JP2006162523A - Speed-measuring apparatus and displacement measurement apparatus for periodically movable object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speed-measuring apparatus and a displacement measuring apparatus for a periodic movable object, acquiring the displacement speed distribution and the displacement amount distribution of a movable object having a mirror plane, in a short measurement time and with high spatial resolution, even when the amount of deformation of the surface to be measured is large. <P>SOLUTION: The speed-measuring apparatus for a periodic movable object comprises a light source 2 for irradiating the object to be measured, which moves substantially periodically, with a pulsed light; a timing adjustment means 12 for adjusting the timing between the displacement of the object to be measured 1 and the emission of the pulsed light by the light source 2, an interference optical system 6 for allowing reflected light from the object to be measured 1 and the reference light to interfere with each other; a photographic means 8 for photographic interference fringes by the interference optical system 6; and an arithmetic unit 11 which detects the contrast of the interference fringes from the image of the interference fringes by the photographic means 8 and determines the displacement speed, in a direction substantially normal to the surface of the object to be measured 1, on the basis of the correlation between the contrast of the interference fringes and the displacement speed in a direction substantially normal to the surface of the object to be measured 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a velocity measuring device and a displacement measuring device for a periodically movable object that measures the displacement speed or the amount of displacement of a mirror surface movable object that moves substantially periodically in the field of optical applied measurement and the performance evaluation of a movable object. .

Conventionally, there are devices that measure the displacement speed or amount of a mirror-moving object that moves in a substantially periodic motion, and there is a concern about the influence of inertial force associated with resonance on the mirror surface during resonance. It is known that the behavior of the mirror surface is evaluated (see, for example, Patent Documents 1 to 4).
FIG. 7 is a schematic perspective view showing a resonant mirror which is an example of a measurement object. The resonant mirror 1 is a component used for beam scanning in various applications such as measuring instruments and image display devices.
In FIG. 7, the resonance mirror 1 scans the light beam irradiated to the mirror surface 1a by resonating (swinging) in the direction of the arrow with the mirror surface 1a attached to the base 1b and having the axis 1c as the rotation axis. To do.
In this case, since there is a concern about the influence of the inertial force accompanying the resonance on the mirror surface 1a during resonance, there is a demand for evaluating the behavior of the mirror surface during resonance as described above.
As a method for measuring the behavior of a movable object, there are a laser Doppler method shown in Patent Document 1 and a laser interferometer (length measuring device) method shown in Patent Document 2.
Since these methods are so-called point measurement that measures the velocity of only the area where the thin laser beam is hit, it is necessary to scan the irradiation laser beam two-dimensionally to obtain the displacement and velocity over the entire surface of the object to be measured. And takes time to measure. Further, since the in-plane spatial resolution is determined by the beam diameter of the laser to be irradiated, there is a problem that the spatial resolution does not increase.
In addition, as a method for obtaining a speed by recording a two-dimensional image, there is a method using a speckle pattern shown in Patent Document 3, but in the speckle method, an object to be measured is microscopically generated in order to generate a speckle pattern. It needs to have a complex surface shape. Since a speckle pattern does not occur on the mirror surface, it is difficult to cope with the object to be measured being a mirror surface movable object.
Further, Patent Document 4 discloses that the surface of the object to be measured being displaced from the obtained interference fringes is generated by irradiating the object to be measured with pulse light that is sufficiently short in time with respect to the displacement speed of the object to be measured. A technique for obtaining a shape is disclosed.
Patent No. 2807778 Patent No. 2592254 Japanese Patent No. 3353365 Japanese Patent No. 3150239

By the way, in the method shown in Patent Document 4, the surface shape at the moment of irradiation with pulsed light can be measured, but the behavior of the mirror surface during resonance cannot be acquired. In addition, if the deformation amount of the object to be measured varies greatly depending on the location of the surface, the interference fringes become too spatially dense and finer than the sampling pitch of the imaging means, making it impossible to measure.
Further, the object to be measured is irradiated with light, and interference fringes are formed from the reflected light. When the surface to be measured is displaced during light irradiation, interference fringes that change the pattern according to the displacement are superimposed within the pulse width of the irradiation pulse light, and the resulting interference fringe image is acquired by the imaging means. The contrast of the image is reduced.
Therefore, the present invention can acquire the displacement velocity distribution and the displacement amount distribution of the mirror surface movable object even in the case where the deformation amount of the surface to be measured is large with a short measurement time and high spatial resolution in consideration of the above-described situation. An object of the present invention is to provide a velocity measuring device and a displacement measuring device for a periodic movable object.
In addition, the present invention improves the versatility of measurement with respect to the displacement speed of the object to be measured, expands the measurement range, and further reduces the measurement error caused by the interference fringe acquisition conditions, thereby measuring the speed of a periodically movable object. An object is to provide a device and a displacement measuring device.

