JP6337543B2 - Shape measuring apparatus and shape measuring method - Google Patents

Description

  The present invention relates to a shape measurement technique using a laser beam, and in particular, an optical frequency comb.

  Conventionally, as a device for measuring the distance to an object, a technique for irradiating a measurement object with laser light and measuring the distance to the object based on the phase of reflected light from the object is known. . And the technique of measuring the three-dimensional shape of the measurement surface of a target object by measuring the distance to a target object while scanning a target object is known.

  Patent Document 1 discloses a method for measuring the surface state of a workpiece by observing diffuse light reflected by a foreign object such as a scratch on a workpiece that is a measurement object. In this method, the presence and position of a foreign object are determined by making a laser beam incident on the foreign object and detecting the diffused light. Then, a two-dimensional image is constructed based on the data obtained by detecting the diffused light, the difference value between adjacent pixels of the pixel of interest is calculated, and the difference value is calculated from the value of the pixel of interest. A value obtained by subtracting the value is used as a noise component, and the difference value is used as a signal component caused by a foreign object. Then, when the signal component exceeds a certain threshold, it is determined that there is a foreign object in the part of the work corresponding to the pixel.

  Patent Document 2 uses two optical frequency comb generators to determine the distance to the workpiece based on the phase of the interference light between the optical frequency comb reflected from the reference surface and the optical frequency comb reflected from the workpiece. A method is disclosed. In this method, the three-dimensional shape of the workpiece is acquired by changing the point where the workpiece is irradiated with the optical frequency comb and measuring the distance each time.

JP 2010-286392 A JP 2011-27649 A

  In the method of Patent Document 1, since a signal component that is a difference value between adjacent pixels is subjected to threshold processing, a value exceeding the threshold cannot be obtained for a foreign material having a small difference value that changes gently. There is a problem that cannot be detected. Moreover, in the method of patent document 2, the distance to a workpiece | work is measured by detecting the direct light reflected directly from a workpiece | work. Therefore, when the workpiece is tilted or when the laser strikes the tilted surface of the workpiece, there is a problem that the distance to the workpiece cannot be measured accurately because direct light does not return to the detector. The method of Patent Document 2 also detects diffused light from a work, but the signal intensity of the diffused light is small, so that the influence of multiple reflected light that penetrates and is reflected in the work appears greatly. . Therefore, sufficient distance measurement accuracy cannot be obtained.

  In view of such a problem, an object of the present invention is to provide a shape measuring device that makes it possible to more accurately measure the distance to a measurement object by reducing the influence of multiple reflected light from the measurement object, and It is to provide a shape measuring method.

In one embodiment of the present invention, a first light generator that generates first light having a first repetition frequency mode, and a second light generation mode that has a second repetition frequency mode different from the first repetition frequency. A second light generator that generates the first light, and a first interference light between the first light and the second light emitted from the first and second light generators via the reference point is detected. And a second detector for detecting a second interference light between the first light reflected from the measurement object and the second light reflected from the reference surface via the reference point. And a phase difference (Δθ _k ^b-a ) between the phase of the second interference light (θ _k ^b ) and the phase of the first interference light (θ _k ^a ), and the phase difference ( A plurality of inter-phase phase differences (ΔΦ) between adjacent modes of Δθ _k ^b−a ) are calculated, and a plurality of phase difference existence probability distributions (N (ΔΦ)) ) Is repeated a predetermined number of times, and a function obtained by multiplying a predetermined number of existence probability distributions (N (ΔΦ)) with each other or a function obtained by adding each other is maximized. providing a phase determination unit, determined mode between phase difference (.DELTA..PHI _D) based on the shape measuring apparatus comprising a distance calculating unit for calculating a distance from the reference point to the object of measurement to determine the .DELTA..PHI _D) To do.

