitted to the control device 4 via the control line L3. . The TV camera 1 picks up the interference image when the wavelength is changed in this manner a predetermined number of times and transmits it to the control device 4 via the control line L3.
Then, image processing described later is performed on the control device 4 that accumulates the interference images in time series, and a vibration fringe image A as illustrated in FIG. 2 is obtained. It is displayed on the video monitor 10.

According to the vibration measuring apparatus according to the present embodiment having the above-described configuration, the amplitude of the measurement surface 6A of the measurement target 6 can be measured in a non-contact manner in real time as follows. As described in FIG. 2, the vibration frequency f can be measured in a non-contact manner and in real time. In other words,
In a state where the measurement surface 6A of the measurement object 6 in FIG. 1 vibrates around the portion represented by the center line CL, as shown in FIG. 1, the laser of the semiconductor laser 2 is directed toward the portion. Irradiate light. The irradiated light is separated into two lights by the first beam splitter 5, and one of the lights is irradiated to the measurement surface 6 </ b> A, is reflected by the surface, and is reflected by the reflected light. Is converged by passing through the convex lens 7, and the passed light is incident on the second beam splitter 9. On the other hand, the other light separated by the first beam splitter 5 passes through the ND filter 8, where the reference light whose power is reduced to correspond to the reflected light is the second beam splitter. 9 and superimposed on the reflected light reflected by the measurement surface 6A. The light superposed in this way is incident on the lens of the TV camera 1 and forms an interference image on the image plane of the TV camera 1.

  Next, the semiconductor laser 2 emits laser light having different wavelengths. An interference image is formed on the image plane of the TV camera 1 each time laser beams having different wavelengths are irradiated. Each interference image obtained by irradiating laser beams of different wavelengths in this way is transmitted to the control device 4 via the control line L3 and stored in the memory.

  Then, the control device 4 performs image processing on the plurality of interference images, that is, the interference image group, to form a vibration fringe image A as shown in FIG. This image processing is performed by a known so-called “maximum value-minimum value method”. Specifically, the interference images are superimposed, and in each pixel of the image, for example, when the number of pixels is 500 × 500, the interference image is formed on 250,000 pixels. For each pixel of each pixel, the lowest luminance value of each interference image is similarly subtracted from the maximum luminance value of each interference image located on that pixel to obtain the value at that pixel. . When an image is drawn by applying the value in each pixel to each pixel in this way, a vibration fringe image A as shown in FIG. 2 is obtained. That is, such processing is referred to as “image processing” in this specification and claims. Then, in the vibration fringe image A shown in FIG. 2, the portion (the portion indicated by the solid line at the center of the band-like portion observed brightest among the plurality of broken lines in FIG. 2) is measured. Move to surface 6A to be measured. This movement is measured by operating the function generator 3 to set the frequency and phase of the modulation signal input to the semiconductor laser 2 to the same value as the vibration frequency and vibration phase, and changing the modulation amplitude. The position where the maximum bright spot Amax is located at the position to be measured on the surface 6A. Specifically, in this embodiment, when it is desired to measure the vibration amplitude L of the portion that is the maximum bright spot Amax shown in FIG. 3, the maximum bright spot Amax is located at that position as shown in FIG. The function generator 3 is operated so that the position becomes the position, the modulation amplitude of the modulation signal to the semiconductor laser 2 is changed, and the wavelength of the light is modulated at the same frequency and the same phase as the vibration.

As described above, when the position of the maximum bright spot Amax of the vibration fringe image A is accurately positioned at the position to be measured on the measurement surface 6A as described above, the modulation signal at that time The value of the modulation amplitude is read by the control device 4.
Then, based on the read value of the modulation amplitude, from the “representing the correlation between the value of the modulation amplitude and the vibration amplitude L of the measurement surface” stored in the memory (see FIG. 4), The vibration amplitude L of the measurement surface corresponding to the value of the modulation amplitude of the modulation signal can be obtained. As a result, the vibration amplitude L at the position of the moved maximum bright spot Amax, which is an arbitrary position on the measurement surface 6A in the vibration state, can be obtained in a non-contact manner and in real time.

  By the way, when the vibration frequency f generated on the measurement surface 6A is measured, first, the above-mentioned procedure (without modulating the wavelength of the semiconductor laser 2, that is, with the modulation signal kept constant). Processing method), an interference image group is obtained, the interference image group is subjected to image processing to form a vibration fringe image A, the luminance of the maximum bright spot Amax 1 in the vibration fringe image A is read as a maximum value, and the control device 4 is stored in the memory. The vibration fringe image A is displayed on the video monitor 10 connected to the control device 4.

Next, an interference image group is obtained by the above-described method by changing the modulation frequency of the modulation signal to the semiconductor laser 2 within a predetermined range, and the interference image group is vibrated by performing the image processing in the control device 4. A fringe image A is obtained. This vibration fringe image A is also displayed on the video monitor 10 connected to the control device 4.
Whether or not the luminance of the maximum bright spot Amax in the vibration fringe image A obtained by changing the modulation frequency in this way matches the maximum value of the maximum bright spot Amax 1 stored in the control device 4. The control device 4 performs a comparison operation.
If they do not match as a result of the comparison operation, the predetermined frequency range of the modulation signal to be modulated to the semiconductor laser 2 is changed and processed in the same procedure as described above. It is compared whether or not the luminance of the maximum bright spot Amax in the striped image A matches the stored maximum value of the maximum bright spot Amax 1. As described above, when the modulation frequency of the modulation signal is sequentially changed within the predetermined range, the overall luminance of the vibration fringe image A changes variously.
Such processing changes the modulation frequency of the modulation signal until the brightness of the maximum bright spot Amax in the vibration fringe image A obtained through the above procedure matches the maximum value of the stored maximum bright spot Amax 1. It is done.

