WO2020129709A1 - Dispositif d'analyse de frange d'interférence, procédé d'analyse de frange d'interférence et dispositif de mesure de distance - Google Patents

Dispositif d'analyse de frange d'interférence, procédé d'analyse de frange d'interférence et dispositif de mesure de distance Download PDF

Info

Publication number
WO2020129709A1
WO2020129709A1 PCT/JP2019/047880 JP2019047880W WO2020129709A1 WO 2020129709 A1 WO2020129709 A1 WO 2020129709A1 JP 2019047880 W JP2019047880 W JP 2019047880W WO 2020129709 A1 WO2020129709 A1 WO 2020129709A1
Authority
WO
WIPO (PCT)
Prior art keywords
frequency
interference fringe
phase
signal
spatial
Prior art date
Application number
PCT/JP2019/047880
Other languages
English (en)
Japanese (ja)
Inventor
藤原　久利
雅 古谷
Original Assignee
アズビル株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP2019110093A external-priority patent/JP2020101517A/ja
Application filed by アズビル株式会社 filed Critical アズビル株式会社
Publication of WO2020129709A1 publication Critical patent/WO2020129709A1/fr

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques

Definitions

  • the present invention relates to an interference fringe analysis device, an interference fringe analysis method, and a distance measurement device, and particularly to an optical interference measurement technique that analyzes an interference fringe of light reflected from an object to measure an object distance to a measurement target.
  • interference fringe frequency the spatial frequency of the interference fringes
  • Patent Document 1 a technique of irradiating a laser light on a measurement target and a reference surface serving as a reference, and analyzing a signal of an interference fringe generated on a light receiving surface due to interference of reflected light reflected by the measurement surface by discrete Fourier transform.
  • the interference fringe frequency is obtained based on the power spectrum obtained by performing a discrete Fourier transform on the interference fringe signal.
  • Non-Patent Document 1 discloses a technique for measuring the frequency of sound with higher accuracy using a phase correction method.
  • the resolution of the interference fringe frequency is the reciprocal of the signal length of the interference fringe, that is, a linear image sensor, a photodiode array, or the like. Is determined by the reciprocal of the length of the light receiving element of the photodetector in the array direction.
  • the length of the light receiving elements in the array direction is limited by the design of the photodetector, it is difficult to obtain the interference fringe frequency with higher accuracy.
  • Non-Patent Document 1 when the conventional phase correction method described in Non-Patent Document 1 is applied to the spatial frequency of the interference fringes, the phase difference is used to obtain the frequency resolution when the signal frequency is obtained by using the discrete Fourier transform. Can also obtain high resolution. However, since the frequency spectrum having a shorter spatial distance is obtained, the resolution of the peak frequency of each frequency spectrum is lowered.
  • Non-Patent Document 1 is premised on a steady state in which the frequency of the signal of interest does not change, and when applied as a method for obtaining the spatial frequency of interference fringes, the distortion of the wavefront due to optical aberration or the like. If the interval of the interference fringes changes due to, it becomes difficult to accurately obtain the interference fringe frequency.
  • the present invention has been made to solve the above-mentioned problems, and an object thereof is to provide an interference fringe analysis technique capable of obtaining an interference fringe frequency with higher accuracy and higher resolution.
  • the interference fringe analysis apparatus is configured to convert an interference fringe signal indicating a light-dark pattern of the interference fringes detected by the photodetector into a spectrum in the spatial frequency domain.
  • a conversion unit a peak frequency detection unit configured to detect a spatial frequency of a peak having a maximum intensity among the peaks included in the spectrum converted by the conversion unit as a reference frequency, and the peak frequency detection unit.
  • a filter configured to transmit the reference frequency detected by a unit, a spectrum configured to transmit the reference frequency by the filter, an inverse transform unit configured to convert a signal in a spatial domain,
  • a phase calculator configured to calculate the phase of the signal in the spatial domain converted by the inverse converter, and to calculate an interference fringe frequency indicating a spatial frequency of the interference fringe signal based on the calculated phase.
  • a frequency calculator configured as described above.
  • the reference frequency is used as a shift amount
  • a frequency shifter configured to shift the spatial frequency axis of the spectrum
  • the inverse conversion unit includes the reference by the filter.
  • a spectrum that is transparent to a frequency and whose spatial frequency axis is shifted by the frequency shifter may be converted into a signal in the spatial domain.
  • the photodetector has a light-receiving surface including a plurality of pixels arranged in a predetermined direction, and the phase calculation unit includes a position of each of the plurality of pixels.
  • the phase of the signal in the spatial domain converted by the inverse conversion unit may be calculated, and the frequency calculation unit may obtain the interference fringe frequency from the spatial change of the calculated phase.
  • the photodetector has a light-receiving surface including a plurality of pixels arranged in a predetermined direction, and the phase calculation unit includes a position of each of the plurality of pixels.
  • the phase of the signal in the spatial domain converted by the inverse conversion unit is calculated, and the frequency calculation unit calculates the phase and the interference fringe frequency at each position of the plurality of pixels from the calculated phase.
  • the difference from the frequency may be calculated as a correction frequency, and the interference fringe frequency may be obtained based on the reference frequency and the correction frequency.
  • the frequency calculation unit may obtain the interference fringe frequency from the slope of the approximate straight line of the spatial change of the phase calculated by the phase calculation unit.
  • the frequency calculation unit is a pixel indicating the interference fringe frequency of the interference fringe signal at each position of the calculated plurality of pixels and the interval between the pixels of the photodetector.
  • the average frequency of the interference fringe signal may be calculated using the pitch and the number of pixels of the photodetector.
  • the peak frequency detection unit may detect, as the reference frequency, the spatial frequency of the peak having the maximum intensity among the positive spatial frequency components included in the spectrum. Good.
  • a DC cut unit configured to remove a DC component included in the interference fringe signal detected by the photodetector is further included, and the conversion unit includes the DC The interference fringe signal from which the DC component has been removed by the cutting unit may be converted into a spectrum in the spatial frequency domain.
  • the distance measuring device is an interference fringe analysis device described above, an irradiation optical system that collects and irradiates light from a light source onto a measurement target, and reflects from the measurement target.
  • the reflected light as incident light
  • the optical system having a diffractive optical element that changes the phase of the incident light to emit diffracted light of two preset orders, and the diffractive optical element that is emitted from the diffractive optical element.
  • a photodetector that detects interference fringes generated by two orders of diffracted light, and an objective distance from the photodetector to the measurement target is calculated based on the frequency of the interference fringes obtained by the interference fringe analyzer.
  • a distance calculator that operates.
  • an interference fringe analysis method includes a first step of converting an interference fringe signal indicating a light-dark pattern of interference fringes detected by a photodetector into a spectrum in a spatial frequency domain.
  • the method further comprises a sixth step of shifting the spatial frequency axis of the spectrum using the reference frequency as a shift amount, and in the fifth step, the reference frequency in the third step is changed.
  • the signal may be converted into a signal in the spatial domain based on the spectrum transmitted and having the spatial frequency axis shifted in the sixth step.
  • the spectrum obtained by transmitting the spatial frequency of the peak having the maximum intensity is converted into the signal in the spatial domain.
  • the interference fringe frequency with high accuracy and high resolution can be obtained.
  • FIG. 1 is a block diagram showing a configuration example of a distance measuring device including an interference fringe analyzing device according to a first embodiment of the present invention.
  • FIG. 2 is a block diagram showing a configuration example of the interference fringe analysis apparatus according to the first embodiment.
  • FIG. 3 is a block diagram showing a configuration example of a computer that realizes the interference fringe analysis apparatus according to the first embodiment.
  • FIG. 4 is a schematic diagram showing a configuration example of the optical system according to the first embodiment.
  • FIG. 5 is a diagram illustrating the principle of distance measurement according to the first embodiment.
  • FIG. 6 is a diagram for explaining diffraction by the diffractive optical element according to the first embodiment.
  • FIG. 7 is a diagram illustrating the relationship between diffracted light of different orders and the light spot spacing according to the first embodiment.
  • FIG. 8 is a diagram illustrating the relationship between the light spot interval and the optical path difference according to the first embodiment.
  • FIG. 9 is a flowchart for explaining an example of the operation of the distance measuring device according to the first embodiment.
  • FIG. 10 is a flowchart for explaining an example of the interference fringe analysis processing according to the first embodiment.
  • FIG. 11 is an image example showing interference fringes generated on the detection surface according to the first embodiment.
  • FIG. 12 is a diagram showing an example of the intensity distribution of the frequency spectrum according to the first embodiment.
  • FIG. 13 is a diagram for explaining the bandpass filter according to the first embodiment.
  • FIG. 14 is a diagram for explaining an example of calculating the phase and the interference fringe frequency of the interference fringe signal according to the first embodiment.
  • FIG. 15 is a block diagram showing a configuration example of the interference fringe analysis device according to the second embodiment.
  • FIG. 16 is a flowchart for explaining an example of the interference fringe analysis processing according to the second embodiment.
  • FIG. 17 is a diagram for explaining the frequency shifter according to the second embodiment.
  • FIG. 18 is a block diagram showing a configuration example of the interference fringe analysis device according to the third embodiment.
  • FIG. 19 is a flowchart for explaining an example of the interference fringe analysis processing according to the third embodiment.