In one embodiment of the present invention, a first step of detecting interference light having a mode with a predetermined repetition frequency, and a second step of calculating a plurality of inter-mode phase differences (ΔΦ) between adjacent modes of the interference light. A step, a third step of creating a plurality of phase difference existence probability distributions (N (ΔΦ)), and a first step to a third step are repeated a predetermined number of times, and a predetermined number of existence probability distributions ( N (.DELTA..PHI)) mode between phase difference that maximizes the resulting function by adding obtainable by Awa multiplying function or together with each other (determining .DELTA..PHI _D), determined mode phase bias (.DELTA..PHI _D) And a step of calculating the distance from the reference point to the object to be measured.

  The shape measuring apparatus and shape measuring method according to an embodiment of the present invention reduces the influence of multiple reflected light on the phase difference between modes used to calculate the distance, thereby more accurately determining the distance from the reference point to the workpiece. Makes it possible to measure.

It is a block diagram of the shape measuring device concerning a 1st embodiment. It is a conceptual diagram of the mode of an optical frequency comb. It is a conceptual diagram of the pulse of an optical frequency comb. It is a conceptual diagram of the reflected light from a workpiece | work. It is a graph of the example of a waveform detected with a detector. It is explanatory drawing of the shape measuring method of 1st Embodiment. It is a flowchart of the shape measuring method which concerns on 1st Embodiment. It is a photograph of the work concerning an example. It is a three-dimensional distance image which concerns on an Example. It is a graph which shows the result which concerns on an Example. It is a block diagram of the shape measuring apparatus which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, dimensions, materials, shapes, relative positions of components, and the like described in the following embodiments are arbitrary, and are changed according to the structure of the apparatus to which the present invention is applied or various conditions. Further, unless otherwise specified, the scope of the present invention is not limited to the form specifically described in the embodiments described below. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

[First Embodiment]
<Configuration of shape measuring device>
FIG. 1 is a block diagram of a shape measuring apparatus 100 according to the first embodiment of the present invention.

The shape measuring apparatus 100 includes an optical frequency comb laser apparatus 110, a lens 120, an arithmetic processing apparatus 130, and a position adjuster 140. The shape measuring apparatus 100 irradiates the work 150 which is a measurement object through the lens 120 from the optical frequency comb laser apparatus 110 with the optical frequency comb, and measures the distance to the work 150 based on the reflected light. Here, the optical frequency comb is a pulse having a plurality of discrete frequency components ("frequency mode" or simply "mode") having a predetermined frequency (oscillator modulation frequency) interval around the frequency ν _{0 of the} laser light source. Light. The shape measuring apparatus 100 may not include the lens 120.

  The optical frequency comb laser device 110 includes a laser light source 111, beam splitters 112a and 112c, polarization beam splitters 112b and 112d, first and second optical frequency comb generators (OFCG) 113a and 113b, a frequency shifter 114, a wave plate 115, A reference surface 116, polarizers 117a and 117b, first and second detectors 118a and 118b, and a fast Fourier transform (FFT) unit 119a and 119b are provided.

The laser light source 111 emits laser light having a single frequency ν ₀ toward the beam splitter 112a. For example, the frequency ν ₀ is 2.5 THz. Laser light from the laser light source 111 is separated toward the first OFCG 113a and the frequency shifter 114 by the beam splitter 112a.

The OFCG 113a as the first light generator is composed of an electro-optic converter (EOM) and a reflecting mirror disposed so as to sandwich the EOM, and a modulation signal having a modulation frequency f _m1 from an external oscillator 113c. In response, an optical frequency comb (“measurement light Ps” as the first light) having a mode with the first repetition frequency f _m1 is generated. By adjusting the modulation frequency f _m1 of the oscillator 113c, the frequency interval f _m1 between the modes of the measurement light Ps emitted from the first OFCG 113a can be adjusted. For example, f _m1 is 25 GHz.

