JP2005069916A - Laser doppler vibration meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser doppler vibration meter capable of precisely measuring the vibration and displacement of a body of revolution. <P>SOLUTION: The difference D of the displacement P obtained by integrating the velocity signal a1+a2 and the displacement P at one revolution cycle before time is obtained as an apparent displacement b2 generated during one revolution cycle by the velocity component a2 generated by the positional deviation between the optical axis of the laser beam and the revolving axis of the body of revolution or dispersion light. The estimation value E of the apparent displacement b2 generated at each time point by the positional displacement between the optical axis of the laser beam and revolving axis of the body of the rotation and the dispersion light is calculated from the difference D, and the value subtracted with the estimation value E from the displacement P is calculated as a value R representing the true displacement b1 of the object 100 to be measured which gives the velocity component a1 to the speed signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laser Doppler vibrometer that measures the vibration and displacement of a rotating body using a Doppler shift caused by the Doppler effect on laser light reflected by the rotating body.

  As a laser Doppler vibrometer that measures the vibration and displacement of a measurement object by using the Doppler shift generated in the laser beam reflected by the rotating body due to the Doppler effect, for example, a heterodyne interferometry shown in FIG. 7 is used. The laser Doppler vibrometer used is known (for example, JP-A-7-120304).

  In the figure, the laser beam having the frequency f0 emitted from the laser light source 1 is bisected by the first beam splitter 2, and one of the bisected beams is frequency-shifted by the frequency fM by the acoustooptic device 3, and the frequency f0 + fM. Is incident on the light receiving unit 5 through the second beam splitter 4. On the other hand, the other divided beam is irradiated onto the measurement object 100 via the third beam splitter 6 and the light transmission / reception head 7, and the reflected beam reflected by the measurement object 100 is received by the transmission / reception head 7. The light enters the light receiving unit 5 through the beam splitter 6, the mirror 8, and the second beam splitter 4.

  Here, a Doppler shift fD corresponding to the speed of the measurement object 100 occurs in the frequency of the reflected beam, and the frequency of the reflected beam is f0 + fD. Therefore, a beat frequency of fM ± fD is observed in the light receiving unit 5 due to interference between the reference beam and the reflected beam. Therefore, by extracting the frequency component of fD and performing FM demodulation, a speed signal corresponding to the vibration speed of the measurement object 100 is obtained, and by integrating this speed signal in the analyzer 9, the displacement of the measurement object 100 is obtained. It is done.

  Further, as a technique for improving the measurement accuracy in such a laser Doppler vibrometer, in order to correct an error due to amplitude modulation caused in the reflected light due to non-uniform surface condition of the measurement object 100, the light receiving unit 5 photoelectrically reflects the reflected light. A technique for controlling the amplification factor of the output voltage so as to keep the DC component of the output voltage of the photodetector to be converted constant is known (for example, Japanese Patent Laid-Open No. 4-54192).

Prior art document information relating to the invention of this application includes the following.
JP 7-120304 A JP-A-4-54192

According to the conventional laser Doppler vibrometer, the following problems occur when measuring vibration and displacement in a direction perpendicular to the rotation axis of the rotating body.
That is, if the rotation axis of the rotating body is not accurately positioned on the optical axis of the laser beam, the influence of the peripheral speed of the rotating body is mixed into the measurement result, and the measurement accuracy is deteriorated. In addition, the degree of accuracy deterioration due to incidence of scattered light components other than specularly reflected light generated on the reflecting surface of the rotating body on the light receiving unit 5 is relatively large.

  Therefore, an object of the present invention is to provide a laser Doppler vibrometer that can accurately measure vibration and displacement in a direction perpendicular to the rotation axis of a rotating body.

  In order to achieve the above object, the present invention irradiates a rotating body with a laser beam from a direction perpendicular to the rotational axis of the rotating body, and integrates a velocity signal obtained from a Doppler shift amount generated in an incident reflected beam. A laser Doppler vibrometer that measures vibration in a direction perpendicular to the rotation axis of the rotating body based on the obtained displacement signal, a rotation period detecting means for detecting the rotation period of the rotating body, and one rotation period of the rotating body An apparent displacement unit calculating means for calculating an amount of change of the displacement signal for a period as an apparent displacement unit, and a rotation axis of the surface of the rotating body included in the speed signal among the displacements represented by the displacement signal; An apparent amount of displacement that is a component caused by a velocity component that does not depend on a displacement in the direction of a vertical measurement object, assuming that the apparent displacement unit is the sum of the apparent displacements for one rotation period. A position estimation unit, from the displacement amount of the displacement signal indicates, the apparent by subtracting the displacement amount, in which a displacement calculating means for the displacement of the rotating body.