In order to achieve the above-mentioned object, the invention described in claim 1 includes a light source for irradiating a measured object that moves substantially periodically with pulsed light, displacement of the measured object, and emission of pulsed light by the light source. Timing adjustment means for adjusting timing, interference optical system for causing reflected light from the object to be measured and reference light to interfere, imaging means for imaging interference fringes by the interference optical system, and the imaging means The contrast of the interference fringe is detected from the interference fringe image obtained from the above, and the substantially normal direction of the surface of the object to be measured is determined from the correlation between the contrast of the interference fringe and the displacement speed of the surface of the object to be measured in the substantially normal direction. And a means for calculating a displacement speed of the periodic movable object.
The invention according to claim 2 further includes an irradiation light amount adjusting means for adjusting the light amount of the light emitted from the light source to the object to be measured in association with a change in the pulse width of the pulsed light from the light source. A speed measuring device for a periodic movable object according to claim 1.
The invention according to claim 3 is the amplitude information of the complex amplitude obtained by Fourier transforming the interference fringe image acquired by the imaging means, removing the tilt component of the interference fringe in the frequency space, and then performing inverse Fourier transform. Alternatively, the periodic movable object speed measurement device according to claim 1, wherein information on the square of the amplitude is used as a contrast of the interference fringes.
According to a fourth aspect of the present invention, the displacement speed in the normal direction of the surface of the object to be measured is V, the wavelength of the light source is λ, and the pulse width when the contrast of the interference fringes is almost eliminated is t. The speed measuring device for a periodic movable object according to claim 2, wherein V is obtained from a relationship of V = λ / (2 · t).

According to a fifth aspect of the present invention, there is provided the periodic movable object speed measuring device according to the second aspect, wherein the imaging unit has the function of the irradiation light amount detection unit.
According to a sixth aspect of the present invention, there is provided a light source for irradiating the object to be measured that moves substantially periodically with a pulsed light, and a timing adjustment for adjusting the timing of the displacement of the object to be measured and the emission of the pulsed light by the light source. An interference optical system for causing the reflected light from the object to be measured and the reference light to interfere with each other, an imaging means for imaging an interference fringe by the interference optical system, and interference from an interference fringe image by the imaging means Calculation for detecting the contrast of the fringe and calculating the displacement of the surface of the object to be measured in the direction of the normal line from the correlation between the contrast of the interference fringes and the amount of displacement of the surface of the object to be measured in the direction of the normal line Means for measuring the displacement of the periodic movable object.
The invention according to claim 7 further includes irradiation light amount adjusting means for adjusting the light amount of the light irradiated from the light source to the object to be measured accompanying the change in the pulse width of the pulsed light from the light source. A displacement measuring apparatus for a periodic movable object according to claim 6.
The invention according to claim 8 is the amplitude information of the complex amplitude obtained by Fourier transforming the interference fringe image acquired by the imaging means, removing the tilt component of the interference fringe in the frequency space, and then performing inverse Fourier transform. Alternatively, the periodic movable object displacement measuring device according to claim 6 or 7, wherein the information of the square of the amplitude is used as the contrast of the interference fringes.
According to a ninth aspect of the present invention, when the amount of displacement of the object to be measured is A, the wavelength of the light source is λ, the displacement frequency of the object to be measured is f, and the contrast of the interference fringes is almost eliminated. The periodic movable object displacement measuring device according to claim 7, wherein the pulse width is t, and A is obtained from a relationship of A = λ / (4 · f · t).
The invention according to claim 10 is characterized in that the displacement measuring device for a periodic movable object according to claim 7, wherein the imaging means has the function of the irradiation light quantity detection means.