  • the distance measuring device 1 irradiates and reflects light on the measurement target T, and measures the objective distance a to the measurement target T based on the interference fringe frequency obtained by analyzing the interference fringes of the reflected light.
  • the distance measuring device 1 includes an optical system 10, a photodetector 11, an interference fringe analysis device 12, a distance calculator 13, a setting device 14, a storage device 15, and a display device 16.
  • the distance measuring device 1 may be housed inside a casing not shown in FIG. 1, for example.
  • the optical system 10 collects the light from the light source 101 and irradiates the measurement target T with the irradiation optical system and the reflected light reflected from the measurement target T as the incident light. And a diffractive optical element 104 that changes the phase and emits diffracted light of two preset orders. An interference fringe is generated by the diffracted light of two orders emitted from the diffractive optical element 104. The details of the optical system 10 will be described later.
  • the photodetector 11 has a detection surface 110 in which a plurality of light receiving elements are spatially arranged, and as shown in FIG. 4, is located on the opposite side of the measurement target T with the diffractive optical element 104 of the optical system 10 interposed therebetween. It is arranged.
  • the photodetector 11 is preferably arranged on the optical axis of the optical system 10 so that the detection surface 110 and the optical axis are orthogonal to each other, and is formed by two orders of diffracted light emitted from the diffractive optical element 104. The bright and dark pattern due to the generated interference fringes is detected.
  • an imaging device such as a CCD (Charged Coupled Device), a linear image sensor or a photodiode array in which light receiving elements such as a CMOS (Complementary Metal Oxide Semiconductor) and a photodiode are spatially arranged Can be used.
  • CCD Charge Coupled Device
  • CMOS Complementary Metal Oxide Semiconductor
  • the interference fringe analysis device 12 obtains the spatial frequency of the interference fringes, that is, the interference fringe frequency, from the interference fringe signal indicating the light-dark pattern of the interference fringes detected by the photodetector 11. Details of the interference fringe analyzer 12 will be described later.
  • the distance calculator 13 calculates the object distance a from the photodetector 11 to the measurement target T based on the interference fringe frequency obtained by the interference fringe analyzer 12.
  • the setting device 14 controls the operations of the optical system 10, the photodetector 11, and the display device 16.
  • the setter 14 also sets the filter coefficient of the bandpass filter 122 included in the interference fringe analyzer 12 according to an external input.
  • the storage device 15 is composed of a storage device such as an HDD or a flash memory, and stores the interference fringes detected by the photodetector 11.
  • the storage device 15 also stores the interference fringe frequency obtained by the interference fringe analysis device 12 and the objective distance a calculated by the distance calculator 13. Further, the storage device 15 stores information regarding initial settings when the setting device 14 controls the drive of the optical system 10, the photodetector 11, and the like.
  • the display device 16 is composed of a display such as a liquid crystal screen, and displays the waveform of the interference fringes detected by the photodetector 11.
  • the display device 16 also displays information indicating the interference fringe frequency obtained by the interference fringe analysis device 12 and information indicating the objective distance a calculated by the distance calculator 13.
  • the interference fringe analyzer 12 includes a Fourier transform unit (transformer) 120, a peak frequency detector 121, a band pass filter (filter) 122, an inverse Fourier transform unit (inverse transform unit) 123, a phase calculator 124, and an interference fringe frequency calculator.
  • a unit (frequency calculation unit) 125 and a storage unit 126 are provided.
  • the Fourier transform unit 120 transforms an interference fringe signal, which shows the light-dark pattern of the interference fringes detected by the photodetector 11, into a spectrum in the spatial frequency domain. More specifically, the Fourier transform unit 120 performs a discrete Fourier transform on the interference fringe signal in the spatial domain and outputs a frequency spectrum showing the spatial frequency distribution of the interference fringe signal.
  • the frequency spectrum obtained by the Fourier transform unit 120 includes a plurality of peaks including a DC component and positive and negative frequency components.
  • the peak frequency detection unit 121 has a spatial frequency (hereinafter, referred to as “reference frequency fr ”) of a peak having the maximum light intensity among the peaks included in the frequency spectrum of the interference fringe signal obtained by the Fourier transform unit 120. To detect. More specifically, the peak frequency detection unit 121 determines the spatial frequency of the peak having the maximum light intensity among the peaks of the positive frequency component excluding the DC component (frequency zero) and the negative frequency component included in the frequency spectrum. Is detected as a reference frequency fr.
  • the bandpass filter 122 is a filter that allows the reference frequency f r to pass through the frequency spectrum obtained by the Fourier transform unit 120. Pass band of the band pass filter 122 is variable according to the reference frequency f r. More specifically, the band-pass filter 122, with respect to the frequency spectrum of the interference fringe signal, is passed through only the frequency band near the reference frequency f r, the DC component and the negative frequency components and a positive included in the interference fringe signal Other frequency components including harmonic components are removed. Bandpass filter 122 may be designed from the reference frequency f r is the center frequency at any bandwidth, e.g., peak adjacent to the reference frequency f r may be used bandwidth is eliminated. As a result, noise included in the interference fringe signal can be reduced.
  • Inverse Fourier transform unit 123 only the frequency band near the reference frequency f r by a band-pass filter 122 is based on the frequency spectrum of the spatial frequencies that are transmitted, to restore the interference fringe signal in the spatial domain. More specifically, the inverse Fourier transform unit 123 performs an inverse discrete Fourier transform on the frequency spectrum output from the bandpass filter 122 to restore an interference fringe signal represented by a complex number.
  • the interference fringe signal output from the inverse Fourier transform unit 123 is a signal obtained by removing the DC component and the negative frequency component from the original interference fringe signal.
  • the Fourier transform unit 120 and the inverse Fourier transform unit 123 described above have configurations corresponding to each other.
  • the phase calculation unit 124 calculates the phase of the interference fringe signal restored by the inverse Fourier transform unit 123. More specifically, the phase calculation unit 124 determines the number of light receiving elements (pixels) of the photodetector 11 based on the real part and the imaginary part of the interference fringe signal represented by the complex number that is restored by the inverse Fourier transform unit 123. The phase of the interference fringe signal at each position is calculated.
  • the phase calculation unit 124 performs phase connection by adding or subtracting an integral multiple of 2 ⁇ when the phase value between adjacent pixels has a phase difference of 2 ⁇ . For example, the phase difference between adjacent pixels may be obtained, and phase connection may be performed when the phase difference exceeds a preset phase threshold value. In this way, the phase calculator 124 obtains the phase of the interference fringe signal in the phase-connected phase distribution.
  • the interference fringe frequency f may be obtained from the slope of.
  • the interference fringe frequency calculation unit 125 can obtain an approximate straight line of the phase ⁇ (i) by the least square method, for example.
  • f(i) is the interference fringe frequency at the i pixel position
  • n is the number of pixels of the photodetector 11
  • p pixel is the distance between the light receiving elements of the photodetector 11, that is, the pixel pitch.
  • the interference fringe frequency that suppresses the influence of the aberration caused by the optical system 10 can be obtained. it can.
  • the storage unit 126 stores the frequency spectrum of the interference fringe signal obtained by the Fourier transform unit 120, the reference frequency f r detected by the peak frequency detection unit 121, and the interference fringe signal restored by the inverse Fourier transform unit 123. ..
  • the storage unit 126 also stores the phase of the interference fringe signal calculated by the phase calculation unit 124 and the interference fringe frequency f calculated by the interference fringe frequency calculation unit 125.
  • the interference fringe signal detected by the photodetector 11 is a sine wave
  • the interference fringe signal is expressed as a function cos( ⁇ 0 x).
  • ⁇ 0 represents the fundamental angular frequency in the interference fringe signal
  • ⁇ 0 2 ⁇ f 0 (f 0 is the fundamental frequency of the interference fringe frequency)
  • x indicates the distance in the arrangement direction of the light receiving elements of the photodetector 11.
  • the frequency spectrum F( ⁇ ) obtained by Fourier transforming the interference fringe signal detected by the photodetector 11 is represented by the following expression (3).
  • the frequency spectrum showing the spatial frequency distribution of the interference fringe signal includes positive and negative frequency components of + ⁇ 0 and ⁇ 0 .
  • the signal obtained by taking out only the positive frequency component + ⁇ 0 from the frequency spectrum and performing the inverse Fourier transform is represented by the following formula (4).
  • the phase ⁇ at each position of a plurality of pixels included in the photodetector 11 can be obtained by the following equation (5).
  • the change in the phase of the interference fringe signal becomes the frequency of the interference fringe obtained here, and the interference fringe frequency f(x) can be obtained by the following equation (6).
  • the interference fringe frequency f(i) can be obtained from the phase ⁇ (i) of the i-th pixel and the phase ⁇ (i+1) of the (i+1)-th pixel by the above-mentioned formula (1).
  • the interference fringe analysis device 12 is, for example, a computer including a CPU 202, a main storage device 203, a communication interface 204, an auxiliary storage device 205, an input/output device 206, which are connected via a bus 201, and these. Can be realized by a program that controls the hardware resources of The interference fringe analysis device 12 is connected to an optical system 10, a photodetector 11, and a display device 16 provided outside via a bus 201, respectively.
  • a program for the CPU 202 to perform various controls and calculations is stored in the main storage device 203 in advance.
  • Each function of the interference fringe analyzer 12 including the phase calculator 124 and the interference fringe frequency calculator 125 shown in FIG. 2 is realized by the CPU 202 and the main storage device 203.
  • the communication interface 204 is an interface circuit for communicating with various external electronic devices via the communication network NW.