  According to such a laser Doppler vibrometer, one rotation period of an apparent displacement that appears in the displacement signal due to a positional deviation between the optical axis of the laser beam and the rotational axis of the rotating body or a velocity component mixed in the velocity signal due to scattered light. Is obtained from the amount of change in the displacement signal for one rotation period of the rotating body. Here, since the sum of one rotation period of the amount of displacement obtained by integrating the speed component due to the true displacement in the direction perpendicular to the rotation axis of the surface of the rotating body included in the speed signal is 0, this is done. Thus, the sum total of one rotation period of the apparent displacement can be accurately calculated. Accordingly, the amount of apparent displacement at each time point is estimated based on the total sum of the apparent displacements obtained in this way and subtracted from the amount of displacement represented by the displacement signal. Vibration and displacement in the direction perpendicular to the rotation axis can be measured with high accuracy.

  As described above, according to the present invention, it is possible to provide a laser Doppler vibrometer that can accurately measure vibration and displacement in a direction perpendicular to the rotation axis of the rotating body.

Embodiments of the present invention will be described below.
FIG. 1 shows a configuration of a laser Doppler vibrometer according to the present embodiment.
As shown in the figure, the laser Doppler vibrometer includes a laser light source 1, a first beam splitter 2, an acoustooptic device 3, a second beam splitter 4, a light receiving unit 5, a third beam splitter 6, a light transmitting / receiving head 7, a mirror 8, An analysis device 9 and a rotation sensor 10 are provided. That is, the laser Doppler vibrometer has a configuration in which the rotation sensor 10 is added to the laser Doppler vibrometer shown in FIG.

  In such a configuration, the laser beam having the frequency f0 emitted from the laser light source 1 is bisected by the first beam splitter 2, and one of the bisected beams has a frequency of fM by the acoustooptic device 3 and has a frequency. It is shifted and enters the light receiving unit 5 through the second beam splitter 4 as a reference beam having a frequency f0 + fM. On the other hand, the other divided beam is irradiated onto the measurement object 100 via the third beam splitter 6 and the light transmission / reception head 7, and the reflected beam reflected by the measurement object 100 is received by the transmission / reception head 7. The light enters the light receiving unit 5 through the beam splitter 6, the mirror 8, and the second beam splitter 4.

  Here, a Doppler shift fD corresponding to the speed of the measurement object 100 occurs in the frequency of the reflected beam, and the frequency of the reflected beam is f0 + fD. Therefore, a beat frequency of fM ± fD is observed in the light receiving unit 5 due to interference between the reference beam and the reflected beam. Therefore, the light receiving unit 5 extracts the frequency component of the input fD and performs FM demodulation to obtain a velocity signal V corresponding to the vibration of the measurement object 100, and the analyzer 9 analyzes the velocity signal V. Thus, the displacement of the measuring object 100 is obtained.

   On the other hand, the rotation sensor 10 is a sensor that detects the rotation period of the measurement object 100 and outputs a synchronization signal synchronized with the rotation of the measurement object 10 to the analysis device 9. Here, for example, as the rotation sensor 10, a laser sensor or the like that detects the reflection marker 101 attached to the measurement object 100 with a laser beam can be used.

Hereinafter, a displacement calculation process for calculating the displacement of the measurement object in such a laser Doppler vibrometer will be described.
First, an outline of the principle of displacement calculation in this embodiment will be described with reference to FIG.
Now, the velocity component generated by the true displacement of the measurement object 100 included in the velocity signal V is indicated by a1, and the positional deviation or scattering between the optical axis of the laser beam included in the velocity signal V and the rotation axis of the rotating body. It is assumed that the speed component generated by light has a uniform speed as indicated by a2.
In this case, the displacement obtained by integrating the velocity signal V includes the displacement of b1 obtained by integrating the velocity component of a1 due to the true displacement of the measurement object 100, the optical axis of the laser beam, and the rotation axis of the rotating body. The displacement P is obtained by adding the apparent displacement b2 obtained by integrating the velocity component of a2 caused by the positional deviation and scattered light.

  Here, as understood from the figure, the displacement b1 obtained by integrating the velocity component of a1 due to the true displacement of the measuring object 100 becomes a periodic signal having the same period as the rotation period of the measuring object 100. The integral value of the period displacement is 0, and the same value of displacement is always obtained for the same rotation angle of the measurement object 100.