Similarly, the OFCG 113b as the second light generator is configured by an EOM and a reflecting mirror disposed so as to face the EOM, and receives a modulation signal having a modulation frequency f _m2 from an external oscillator 113d. Then, an optical frequency comb having a mode of the second repetition frequency _fm2 ("reference light Pr" as the second light) is generated. f _m2 is f _m2 = f _m1 + Δf, and Δf is a sufficiently smaller value than f _m1 and f _m2 , for example, 500 kHz. The oscillators 113c and 113d are phase-synchronized by a common reference oscillator (not shown), and the relative frequency between the modulation frequencies f _m1 and f _m2 is stable. Thereby, the coherence between the measurement light Ps and the reference light Ps is improved, the repetition frequency is stabilized, and a short pulse width can be generated.

The first and second OFCGs 113a and 113b include phase modulators, intensity modulators, and semiconductors using nonlinear crystals such as LiNbO ₃ , ADP (ammonium dihydrogen phosphate), and KDP (potassium dihydrogen phosphate). It may be a modulator that utilizes absorption or phase change.

Frequency shifter 114, for example, acousto-optic modulator (Acousto-Optic modulator) and is, operating in the modulation signal from the oscillator 114a, the second shifts the frequency of the laser light by the modulation frequency f _alpha from the laser light source 111 Output to the OFCG 113b. By shifting the frequency of the light incident on the second OFCG 113b by the frequency shifter 114, the beat frequency of the interference light Pi between the measurement light Ps and the reference light Pr in the detectors 118a and 118b is not a DC signal but a frequency f. It becomes an AC signal of _α , facilitating phase comparison.

The wave plate 115 is a half-wave plate and adjusts the polarization direction of the reference light Pr from the second OFCG 113b. Polarizing beam splitter 112b is emitted to the beam splitter 112c as mixed light Pi ₁ superimposed with polarized light orthogonal to the reference optical power Pr and the measurement light Ps. The beam splitter 112c separates the mixed light Pi ₁ toward the polarizer 117a and the polarization beam splitter 112d.

Polarization beam splitter 112d is a mixed light Pi ₁ from the beam splitter 112c is separated into a reference beam Pr and the measurement light Ps according to the polarization, the measurement light Ps emitted to the workpiece 150, the reference light beam Pr to the reference surface 116 Exit. Further, the polarization beam splitter 112d returns the mixed light Pi ₂ obtained by mixing the reference beam Pr reflected from the reference surface 116 and the measurement light Ps reflected from the workpiece 150 to the beam splitter 112c. The reference surface 116 is a surface that reflects light, for example, a mirror surface.

Since the polarization of the reference beam Pr the polarization of the measuring light Ps in the mixed light Pi ₁ from the polarization beam splitter 112c are orthogonal to each other, a polarizer 117a is adjusting the direction to be oblique to both polarizations Arranged. Therefore, the detector 118a detects the interference light between the measurement light Ps and the reference light Pr.

Similarly, since the polarization of the reference beam Pr the polarization of the measuring light Ps in the mixed light Pi ₂ from the polarization beam splitter 112c are orthogonal to each other, a polarizer 117b is to be oblique to both polarizations Arrange the orientation. Therefore, the detector 118b detects interference light between the measurement light Ps reflected from the workpiece 150 and the reference light Pr reflected from the reference surface 116.

  The detector 118a receives the interference light between the measurement light Ps and the reference light Pr from the polarizer 117a, and outputs an interference signal corresponding to the interference light. The detector 118a is a detector for obtaining a reference phase in the generation process of the measurement light Ps generated by the first OFCG 113a and the reference light Pr generated by the OFCG 113b.

Here, as shown in FIG. 2B, the measurement light Ps and the reference light Pr in the detector 118a (or the detector 118b) have different repetition frequencies, so the pulse of the measurement light Ps and the reference light Pr are always somewhere. An instant (time t ₁ , t ₂ ) where the pulse overlaps appears. The overlapping moments (time t ₁ , t ₂ ) appear periodically at a repetition frequency (that is, Δf) corresponding to the difference between the repetition frequency of the measurement light Ps and the repetition frequency of the reference light Pr. Since Δf is sufficiently smaller than the light frequency, phase information can be detected by a detector (electronic circuit).