According to the first and sixth aspects of the present invention, the object to be measured is irradiated with light, and interference fringes are formed from the reflected light. Therefore, if the surface to be measured is displaced during light irradiation, the object is displaced. Interference fringes that change the pattern accordingly are superimposed within the pulse width time of the irradiation pulse light, and as a result, the contrast of the interference fringe image acquired by the imaging means decreases, but the contrast of the interference fringe image and the object to be measured Since there is a correlation between the displacement speed or the displacement amount, the displacement velocity distribution and the displacement amount distribution of the object to be measured can be obtained by detecting the contrast of the interference fringes by the calculation means. In this way, since surface measurement is possible, it takes less time to measure, and high spatial resolution can be obtained, and speckle patterns are not required, so even specular objects can be measured. become able to.
In addition, since the surface deformation is detected by detecting the displacement speed of the surface to be measured, it is possible to acquire comprehensive information on behavior rather than information at a certain moment of the surface, and to acquire information even when the amount of surface deformation is large Can do.
According to the invention of claim 2, since the pulse width is changed by the irradiation light amount adjusting means, it is possible to cope with a wide range of displacement speeds of the object to be measured. Thereby, the versatility of the measurement with respect to the displacement speed of the object to be measured can be improved, the measurement range can be expanded, and the measurement error due to the interference fringe acquisition condition can be reduced.
According to the third and eighth aspects of the present invention, if Fourier transform is performed by a two-dimensional FFT operation or the like, processing can be performed at high speed, so that processing time and measurement time can be shortened.
According to the invention of claim 4, the correlation data obtained experimentally is obtained by theoretically calculating the displacement speed with the object to be measured from the pulse width of the irradiation pulse light when the contrast of the interference fringes almost disappears. Since it is not acquired, it is possible to reduce the measurement error and save the time for acquiring correlation data.
According to the fifth and tenth aspects of the present invention, since the function of the irradiation light quantity detecting means is also provided to the interference fringe imaging means, it is not necessary to add an additional part for detecting the light quantity, thereby simplifying the configuration and reducing the cost. I can plan.
According to the invention of claim 7, since the pulse width is changed by the irradiation light amount adjusting means, it is possible to cope with a wide range of displacement of the object to be measured. Thereby, the versatility of the measurement with respect to the displacement speed of the object to be measured can be improved, the measurement range can be expanded, and the measurement error due to the interference fringe acquisition condition can be reduced.
According to the invention of claim 9, experimentally obtained correlation data is obtained by calculating the amount of displacement with the object to be measured from the pulse width of the irradiation pulse light when the contrast of the interference fringes is almost lost. Since it is not acquired, it is possible to reduce the measurement error and save the time for acquiring correlation data.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of a periodic movable object displacement measuring apparatus according to a first embodiment.
In the periodic movable object displacement measuring apparatus A shown in FIG. 1, a semiconductor laser as a light source 2 is driven by a semiconductor laser driver 3 to emit pulsed light having a predetermined time width (pulse width). In order to adjust the intensity of light from the semiconductor laser 2, an ND filter 4 is provided, followed by a beam expander 5. A part of the light expanded by the beam expander 5 passes through the beam splitter 6, and a part thereof is reflected by the beam splitter 6.
The light that has passed through the beam splitter 6 is irradiated onto the DUT 1. The light reflected by the DUT 1 travels back along the optical path, is reflected by the beam splitter 6, and reaches the CCD camera 8 via the lens 7.
On the other hand, the light reflected by the beam splitter 6 is reflected by the mirror 9. The reflected light from the mirror 9 travels backward along the optical path, passes through the beam splitter 6, and reaches the CCD camera 8 through the lens 7.
For the object light reflected by the DUT 1 and the reference light reflected by the mirror 9, the difference between the optical path length of the object light and the optical path length of the reference light is set to be equal to or less than the coherence length of the semiconductor laser 2 as the light source. In addition, when the optical axes of the object light and the reference light are substantially matched, if the DUT 1 is stationary, the two interfere with each other to generate interference fringes.
The position of the lens 7 is adjusted so that the image of the DUT 1 is formed on the imaging surface of the CCD camera 8. The DUT 1 is a resonant mirror as shown in FIG. Interference fringes generated between the object light and the reference light are imaged by the CCD camera 8.
The captured interference fringes are captured by the frame grabber 10, transferred to the computer 11, stored in the memory of the computer 11, and displayed on the monitor of the computer 11. The ND filter 4 is used to adjust the interference fringe intensity.

・・・（１）
を満たすとき干渉縞が発生する。
被測定物１の共振とＣＣＤカメラ８の露光とのタイミングは、例えば被測定物１を駆動するための信号発生器とＣＣＤカメラ８へ露光トリガを与えるための信号発生器とに共通のものを用いる。
そこで、そのタイミングは、信号発生器の一方のチャンネルで被測定物１を駆動し、他方のチャンネルで被測定物１の駆動周波数と同じ周波数か、もしくは約数の周波数の信号でＣＣＤカメラ８へ露光のトリガをかけ、両チャンネル間の信号の位相を調整することにより調整することができる。図１において、符号１２は２チャンネルの出力を有する信号発生器であり、符号１３は共振ミラー１のドライバである。 When the DUT 1 vibrates in the direction of the broken arrow in the figure, the CCD camera 8 is exposed at a timing at which the measurement surface becomes substantially perpendicular to the optical axis of the measurement optical system. When the amount of displacement of the surface to be measured within (shutter speed) is smaller than half of the light source wavelength, interference fringes are generated.
That is, when the displacement speed in the normal direction of the surface at an arbitrary position x, y on the surface to be measured is V (x, y), the exposure time of the CCD camera 8 is t, and the wavelength of the semiconductor laser is λ,