  • the communication interface 204 for example, an operation interface and an antenna compatible with wireless data communication standards such as LTE, 3G, wireless LAN, and Bluetooth (registered trademark) can be used.
  • wireless data communication standards such as LTE, 3G, wireless LAN, and Bluetooth (registered trademark)
  • the auxiliary storage device 205 is composed of a readable/writable storage medium and a drive device for reading/writing various information such as programs and data from/to the storage medium.
  • a semiconductor memory such as a hard disk or a flash memory can be used as a storage medium.
  • the auxiliary storage device 205 has a storage area for storing data indicating the interference fringes detected by the photodetector 11 and a program storage area for storing a program for the interference fringe analysis device 12 to analyze the interference fringes. .. Further, for example, it may have a backup area for backing up the above-mentioned data and programs.
  • the input/output device 206 is composed of I/O terminals for inputting signals from external devices such as the optical system 10, the photodetector 11 and the display device 16 and outputting signals to the external devices.
  • the program stored in the program storage area of the auxiliary storage device 205 may be a program that is processed in time series in accordance with the order of the interference fringe analysis processing described in this specification, or in parallel.
  • the program may be a program that is processed at a necessary timing such as when the call is made.
  • the program may be processed by one computer or may be processed in a distributed manner by a plurality of computers.
  • the distance calculator 13 described in FIG. 1 can be realized by a computer similar to the above-mentioned interference fringe analyzer 12. Further, the distance measuring device 1 described with reference to FIG. 1 can also be realized by a similar computer. The distance calculator 13 and the interference fringe analyzer 12 may be configured by the same computer.
  • the optical system 10 includes a light source 101, a light source lens 102, a beam splitter 103, a diffractive optical element 104, and a condenser lens 105.
  • the interference fringes generated by the optical system 10 are detected by the detection surface 110 of the photodetector 11 and input to the interference fringe analyzer 12.
  • the light source 101, the light source lens 102, and the beam splitter 103 constitute an irradiation optical system that collects and irradiates the light emitted from the light source 101 on the measurement target T.
  • the light source 101 is a device that emits light of a single wavelength (monochromatic light) used for distance measurement.
  • a semiconductor laser device a monochromatic light such as a sodium lamp, or a device that emits light having a single wavelength by a white light source and a narrow band pass filter can be used.
  • the light source lens 102 collects the light emitted from the light source 101 and emits it to the beam splitter 103.
  • the beam splitter 103 is arranged on the optical path O of the collection optical system, reflects the light from the light source 101 condensed by the light source lens 102, and irradiates the light spot A of the measurement target T along the optical path O. .. Further, the beam splitter 103 causes the reflected light reflected in the optical path O direction among the reflected light diffusely reflected by the light spot A to enter the diffractive optical element 104.
  • the diffractive optical element 104 is arranged on the optical path O, and the reflected light from the measurement target T transmitted through the beam splitter 103 is incident on the diffractive optical element 104.
  • the diffractive optical element 104 controls incident light according to a preset diffraction characteristic, changes the phase of the incident light, and emits only diffracted light of two preset orders based on the diffraction characteristic.
  • the diffractive optical element 104 is composed of a diffraction grating in which uneven structures are arranged two-dimensionally and periodically.
  • a transmission type phase diffraction grating is used as the diffractive optical element 104 will be described, but a reflection type phase diffraction grating may be used.
  • the diffractive optical element 104 is an element in which a fine concavo-convex structure is formed on the surface of an optical substrate such as quartz or ZnSe, and the intensity distribution of incident light can be shaped into a desired distribution by utilizing the diffraction phenomenon of light due to the concavo-convex structure. Is. More specifically, the diffractive optical element 104 can output only the diffracted light of the required order, for example, the ⁇ 1st order diffracted light, and can not emit the diffracted light of other unnecessary orders.
  • the concave-convex structure of the diffractive optical element 104 may have, for example, a sinusoidal cross-sectional shape. By having a sinusoidal cross-sectional shape, the diffractive optical element 104 can emit only ⁇ 1st-order diffracted light and remove high-order diffracted light.
  • the diffractive optical element 104 is a transmissive phase diffraction grating, in order to remove the 0th-order diffracted light, the step D between the peak and the valley which the sine wave shape has is the optical path length.
  • D n(m+1/2) ⁇ cos ⁇ (7)
  • n is the refractive index of the material of the diffractive optical element 104
  • ⁇ is the wavelength of light emitted from the light source 101
  • ⁇ is An arbitrary angle of incidence on the diffractive optical element 104 is shown.
  • the step D between the peak and the valley of the sinusoidal shape can be configured to satisfy the following expression (8) in terms of optical path length.
  • D (m+1/2) ⁇ cos ⁇ /2 (8)
  • ⁇ is the wavelength of light emitted from the light source 101
  • ⁇ is an arbitrary incident angle on the diffractive optical element 104.
  • the step D may be designed so that it becomes ⁇ in terms of phase. That is, the phases of the diffracted lights emitted from the diffractive optical element 104 are opposite to each other and cancel each other out, so that the 0th-order diffracted lights are removed.
  • the grating period d of the phase type grating which is the diffractive optical element 104 is sufficiently larger than the wavelength ⁇ of the light of the light source 101, for example, d>10 ⁇ . As a result, a structure suitable for practical use as a phase type grating can be obtained.
  • the grating shape of the diffractive optical element 104 is determined based on the spatial optical path distribution obtained by performing the inverse Fourier transform on the distribution of the emitted light of the desired order. It just has to be designed.
  • the condenser lens 105 condenses the diffracted light of two orders by the diffractive optical element 104.
  • the condensing lens 105 is composed of, for example, a convex lens, is arranged on the optical path O, and condenses the diffracted light of two orders emitted from the diffractive optical element 104 onto the imaging plane F.
  • the photodetector 11 detects the interference fringes generated by the diffracted light of two orders emitted from the diffractive optical element 104, and outputs the detection result. More specifically, the photodetector 11 has a detection surface 110, and detects a bright-dark pattern of interference fringes on the detection surface 110.
  • one longitudinal direction (perpendicular to the paper surface) of the grating in the diffractive optical element 104 formed of the phase diffraction grating is defined as the X direction, and is in the plane of the grating and orthogonal to the longitudinal direction of the grating.
  • the direction (vertical direction on the paper surface) is the Y direction
  • the direction perpendicular to the lattice plane is the Z direction.
  • the lens has two principal points according to the incident direction of light, and the respective positions are different.
  • the condensing lens 105 is a thin single lens, Each equation was derived assuming that there is only one principal point at the lens center.
  • the objective distance from the measurement target T to the principal point M that is, the position of the condenser lens 105 is a
  • the distance from the principal point to the image plane F is b
  • the focal length of the condenser lens 105 is Where f is f, these relationships are expressed by the following formula (9) by the formula of imaging (formula of lens).
  • the position of the image plane F also changes according to the change of the object distance a from the condenser lens 105 to the measurement target T.
  • the interval of the concavo-convex structure formed in the diffractive optical element 104 that is, the grating period is d
  • the wavelength of the light source 101 is ⁇
  • the diffraction angle ⁇ k of each diffracted light is expressed by the following equation (10).
  • the diffracted light emitted from the diffractive optical element 104 forms a plurality of light spots on the imaging plane F in the Y direction by the condenser lens 105.
  • the diffraction angles of the diffracted lights of two different orders k and k′ are ⁇ k and ⁇ k′, and the light spots by these diffracted lights are Ak and Ak′, and the light spot from the point A0 where the optical axis intersects the image plane.
  • the distances to Ak and Ak′ along the Y direction are W1 and W2
  • the deviation width W of these light spots Ak and Ak′ in the Y direction is expressed by the following equation (11).
  • the grating period d of the actual concavo-convex structure in the diffractive optical element 104 is sufficiently larger than k ⁇ and k′ ⁇ , and k ⁇ /d and k′ ⁇ /d are sufficiently small values. Therefore, the equation (11) is approximated by the following equation (12).
  • the light spot distance between the light spots Ak and Ak′ on the image plane F is W, and the diffracted light from the light spots Ak and Ak′ reaches the detection surface 110 of the photodetector 11.
  • the reached point is V.
  • a point where a line extending from the midpoint between the light spots Ak and Ak′ in the Z direction and the detection surface 110 of the photodetector 11 intersect is defined as V0, and V0 to V along the Y direction on the detection surface 110 Let P be the distance.
  • the optical path length Lk of the diffracted light from the light spot Ak to the arrival point V is obtained by the Pythagorean theorem.
  • the light spot interval W and the distance P are sufficiently smaller than the distance c, it can be approximated by the following equation (13).
  • optical path length Lk′ of the diffracted light from the light spot Ak to the arrival point V can be approximated by the following Expression (14) in the same manner as the optical path length Lk.
  • the optical path difference ⁇ L between these optical path lengths Lk and Lk′ is obtained by the following equation (15).
  • the optical path difference ⁇ L is an integer j (j is an integer of 0 or more) times the wavelength ⁇ of light, a bright line is generated on the detection surface 110.
  • the interference fringe pitch p of the interference fringes generated on the detection surface 110 of the photodetector 11 is obtained by the following equation (16) by modifying the equation (15).
  • the distance b from the principal point of the condenser lens 105 to the image plane F and the distance c from the image plane F to the detection plane 110 are represented by the condenser lens.
  • the distance L from the principal point of 105 to the detection surface 110 is replaced.
  • the equation (17) becomes the following equation (18).
  • the interference fringe pitch p is obtained by a function that depends on the distance L from the principal point of the condenser lens 105 to the detection surface 110.