  On the other hand, the integrated value of the displacement of one period of the apparent displacement b2 caused by the positional deviation between the optical axis of the laser beam and the rotating shaft of the rotating body or the scattered light is not usually 0, and the optical axis of the laser beam and the rotating body. When the velocity component a2 generated by the positional deviation from the rotation axis or scattered light is uniform, it increases monotonously as shown by b2. On the other hand, the velocity component a2 generated by the positional deviation between the optical axis of the laser beam and the rotation axis of the rotating body or the scattered light becomes a periodic signal having the same period as the rotation period of the measurement object 100, and the same rotation angle of the measurement object 100. Since the same speed is always obtained, the apparent displacement b2 caused by the positional deviation between the optical axis of the laser beam and the rotational axis of the rotating body or the scattered light, which occurs during one rotation period of the measurement object 100, is obtained. The amount of change in displacement is always constant.

Therefore, the value D obtained by subtracting the displacement P at the time before one rotation period from the displacement P at a certain time is a positional deviation between the optical axis of the laser beam generated during one rotation period and the rotation axis of the rotating body. This represents the amount of change in the apparent displacement b2 caused by the scattered light.
If the a2 caused by the positional deviation between the optical axis of the laser beam and the rotational axis of the rotating body or the scattered light is uniform, the positional deviation between the optical axis of the laser beam and the rotational axis of the rotating body from the difference D. It is possible to estimate the apparent displacement E that occurs at each time point by using scattered light, and measure the displacement P as a value R obtained by subtracting the estimated value E from the displacement P ′ obtained by delaying the displacement P by the time required to estimate the estimated value E. The true displacement b1 of the object 100 is obtained.

Hereinafter, a configuration for performing such displacement calculation processing will be described.
FIG. 3A shows an example of the configuration of a displacement calculation block that performs displacement calculation processing in the analysis device 9.
In the illustrated configuration, the speed signal V input from the light receiving unit 5 is digitally converted by the A / D converter 301 into the speed data V, and the speed data V is integrated in the integration block 302 to obtain the displacement data P. The difference block 304 obtains the difference between the displacement data P and the delay displacement data P ′ obtained by delaying the displacement data P by the delay block 303 by one rotation cycle of the measurement object, and the difference data D is obtained. Then, in the integration block 306, the integral value of the value obtained by multiplying the difference data by 1 / m by the multiplier 305 is obtained and used as the apparent displacement estimation data E. E is subtracted in the subtraction block 307 to obtain calculated displacement data R. Here, m used for multiplication by the multiplier is a sampling number of the speed data V of the A / D converter 301 generated during one rotation period of the measurement object 100.

  The sequence control unit 308 controls the operation of each unit in synchronization with the rotation synchronization signal input from the rotation sensor. Specifically, the sampling clock of the A / D converter 301 is generated in synchronization with the rotation synchronization signal input from the rotation sensor 10. Further, the sequence control unit 308 delays the start of the integration operation of the integration block 306 and the start of the output operation of the calculated displacement data R of the subtraction block 307 by one rotation cycle from the start of the integration operation of the integration block 302. As a result, as shown in FIG. 2, the calculation of the apparent displacement estimation data E and the calculated displacement data R is started with a delay of one rotation period from the start of generation of the displacement data P.

By the way, such displacement calculation processing can also be realized by software processing.
FIG. 3b shows a configuration example of a displacement calculation block when the displacement calculation process is performed by software processing in the analysis device 9.
As shown in the figure, in this displacement calculation block, the A / D converter 351 digitally converts the speed signal V input from the light receiving unit 5 and stores it in the input buffer 353 as speed data V. On the other hand, the rotary encoder 352 generates the sampling clock of the A / D converter 351 in synchronization with the rotation synchronization signal input from the rotation sensor 10, and what speed cycle data V after the start of measurement The writing position of the speed data V in the input buffer 353 is controlled so that the speed data V is stored in the input buffer 353 so that the speed data V can be identified.

