JP2005331349A - Dynamic shape-measuring device, measuring method, and measurement error correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic shape-measuring device and a method capable of making the measurement accuracy of a polygon mirror stabilized. <P>SOLUTION: A threshold is provided in a peak wavenumber of an interference fringe recorded, corresponding to measurement accuracy required for measurement, and it is determined by a computer 10 whether the peak wavenumber is below the threshold, and thereby only the interference fringe having the peak wavenumber below the threshold is used for measurement. This device is provided with an optical system for irradiating the polygon mirror 1 with light from a semiconductor laser 2; an optical system for generating the interference fringe between reflected light from the polygon mirror 1 and reference light; a CCD camera 7 for imaging an interference fringe image of the polygon mirror 1, the computer 10 for detecting the peak wavenumber of the interference fringe in the interference fringe image, a computing unit 17 for determining the shape during operation of the polygon mirror 1; and a pulse generator 11 for adjusting a timing between the operation of the polygon mirror 1 and emission from the semiconductor laser 2. In the device, it is determined by the computer 10 whether the peak wavenumber is below the threshold, and thereby only the interference fringe having the peak wavenumber below the threshold is used for the measurement. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dynamic shape measuring apparatus and a dynamic shape measuring method for measuring a dynamic shape of a movable object that is a movable object to be measured that operates at a substantially constant period.

It has been known in the art to obtain the shape of a rotating polygon mirror surface by scanning the rotating polygon mirror surface with a laser beam and detecting the difference in tilt depending on the location of the mirror surface as a time difference (for example, patents). Reference 1).
In the polygon mirror dynamic surface shape measuring instrument disclosed in Patent Document 1, since a beam is scanned, a mechanical drive unit is required, and it takes a measurement time and a drive error becomes a measurement error.
Although the error of the mechanical drive unit is corrected by turning back the mirror, the number of components increases for correction, and error factors such as installation error and misalignment error increase.
Furthermore, since the in-plane spatial resolution depends on the beam diameter to be scanned, generally high spatial resolution cannot be expected, and if the beam diameter is reduced to increase the spatial resolution, the measurement time becomes enormous.
In the measurement apparatus for minute periodic vibration displacement disclosed in Patent Document 2, a slight difference is given between the period of the signal input to the object to be measured and the period of the signal for causing the light source to emit pulses, and The surface displacement is measured as a beat signal based on the difference between the two periods. However, in this disclosure, it is assumed that the surface displacement of the object to be measured is complete periodic vibration.
For example, since a polygon mirror performs mechanical rotational movement, it is difficult for the rotating mirror surface to always return to the same position at the nanometer level (order) due to rotational eccentricity of the mirror. That is, it is difficult to achieve a complete periodic motion. Therefore, since the apparatus of this disclosure detects a difference in period, a non-periodic component of the displacement of the object to be measured becomes a measurement error, and accurate measurement becomes difficult.

In the method disclosed in Patent Document 2, the surface displacement is captured and measured as still image data by instantaneously generating a light source in synchronism with a signal given to a measurement object that is displaced according to the signal. Yes.
Even in this method, if there is a non-periodic component in the movement of the object to be measured, the displacement to the object to be measured and the light emission of the light source cannot be synchronized, and it becomes difficult to obtain still image data and measurement is impossible.
In the simultaneous amplitude-contrast and quantitative phase-contrast microscopy methods disclosed in Non-Patent Document 1 and Non-Patent Document 2 by Fourier transform, optical application measurement, and numerical configuration of Fresnel off-axis hologram, the dynamic shape of the resonant mirror And measure the angle to the resonating base.
In addition, among other studies, there is a technique in which the dynamic shape of the resonant mirror and the angle with respect to the base in resonance are measured and measured by pulsed light interference and the phase shift method or the Fourier transform method. Further, there is a technique for measuring the rotational speed distribution of the object to be measured by generating interference fringes on the rotating polygon mirror surface and detecting the change in interference fringe contrast due to the rotational speed of the mirror.
Patent No. 3017998 Japanese Patent No. 3150239 "Fourier transform and applied optical measurement", Optical Technology Contact, Vol.36, No.2 (1998) "Simultaneous amplitude-contrast and quantitative phase-contrast microscopy by numerical construction of Fresnel off-axis holograms", Applied Optics (Applied Optic), 38, 34 (1999)

Both are so-called spatial modulation methods in which a single interference image is recorded and the surface shape of the object to be measured is obtained, and the shape is obtained from the spatial intensity distribution of the interference fringes. If the method of instantaneously emitting a light source in synchronism with a signal given to an object to be measured in Patent Document 2 is combined with the spatial modulation method, the dynamic shape of the object to be measured is measured from a single interference image recording. Can do.
Therefore, even if there is a non-periodic component in the movement of the object to be measured and the interference fringes are not completely stationary, the dynamic shape can be measured if the interference fringes are recorded in the image captured at an arbitrary timing. Therefore, even if the object to be measured has a non-periodic motion component such as a polygon mirror, the dynamic shape measurement can be performed.
However, the spatial modulation method has a property that, when the intensity distribution of interference fringes is spatially modulated by factors other than the shape of the object to be measured, a measurement error is caused thereby. In order to spatially modulate the interference fringes, it is necessary to give an inclination to the reflected light and the reference light of the object to be measured. If the inclination of both is increased, the peak wave number of the interference fringes increases.
Therefore, if the inclination of both is large, the spatial intensity distribution of the interference fringes is modulated due to the influence of aberrations of the optical system, etc. Therefore, the measurement error increases as the peak wave number of the interference fringes increases. When measuring an object with a large centimeter level (order), such as a polygon mirror, there are many off-axis rays, making it more susceptible to optical system aberrations, and the measurement error corresponding to the peak wavenumber tends to increase accordingly. .
In addition, if the non-periodic motion component is large, the peak wave number of the interference fringe will be different each time the interference fringe is recorded, so that the measurement accuracy will vary depending on the peak wave number of the recorded interference fringe each time measurement is performed. A malfunction occurs.
An object of the present invention is to consider the above-described situation, and in the dynamic shape measurement of an object having a non-periodic motion component, the peak wave number of the interference fringe changes every time the interference fringe is recorded. When the peak wave number of the interference fringe changes, the measurement accuracy becomes unstable because the shape measurement error due to spatial interference fringe modulation caused by factors other than the unevenness of the object to be measured changes. In order to avoid this, a threshold is provided for the peak wave number of the interference fringes recorded according to the measurement accuracy required for the measurement, and peak wave number inspection means for determining whether or not the peak wave number is equal to or less than the threshold is added to the configuration. Accordingly, it is an object of the present invention to provide a dynamic shape measuring apparatus and method that can use only interference fringes having a peak wave number equal to or less than a threshold value for measurement, thereby stabilizing measurement accuracy.