... (1)
Interference fringes are generated when the condition is satisfied.
The timing of the resonance of the DUT 1 and the exposure of the CCD camera 8 is common to, for example, a signal generator for driving the DUT 1 and a signal generator for giving an exposure trigger to the CCD camera 8. Use.
Therefore, the timing is such that the device under test 1 is driven in one channel of the signal generator and the same frequency as the drive frequency of the device under test 1 is used in the other channel or a signal of a divisor frequency to the CCD camera 8. It can be adjusted by triggering exposure and adjusting the phase of the signal between both channels. In FIG. 1, reference numeral 12 denotes a signal generator having two channel outputs, and reference numeral 13 denotes a driver of the resonant mirror 1.

FIG. 2 is a schematic diagram showing an image of the measurement surface observed by the optical system shown in FIG. 1 and the appearance of interference fringes generated on the measurement surface. FIG. 2 shows an image of a measured surface (corresponding to the mirror surface in FIG. 7) 1a observed by the optical system shown in FIG. 1 and the state of interference fringes 1d generated on the measured surface 1a. Reference numeral 11a represents a computer monitor.
In FIG. 2, the contrast of the interference fringe (ratio of the CCD intensity between the dark part and the bright part of the interference fringe) becomes the highest near the axis 1c where there is almost no displacement in the normal direction of the measured surface 1a. The contrast of the interference fringes becomes the lowest at the part where the displacement amount at the distant position is the largest.
In a portion where the amount of displacement is large, the displacement speed increases, and the interference fringes whose pattern changes with the change in the position of the surface to be measured 1a are superimposed within the exposure time of the CCD camera 8 (see FIG. 1), thereby reducing the contrast. .
As shown in FIG. 2, an interference fringe image is acquired, the ratio of the dark part and the bright part of the interference fringe is obtained for each location of the surface to be measured 1a, and the displacement speed of the surface to be measured 1a and the interference fringe obtained in advance are obtained. From the correlation with contrast, the displacement speed of the surface to be measured 1a can be obtained.
When deformation (swell) is generated on the surface to be measured 1a due to the influence of inertial force accompanying vibration, the displacement speed varies depending on the location of the surface, and the displacement speed distribution is measured.
If the number of interference fringes (the number of pairs of dark portions and bright portions) is increased, the spatial resolution in the plane can be increased. Correlation data between the displacement speed of the surface to be measured 1a and the contrast of the interference fringes is obtained, for example, using a jig described later.
FIG. 3 is a schematic diagram showing a jig used to acquire correlation data between the displacement speed of the surface to be measured and the contrast of interference fringes.
In FIG. 3, the mirror 14 is bonded to the base 16 via the piezo element 15. By applying a voltage to the piezo element 15, the mirror surface 14a can be displaced in the direction of the arrow.
The jig of FIG. 3 is installed as the DUT 1 in the optical system of FIG. 1 to generate interference fringes. By changing the voltage or frequency of the signal applied to the piezo element 15 to change the displacement speed of the mirror 14 surface, the contrast of the interference fringes obtained at that time is detected.