  On the other hand, the detector 118b receives the interference light of the measurement light Ps and the reference light Pr from the polarizer 117b, and outputs an interference signal corresponding thereto. The detector 118b is a detector for obtaining a delay time corresponding to the difference between the distance to the reference surface 116 and the distance to the workpiece 150 with respect to the beam splitter 112c (reference point: RP).

  The FFT units 119a and 119b input interference signals based on the interference light detected by the detectors 118a and 118b, respectively, perform predetermined signal processing such as fast Fourier transform (FFT), and the frequency of each mode of the interference light. Information, phase information, amplitude information, and the like are output to the arithmetic processing unit 130.

  The lens 120 is a lens for irradiating the workpiece 150 with the measurement light Ps from the optical frequency comb laser device 110, and returns the reflected light from the workpiece 150 to the optical frequency comb laser device 110 through the lens. The lens 120 may be attached to a moving mechanism for moving the lens to a predetermined position manually by an operator or in response to a control signal from the arithmetic processing unit 130.

  The arithmetic processing unit 130 is a computer including an input / output interface (not shown), a CPU (Central Processing Unit) (not shown), and a storage unit 131 such as a ROM (Read Only Memory) or a RAM (Random Access Memory). . The CPU of the arithmetic processing device 130 causes each function of the position control unit 132, the phase determination unit 133, the distance calculation unit 134, and the image generation unit 135 according to a predetermined program stored in the storage unit 131.

  The position control unit 132 can move the work 150 to a predetermined position by outputting a control signal for adjusting the position of the work 150 to the position adjuster 140. Here, the movement includes parallel movement, rotation, and tilting of the workpiece. Then, the position control unit 132 outputs the position information of the workpiece 150 to the storage unit 131, and the storage unit 131 stores the position information of the workpiece 150, information on the distance to the workpiece 150, and the like in association with each other.

  The image generation unit 135 assigns information on the distance to the workpiece 150 to, for example, a predetermined gradation, and generates a three-dimensional distance image as light and shade information on the corresponding position. For example, the image generation unit 135 sets the predetermined gradation to 8 bits, sets the largest distance value calculated by the distance calculation unit 134 to black (value 0), and sets the smallest distance value to white (value 255). A distance value between the two is assigned as a shade, and a three-dimensional distance image is generated based on position information associated with each distance value.

  The phase determination unit 133, the distance calculation unit 134, and the image generation unit 135 will be described later.

  The position adjuster 140 includes a stage for holding the work 150 and a power mechanism for moving, rotating, turning, and the like of the stage. The position adjuster 140 moves the work 150 to a predetermined position in accordance with a control signal from the position control unit 132. Move to.

<Relationship between phase and measurement distance>
The relationship between the phase difference (θ = φ _s −φ _r ) between the measurement light Ps (phase φ _s ) and the reference light Pr (phase φ _r ) and the distance from the reference point RP to the workpiece 150 will be described.

As shown in FIG. 2A, the measurement light Ps generated by the first OFCG 113a has a plurality of frequency modes having a frequency interval (repetition frequency f _m1 ) that matches the modulation frequency f _m1 of the oscillator 113c. Here, the frequency ν ₀ of the laser light from the laser light source 111 is set to the 0th order mode, and n is an integer of 0, ± 1, ± 2,. The reference light Pr generated by the second OFCG 113b has a plurality of frequency modes having a frequency interval (repetition frequency f _m2 ) corresponding to the frequency f _m2 (= f _m1 + Δf) of the modulation signal of the oscillator 113d. Here, the frequency ν ₀ + f _α of the light frequency-shifted by the frequency shifter 114 is set to the 0th order mode.

Each mode of the reference light Pr, for each mode of the measurement light Ps, differ only _fα In order mode, only f _alpha + Delta] f in the primary mode differs, differ in the n-th order mode only f α + _nΔf. Therefore, the beat frequency of the kth-order mode of the interference light between the measurement light Ps and the reference light Pr is (ν ₀ + f _α + kf _m1 + kΔf) − (ν ₀ + kf _m1 ) = f _α + kΔf (k is _{0 to} n). Integer).