In order to solve the above-mentioned problem, a dynamic shape measuring apparatus according to claim 1 includes a pulse light source that emits pulsed light having a predetermined time width at a predetermined period and a movable object to be measured that operates at a substantially constant period. An irradiation optical system for irradiating light from the pulse light source, an interference optical system for generating an interference fringe between reflected light from the object to be measured and reference light, and an interference fringe image of the object to be measured An imaging means for imaging, a detecting means for detecting a peak wave number of the interference fringe in the interference fringe image, and a phase of the interference fringe based on the interference fringe image of the object to be measured by the imaging means and the peak wave number of the interference fringe A spectrum is obtained, calculation means for obtaining the shape of the object under operation from the phase spectrum, and timing of the operation of the object to be measured and emission of the pulsed light source to generate the interference fringes. Taimi The apparatus for measuring a dynamic shape of a movable object, comprising: a peak adjustment unit for determining whether or not the peak wave number of the interference fringes is within a predetermined value range. And
The dynamic shape measuring apparatus according to claim 2, in order to suppress the wave number of the interference fringe to a predetermined value or less, detect the wave number of the interference fringe, adjust the timing of the measured object operation-pulse light source emission, It is characterized by comprising interlocking means for interlocking with the imaging of the interference fringe image.
The dynamic shape measuring apparatus according to claim 3, wherein the interference fringe peak wave number detection, the measurement object operation-pulse light source emission timing adjustment, the interference fringe image imaging, the measurement object reflected light, and the reference light are detected. An interlocking means for interlocking with the adjustment of the relative inclination is provided.

The dynamic shape measuring apparatus according to claim 4, wherein a second light source for irradiating the object to be measured from a direction other than the optical axis of the irradiation optical system, and the light from the second light source. It is characterized by comprising a light receiving element for detecting reflected light from the object to be measured and an arithmetic means for obtaining light source light emission timing based on the output of the light receiving element.
The dynamic shape measuring apparatus according to claim 5 is characterized in that the peak wave number detecting means of the interference fringes is a Fourier transform calculator.
The dynamic shape measuring method according to claim 6 irradiates light from the pulse light source to a pulse light source that emits pulse light having a predetermined time width at a predetermined period and a movable object to be measured that operates at a substantially constant period. An irradiating optical system, an interference optical system for generating an interference fringe between the reflected light from the object to be measured and a reference light, an imaging means for capturing an interference fringe image of the object to be measured, and A detection means for detecting a peak wave number of the interference fringe in the interference fringe image; a phase spectrum of the interference fringe is obtained based on the interference fringe image of the object to be measured by the imaging means and the peak wave number of the interference fringe; Dynamic form comprising computing means for obtaining the shape of the measurement object during operation, and timing adjustment means for adjusting the timing of the operation of the measurement object and emission of the pulsed light source to generate the interference fringes In the dynamic shape measuring method for measuring the dynamic shape of a movable object using a measuring device, when the object to be measured is a rotating polyhedron, the operation of the object to be measured and pulsed light irradiation to the object to be measured By adjusting the timing, a predetermined surface of the rotating polyhedron is selected as a surface to be measured, and an interference fringe image of the surface to be measured is captured.

The dynamic shape measurement error correction method according to claim 7 includes: a pulsed light source that emits pulsed light having a predetermined time width at a predetermined period; and a light from the pulsed light source that is movable at a substantially constant period. Irradiating optical system for irradiating light, interference optical system for generating interference fringes between reflected light from the object to be measured and reference light, and imaging means for capturing an interference fringe image of the object to be measured And detecting means for detecting a peak wave number of the interference fringe in the interference fringe image; obtaining a phase spectrum of the interference fringe based on the interference fringe image of the object measured by the imaging means and the peak wave number of the interference fringe; Calculation means for determining the shape of the object under operation during operation, and timing adjustment means for adjusting the timing of the operation of the object under test and emission of the pulsed light source to generate the interference fringes In the dynamic shape measurement error correction method for correcting the measurement error of the dynamic shape of the movable object using the dynamic shape measurement device, the shape due to the spatial distortion of the interference fringes caused by other than the shape of the measurement object A measurement error is obtained in advance, and is subtracted from the measured dynamic shape value of the object to be measured, thereby correcting the shape measurement error due to the spatial distortion of the interference fringes.
The dynamic shape measurement error correction method according to claim 8, wherein the shape measurement error due to the spatial distortion of the interference fringes is obtained by measuring an arbitrary surface having a known shape with the dynamic shape measurement device. It is characterized by doing.
The dynamic shape measurement error correction method according to claim 9, wherein the shape measurement error due to the spatial distortion of the interference fringes is obtained by performing a ray tracing simulation of the locus of the reflected light of the object measured by the imaging optical system. It is characterized by doing.
The dynamic shape measurement error correction method according to claim 10, wherein a shape measurement error due to a spatial distortion of the interference fringes is acquired in advance for each peak wave number of the interference fringes, and the object to be measured is dynamically In accordance with the peak wave number of the interference fringe imaged when measuring the shape, correction is performed using the shape measurement error acquired for each peak wave number of the interference fringe.