FIG. 4 is a graph showing the correlation between the displacement speed and the contrast.
From the detection of the interference fringe contrast, data representing the correlation between the displacement speed V and the contrast C can be acquired as shown in FIG.
The relationship between the voltage or frequency of the signal applied to the piezo element 15 and the displacement speed of the mirror 14 surface may be acquired separately using a displacement meter or the like. Further, an approximate expression may be obtained from the graph of FIG. 4, and the displacement speed may be calculated from the contrast value of the interference fringes.
The exposure time of the CCD camera 8 (see FIG. 1) is too long with respect to the displacement speed of the surface to be measured 1a. If the above equation (1) is not satisfied, the interference fringes disappear and the exposure time of the CCD camera 8 is short. If it is too large, the contrast change of the interference fringes becomes too small to be detected. For this reason, based on the specification value of the displacement speed of the DUT 1, the product of the maximum displacement speed of the DUT 1 and the exposure time, for example, is approximately the same value as half the light source wavelength. It is necessary to set an appropriate exposure time.
As described above, in the first embodiment, the object to be measured 1 is irradiated with light, and interference fringes are formed from the reflected light. Since there is a correlation between the contrast of the interference fringe image and the displacement speed or displacement of the object to be measured 1, the displacement of the surface of the object to be measured 1 in the normal direction is detected by detecting the contrast of the interference fringes. A velocity distribution and a displacement distribution can be obtained. In order for the reflected light of the device under test 1 to reach the image pickup means, the timing of the displacement of the device under test 1 and the exposure in the image pickup means (CCD camera) 8 is adjusted. Since it is surface measurement, time is not required for measurement and high spatial resolution can be obtained. Further, since a speckle pattern is not required, measurement is possible even for a specular object.
In addition, since the contrast change of the interference fringes due to the displacement of the surface to be measured 1a is detected, comprehensive information on the behavior can be acquired instead of information at a certain moment of the surface, and information can be acquired even when the deformation amount of the surface is large. it can.

In the above-described embodiment, instead of the correlation data between the displacement speed of the DUT 1 and the contrast of the interference fringes, correlation data between the displacement amount of the DUT 1 and the contrast of the interference fringes is acquired in advance. Therefore, the displacement distribution of the DUT 1 can be obtained from the contrast of the interference fringe image acquired in the measurement optical system. Alternatively, the displacement rate distribution of the device under test 1 may be obtained by the method described in the above-described embodiment, and the displacement amount distribution may be obtained by multiplying it by the resonance period of the device under test 1.
Here, the exposure time of the CCD camera 8 is variable. For example, the exposure time of the CCD camera 8 is shortened in the initial state, and the exposure time is gradually increased while acquiring interference fringes. Then, in the initial state, even if the interference fringe contrast is high, the exposure time becomes long, and the interference fringe contrast decreases as it approaches the boundary of the interference fringe generation condition of the above formula (1).
Then, the CCD exposure time when the contrast of the interference fringes is almost lost (the CCD intensity in the dark part and the bright part is equal) is stored. If the correlation data between the exposure time when the interference fringe contrast is almost lost and the displacement speed of the DUT 1 are acquired in advance, the CCD exposure time when the interference fringe contrast is almost lost is obtained from the CCD exposure time. The displacement speed can be determined.
According to the present embodiment, the contrast of the interference fringes is detected while gradually changing the exposure time in the imaging means, and the exposure time when the contrast of the interference fringes almost disappears is obtained for each location of the surface to be measured 1a. Then, the displacement speed of the device under test 1 is obtained from the correlation between the exposure time and the displacement speed of the device under test 1. Since the exposure time is changed, a wide range of displacement speeds of the DUT 1 can be dealt with.

FIG. 5 is a flowchart showing an outline of the measurement procedure.
In FIG. 5, t ₀ is the initial value of the CCD exposure time, Δt is the pitch for changing the exposure time, i is an integer (0, 1, 2,...), N is the number of times for changing the exposure time, and t (x, y) is the exposure time when the contrast of interference fringes at the coordinates x and y of the CCD image is almost eliminated, and V (x, y) is the displacement speed at the coordinates x and y of the CCD image.
Referring to FIG. 5, exposure time> = t ₀ + Δt · i (S1), and interference fringes are recorded (S2). Next, contrast is detected (S3), and it is determined whether i <N (S4). If i <N, an exposure time t (x, y) when the contrast is minimized for each pixel is obtained (S5). ). The speed V (x, y) is acquired for each pixel from t (x, y) (S6).
The CCD exposure time when the contrast of the interference fringes is almost eliminated is not easily affected by the background light, so that more accurate measurement can be performed. Even interference fringes that did not occur during a specific CCD exposure time are generated by changing the exposure time.
Or, conversely, even if an interference fringe has almost no change in contrast at a specific CCD exposure time, a change in the contrast can be seen by changing the exposure time. You can also expand the range.
In this embodiment, the contrast of the interference fringes is detected while gradually changing the exposure time in the image pickup means (CCD camera) 8, and the exposure time when the contrast of the interference fringes almost disappears is determined for each location on the surface to be measured. Ask. Then, the amount of displacement of the object to be measured is obtained from the correlation between the exposure time and the amount of displacement of the object to be measured.
In order to change the exposure time, it is possible to cope with a wide range of displacement of the DUT 1. In addition, the versatility of measurement with respect to the amount of displacement of the object to be measured can be improved, the measurement range can be expanded, and measurement errors due to interference fringe acquisition conditions can be reduced.
Instead of the correlation data between the CCD exposure time when the interference fringe contrast is almost eliminated and the displacement speed of the DUT 1, the CCD exposure time when the displacement amount of the DUT 1 and the contrast of the interference fringes are almost eliminated The correlation amount distribution of the object to be measured 1 can be obtained from the CCD exposure time acquired in the measurement.
The amplitude spectrum of the interference fringe may be obtained from the interference fringes generated by the interference between the reflected light of the DUT 1 and the reference light by the principle of the Fourier transform method, and the amplitude spectrum may be used as the interference fringe contrast.