  When the brightness of the maximum bright spot Amax in the vibration fringe image A matches the maximum value of the stored maximum bright spot Amax1, the modulation frequency of the modulation signal input to the semiconductor laser 2 at that time is controlled. The modulation frequency read by the apparatus 4 becomes the vibration frequency f of the measurement surface 6A to be measured.

  As described above, the luminance change of the maximum bright spot Amax portion of the vibration fringe image A is displayed on the video monitor 10 and can be visually recognized by the operator. While the operator visually recognizes the video monitor 10, the function generator 3 is sequentially adjusted to visually find the modulation frequency at which the maximum bright spot Amax having the same luminance as the maximum value is obtained, and the vibration frequency f of the measurement surface 6A is detected. May be.

  Alternatively, without obtaining the maximum value of the maximum bright spot Amax 1 in advance as described above, by sequentially comparing the maximum values of the maximum bright spot Amax of the vibration fringe image, the maximum value of the maximum bright spot Amax 1 is obtained. You may comprise so that a corresponding maximum value may be calculated | required.

  Further, in the series of measurements, by reducing the amplitude M of the modulation frequency (refer to the equation (1)), it is possible to measure the vibration frequency f accurately in a short time that can be actually used. That is, the phase “θ (t)” of the interference light that forms the interference image can be expressed by the above equation (1). However, if the value of “M” is decreased, Even in the case of different phases, the amount of change in the phase θ (t) within the TV camera accumulation time (shutter speed: for example, 1/30 second) becomes small. Since the change in luminance becomes gradual as shown in FIG. 5, even if the modulation frequency fm and the vibration frequency f are different, the modulation frequency at which the luminance of the maximum bright spot becomes equal to the maximum value (“Z” in FIG. 5). This is because the modulation frequency at the position indicated by “” can be easily found.

  In each of the above embodiments, the semiconductor laser oscillator is described as being built-in. However, when the oscillator is an external oscillator, the length of the oscillator may be changed and modulated. The present invention can be implemented in the same manner as in the examples.

  In addition, the present invention can be carried out using a laser other than a semiconductor laser. In such a case, the modulation of the wavelength of the laser beam may be made corresponding to the type of each laser.

  The vibration measuring method and the vibration measuring apparatus according to the present invention can be used to measure the amplitude and vibration frequency of a vibrating part of a precision instrument or an in-vehicle apparatus.

1 is an overall view schematically showing the overall configuration of a vibration measuring apparatus according to an embodiment of the present invention. It is a figure which shows the vibration fringe image displayed on the video monitor of the vibration measuring device shown in FIG. It is a figure which shows the state after moving the part of the maximum bright spot in the vibration fringe image shown in FIG. 2 by changing the wavelength of a semiconductor laser. 3 is a table showing the correlation between the amplitude of an injection current i and the amplitude L of a measurement surface stored in the memory of the control device shown in FIG. The horizontal axis represents the modulation frequency “fm”, the vertical axis represents the luminance value of the maximum bright spot, and the modulation frequency which becomes the maximum luminance value change state and the maximum bright spot luminance value accompanying the change of the modulation frequency. It is a figure showing position "Z".

Explanation of symbols

A: Vibration fringe image Amax: Maximum bright spot of vibration fringe image
2 ... Semiconductor laser
6 ... measured object
6A ... Measurement surface
L: Vibration amplitude

Claims (4)

A laser is used as a light source, the laser light is separated, and the reflected light obtained by irradiating the separated surface onto the measurement surface is overlapped with the reference light composed of the separated light. In the electronic speckle interferometry, which forms an interference image on the image plane, obtains a vibration fringe image by image processing the interference image group accumulated in time series, and measures the vibration of the object to be measured.
The modulation frequency of the modulation signal that modulates the wavelength of the laser light is changed within a predetermined range until the maximum value of the brightness of the maximum bright spot in the vibration fringe image is obtained, and the above processing is repeated to obtain the maximum value. A vibration frequency of the measurement surface is obtained using a modulation frequency of the modulation signal as a vibration frequency of the measurement surface. A vibration measurement method for obtaining a maximum value of luminance of a maximum bright spot according to claim 1 ,
Obtained in advance as the maximum value to compare the brightness of the maximum bright spot in the vibration fringe image obtained without inputting a modulation signal to the laser,
Next, the modulation frequency of the modulation signal input to the laser is changed within a predetermined range, and the brightness of the maximum bright spot in the obtained vibration fringe image is compared with whether or not the maximum value to be compared matches. The method is characterized in that the vibration frequency of the measurement surface is obtained by changing the modulation frequency within the predetermined range and repeating the processing, and using the modulation frequency of the modulation signal when the two coincide with each other as the vibration frequency of the measurement surface. The method according to claim 1 , wherein when the interference image group is obtained by changing the modulation frequency of the modulation signal within a predetermined range, the amplitude of the modulation signal is reduced. A vibration measurement device for carrying out the method for measuring vibration of a measurement surface according to claim 1 , wherein the vibration measurement device comprises:
The laser capable of modulating the wavelength by inputting a modulation signal;
Modulation signal changing means capable of changing the frequency of the modulation signal;
Separate the light emitted from the laser, irradiate one of the light on the measurement surface to obtain the reflected light, and use the other light as the reference light, superimposing the reflected light and the reference light, An optical system that forms an image on the imaging plane;
A TV camera that captures an image formed on the imaging surface;
A control device that obtains the maximum value of the brightness of the maximum bright spot in the vibration fringe image obtained by changing the modulation frequency of the modulation signal in an appropriate range, and uses the modulation frequency when the maximum value is obtained as the vibration frequency of the measurement surface A vibration measuring apparatus comprising:

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