According to the present invention, a threshold value is provided for the peak wave number of interference fringes recorded according to the measurement accuracy required for measurement, and a peak wave number inspection means for determining whether the peak wave number is equal to or less than the threshold value is added to the configuration. Therefore, only interference fringes whose peak wave number is equal to or less than the threshold value are used for measurement. Thereby, the measurement accuracy can be stabilized.
In addition, the shape measurement error associated with the spatial modulation was obtained by actual measurement and used to correct the measurement results. However, if the level of the spatial modulation of the interference fringes other than the shape of the object to be measured can be estimated, the shape measurement error is obtained as an estimated value. be able to.
Furthermore, because the component of the measurement optical system's aberration is a major factor in spatially modulating interference fringes other than the shape of the object being measured, the level of interference fringe spatial modulation due to aberrations in the measurement optical system is estimated, and the shape is measured from there. By estimating the error, it is possible to acquire a shape measurement error accompanying spatial modulation during measurement.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic perspective view showing an example of a movable object to be measured in the present invention. FIG. 1 shows a polygon mirror used in a writing optical system of an image device such as a laser printer or a digital copying machine.
The polygon mirror 1 rotates at high speed around the axis 1b, and scans the light beam irradiated from the light source onto the polygon mirror surface (1a in the figure) at high speed. The rotation speed of the polygon mirror is determined according to the writing speed required for the image equipment.
In recent polygon mirrors that require high-speed writing and high-speed rotation, the mirror surface 1a may be deformed due to the influence of heat or centrifugal force accompanying rotation. Since the beam reflected by the deformed surface does not form an image at a predetermined position, there is a demand for accurately measuring and evaluating the surface shape of the polygon mirror 1 during high-speed rotation.
An interferometer can be used for measuring the surface shape of the polygon mirror 1 in a stationary state. However, since the interference fringes cannot be observed when the mirror surface rotates, the rotating polygon mirror surface shape cannot be measured. As a method for measuring the surface shape of a rotating polygon mirror, it is described in the above-mentioned prior art.
Examples of a method for obtaining a surface shape of an object to be measured by recording a single interference image include interference fringes such as a Fourier transform method (Non-Patent Document 1) and an off-axis digital holography method (Non-Patent Document 2). There is a so-called spatial modulation method in which a shape is obtained from the spatial intensity distribution.

FIG. 2 is a schematic view showing a first embodiment of the configuration of the dynamic shape measuring apparatus according to the present invention. FIG. 2 shows an ND filter 3 and a beam expander 4 for adjusting the intensity of light from the semiconductor laser 2 as a light source that emits pulsed light having a predetermined pulse width.
The light of the semiconductor laser 2 is collimated by a beam shaping lens and a collimating lens (not shown). A part of the light expanded by the beam expander 4 passes through the beam splitter 5, and a part thereof is reflected by the beam splitter 5.
The light that has passed through the beam splitter 5 is irradiated to the device under test 1 (polygon mirror), and the light reflected by the device under test 1 travels back along the incoming optical path and is reflected by the beam splitter 5 to pass through the lens 6. To the CCD camera 7.
On the other hand, the light reflected by the beam splitter 5 irradiates the reference mirror 8, and the light reflected by the reference mirror 8 travels back through the optical path that has arrived, passes through the beam splitter 5, and passes through the lens 6. To reach the CCD 7.
For the object light reflected by the DUT 1 and the reference light reflected by the reference mirror 8, the difference between the optical path length of the object light and the optical path length of the reference light is made equal to or less than the coherence length of the semiconductor laser 2 as the light source. If it is set and the optical axes of the object beam and the reference beam are substantially coincident with each other, they cause interference to generate interference fringes.
The position of the lens 6 is adjusted so that the image of the DUT 1 is formed on the imaging surface of the CCD camera. The DUT 1 is a polygon mirror as shown in FIG.
Interference fringes generated between the object light and the reference light are picked up by the CCD camera 7, captured by the frame grabber 9, transferred to the computer 10, stored in the memory of the computer 10, and monitored by the computer 10. Is displayed.

If the DUT 1 is an object that is displaced in a direction substantially parallel to the optical axis of the optical system in FIG. 2, the DUT 1 can be irradiated with pulsed light at any timing during the operation of the DUT 1. However, in the case of a polyhedron having a plurality of surfaces, the angle of the surface to be measured with respect to the optical axis of the optical system changes during operation as in the polygon mirror 1, the object to be measured 1 moves along with the rotation of the object to be measured 1. The angle of the surface when irradiated with light changes with time.
For this reason, the interference fringe image cannot be observed because the measured object reflected light and the reference light do not interfere at any timing. Therefore, it is necessary to adjust the timing between the rotation of the object to be measured and the irradiation of the pulsed light after synchronizing.
In FIG. 2, a pulse generator 11 outputs a signal to a polygon mirror driver 12 for rotating the polygon mirror 1. The pulse generator 11 has two or more channels, and outputs a trigger signal for irradiating the semiconductor laser driver 13 with pulsed light using channels other than the signal output to the polygon mirror driver 12.
By using the signal from the same pulse generator 11, the driving of the polygon mirror 1 and the pulsed light irradiation can be synchronized. For example, if the rotation speed of the polygon mirror 1 is 1800 rpm, the frequency at which a specific surface of the polygon mirror 1 returns to the same position is 30 Hz.