  • the distance b from the principal point of the condenser lens 105 to the image plane F is determined by the objective from the measurement target T to the principal point M, that is, the position of the condenser lens 105, as shown in the equation (9). It is represented by the distance a and the focal length f of the condenser lens 105. From this, equation (18) can be transformed into equation (19).
  • the focal length f of the condenser lens 105, the distance L from the principal point of the condenser lens 105 to the detection surface 110, and the order difference ⁇ k between the diffraction orders k and k′ are known values. From this, as a result, it is understood that the interference fringe pitch p is a function of the object distance a from the measurement target T to the principal point M, that is, the position of the condenser lens 105. Therefore, by measuring the interference fringe pitch p detected on the detection surface 110 of the photodetector 11, the objective distance a to the measurement target T can be obtained by the following equation (20).
  • the measurement target T is arranged in a predetermined measurement region of the optical system 10. Further, the setter 14 performs initial adjustment of the light amount of the light source 101, the exposure time, etc. by an input from the outside.
  • the light emitted from the light source 101 is condensed by the light source lens 102, and is irradiated toward the measurement target T by the beam splitter 103 (step S1).
  • the light reflected on the surface of the measuring object T passes through the beam splitter 103 and enters the diffractive optical element 104.
  • the diffractive optical element 104 controls incident light according to a preset diffractive characteristic, changes the phase of the incident light, and emits only diffracted light of two preset orders based on the diffractive characteristic (step S2). ..
  • the two orders of diffracted light emitted from the diffractive optical element 104 are condensed by the condenser lens 105. Then, the interference fringes generated by the two orders of diffracted light are detected by the photodetector 11 (step S3).
  • the photodetector 11 inputs the interference fringe signal indicating the detected contrast pattern of the interference fringes to the interference fringe analysis device 12 (step S4). Then, the interference fringe analysis device 12 performs a calculation based on the above-described principle of the interference fringe analysis to obtain the interference fringe frequency f (step S5).
  • the distance calculator 13 uses the interference fringe frequency f obtained by the interference fringe analyzer 12 to perform a calculation based on the above-described principle of distance measurement, and the objective distance from the condenser lens 105 to the measurement target T. a is calculated (step S6).
  • the interference fringe analysis processing by the interference fringe analyzer 12 (step S5 in FIG. 9) will be described with reference to the flowchart in FIG. First, for example, the light-dark pattern of the interference fringes shown in FIG. 11 detected by the photodetector 11 is input to the interference fringe analysis device 12 as an interference fringe signal.
  • the horizontal axis indicates the pixel position [pic] of the image along the Y direction orthogonal to the interference fringe, and the vertical axis indicates the light intensity (no unit) at each pixel position.
  • the obtained detection result has a substantially sinusoidal shape, and its peak position corresponds to the bright line.
  • the Fourier transform unit 120 Fourier transforms the interference fringe signal detected by the photodetector 11 and outputs the frequency spectrum of the interference fringe signal (step S50).
  • FIG. 12 is a diagram showing an example of the intensity distribution of the frequency spectrum output from the Fourier transform unit 120.
  • the horizontal axis represents the spatial frequency and the vertical axis represents the light intensity.
  • the peak pk0 of the direct current component of frequency zero, the peak pk2 of the negative frequency, and the pair thereof are shown. It includes a plurality of peaks such as a positive frequency peak pk1.
  • the peak frequency detection unit 121 detects the positive frequency component excluding the peak of the DC component and the peak of the negative frequency component among the plurality of peaks included in the frequency spectrum of the interference fringe signal obtained in step S50. Among the peaks, the spatial frequency of the peak having the maximum light intensity is detected (step S51). In the example of FIG. 12, the peak frequency detecting unit 121 detects the peak pk1, the storage unit 126 to the spatial frequency as the reference frequency f r.
  • the band-pass filter 122 among the spatial frequency components included in the frequency spectrum of the interference fringe signal, and transmits the frequency band near the reference frequency f r (step S52). More specifically, as shown by a thick line in FIG. 13, the band-pass filter 122, is transmitted through the frequency band near the reference frequency f r, including the peak pk2 peak pk0 and negative frequency components of the other DC components The frequency component indicated by the dotted line is removed.
  • the inverse Fourier transform unit 123 a frequency band near the reference frequency f r is inverse Fourier transform on the transmission frequency spectrum in the step S51 (step S53). More specifically, the inverse Fourier transform unit 123 performs the inverse Fourier transform according to the calculation (formula (4)) based on the principle of the interference fringe analysis described above.
  • the phase calculation unit 124 calculates the phase of the interference fringe signal in the spatial domain restored by the inverse Fourier transform unit 123 (step S54). More specifically, the phase calculation unit 124 calculates each of a plurality of pixels included in the photodetector 11 from the real part and the imaginary part (Equation (4)) of the interference fringe signal represented by the complex number obtained by the inverse Fourier transform. The phase at the position is calculated (equation (5)).
  • the phase calculation unit 124 performs phase connection based on the phase difference between adjacent pixels in the phase calculated in step S54 (step S55).
  • the phase ⁇ (i) of the interference fringe signal at the i pixel position is convolved between ⁇ and ⁇ , and has a discontinuous value in 2 ⁇ cycles. Therefore, the phase calculation unit 124 performs phase connection by adding or subtracting an integer multiple of 2 ⁇ when the phase value between adjacent pixels has a phase difference of 2 ⁇ .
  • the interference fringe frequency calculation unit 125 calculates the interference fringe frequency f based on the phase of the restored interference fringe signal calculated by the phase calculation unit 124 (step S56). More specifically, the interference fringe frequency calculation unit 125 obtains the spatial change of the phase of the interference fringe signal at each position of the plurality of pixels of the photodetector 11 as the interference fringe frequency f (equation (6)). The interference fringe frequency calculation unit 125 may obtain the slope of the approximate straight line by the method of least squares from the phase data for each pixel position, as shown in FIG. 14, and obtain this as the interference fringe frequency f.
  • the interference fringe frequency calculation unit 125 may calculate the average frequency at the array distance of the light receiving elements in the photodetector 11 based on the interference fringe frequency calculated in step S56 (equation (2)).
  • the DC component and the negative frequency component are removed in the spatial frequency region of the interference fringe signal, so that a more accurate interference fringe frequency can be obtained. Further, by obtaining the average frequency of the interference fringe frequencies, it is possible to obtain the interference fringe frequency in which the influence of aberration is reduced.
  • the process returns to step S6 of FIG. 9, and the distance calculator 13 calculates the object distance a based on the interference fringe frequency or the average frequency of the interference fringe signal.
  • the interference fringe analysis device 12 separates a DC component or a negative frequency component, which causes noise, from the interference fringe signal.
  • the interference fringe frequency with higher accuracy and higher resolution can be obtained without being restricted by the design of the arrangement of the light receiving elements.
  • the phase change obtained by performing the inverse Fourier transform on the signal obtained by separating the DC component and the negative frequency component from the interference fringe signal is frequency-converted. It is possible to obtain an interference fringe frequency with higher accuracy and higher resolution while suppressing the amount of calculation and the circuit scale.
  • the distance measuring device 1 since the interference fringe frequency with high accuracy and high resolution is used, it is possible to improve the measurement accuracy of the object distance a.
  • the peak frequency detector 121 has been described for detecting the reference frequency f r from the frequency spectrum of the interference fringe signal, it retrieves the reference frequency f r by a different method from this Good. For example, by detecting the zero-cross point by removing a DC component from the interference fringe signal detected by the photodetector 11, it may be obtained a signal synchronized with its zero-crossing point as the reference frequency f r.
  • the peak frequency detector 121 differentiates the interference pattern signal detected by the photodetector 11, may be determined reference frequency f r by detecting switching to increase from decrease in the differential value.
  • the second embodiment further includes a frequency shifter 127 that performs frequency shift on the frequency spectrum transmitted through the bandpass filter 122.
  • a frequency shifter 127 that performs frequency shift on the frequency spectrum transmitted through the bandpass filter 122.
  • the interference fringe analysis device 12A includes a Fourier transform unit 120, a peak frequency calculation unit 121, a bandpass filter 122, an inverse Fourier transform unit 123, a phase calculation unit 124, and an interference.
  • a stripe frequency calculation unit 125, a storage unit 126, and a frequency shifter 127 are provided.
  • the configuration of the distance measuring device 1 including the interference fringe analysis device 12A is similar to that of the first embodiment described in FIG.
  • the frequency shifter 127 performs frequency shift to shift the spatial frequency axis of the frequency spectrum obtained by the Fourier transform unit 120, using the reference frequency fr as the shift amount. More specifically, the frequency shifter 127 performs frequency shift on the frequency spectrum output from the bandpass filter 122. Frequency shifter 127, the peak position of the intensity of the frequency spectrum with a reference frequency f r is shifted spatial frequency axis of the frequency spectrum as a position of zero frequency by -f r.
  • the frequency shifter 127 has a space corresponding to the spatial frequency of the reference frequency f r , that is, when the spatial frequency of the peak at which the intensity of the frequency spectrum is maximum is the carrier frequency. by removing the frequency, the modulation frequency component modulates the reference frequency f r or is to be extracted spatial frequency components of the fluctuation.
  • the frequency shifter 127 may perform frequency shift on the frequency spectrum of the interference fringe signal including the DC component before passing through the bandpass filter 122.