・・・（２）
実験的に取得した相関関係のデータを取得しないため、測定誤差の低減、相関データ取得のための手間を省ける。
干渉縞のコントラストを検出しながらＣＣＤカメラ８の露光時間を変化させ、干渉縞のコントラストがほぼ無くなるときの露光時間を求める。そしてそれを次の式（３）におけるｔ（ｘ，ｙ）に代入することにより被測定面１ａの場所ごとで変位量Ａ（ｘ，ｙ）を算出することができる。

・・・（３）
実験的に取得した相関関係のデータを取得しないため、測定誤差の低減、相関データ取得のための手間を省くことができる。 As described above, it is possible to perform high-speed arithmetic processing when the contrast is obtained by obtaining the ratio of the intensity of the dark part and the bright part of the interference fringes for each region. Further, the displacement amount distribution may be obtained by obtaining the displacement velocity distribution of the object to be measured by this method and multiplying it by the vibration period of the object to be measured.
In the apparatus described above, when detecting the contrast of interference fringes, the ratio of the bright part to the dark part of the interference fringes may be taken, but the processing becomes complicated and takes time. In the present invention, the amplitude information of the complex amplitude or the square of the amplitude obtained by Fourier-transforming the interference fringe image acquired by the imaging means and removing the slope component of the interference fringe in the frequency space and then performing the inverse Fourier transform is obtained. The contrast of the interference fringes is used.
If the Fourier transform is performed by a two-dimensional FFT calculation or the like, the processing time and the measurement time can be shortened because the processing can be performed at high speed. This simplifies the calculation process in the measurement and improves the processing speed.
While detecting the interference fringe contrast, the exposure time of the CCD camera 7 is changed to obtain the exposure time when the interference fringe contrast is almost eliminated. Then, by substituting it into t (x, y) in the following equation (2), the displacement velocity V (x, y) can be calculated for each location on the surface to be measured 1a.

... (2)
Since experimentally acquired correlation data is not acquired, the measurement error can be reduced and the labor for acquiring correlation data can be saved.
The exposure time of the CCD camera 8 is changed while detecting the contrast of the interference fringes, and the exposure time when the contrast of the interference fringes almost disappears is obtained. Then, by substituting it into t (x, y) in the following equation (3), the displacement amount A (x, y) can be calculated for each location of the measured surface 1a.

... (3)
Since experimentally acquired correlation data is not acquired, it is possible to reduce measurement errors and save time for acquiring correlation data.

When the exposure time of the CCD camera 8 is changed, the amount of light exposed to the imaging surface increases or decreases, so that the captured interference fringe image becomes brighter or darker as a whole.
If the change in the amount of light accompanying the exposure time increases, the SN ratio may change when detecting the contrast of the interference fringes, and a detection error may occur. In the present invention, for example, according to a change in exposure time of the CCD camera 8, the amount of light applied to the object to be measured 1 is changed by an injection current to the semiconductor laser 2 of the light source.
When the exposure time is short, the amount of light of the image decreases, so that the current to be measured 1 is irradiated with strong light by increasing the injection current to the semiconductor laser 2. When the exposure time is long, the amount of light of the image increases. Therefore, the current to be measured 1 is irradiated with weak light by reducing the injection current to the semiconductor laser 2. Correlation data between the injection current and the exposure time may be acquired in advance, and the injection current may be changed according to the exposure time during measurement.
Automatic adjustment and automatic measurement are possible by changing the exposure time of the CCD camera 8 from the personal computer 11 via the signal generator 12 and the like, and changing the injection current to the semiconductor laser 2 via the DA converter or the like. Instead of changing the injection current to the semiconductor laser 2, an intensity filter may be installed in the irradiation optical path, and the irradiation light quantity may be adjusted by changing the filter intensity.
In the above-described apparatus, the irradiation light intensity is adjusted based on the correlation data between the injection current and the exposure time. Detect the brightness of the image.
For example, in the measurement procedure of FIG. 5 described above, after recording an interference fringe image in the initial state, the CCD pixel intensity I ₀ (x, y) constituting the bright part of the interference fringe is detected and stored as the reference intensity. Keep it. Then, after changing the exposure time, an interference fringe image is recorded, and the intensity I (x, y) at the CCD pixel at the same position as before is detected. If I (x, y) is different from the reference value I ₀ (x, y), the injection current to the semiconductor laser 2 is adjusted so that both are substantially the same value. It is only necessary to detect the CCD pixel intensity and adjust the injection current to the semiconductor laser 2 each time the exposure time is changed.