FIG. 3 is a diagram for explaining the phase adjustment of the signal to the polygon mirror and the signal to the semiconductor laser driver. Therefore, the emission trigger signal is repeatedly output to the semiconductor laser driver 13 at a frequency of 30 Hz, until the interference fringes on a specific surface of the polygon mirror 1 can be observed, as shown in FIG. The phase of the signal to the laser driver 13 is adjusted.
The phase adjustment may be performed using a phase adjustment function between channels using a rotary knob or the like possessed by the pulse generator 11. By adjusting the phase between the channels, an arbitrary surface of the polygon mirror 1 becomes substantially perpendicular to the optical axis of the optical system, and interference fringes generated on the surface of the polygon mirror 1 can be observed.
When measuring a specific surface, the surface is marked and phase adjustment is performed until the interference fringes on the marked surface are observed. In the above description, the emission frequency of the semiconductor laser 2 is made to coincide with the rotational frequency of the polygon mirror 1, but interference fringes can be observed similarly even if the emission frequency of the semiconductor laser 2 is set to a divisor of the rotational frequency of the polygon mirror 1. .
When the emission frequency of the semiconductor laser 2 exceeds the imaging frequency (frame rate) of the CCD camera 7, an interference image is obtained by averaging only the integer value of the quotient obtained by dividing the emission frequency of the semiconductor laser 2 by the imaging frequency of the CCD camera 7. Will be.
When the emission frequency of the semiconductor laser 2 is lower than the imaging frequency of the CCD camera 7, an image can be taken without omission by triggering the CCD camera driver 14 in synchronization with the emission of the semiconductor laser 2.
In the above description, the light emission of the semiconductor laser 2 and the rotation of the polygon mirror (measurement object) 1 are synchronized. However, the same effect can be obtained by synchronizing the imaging of the CCD camera 7 and the rotation of the polygon mirror 1.
Further, the pulsed light from the semiconductor laser 2 may be generated by applying linear modulation, or may be generated by applying pulse modulation. As the pulse light source, not only the semiconductor laser 2 but also another pulse laser such as a solid-state laser may be used.

・・・（１）
ここで、ｆはポリゴンミラーの回転周波数、他の記号は図５に示した通りである。ポリゴンミラー１の変位速度に対して光源のパルス発光幅が十分速い、すなわち時間的に短ければ、ポリゴンミラー１面の全面で十分コントラストの高い干渉縞が得られる。
図４の干渉縞において、ポリゴンミラー１面反射光の光軸と参照光の光軸が略一致したとき干渉縞の本数は最も少なくなるが、ここでは単一干渉縞画像からポリゴンミラー１面の表面形状を求めるために、干渉縞に空間的な変調を掛ける。
すなわちポリゴンミラー１面反射光と参照光の光軸を傾けて多数の干渉縞を発生させる。そしてポリゴンミラー１面の表面に凹凸があると、凹凸により干渉縞の明暗分布が変化するため、その変化を検出することによりポリゴンミラー１面の表面形状を求めることができる。そのような形状測定法は空間変調法と呼ばれる。
ポリゴンミラー１を測定する場合、ポリゴンミラー１の回転平面と垂直な方向（ここではＹ方向と呼ぶ）におけるポリゴンミラー１面反射光と参照光との傾きは、参照ミラー８かポリゴンミラー１かのどちらかをＹ方向に傾けておくことにより与えることができる。
またポリゴンミラー１の回転平面と平行な方向（ここではＸ方向と呼ぶ）におけるポリゴンミラー１面反射光と参照光との傾きは、ポリゴンミラー１に供給する信号と半導体レーザ光源２を発光させるための信号のタイミングを調整することにより与えることができる。ポリゴンミラー１面反射光と参照光の光軸との傾きが大きくなるほど干渉縞の本数が多くなる。 FIG. 4 is a diagram showing an image of a polygon mirror surface observed by the optical system of FIG. 2 and interference fringes generated on the polygon mirror surface. FIG. 4 shows an image of the polygon mirror surface 1a observed by the optical system of FIG. 2 and the state of the interference fringes 1d generated on the polygon mirror surface. Reference numeral 10a represents a computer monitor.
FIG. 5 is a diagram showing a state of out-of-plane displacement accompanying rotation in the polygon mirror. Referring to FIG. 5, since the distance r from the center of the polygon mirror changes in accordance with the distance x from the center of the polygon mirror surface, the displacement speed V varies depending on the location on the polygon mirror surface, as shown in Equation (1). expressed.

... (1)
Here, f is the rotational frequency of the polygon mirror, and other symbols are as shown in FIG. If the pulse emission width of the light source is sufficiently fast, that is, temporally short with respect to the displacement speed of the polygon mirror 1, interference fringes with sufficiently high contrast can be obtained on the entire surface of the polygon mirror 1.
In the interference fringes in FIG. 4, the number of interference fringes is the smallest when the optical axis of the reflected light on the polygon mirror 1 surface and the optical axis of the reference light are substantially the same. In order to obtain the surface shape, spatial modulation is applied to the interference fringes.
That is, many interference fringes are generated by tilting the optical axes of the polygon mirror 1 surface reflection light and the reference light. If the surface of the polygon mirror 1 is uneven, the light / dark distribution of the interference fringes changes due to the unevenness, so that the surface shape of the polygon mirror 1 surface can be obtained by detecting the change. Such a shape measuring method is called a spatial modulation method.
When measuring the polygon mirror 1, the inclination of the polygon mirror 1 surface reflected light and the reference light in the direction perpendicular to the plane of rotation of the polygon mirror 1 (referred to herein as the Y direction) is either the reference mirror 8 or the polygon mirror 1. Either can be given by tilting in the Y direction.
In addition, the inclination of the polygon mirror 1 surface reflected light and the reference light in a direction parallel to the plane of rotation of the polygon mirror 1 (referred to herein as the X direction) causes the signal supplied to the polygon mirror 1 and the semiconductor laser light source 2 to emit light. Can be provided by adjusting the timing of the signal. The greater the inclination between the polygon mirror one-surface reflected light and the optical axis of the reference light, the greater the number of interference fringes.