  • Inverse Fourier transform unit 123 only the frequency band near the reference frequency f r by a band-pass filter 122 is transmitted, and, based on the frequency spectrum of the spatial frequency whose frequency is shifted by the frequency shifter 127, the interference fringes in the spatial domain Restore the signal. More specifically, the inverse Fourier transform unit 123 performs an inverse discrete Fourier transform on the frequency spectrum output from the frequency shifter 127, and restores an interference fringe signal represented by a complex number.
  • the interference fringe signal output by the inverse Fourier transform unit 123 is a signal obtained by removing the direct current component, the negative frequency component, and the spatial carrier frequency component (reference frequency fr ) from the original interference fringe signal.
  • the phase calculation unit 124 calculates the phase of the interference fringe signal restored by the inverse Fourier transform unit 123. More specifically, the phase calculation unit 124 determines the number of the light receiving elements (pixels) of the photodetector 11 based on the real part and the imaginary part of the interference fringe signal represented by the complex number that is restored by the inverse Fourier transform unit 123. The phase of the interference fringe signal at each position is calculated.
  • the phase calculation unit 124 performs phase connection by adding or subtracting an integral multiple of 2 ⁇ when the phase value between adjacent pixels has a phase difference of 2 ⁇ . For example, the phase difference between adjacent pixels may be obtained, and phase connection may be performed when the phase difference exceeds a preset phase threshold value. In this way, the phase calculator 124 obtains the phase of the interference fringe signal in the phase-connected phase distribution.
  • the correction frequency f c may be obtained by obtaining the slope of
  • the interference fringe frequency calculation unit 125 may obtain the approximate straight line of the phase ⁇ (i) by the least square method, for example.
  • the interference fringe frequency calculator 125 calculates the spatial frequency plus the correction frequency f c to the reference frequency f r as an interference fringe frequency f.
  • the interference fringe frequency calculation unit 125 uses the interference fringe frequency f(i) at the i pixel position obtained by the above equation (1) to calculate the average frequency f avg of the interference fringe signal by the above equation (2). You can ask.
  • the interference fringe frequency that suppresses the influence of the aberration caused by the optical system 10 can be obtained. it can.
  • the storage unit 126 stores the frequency spectrum of the interference fringe signal obtained by the Fourier transform unit 120, the reference frequency f r detected by the peak frequency detection unit 121, and the interference fringe signal restored by the inverse Fourier transform unit 123. ..
  • the storage unit 126 also stores the phase of the interference fringe signal calculated by the phase calculation unit 124, the correction frequency f c calculated by the interference fringe frequency calculation unit 125, and the corrected interference fringe frequency f.
  • the signal obtained by Fourier transforming the interference fringe signal detected by the photodetector 11 is defined as F( ⁇ - ⁇ r ).
  • a signal obtained by performing an inverse Fourier transform on the signal F( ⁇ - ⁇ r ) obtained by Fourier transforming the above interference fringe signal is represented by the following equation (21).
  • x represents the distance in the arrangement direction of the light receiving elements of the photodetector 11.
  • the interference fringe frequency f(x) of the above equation (21) is represented by the following equation (22).
  • the change d.phi c of shows the relationship between the phase phi c of the interference fringe signal (x) and an interference fringe frequency f (x), the phase phi c between the pixel (x) (x) / dx is proportional to the difference f c (x) of the interference fringe frequency f and the reference frequency f r.
  • the interference fringe analysis processing by the interference fringe analyzer 12A will be described with reference to the flowchart in FIG.
  • the distance measuring method according to this embodiment is the same as that of the first embodiment (FIG. 9).
  • the light-dark pattern of the interference fringes shown in FIG. 11 detected by the photodetector 11 is input to the interference fringe analysis device 12 as an interference fringe signal.
  • the horizontal axis represents the pixel position [pic] of the image along the Y direction orthogonal to the interference fringe
  • the vertical axis represents the light intensity (no unit) at each pixel position.
  • the obtained detection result has a substantially sinusoidal shape, and its peak position corresponds to the bright line.
  • the Fourier transform unit 120 Fourier transforms the interference fringe signal detected by the photodetector 11, and outputs the frequency spectrum of the interference fringe signal (step S50A).
  • the peak pk0 of the direct current component of frequency zero, the peak pk2 of the negative frequency, and the pair thereof are shown in the frequency spectrum obtained by Fourier transforming the interference fringe signal by the Fourier transform unit 120. It includes a plurality of peaks such as a positive frequency peak pk1.
  • the peak frequency detection unit 121 detects the positive frequency component excluding the peak of the DC component and the peak of the negative frequency component among the plurality of peaks included in the frequency spectrum of the interference fringe signal obtained in step S50A. Among the peaks, the spatial frequency of the peak having the maximum light intensity is detected (step S51A). In the example of FIG. 12, the peak frequency detecting unit 121 detects the peak pk1, the storage unit 126 to the spatial frequency as the reference frequency f r.
  • the band-pass filter 122 among the spatial frequency components included in the frequency spectrum of the interference fringe signal, and transmits the frequency band near the reference frequency f r (step S52A). More specifically, as shown by a thick line in FIG. 13, the band-pass filter 122, is transmitted through the frequency band near the reference frequency f r, including the peak pk2 peak pk0 and negative frequency components of the other DC components The frequency component indicated by the dotted line is removed.
  • the frequency shifter 127 frequency-shifts the frequency spectrum output from the bandpass filter 122 (step S53A). More specifically, as shown in FIG. 17, the frequency shifter 127 sets the frequency of the reference frequency f r as the shift amount and sets the frequency of the peak pk1 to the position of the origin (frequency zero) in the frequency spectrum of the interference fringe signal. To shift the spatial frequency axis.
  • the inverse Fourier transform unit 123 performs the inverse Fourier transform in accordance with the calculation (formula (21) to formula (23)) based on the above-described principle of interference fringe analysis.
  • the phase calculation unit 124 calculates the phase of the interference fringe signal in the spatial domain restored by the inverse Fourier transform unit 123 (step S55A). More specifically, the phase calculation unit 124 uses the real part and the imaginary part (Equation (24)) of the interference fringe signal in the complex number expression obtained by the inverse Fourier transform to calculate the pixel count of each of the plurality of pixels included in the photodetector 11. Calculate the phase at the position.
  • the phase calculation unit 124 performs phase connection based on the phase difference between adjacent pixels in step S55A.
  • the phase ⁇ c (i) of the interference fringe signal at the i pixel position is convolved between ⁇ and ⁇ , and becomes a discontinuous value in 2 ⁇ cycles. Therefore, the phase calculation unit 124 performs phase connection by adding or subtracting an integer multiple of 2 ⁇ when the phase value between adjacent pixels has a phase difference of 2 ⁇ . For example, the phase difference between adjacent pixels may be obtained, and phase connection may be performed when the phase difference exceeds a preset phase threshold value. In this way, the phase calculator 124 obtains the phase ⁇ c (i) of the interference fringe signal in the phase-connected phase distribution.
  • the interference fringe frequency calculation unit 125 calculates the correction frequency f c based on the phase of the restored interference fringe signal calculated by the phase calculation unit 124 (step S56A). More specifically, the interference fringe frequency calculation unit 125 obtains a spatial change in the phase of the interference fringe signal at each of the positions of the plurality of pixels of the photodetector 11 as the correction frequency f c . For example, as shown in FIG. 14, the interference fringe frequency calculation unit 125 may obtain the slope of the approximate straight line by the method of least squares from the phase data for each pixel position, and use this as the correction frequency f c .
  • the interference fringe frequency calculator 125 corrects the reference frequency f r in the correction frequency f c which is calculated in step S56A, obtaining the interference fringe frequency f (step S57A). More specifically, the interference fringe frequency calculator 125, by adding the reference frequency f r and the correction frequency f c, calculates a corrected interference fringe frequency f.
  • the interference fringe frequency calculation unit 125 may calculate the average frequency at the array distance of the light receiving elements in the photodetector 11 based on the interference fringe frequency calculated in step S57A.
  • the interference fringe analysis method since the direct current component and the negative frequency component are removed in the spatial frequency region of the interference fringe signal to perform the frequency shift, a more accurate interference fringe frequency is obtained. be able to. Further, by obtaining the average frequency of the interference fringe frequencies, it is possible to obtain the interference fringe frequency in which the influence of aberration is reduced.
  • the process returns to step S6 of FIG. 9, and the distance calculator 13 calculates the object distance a based on the interference fringe frequency or the average frequency of the interference fringe signal.
  • the interference fringe analysis device 12 corrects the interference fringe signal by separating the DC component or the negative frequency component that causes noise from the interference fringe signal. Therefore, it is possible to obtain the interference fringe frequency with higher accuracy and higher resolution without being restricted by the design of the arrangement of the light receiving elements such as the linear image sensor.
  • the distance measuring device 1 since the interference fringe frequency with high accuracy and high resolution is used, it is possible to improve the measurement accuracy of the object distance a.
  • the frequency shifter 127 has been described a case where the frequency band near the reference frequency f r which is output from the band pass filter 122 performs a frequency shift for the transmitted frequency spectrum.
  • the order in which these procedures are performed is not limited to this.
  • the frequency shifter 127 may shift the frequency spectrum of the interference fringe signal, and then pass the bandpass filter 122.
  • the frequency shifter 127, the reference frequency f r as the shift amount, the peak of the reference frequency f r is such that the position of the origin (zero frequency), has been described a case where a frequency shift with respect to the spatial frequency axis of the frequency spectrum