The amplitude E _k (t) of the electric field of the k-th mode of the interference light between the measurement light Ps and the reference light Pr in the detector 118a (or the detector 118b) is expressed by Equation 1:
It is represented by Here, A _k is the electric field of the measurement light Ps, B _k is the electric field of the reference light Pr, and θ _k is the phase φ _s of the measurement light Ps and the phase φ _{r of the} reference light Pr in the k-order mode. The phase difference between and. In other words, it is the relative phase (that is, θ _k = φ _s −φ _r ) of the _k -th mode of the measurement light Ps based on the phase φ _r of the k-th mode of the reference light Pr.

Interference signal between the following numbers of different modes, to appear on and around the modulation frequency f _m, by although the bandwidth of the detector 118a sufficiently wide as compared with f _alpha and Δf takes less than f _m, or filter etc. By using it to remove high frequency components, only the beat frequency between modes of the same order remains. Therefore, interference between modes of different orders is not considered.

The output current I _k (t) for the k-th order mode of the detector 118a (or detector 118b) is expressed by Equation 2:
It is represented by The frequency difference (f _α + kΔf) between the measurement light Ps and the reference light Pr is the beat frequency F.

The meaning of the time delay that gives the phase θ _k (= φ _s −φ _r ) of the k-th mode in Equation 2 differs between the detectors 118a and 118b. That is, the phase θ _k detected by the detector 118a is caused by the length of the optical path length from when the light is separated by the beam splitter 112a until it is mixed by the polarization beam splitter 112b. Then, this time delay are the common to the detectors 118a and detector 118b, the detector phase that is detected by 118b theta _k ( "theta _k ^b") phase theta _k detected by the detector 118a from ( It is removed by subtracting “θ _k ^a ”). Then, the time difference of the interference signal detected by the interference signal detector 118b detected by the detector 118a, the phase difference between the modes of the reference beam Pr and the measurement light Ps in the frequency domain (θ _k ^b -θ _k ^a) The rate of change (gradient) with respect to the order k.

As can be seen from FIG. 2A, the relationship between the angular frequency ω _s of the measurement light Ps and the frequency ω _r of the reference light Pr regarding the k-th mode is
ω _r = ω _s + ω _α + kΔω
It is represented by Here, ω _s = 2πf _m1 , ω _r = 2πf _m2 , ω _α = 2πf _α , and Δω = 2πΔf.

Next, the phase phi _r ^a phase phi _s ^a and the reference light Pr of the measuring light Ps for the k-order mode towards the detector 118a from the beam splitter 112c (reference point RP) at time t, respectively,
φ _s ^a = ω _s t
φ _r ^a = ω _r t
It is.

On the other hand, the phase φ _s ^b of the measurement light Ps and the phase φ _r ^b of the reference light Pr for the kth order mode from the reference point RP to the detector 118b through the workpiece 150 and the reference surface 116 are respectively at time t.
φ _s ^b = ω _s {t−2 (L ₀ + L _s ) / V _c }
^{_{φ r b = ω r {t}} -2 (L 0 + L r) / V c}
It is. Here, V _c is the speed of light, L ₀ is the distance (optical path length) from the reference point RP to the polarizing beam splitter 112d, and L _s and L _r are the distances from the reference point RP to the workpiece 150 and the reference plane 116, respectively ( Optical path length).

Then, with respect to the k-th mode, the phase θ _k ^b (= φ _s ^b −φ _r ^b ) of the interference signal output from the detector 118b and the phase θ _k ^a (= φ of the interference signal output from the detector 118a). _s ^a −φ _r ^a ), Δθ _k ^b−a ,
It becomes. In Equation 3, the first term is a phase that changes according to the distance | L _s −L _r | to the workpiece 150, and the second term is a phase offset that depends on the fixed distances L ₀ and L _r .