・・・（２）
式（２）において、形状測定に不要な項ａ（ｘ，ｙ）、ｂ（ｘ，ｙ）を除去し、ポリゴンミラー１面反射光の位相φ（ｘ，ｙ）を抽出して、それを形状に変換することにより、表面形状が求められる。
空間変調法では参照光と物体反射光との間に傾きをあたえた状態で両者を干渉させることにより、式（３）に示されるような空間キャリヤ周波数ｆＸ０とｆＹ０を有する干渉縞を得る。

・・・（３） Regarding the calculation processing method for obtaining the shape from the interference fringe image, the intensity distribution of the spatially modulated interference fringe is expressed by the following equation (2). In Expression (2), x and y represent coordinates on the imaging surface of the CCD camera 7.
I (x, y) is an interference fringe intensity distribution, a (x, y) is an interference fringe background intensity distribution, b (x, y) is an interference fringe amplitude distribution, and φ (x, y) is a polygon mirror 1. This represents the phase distribution of interference fringes corresponding to the surface shape.

... (2)
In the expression (2), the terms a (x, y) and b (x, y) unnecessary for the shape measurement are removed, the phase φ (x, y) of the polygon mirror 1 surface reflection light is extracted, By converting into a shape, the surface shape is determined.
In the spatial modulation method, interference fringes having spatial carrier frequencies fX0 and fY0 as shown in Expression (3) are obtained by causing the reference light and the object reflected light to interfere with each other with an inclination.

... (3)

・・・（４）

・・・（５）
空間キャリヤ周波数ｆＸ０とｆＹ０に対してバックグラウンド強度分布ａ（ｘ，ｙ）や干渉縞の複素振幅分布ｃ（ｘ，ｙ）の変化が緩やかであれば、各スペクトルがキャリヤ周波数により分離される。
このため、式（４）における第２項の成分のみを抽出し、フーリエスペクトル座標における原点の位置に移動することにより空間キャリヤ周波数ｆＸ０とｆＹ０を取り除き、Ｃ（ｆＸ，ｆＹ）を得ることができる。
空間キャリヤ周波数ｆＸ０とｆＹ０は、干渉縞画像をフーリエ変換したときのＸ方向、Ｙ方向のピーク波数からそれぞれ求めることができる。スペクトルＣ（ｆＸ，ｆＹ）の逆フーリエ変換により式（５）の複素振幅分布が得られる。
得られた複素振幅の虚部と実部の比のアークタンジェントをとることにより式（６）のように位相φ（ｘ，ｙ）を求めることができ、式（６）の位相を形状に変換することにより被測定物の表面形状を求めることができる。

・・・（６） When the interference image of Equation (3) is Fourier transformed with respect to the variables x and y, a two-dimensional spatial frequency spectrum as shown in Equation (4) is obtained. Here, * is a complex conjugate, A (fX, fY) is the Fourier spectrum of a (x, y), and C (fX, fY) is the complex amplitude distribution c () of the interference fringes expressed by Equation (5). x, y) represents the Fourier spectrum.

... (4)

... (5)
If the background intensity distribution a (x, y) and the interference amplitude complex amplitude distribution c (x, y) change gradually with respect to the spatial carrier frequencies fX0 and fY0, the respective spectra are separated by the carrier frequency.
Therefore, by extracting only the component of the second term in Equation (4) and moving to the position of the origin in the Fourier spectrum coordinates, the spatial carrier frequencies fX0 and fY0 can be removed, and C (fX, fY) can be obtained. .
Spatial carrier frequencies fX0 and fY0 can be obtained from peak wavenumbers in the X and Y directions when the interference fringe image is Fourier transformed. The complex amplitude distribution of Expression (5) is obtained by inverse Fourier transform of the spectrum C (fX, fY).
By taking the arc tangent of the ratio between the imaginary part and the real part of the obtained complex amplitude, the phase φ (x, y) can be obtained as in equation (6), and the phase in equation (6) is converted into a shape. By doing so, the surface shape of the object to be measured can be obtained.

... (6)

In the above method, the interference fringes are almost stationary if the light emission period of the pulsed light from the semiconductor laser 2 and the rotation period of the polygon mirror 1 substantially coincide with each other. The rotation period slightly shifts depending on the component, and the peak wave number in the X direction of the carrier interference fringe varies with the rotation.
Further, when the peak wave number of the carrier interference fringe is increased, the intensity distribution of the interference fringe is distorted due to the influence of optical system aberrations and the like, so that the measurement error increases. Therefore, a peak wave number of interference fringes that can be allowed for the required measurement accuracy is obtained in advance, and after the interference fringe image is recorded at the time of measurement, two-dimensional Fourier transform is performed.
By comparing the peak wave numbers in the X and Y directions detected by the two-dimensional Fourier transform with the allowable interference fringe peak wave number, it is determined whether or not the recorded interference fringes can be used for measurement. Only interference fringes are used for shape calculation.
Repeat interference fringe recording operation until usable interference fringes can be recorded. By using an interference fringe having an allowable interference fringe peak wave number or less for measurement, stable measurement accuracy can be obtained without being affected by fluctuations in the interference fringe peak wave number.
The method of obtaining the allowable interference fringe peak wave number is, for example, by measuring the stationary polygon mirror 1 while changing the peak wave number of the interference fringe by changing the inclination of the object to be measured (polygon mirror) 1 or the reference light. What is necessary is just to obtain | require measurement accuracy and to obtain | require the upper limit of the interference fringe peak wave number which satisfy | fills permissible measurement accuracy.