  • the present invention is not limited to this.
  • the frequency shifter 127 does not necessarily have to shift the frequency so as to match the position of the origin, as long as the frequency shifter 127 shifts the frequency to near zero frequency using a predetermined shift amount.
  • the interference fringe analysis device 12 includes the DC cut unit 128, and removes the DC component from the interference fringe signal input to the Fourier transform unit 120 in advance.
  • the configuration different from the first and second embodiments will be mainly described.
  • the interference fringe analysis device 12B includes a Fourier transform unit 120, a peak frequency detection unit 121, a bandpass filter 122, an inverse Fourier transform unit 123, a phase calculation unit 124, an interference fringe frequency calculation unit 125, and a storage unit. It includes a 126, a frequency shifter 127, and a DC cut section 128.
  • the DC cut unit 128 removes the DC component contained in the interference fringe signal detected by the photodetector 11.
  • the DC cut unit 128 removes the DC component by, for example, obtaining an average value of the values (luminance) corresponding to the light receiving elements (pixels) of the photodetector 11 and obtaining the difference between this average value and the luminance for each pixel. can do.
  • the interference fringe signal from which the DC component has been removed by the DC cut unit 128 is input to the Fourier transform unit 120. By reducing the direct current component from the interference fringe signal input to the Fourier transform unit 120 in advance, the noise included in the interference fringe signal can be reduced more reliably.
  • the DC cut unit 128 removes the DC component from the interference fringe signal indicating the light and dark pattern of the interference fringes detected by the photodetector 11 (step S150).
  • the Fourier transform unit 120 Fourier transforms the interference fringe signal from which the DC component has been removed by the DC cut unit 128, and outputs a frequency spectrum (step S151).
  • the peak frequency detection unit 121 determines the spatial frequency of the peak having the maximum light intensity in the positive frequency band among the peaks included in the frequency spectrum from which the DC component has been removed, obtained in step S151. It is detected (step S152). Peak frequency detection unit 121 stores in the storage unit 127 the spatial frequency of the detected peak as the reference frequency f r.
  • the band-pass filter 122 of the spatial frequency band included in the interference fringe signal, and transmits the frequency band near the reference frequency f r (step S153). More specifically, the band-pass filter 122, in the frequency spectrum of the interference fringe signal DC component has been removed, by transmitting only the frequency band near the reference frequency f r, components other spatial frequencies including the negative frequency component To remove.
  • the frequency shifter 127 performs frequency shift on the frequency spectrum of the interference fringe signal output from the bandpass filter 122 (step S154). Specifically, the frequency shifter 127 shifts the frequency of the frequency spectrum with respect to the spatial frequency axis so that the peak of the reference frequency f r is located at the origin (frequency zero) with the reference frequency f r as the shift amount.
  • the inverse Fourier transform unit 123 is transmitted through the frequency band near the reference frequency f r in step S153, an inverse Fourier transform of the frequency spectrum of the interference fringe signal frequency shift at step S154 (step S155).
  • the inverse Fourier transform unit 123 performs an inverse Fourier transform on the frequency spectrum in the spatial frequency domain to restore the interference fringe signal in the spatial domain (Equation (21) to (Equation (23)).
  • the phase calculation unit 124 calculates the phase of the interference fringe signal in the spatial domain restored by the inverse Fourier transform unit 123 (step S156). More specifically, the phase calculation unit 124 calculates each of the plurality of pixels included in the photodetector 11 from the real part and the imaginary part (Equation (24)) of the interference fringe signal represented by the complex number obtained by the inverse Fourier transform. Calculate the phase at the position.
  • the interference fringe frequency calculation unit 125 calculates the correction frequency f c based on the phase of the restored interference fringe signal calculated by the phase calculation unit 124 (step S157). More specifically, the interference fringe frequency calculation unit 125 obtains a spatial change in the phase of the interference fringe signal at each of the positions of the plurality of pixels of the photodetector 11 as the correction frequency f c . The interference fringe frequency calculation unit 125 may obtain the slope of the regression line by the method of least squares from the phase data for each pixel position, and use this as the correction frequency f c .
  • the interference fringe frequency calculator 125 corrects the reference frequency f r in the correction frequency f c which is calculated in step S157, obtaining the interference fringe frequency f (step S158). More specifically, the interference fringe frequency calculator 125, by adding the reference frequency f r and the correction frequency f c, calculates a corrected interference fringe frequency f.
  • the interference fringe frequency calculation unit 125 may calculate the average frequency at the array distance of the light receiving elements in the photodetector 11 based on the interference fringe frequency calculated in step S158.
  • the process returns to step S6 of FIG. 9, and the distance calculator 13 calculates the object distance a based on the interference fringe frequency or the average frequency of the interference fringe signal.
  • the interference fringe analysis device 12B according to the third embodiment has been described using the configuration including the frequency filter 127, the interference fringe analysis device 12B does not include the frequency filter 127 in the first embodiment. It can also be applied to the same configuration as the interference fringe analysis device 12 according to the embodiment.
  • the DC cut unit 128 removes the DC component of the interference fringe signal detected by the photodetector 11 in advance. It is possible to more reliably suppress the influence of noise in the transmission frequency band of the removal and the region around the center frequency f r of the negative frequency band by detecting and band-pass filter 122 of the frequency f r. As a result, it is possible to obtain a more accurate interference fringe frequency and improve the measurement accuracy of the object distance a.
  • the reflected light reflected from the measuring object T is used as the incident light, and only the diffracted light of two orders set in advance by changing the phase of the incident light is used. Since the diffractive optical element 104 that emits light is included, a spatial filter is unnecessary, and the objective distance a can be measured using the more simplified optical system 10.
  • the distance measuring device 1 can measure the objective distance a without performing precise position adjustment in the optical system such as installing a spatial filter at the position of the Fourier transform surface.
  • the distance measuring device 1 according to the described embodiment emits diffracted light without blocking a part of incident light in the diffractive optical element 104. Therefore, compared with the case where the amplitude type diffraction grating is used, the distance measuring device 1 according to the present embodiment can obtain higher diffraction efficiency for diffracted light of a desired order. As a result, distance measurement can be performed using light with stronger signal intensity.
  • the optical system 10 can be composed of a reflective optical system having a mirror or the like.
  • the photodetector 11 can be configured using, for example, a scintillator or the like.
  • the phase calculation unit 124 calculates the phase ⁇ (i) at the i pixel position, and the interference fringe frequency calculation unit 125 corrects the interference fringe signal by changing the phase, that is, differentiating the phase.
  • the case of obtaining the interference fringe frequency f(i) has been described.
  • the phase calculation unit 124 may correct the influence of the interference fringes due to the aberration caused by the optical system 10 on the calculated phase ⁇ (i) at the i pixel position, for example.
  • the shape or displacement of the measurement target T may be measured based on the interference fringe frequency calculated by the interference fringe analyzer 12. ..
  • the distance measuring device 1 is provided with the condenser lens 105 to form convergent light.
  • a lens that generates parallel light or divergent light may be used instead of the condenser lens 105.
  • the photodetector 11 directly detects the interference fringes generated by the diffracted light of two orders emitted from the diffractive optical element 104 without using the condenser lens 105. ..
  • the distance measuring device 1 measures the distance from the detection surface 110 of the photodetector 11 to the measurement target T as the objective distance a.
  • two light beams are provided on the optical path O between the diffractive optical element 104 and the photodetector 11 in the direction orthogonal to the diffraction direction of the diffractive optical element 104 and the optical axis.
  • a means for collecting the diffracted light of the order may be provided.
  • the light condensing unit include a cylindrical lens that uses refraction of light, a reflecting mirror, and the like.
  • the diffractive optical element 104 itself may be provided with a lens function to constitute a light condensing unit.
  • the distance measuring device 1 can further increase the signal intensity of the diffracted light by further including such a condensing unit.
  • the distance measuring device 1 includes the diffractive optical element 104 including a phase diffraction grating.
  • the diffractive optical element 104 is not limited to the phase diffraction grating, and for example, a spatial light modulator can be used.
  • the spatial light modulator has, for example, a liquid crystal layer and a plurality of electrodes arranged along the surface of the liquid crystal layer, and a voltage is individually applied to the liquid crystal layer from each of the plurality of electrodes to form a liquid crystal layer. Phase modulation is performed on the incident light that is incident, and only diffracted light of two preset orders is emitted. By using the spatial light modulator, the orders of the two diffracted lights emitted can be made variable according to the application.
  • a microprocessor can be used as a general-purpose processor, but a conventional processor, controller, microcontroller, or state machine can be used instead.
  • the processor may be implemented, for example, as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors connected to a DSP core, or a combination of computing devices of any such configuration. Is.
  • the interference fringe analysis device the interference fringe analysis method, and the distance measuring device of the present invention have been described above, the present invention is not limited to the described embodiments, and the invention described in the claims. Various modifications that can be envisioned by those skilled in the art can be made within the range.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