The distance | L _s −L _r | to be measured is obtained from the rate of change between the modes of the phase. Since the frequency interval between the k + 1-order mode and the k-th mode of the measuring light Ps as described above is _{f m1,} between modes and [Delta] [theta] _k ^b-a of the [Delta] [theta] of the k + 1-order mode _k ^{+ 1 b-a} and k-th order mode The phase difference is given by Equation 4:
It is. Here, ω _m1 = 2πf _m1 .

As can be seen from Equation 4, in order to obtain an accurate distance | L _r −L _s | from the phase difference between modes (Δθ _{k + 1} ^b−a− Δθ _k ^b−a ) between the k + 1 order mode and the kth order mode. Is preferably the value of the phase difference when Δω = 0 that is not affected by the second term of Equation 4. In order to obtain the value of the phase difference when Δω = 0, the phase difference is measured by changing the value of Δω several times, and the obtained result is extrapolated to obtain the level difference when Δω = 0. The value of the phase difference may be obtained, and the distance | L _r −L _s | may be obtained from the value. The phase difference value when Δω = 0 may be obtained by averaging the phase difference values obtained as Δω = ± (predetermined value).

In this way, the interference light detected by the detector 118b phase _{^{θ k b (= φ s b}} -φ r b) and the interference light of the phase detected by the detector _{^{118a θ k a (= φ s}} a - The distance | L _r −L _s | to the workpiece 150 is calculated based on the phase difference between the modes Δφ _k ^b−a with respect to φ _r ^a ) (that is, Δθ _{k + 1} ^b−a− Δθ _k ^b−a ). Can be sought.

<Reflected light from the workpiece>
The shape measuring apparatus 100 according to the present embodiment irradiates the surface 150s of the workpiece 150 with the measurement light Ps, and measures the distance to the surface 150s of the workpiece 150 based on the phase of the reflected light. Then, the shape measuring apparatus 100 measures the three-dimensional shape of the surface of the workpiece 150 by measuring the distance while scanning the surface of the workpiece 150 while appropriately adjusting the position of the workpiece 150 by the position adjuster 140. Can do. First, the reflected light from the workpiece 150 will be described.

  As shown in FIG. 3A, the reflected light returning to the optical frequency comb laser device 110 is reflected from the directly reflected light 301 reflected at an angle equal to the incident angle of the measuring light Ps and the other indirectly reflected light 302. Become. The signal intensity and S / N ratio (signal-to-noise ratio) of the directly reflected light 301 detected by the optical frequency comb laser device 110 is larger than that of the indirect reflected light 302.

  As shown in FIG. 3B, the indirect reflected light 302 includes first diffused light 302 a in which the measurement light Ps diffuses in various directions on the surface 150 s of the workpiece 150, and a first portion formed on the main body 150 b of the workpiece 150. And the multi-reflected light 302b that returns to the optical frequency comb laser device 110 after being reflected a plurality of times inside the layer 150a. The first layer 150a is a layer that multiple-reflects light incident on the first layer 150a, and is, for example, a coating film applied to the main body 150b of the workpiece 150.

  The optical path length of the multiple reflected light 302b becomes longer than the optical path length of the diffused light 302a due to the influence of multiple reflections in the first layer 150a. Therefore, the phase of the diffused light 302a to be detected and the phase of the multiple reflected light 302b are different from each other.

  As shown in FIG. 3A, when the measurement light Ps is irradiated onto the flat surface 150 f of the surface of the workpiece 150, the direct reflected light 301 is reflected by the flat surface 150 f and returns to the optical frequency comb laser device 110. Therefore, the waveform detected by the optical frequency comb laser device 110 is greatly influenced by the directly reflected light 301 having a relatively large signal intensity and S / N ratio.