FIG. 6 is a flowchart showing a process flow for determining whether or not to use interference fringes. In FIG. 6, Kx and Ky are peak wave numbers in the X direction and Y direction of the carrier interference fringes, respectively, and Kt is an allowable value of the peak wave number.
In FIG. 6, interference fringes are recorded (S1), and Kx and Ky are detected (S2). Thereafter, it is determined whether or not Kx ≦ Kt and Ky ≦ (S3), and if so, shape measurement calculation is performed (S4). If Kx ≦ Kt and Ky ≦ are not satisfied in step (S3), steps (S1) and (S2) are repeated.
In the first embodiment, the peak wave number of the interference fringes is adjusted by adjusting the phase between channels of the pulse generator 11 that supplies a signal for rotating the polygon mirror 1 and a signal for emitting the semiconductor laser 2 to the drivers 12 and 13. Then, the peak wave number of the interference fringes in the recorded interference image was detected, and the detected peak wave number was compared with the allowable peak wave number.
As a result of comparison, if the recorded interference fringe image cannot be used for measurement, the interference image is recorded again and the above operation is repeated. Therefore, it takes time to obtain an interference image having a predetermined peak wave number unless the measurer is skilled. It was.

The personal computer 10 and the pulse generator 11 in FIG. 2 are connected via a digital output board, the peak wave number in the X direction of the interference fringes is obtained from the recorded interference image, and a predetermined phase is applied to the pulse generator 11 according to the peak wave number. Input the adjustment signal.
Interference fringe recording → Calculation of peak wave number in X direction → Phase adjustment signal calculation → Input of phase adjustment signal to pulse generator 11 → Interference fringe recording Repeats automatically until Since automatic adjustment is performed, interference fringes having a predetermined peak wave number can be acquired without requiring skill of the measurer.
In the above description, only the peak wave number in the X direction of the interference fringes can be adjusted, but even a device to be measured that originally operates in one direction may be moved in another direction due to an arbitrary error factor. For example, the polygon mirror 1 originally does not move in the direction in which the mirror surface bows with rotation, but may actually move due to surface tilt or rotational eccentricity, and may change the peak wavenumber of the interference fringes in the Y direction. .
In that case, either the polygon mirror 1 or the reference mirror 8 in FIG. 2 is mounted on a stage with a tilt mechanism so that the peak frequency of interference fringes in the Y direction can be adjusted.
A motor is attached and the stage has an automatic adjustment function. The stage is connected to a personal computer via a pulse controller for the stage, and the peak wave number in the Y direction of the interference fringes is obtained from the recorded interference image. Input the adjustment signal.
Interference fringe recording → X direction peak wave calculation → Phase adjustment signal calculation → Phase adjustment signal input to pulse generator 11 → Y direction peak wave number calculation → tilt adjustment signal calculation → tilt adjustment signal input to stage → Interference fringe recording A series of operations are automatically repeated until the peak wave numbers of the interference fringes in the X and Y directions are both equal to or less than the threshold value. Since automatic adjustment is performed, interference fringes having a predetermined peak wave number can be acquired without requiring skill of the measurer.

FIG. 7 is a schematic view showing a second embodiment of the configuration of the dynamic shape measuring apparatus according to the present invention. In the second embodiment, a second semiconductor laser 15 for irradiating light to the polygon mirror 1 and a photodiode 16 for receiving reflected light from the polygon mirror 1 are provided.
Light from the second semiconductor laser 15 is collimated by a beam shaping lens and a collimating lens (not shown). The arithmetic unit 17 is provided for converting the output of the photodiode into current and voltage, counting the reflected light output from each surface of the polygon mirror, and outputting a pulse after counting a predetermined number of times.
When the number of surfaces of the polygon mirror 1 is 6, since one cycle is obtained by counting 6 times, one pulse is output when the reflected light output is counted 6 times. The output from the calculator 17 is input to the pulse generator 11, and a trigger signal is output to the semiconductor laser driver 13 in synchronization with the signal input from the calculator 17. The second semiconductor laser 15 emits light in response to a trigger signal from the pulse generator 11.
If the output timing from the photodiode 16 is matched with the angle of the polygon mirror 1 surface relative to the optical axis of the optical system, the angle of the polygon mirror surface relative to the optical axis of the measuring optical system can be grasped by detecting the output of the photodiode 16. .
For this reason, even if the rotation of the polygon mirror 1 suddenly fluctuates at a high frequency, the sudden high frequency fluctuation of the interference fringes can be suppressed by the pulsed light irradiation synchronized with the output detection of the photodiode 16. Thereby, the interference fringe peak wave number can be easily adjusted to a predetermined threshold value or less.
When the spot of the second semiconductor laser 15 irradiated to the polygon mirror 1 for detecting the rotational frequency fluctuation is observed in the interference image, a light source having a wavelength different from that for the interference fringe observation is used, and the CCD camera 7 is in front. In addition, by installing a bandpass filter that can transmit only the wavelength for observing interference fringes, the spot of the second semiconductor laser 15 that is irradiated for detecting the rotational frequency fluctuation can be removed from the interference image.
Further, the peak wave number detection of the interference fringes may be performed by detecting the number of interference fringes by image processing. However, if the peak wave number is obtained by Fourier transform, higher speed calculation is possible.