Dispositif d'analyse de frange d'interférence (12), qui comprend : une unité de transformée de Fourier (120) pour convertir un signal de frange d'interférence en un spectre dans le domaine des fréquences spatiales ; une unité de détection de fréquence de crête (121) pour détecter, en tant que fréquence standard fr, la fréquence spatiale du pic parmi les pics inclus dans le spectre qui a l'intensité lumineuse la plus élevée ; un filtre passe-bande (122) pour permettre à la fréquence standard fr de passer ; une unité de transformée de Fourier inverse (123) pour convertir le spectre après le passage de la fréquence standard fr en un signal de domaine spatial ; une unité de calcul de phase (124) pour calculer la phase du signal de domaine spatial converti ; et une unité de calcul de fréquence (125) pour calculer une fréquence de frange d'interférence f sur la base de la phase calculée.
PCT/JP2019/047880 2018-12-20 2019-12-06 Dispositif d'analyse de frange d'interférence, procédé d'analyse de frange d'interférence et dispositif de mesure de distance WO2020129709A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2018-238160 2018-12-20
JP2018238160 2018-12-20
JP2019110093A JP2020101517A (ja) 2018-12-20 2019-06-13 干渉縞解析装置、干渉縞解析方法、および距離測定装置
JP2019-110093 2019-06-13