FIG. 6 is a schematic diagram showing a configuration of a periodic movable object displacement measuring apparatus according to the second embodiment. In the displacement measuring apparatus according to the first embodiment, the irradiation light intensity is adjusted based on the correlation data between the injection current and the pulse width. In the second embodiment, for example, an apparatus as shown in FIG. Is used to detect the irradiation intensity of light from the semiconductor laser.
In FIG. 6, the same parts as those of the displacement measuring apparatus shown in FIG.
In the displacement measuring apparatus shown in FIG. 6, a beam sampler 17 for extracting a part of light from the semiconductor laser of the light source 2 and a photodiode 18 for detecting the intensity of the light extracted by the beam sampler 17 are provided. It is assumed that the difference is different from the displacement measuring apparatus shown in FIG.
The output of the photodiode 18 is monitored by an oscilloscope 19. For example, in the measurement procedure shown in FIG. 5, after recording the interference fringe image in the initial state, the photodiode output I ₀ is detected and stored as the reference intensity. Then, after changing the pulse width, an interference fringe image is recorded and the photodiode output I is detected.
If the photodiode output I is different from the reference intensity I ₀ while being monitored by the oscilloscope 19, the injection current to the semiconductor laser is adjusted so that both values are substantially the same.
The detection of the photodiode output I and the adjustment of the injection current to the semiconductor laser may be performed each time the pulse width is changed. Photodiode output I may be taken into a personal computer via an AD converter or the like and automatically measured in cooperation with current injection into the semiconductor laser.
When detecting the contrast of the interference fringes while changing the pulse width of the pulsed light from the light source, changing the pulse width changes the total light amount of the acquired interference fringe image. For this reason, every time the pulse width is changed, the contrast detection accuracy changes, which may cause a measurement error.
In this embodiment, an irradiation light amount adjusting means for adjusting the amount of light emitted from the light source to the object to be measured is added to the configuration accompanying the change in the pulse width, and the measurement is performed according to the change in the pulse width. The amount of light applied to the object is adjusted.
Accordingly, since the entire light amount of the interference fringe image is always obtained regardless of the change in the pulse width, it is possible to suppress the change in contrast detection accuracy due to the change in the pulse width. Measurement errors due to changes in pulse width can be reduced.

In the displacement measuring apparatus according to the second embodiment, a part of the light from the semiconductor laser 2 is extracted and the irradiation light intensity is detected. However, this is merely an example, and in the present invention, for example, an interference fringe image is used. The brightness of the interference fringe image may be detected by detecting the CCD pixel intensity of the bright part of the interference fringe.
For example, in the measurement procedure of FIG. 5, after recording the interference fringe image in the initial state, the CCD pixel intensity I ₀ (x, y) constituting the bright part of the interference fringe is detected and stored as the reference intensity. . Then, after changing the pulse width, an interference fringe image is recorded, and the intensity I (x, y) at the same CCD pixel as before is detected.
If the intensity I (x, y) is different from the reference intensity I ₀ (x, y), the injection current to the semiconductor laser is adjusted so as to be almost the same value. It is sufficient to detect the CCD pixel intensity and adjust the injection current to the semiconductor laser each time the pulse width is changed.
According to the present invention, an irradiation light amount detection means for detecting the light amount of light irradiated from the light source to the object to be measured accompanying the change in the pulse width of the irradiation pulse light is added to the configuration. The amount of light irradiated to the object to be measured is adjusted based on the output of.
As a result, the entire light amount of the interference fringe image can always be obtained regardless of the change in the pulse width, so that the change in contrast detection accuracy due to the change in the pulse width can be suppressed, and the correlation data is not used. Therefore, there is no adjustment error in the amount of irradiation light due to the difference in conditions between the correlation data acquisition time and the measurement time. Measurement errors due to changes in pulse width can be reduced.
By providing the interference fringe imaging means with the function of the irradiation light quantity detection means, it is not necessary to add an additional component for light quantity detection. The apparatus configuration can be simplified and the apparatus cost can be reduced.