In the configuration of the first embodiment, a reference mirror is installed as an object to be measured instead of the polygon mirror 1. The reference mirror (not shown) has a shape B (x, y) measured by a separate general shape measuring device. x and y are coordinates representing the positions in the x and y directions on the imaging surface of the CCD camera 7, respectively.
The reference mirror may be either a movable object or a non-movable object (stationary object), but in the case of a movable object, an object that does not deform due to its operation, for example, a mirror with sufficient thickness, etc., is preferable. .
As long as the surface accuracy is sufficiently guaranteed with respect to the accuracy required for the apparatus, the mirror may be treated as an ideal plane having a shape error B (x, y) of zero. Here, a description will be given assuming that the reference mirror is a non-movable object.
After setting the reference mirror as an object to be measured, an interference fringe is generated. Either the reference mirror or the reference mirror 8 is tilted and the interference fringes are spatially modulated with a predetermined peak wavenumber, and the shape S (x, y) of the reference mirror is obtained by the method described above for the first embodiment.
Since {S (x, y) −B (x, y)} is a shape measurement error E (x, y) accompanying spatial modulation, it is stored. If the measurement is performed with the reference mirror tilted for the interference fringe spatial modulation in the x direction and the reference mirror 8 tilted for the interference fringe spatial modulation in the y direction, it is convenient because the state becomes close to the actual measurement.
After setting the polygon mirror as the object to be measured in the measuring apparatus, the measurement is performed to obtain the polygon mirror shape P (x, y). By subtracting E (x, y) from P (x, y), a measurement result in which a shape error associated with spatial modulation is corrected is obtained.
If the shape error associated with spatial modulation can be corrected, the interference fringe peak wave number threshold in measurement can be increased, thereby increasing the probability of obtaining interference fringes that can be used in measurement and reducing measurement time. Measurement operability can be improved. Furthermore, the in-plane spatial resolution of measurement can be improved.

In the method described above, the shape measurement error due to spatial modulation was obtained by actual measurement and used to correct the measurement result.However, if the level of spatial modulation of interference fringes other than the shape of the object to be measured can be estimated, the shape measurement error is used as the estimated value. Can be acquired. For this purpose, a ray tracing simulation is performed by modeling optical components used in the measurement optical system.
The reason for the spatial modulation of interference fringes other than the shape of the object being measured is that the aberration component of the measurement optical system is large. By estimating, it is possible to obtain a shape measurement error accompanying spatial modulation during measurement. Thereafter, the shape measurement error associated with the spatial modulation in the measurement can be corrected by the method described above.
In the method described above, the shape error associated with the spatial modulation is acquired only at a single predetermined interference fringe peak wave number. However, if the shape measurement error is acquired for each of the plurality of interference fringe peak wave numbers, the correction accuracy is improved. The range of application can be expanded.
The above-described shape measurement error acquisition method at a predetermined peak wave number is performed for a plurality of interference fringe peak wave numbers, and the shape measurement error is acquired for each peak wave number. The method of the present invention can be implemented by selecting a shape measurement error according to the peak wave number of the interference fringes recorded at the time of measurement and using it for correction.

According to the present invention, the interlocking means for cooperatively operating the interference fringe peak wave number detection, the measured object operation-light source light emission timing adjustment, and the interference fringe image capturing is added to the configuration, and these are cooperated. Thus, the peak wave number of the interference fringes is reduced below the set threshold value. Measurement time can be shortened and operability can be improved.
By adding a means for adjusting the relative inclination between the reflected light of the object to be measured and the reference light in the direction substantially perpendicular to the operation plane of the object to be measured, in the direction substantially perpendicular to the operation plane of the object to be measured. The peak wave number of the interference fringes can be adjusted. Thereby, the peak wave number of the interference fringes can be reduced below the set threshold value, the measurement time can be shortened, and the operability can be improved.
According to the present invention, the operation of the object to be measured and the timing adjustment of the light source emission are configured by the light source, the light receiving element, and the arithmetic unit for obtaining the light source light emission timing based on the light receiving element output. Automates and speeds up operation and timing adjustment of light emission. This facilitates acquisition of interference fringes having a peak wave number below a predetermined threshold. The present invention can improve the operability of measurement and shorten the measurement time even if the non-periodic motion component of the object to be measured is a high frequency.
According to the present invention, a shape measurement error due to the spatial distortion of the interference fringes caused by other than the shape of the object to be measured is obtained in advance, and the error is corrected by subtracting from the dynamic shape measurement value. Measurement accuracy fluctuation can be suppressed. As a result, the measurement time can be shortened, the measurement operability can be improved, and further, the in-plane spatial resolution of the measurement can be improved.
According to the present invention, the correction data is acquired for each peak wave number of the interference fringes, and the measurement data fluctuation is suppressed by using the optimum correction data according to the peak wave number of the interference fringes recorded during the measurement. Since the peak wave number threshold value can be set to a large value, the measurement time can be shortened and the measurement operability can be improved by using correction data corresponding to the peak wave number of the captured interference fringes.