Then, the CPU 355 performs a displacement calculation process using the memory 354, calculates the calculated displacement data R based on the speed data velocity data V stored in the input buffer 353, and stores it in the output buffer 356.
Next, the procedure of the displacement calculation process performed by this CPU is shown in FIG.
As shown in the figure, in this process, the speed data V is read from the input buffer 353 in the order of measurement (steps 402, 414, 418, 416), and the following process is performed.
That is, each speed data V measured prior to the speed data V (n, i) and the speed data V (n, i) where the i-th speed data of the n-th rotation period is V (n, i). And is stored in the memory 354 as i-th displacement data P (n, i) of the n-th rotation cycle (step 404).
If the obtained displacement data P is displacement data for the second and subsequent rotation cycles (step 406), the displacement data P (n, i) stored in the memory 354 is stored. The displacement data P ′ = P (n−1, i) one rotation period before the data P is subtracted to obtain i-th difference data D (n, i) of the n-th rotation period (step 408). Then, 1 / Max of the difference data D (n, i) and the sum of the difference data D obtained in advance of the difference data D (n, i) is obtained (step 410), and the n-1st rotation. The i-th apparent displacement estimation data E (n−1, i) of the cycle is used. However, iMax is the number of samples of the speed data V during one rotation period.

Then, the apparent displacement estimation data E (n−1, i) is subtracted from the displacement data P (n−1, i) read from the memory 354, and the i th calculated displacement data R of the n−1 first rotation cycle is subtracted. (N-1, i) is stored in the output buffer (step 412).
Now, the analysis device 9 obtains the displacement value obtained for the same rotation angle (the same value of i) in each rotation cycle of the measured object 100 with respect to the calculated displacement data R obtained by the displacement calculation process as described above. And the final post-processing is performed to output the displacement of the final measurement object 100 with respect to each rotation angle.

The embodiment of the present invention has been described above.
As described above, according to the present embodiment, when the velocity component generated by the positional deviation or scattered light between the optical axis of the laser beam and the rotating shaft of the rotating body is uniform, the apparent displacement caused by this is reduced. The true displacement of the measurement object 100 can be calculated by eliminating it.
By the way, in the present embodiment, even when the positional deviation between the optical axis of the laser beam and the rotational axis of the rotating body and the velocity component caused by the scattered light are not uniform, the optical axis of the laser beam and the rotational axis of the rotating body A measurement error due to an apparent displacement caused by a positional shift or scattered light can be suppressed to some extent.

  That is, for example, as shown in FIG. 5, the velocity component generated by the true displacement of the measurement object 100 included in the velocity signal V is indicated by a1, and the optical axis of the laser beam included in the velocity signal V and the rotating body It is assumed that the velocity component generated by the positional deviation with respect to the rotation axis and the scattered light fluctuates during one rotation cycle as indicated by a2.

  For this example, the displacement obtained by integrating the velocity component of a1 due to the true displacement of the measured object 100 is b1, and the positional deviation between the optical axis of the laser beam and the rotational axis of the rotating body or scattered light. The apparent displacement obtained by integrating the velocity component of a2 generated by is as shown in b2. Therefore, the displacement P, the difference signal D, and the apparent displacement estimated value E are obtained as shown in the figure, and the calculated displacement R obtained by subtracting the apparent estimated value E from the displacement P ′ is calculated as shown in the figure. Compared to P, the error from the true displacement b1 is suppressed.

  Here, the degree of suppression of the error in this case depends on the positional deviation between the optical axis of the laser beam included in the velocity signal V and the rotational axis of the rotating body, the size of the velocity component a2 generated by the scattered light, and the generation pattern. In any case, according to the displacement calculation processing according to the present embodiment, an apparent displacement exceeding one rotation cycle is not accumulated as an error in displacement calculation.

  By the way, in the above embodiment, the estimated value E of the apparent displacement is the number of samples corresponding to one rotation period of the integral value of the difference data D (n, i) from the displacement data P one rotation period before the displacement data P. The estimated value E of the apparent displacement may be obtained as follows.

  That is, the difference data D (n, i) obtained for the displacement data P (n, i) of the second and subsequent rotation cycles and all the differences obtained for the same i preceding the difference data D (n, i) The sum of the data D (j, i) is assumed to be an apparent displacement estimated value E ′ (n, i), and P (n, i) −E ′ (n, i) is calculated as the calculated displacement R (n−1, i). You may make it. However, j is an integer of 2 or more and less than n. By doing so, the velocity component generated by the true displacement of the measurement object 100 included in the velocity signal V shown in FIG. 5 is a1, the optical axis of the laser beam included in the velocity signal V, and the rotation axis of the rotating body. The estimated displacement E ′ of the apparent displacement is obtained as shown in FIG. 6A with respect to the velocity component a2 caused by the positional deviation and scattered light, and the displacement data P is subtracted from the displacement data P by subtracting this E ′ from the displacement data P. Calculated displacement data R obtained by removing the apparent displacement that has occurred up to the previous rotation period from the calculated displacement is obtained. As can be understood from the figure, even in this case, it is possible to eliminate that the apparent displacement of one rotation period or more is accumulated as an error of the calculated displacement.