Schematic which showed the structure of the displacement measuring apparatus of the periodic movable object which concerns on the 1st Embodiment of this invention. FIG. 2 is a schematic diagram showing an image of a measurement surface observed by the optical system shown in FIG. 1 and the state of interference fringes generated on the measurement surface. Schematic of the jig | tool used for acquiring the correlation data of the displacement speed of a to-be-measured surface, and the contrast of an interference fringe. The graph of the correlation between displacement speed and contrast. The flowchart which shows the outline of a measurement procedure. Schematic which showed the structure of the displacement measuring apparatus of the periodic movable object which concerns on 2nd Embodiment. The schematic perspective view which shows the resonance mirror which is one term of a measuring object.

Explanation of symbols

A Periodic movable object velocity and displacement measuring device, 1 object to be measured (resonant mirror), 1a surface to be measured, 2 light source (semiconductor laser), 4 ND filter (irradiation light amount adjusting means), 5 interference optical system (lens), 6 Interfering optical system (beam splitter), 8 Imaging means (CCD camera), 9 Interfering optical system (mirror), 11 Calculator (computer), 11a Computer monitor, 12 Timing adjusting means (signal generator), 18 Irradiation light quantity detection Means (photodiode)

Claims (10)

  A light source for irradiating pulsed light to the object to be measured that moves substantially periodically; timing adjusting means for adjusting timing of displacement of the object to be measured and emission of pulsed light by the light source; and reflection from the object to be measured An interference optical system for causing light and reference light to interfere with each other, an imaging means for imaging an interference fringe by the interference optical system, a contrast of the interference fringe from an interference fringe image by the imaging means, and the interference fringe Calculating means for obtaining a displacement speed in a direction substantially normal to the surface of the object to be measured from a correlation between the contrast of the surface of the object to be measured and a displacement speed in a direction substantially normal to the surface of the object to be measured. Speed measuring device for periodic moving objects.   2. The irradiation light amount adjusting means for adjusting a light amount of light emitted from the light source to the object to be measured accompanying a change in a pulse width of the pulsed light from the light source. Speed measurement device for periodic movable objects.   The interference fringe image acquired by the imaging means is Fourier transformed, and the amplitude information of the complex amplitude or the square of the amplitude obtained by performing inverse Fourier transform after removing the inclination component of the interference fringe in the frequency space is used for the interference fringe. The apparatus for measuring a speed of a periodic movable object according to claim 1 or 2, wherein the contrast of   The displacement speed in the normal direction of the surface of the object to be measured is V, the wavelength of the light source is λ, the pulse width when the contrast of the interference fringes is almost lost is t, and V = λ / (2 · t The velocity measuring device for periodic movable objects according to claim 2, wherein V is obtained from the relationship of   The apparatus for measuring a speed of a periodic movable object according to claim 2, wherein the imaging means has a function of the irradiation light quantity detection means.   A light source for irradiating pulsed light to the object to be measured that moves substantially periodically; timing adjusting means for adjusting timing of displacement of the object to be measured and emission of pulsed light by the light source; and reflection from the object to be measured An interference optical system for causing light and reference light to interfere with each other, an imaging means for imaging an interference fringe by the interference optical system, a contrast of the interference fringe from an interference fringe image by the imaging means, and the interference fringe Calculating means for obtaining a displacement amount of the surface of the object to be measured in a substantially normal direction from a correlation between the contrast of the surface of the object to be measured and a displacement amount of the surface of the object to be measured in a substantially normal direction. Displacement measuring device for periodic movable objects.   The irradiation light quantity adjusting means for adjusting the light quantity of the light emitted from the light source to the object to be measured accompanying the change in the pulse width of the pulsed light from the light source. Displacement measuring device for periodic movable objects.   The interference fringe image acquired by the imaging means is Fourier-transformed, the amplitude component of the complex amplitude obtained by performing inverse Fourier transform after removing the interference fringe tilt component in the frequency space, or the square information of the amplitude is obtained as the interference fringe. The apparatus for measuring a displacement of a periodic movable object according to claim 6 or 7, wherein the contrast of   The displacement amount of the object to be measured is A, the wavelength of the light source is λ, the displacement frequency of the object to be measured is f, the pulse width when the contrast of the interference fringes is almost eliminated is t, and A = λ / The apparatus for measuring a displacement of a periodic movable object according to claim 7, wherein A is obtained from a relationship of (4 · f · t).   8. The periodic movable object displacement measuring device according to claim 7, wherein the imaging means has a function of the irradiation light quantity detection means.

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