The schematic perspective view which shows an example of the movable object used as a measuring object in this invention. BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows 1st Embodiment of a structure of the dynamic shape measuring apparatus by this invention. The figure explaining the phase adjustment of the signal to a polygon mirror, and the signal to a semiconductor laser driver. The figure which shows the mode of the interference fringe which generate | occur | produced on the image of the polygon mirror surface observed with the optical system of FIG. The figure which shows the mode of the out-of-plane displacement accompanying rotation in a polygon mirror. The flowchart which shows the usability determination processing flow of an interference fringe. Schematic which shows 2nd Embodiment of the structure of the dynamic shape measuring apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measured object (polygon mirror), 2 pulse light source (semiconductor laser), 3 irradiation optical system (ND filter), 4 irradiation optical system (beam expander), 5 interference optical system (beam splitter), 6 imaging optical system (Lens), 7 imaging means (CCD camera), 8 interference optical system (reference mirror), 10 computer (interference fringe peak wave number detection means), 10a computer monitor, 11 timing adjustment means (pulse generator, peak wave number detection) Means), 12 polygon mirror driver, 13 semiconductor laser driver, 14 CCD camera driver, 15 second light source (second semiconductor laser), 16 light receiving element (photodiode, peak wave number inspection means), 17 computing unit (timing adjustment) Means, interference fringe peak wave number detection means)

Claims (10)

  A pulsed light source that emits pulsed light of a predetermined time width at a predetermined period, an irradiation optical system for irradiating light from the pulsed light source to a movable measured object that operates at a substantially constant period, and the measured object An interference optical system for generating an interference fringe between the reflected light and the reference light, an imaging means for capturing an interference fringe image of the object to be measured, and detecting a peak wave number of the interference fringe in the interference fringe image Calculation for obtaining the phase spectrum of the interference fringe based on the interference fringe image of the object to be measured and the peak wave number of the interference fringe by the detection means and the shape of the object under operation from the phase spectrum In the apparatus for measuring a dynamic shape of a movable object comprising: means for adjusting the timing of the operation of the object to be measured and the light emission of the pulse light source in order to generate the interference fringes. Dynamic shape measuring apparatus in which the peak wavenumber, characterized in that it comprises a peak wavenumber inspection means for determining whether or not within a predetermined value range of stripes.   In order to suppress the wave number of the interference fringe to a predetermined value or less, interlocking means for linking the detection of the wave number of the interference fringe, the timing adjustment of the measurement object operation-pulse light source emission, and the imaging of the interference fringe image. The dynamic shape measuring apparatus according to claim 1, further comprising:   Interlock means for interlocking detection of the peak wave number of the interference fringe, operation of the object to be measured-pulse light source emission, imaging of the interference fringe image, and adjustment of the relative inclination of the object reflected light and the reference light The dynamic shape measuring apparatus according to claim 1, wherein:   A second light source for irradiating the object to be measured from a direction other than the optical axis of the irradiation optical system, and light reception for detecting light reflected by the object to be measured from the second light source. 2. The dynamic shape measuring apparatus according to claim 1, further comprising: an element; and a calculation means for obtaining a light source emission timing based on the output of the light receiving element.   2. The dynamic shape measuring apparatus according to claim 1, wherein the interference fringe peak wave number detecting means is a Fourier transform calculator.   A pulsed light source that emits pulsed light of a predetermined time width at a predetermined period, an irradiation optical system for irradiating light from the pulsed light source to a movable measured object that operates at a substantially constant period, and the measured object An interference optical system for generating an interference fringe between the reflected light and the reference light, an imaging means for capturing an interference fringe image of the object to be measured, and detecting a peak wave number of the interference fringe in the interference fringe image A calculation means for obtaining a phase spectrum of the interference fringe based on the interference fringe image of the object to be measured by the detecting means and the imaging means and the peak wave number of the interference fringe, and obtaining the shape of the object under operation from the phase spectrum Dynamic shape of a movable object using a dynamic shape measuring device comprising: means; and timing adjusting means for adjusting timing of operation of the object to be measured and light emission of the pulse light source to generate the interference fringes In the dynamic shape measuring method to be measured, when the object to be measured is a rotating polyhedron, by adjusting the timing of the operation of the object to be measured and pulsed light irradiation to the object to be measured, a predetermined in the rotating polyhedron A dynamic shape measuring method comprising: picking an interference fringe image of a surface to be measured by selecting the surface of the surface to be measured.   A pulsed light source that emits pulsed light of a predetermined time width at a predetermined period, an irradiation optical system for irradiating light from the pulsed light source to a movable measured object that operates at a substantially constant period, and the measured object An interference optical system for generating an interference fringe between the reflected light and the reference light, an imaging means for capturing an interference fringe image of the object to be measured, and detecting a peak wave number of the interference fringe in the interference fringe image Calculation for obtaining the phase spectrum of the interference fringe based on the interference fringe image of the object to be measured and the peak wave number of the interference fringe by the detection means and the shape of the object under operation from the phase spectrum Dynamic shape of a movable object using a dynamic shape measuring device comprising: means; and timing adjusting means for adjusting timing of the operation of the object to be measured and light emission of the pulse light source to generate the interference fringes In the dynamic shape measurement error correction method for correcting the measurement error, the shape measurement error due to the spatial distortion of the interference fringes caused by other than the shape of the measurement object is obtained in advance, and the dynamic shape measurement of the measurement object is performed. A dynamic shape measurement error correction method, wherein a shape measurement error due to spatial distortion of the interference fringes is corrected by subtracting from a value.   The shape measurement error due to the spatial distortion of the interference fringes is obtained by measuring an arbitrary surface with a known shape by the dynamic shape measurement device. Measurement error correction method.   8. The dynamic shape of claim 7, wherein a shape measurement error due to a spatial distortion of the interference fringes is obtained by performing a ray tracing simulation of a trajectory of reflected light of the object measured by the imaging optical system. Measurement error correction method. The shape measurement error due to the spatial distortion of the interference fringes is acquired in advance for each peak wave number of the interference fringes, and according to the peak wave number of the interference fringes imaged when the object to be measured is subjected to dynamic shape measurement. 8. The dynamic shape measurement error correction method according to claim 7, wherein correction is performed using a shape measurement error acquired for each peak wave number of the interference fringes.

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