  Alternatively, the value obtained by subtracting {i × D (2, i)} / iMax from E ′ (n, i) thus obtained is set to E ″ (n, i), and P (n, i) − E ″ (n, i) may be the calculated displacement R (n−1, i). In this case, when the magnitude of the velocity component a2 caused by the positional deviation between the optical axis of the laser beam included in the velocity signal V and the rotational axis of the rotating body or the scattered light is constant, the calculated displacement R obtained is This is the same as the calculated displacement R obtained using the apparent displacement estimation data E of the above embodiment. That is, for example, the velocity component generated by the true displacement of the measurement object 100 included in the velocity signal V shown in FIG. 2 is a1 and the positions of the optical axis of the laser beam included in the velocity signal V and the rotation axis of the rotating body. An estimated value E ″ of the apparent displacement is obtained as shown in FIG. 6A with respect to the velocity component a2 caused by the deviation or scattered light, and by subtracting this E ″ from the displacement data P, the previous rotation period is derived from the displacement data P. The calculated displacement data R obtained by removing the apparent displacement generated up to this point from the calculated displacement is obtained.

It is a figure which shows the structure of the laser Doppler vibrometer which concerns on embodiment of this invention. It is a figure which shows the principle of the displacement calculation which concerns on embodiment of this invention. It is a block diagram which shows the structure of the displacement calculation block which concerns on embodiment of this invention. It is a flowchart which shows the procedure of the displacement calculation process which concerns on embodiment of this invention. It is a figure which shows the example of a displacement calculation which concerns on embodiment of this invention. It is a figure which shows the example of a displacement calculation which concerns on embodiment of this invention. It is a figure which shows the structure of the conventional laser Doppler vibrometer.

Explanation of symbols

  1: laser light source, 2: first beam splitter, 3: acousto-optic element, 4: second beam splitter, 5: light receiving unit, 6: third beam splitter, 7: light transmitting / receiving head, 8: mirror, 9: analysis Apparatus: 10: rotation sensor, 100: measurement object, 101: reflection marker, 301: A / D converter, 302: integration block, 303: delay block, 304: difference block, 305: multiplier, 306: delay block, 307: Subtraction block, 308: Sequence control unit, 351: A / D converter, 352: Rotary encoder, 353: Input buffer, 354: Memory, 355: CPU, 356: Output buffer

Claims (2)

Based on a displacement signal obtained by irradiating the rotating body with a laser beam from a direction perpendicular to the rotational axis of the rotating body and integrating a speed signal obtained from the Doppler shift amount generated in the incident reflected beam, A laser Doppler vibrometer that measures vibration in a direction perpendicular to the rotation axis,
A rotation period detecting means for detecting a rotation period of the rotating body;
Apparent displacement unit calculation means for calculating the amount of change of the displacement signal for one rotation period of the rotating body as an apparent displacement unit;
Of the displacement amount represented by the displacement signal, the apparent displacement amount, which is a component caused by a velocity component that does not depend on the displacement in the measurement target direction perpendicular to the rotation axis of the surface of the rotating body included in the velocity signal, is the apparent displacement amount. An apparent displacement amount estimating means for estimating that a displacement amount unit is a sum of the apparent displacement amounts for one rotation period;
A laser Doppler vibrometer, comprising: a displacement calculating unit that subtracts the apparent displacement amount from a displacement amount represented by the displacement signal to obtain a displacement amount of the rotating body.
Based on a displacement signal obtained by irradiating the rotating body with a laser beam from a direction perpendicular to the rotational axis of the rotating body and integrating a speed signal obtained from the Doppler shift amount generated in the incident reflected beam, In a laser Doppler vibrometer that measures vibration in a direction perpendicular to the rotation axis, a displacement calculation method for calculating displacement in a direction perpendicular to the rotation axis of the surface of the rotating body,
Calculating the amount of change of the displacement signal for one rotation period of the rotating body as an apparent displacement unit;
Of the displacement amount represented by the displacement signal, the apparent displacement amount, which is a component caused by a velocity component that does not depend on the displacement in the measurement target direction perpendicular to the rotation axis of the surface of the rotating body included in the velocity signal, is the apparent displacement amount. Estimating a displacement unit as a sum of the apparent displacements for one rotation period;
Subtracting the apparent displacement amount from the displacement amount represented by the displacement signal to obtain a displacement amount of the rotating body.

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