Publications (1)

Publication Number Publication Date
WO2020129709A1 true WO2020129709A1 (fr) 2020-06-25

Family

ID=71101739

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2019/047880 WO2020129709A1 (fr) 2018-12-20 2019-12-06 Dispositif d'analyse de frange d'interférence, procédé d'analyse de frange d'interférence et dispositif de mesure de distance

Country Status (1)

Country Link
WO (1) WO2020129709A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112200018A (zh) * 2020-09-21 2021-01-08 江苏大学 一种基于残差网络的相位体干涉图识别方法
CN117805834A (zh) * 2024-02-29 2024-04-02 广东海洋大学 基于频谱共振峰的多目标空间位置关系预报方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003090765A (ja) * 2001-09-19 2003-03-28 Fuji Photo Optical Co Ltd 波長ゆらぎ測定方法および装置
WO2006137448A1 (fr) * 2005-06-21 2006-12-28 National University Corporation Hokkaido University Système et procédé de mesure de quantité de dilatation/contraction d’un échantillon
JP2017075832A (ja) * 2015-10-14 2017-04-20 アズビル株式会社 距離測定装置および方法
JP2017533445A (ja) * 2014-10-03 2017-11-09 サントル ナショナル ドゥ ラ ルシェルシュ シアンティフィク 光遠隔測定装置

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003090765A (ja) * 2001-09-19 2003-03-28 Fuji Photo Optical Co Ltd 波長ゆらぎ測定方法および装置
WO2006137448A1 (fr) * 2005-06-21 2006-12-28 National University Corporation Hokkaido University Système et procédé de mesure de quantité de dilatation/contraction d’un échantillon
JP2017533445A (ja) * 2014-10-03 2017-11-09 サントル ナショナル ドゥ ラ ルシェルシュ シアンティフィク 光遠隔測定装置
JP2017075832A (ja) * 2015-10-14 2017-04-20 アズビル株式会社 距離測定装置および方法

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112200018A (zh) * 2020-09-21 2021-01-08 江苏大学 一种基于残差网络的相位体干涉图识别方法
CN112200018B (zh) * 2020-09-21 2024-05-14 江苏大学 一种基于残差网络的相位体干涉图识别方法
CN117805834A (zh) * 2024-02-29 2024-04-02 广东海洋大学 基于频谱共振峰的多目标空间位置关系预报方法
CN117805834B (zh) * 2024-02-29 2024-05-07 广东海洋大学 基于频谱共振峰的多目标空间位置关系预报方法

Similar Documents

Publication Publication Date Title
JP4323955B2 (ja) 波面を測定するためのシステムおよび方法
US20100201811A1 (en) Depth ranging with moire patterns
JP6537293B2 (ja) Ｘ線トールボット干渉計及びｘ線トールボット干渉計システム
WO2020129709A1 (fr) Dispositif d'analyse de frange d'interférence, procédé d'analyse de frange d'interférence et dispositif de mesure de distance
JP5660514B1 (ja) 位相シフト量測定装置及び測定方法
JP2014190705A5 (fr)
US10488561B2 (en) Imaging device
JP2020101517A (ja) 干渉縞解析装置、干渉縞解析方法、および距離測定装置
US10209207B2 (en) X-ray talbot interferometer
WO2020129710A1 (fr) Dispositif d'analyse de frange d'interférence, procédé d'analyse de frange d'interférence et dispositif de mesure de distance
JP2015094756A (ja) 計測装置、および物品の製造方法
JP2020030166A (ja) 距離測定装置および方法
KR101436403B1 (ko) 정현파 격자를 이용한 섀도우모아레 방법 및 이를 이용한 측정 장치
JP6616650B2 (ja) 距離測定装置および方法
WO2019176300A1 (fr) Dispositif et procédé de mesure de distance
JPH04324316A (ja) 定点検出装置
JP6130805B2 (ja) 距離測定装置および方法
US10622238B2 (en) Overlay measurement using phase and amplitude modeling
JP2022134769A (ja) 干渉縞解析装置、干渉縞解析方法、距離測定装置および距離測定方法
JP2009145068A (ja) 表面形状の測定方法および干渉計
JP2021173679A (ja) 距離測定装置および距離測定方法
JP2007147505A (ja) 表面形状測定方法及びその測定装置
JP6608246B2 (ja) Ｘ線回折格子及びｘ線トールボット干渉計
JP2019100903A (ja) 距離測定装置および方法
JP2019100905A (ja) 距離測定装置および方法

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19900007

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19900007

Country of ref document: EP

Kind code of ref document: A1