  On the other hand, as shown in FIG. 3C, when the measurement light Ps is irradiated onto the inclined surface 150 c on the surface of the workpiece 150, the direct reflected light 301 is reflected by the inclined surface 150 c and almost returns to the optical frequency comb laser device 110. It does n’t come. For this reason, the waveform detected by the optical frequency comb laser device 110 is greatly influenced by the indirect reflected light 302 having a relatively small signal intensity and S / N ratio. Here, the inclined surface 150c is a surface having an inclination of several degrees (for example, 3 degrees) or more with respect to the flat surface 150f.

  As described above, the indirectly reflected light 302 includes the diffused light 302a and the multiple reflected light 302b, and the S / N ratios of the diffused light 302a and the multiple reflected light 302b are approximately the same. Therefore, when the measurement light Ps is irradiated onto the inclined surface 150c of the workpiece 150 and the distance to the measurement light Ps is measured, the influence of the multiple reflected light 302b appears relatively large in the waveform detected by the optical frequency comb laser device 110. .

  One approach for accurately measuring the distance of the workpiece 150 to the inclined surface 150c is to allow the optical frequency comb laser device 110 to detect the directly reflected light 301 from the inclined surface 150c of the workpiece 150. In this approach, it is necessary to arrange an additional device such as a mirror surface or a lens on the optical path of the directly reflected light 301 so that the reflected light 301 is directly returned to the optical frequency comb laser device 110. However, it is necessary to adjust the additional device each time measurement is performed based on the position of the inclined surface 150c of the workpiece 150, the degree of inclination, and the like, which may cause problems in the configuration of the apparatus and the time spent adjusting the additional device. There is a problem that the measurement time becomes longer due to the increase.

  Therefore, more accurately measuring the distance to the inclined surface 150c of the workpiece 150 while reducing the influence of the multiple reflected light 302b based on the indirectly reflected light 302 that can be detected without changing the device configuration. Is desirable.

<Work shape measurement method>
First, as shown in FIG. 4, the measurement light Ps is irradiated onto the inclined surface 150c of the workpiece 150 to which the coating film as the first layer 150a is applied, and the waveform detected by the optical frequency comb laser device 110 a plurality of times. A waveform 408 obtained by superimposing 402 to 407 was observed. As a result, it was found that there are a portion 409 where the phases are aligned regardless of the measurement, and a portion 410 where the waveform is different for each measurement and the phase is shifted.

  The waveform 401 is a waveform detected by the optical frequency comb laser device 110 by irradiating the flat surface 150 f of the workpiece 150 with the measurement light Ps. Therefore, it can be seen that the waveform 401 is greatly affected by the direct reflected light 301, the signal intensity is strong, and the S / N ratio is good. Moreover, in order to acquire the waveform 401, on the inclined surface of the main body 150b of the workpiece 150 to which the coating film is not applied (that is, the same position as the inclined surface irradiated with the measurement light when acquiring the waveforms 402 to 407). Alternatively, the measurement light Ps may be irradiated and detected. The waveform 401 in this case is substantially composed of the signal component of the diffused light 302a and hardly contains the signal component of the multiple reflected light 302b.

  Considering that the multiple reflected light 302b is caused by random reflection in the coating film of the workpiece 150, the phase-matched portion 409 is caused by one or both of the reflected light 301 and the diffused light 302a regardless of the measurement. Therefore, it is considered that the portion 410 whose phase is shifted every measurement is caused by the multiple reflected light 302b.

  In other words, since the directly reflected light 301 and the diffused light 302a are reflected by the surface (inclined surface 150c) of the workpiece 150, they are detected almost the same time after generation of light by the optical frequency comb laser device 110 regardless of measurement. Become. For this reason, the phases of the direct reflected light 301 and the diffused light 302a are aligned every measurement. On the other hand, since the optical path length of the multiple reflected light 302b changes according to the number of random reflections within the coating film of the workpiece 150, the phase of the multiple reflected light 302b differs for each measurement.

Therefore, in the shape measurement method according to the present embodiment, the optical frequency comb laser device 110 (detectors 118a and 118b) detects the interference light between the measurement light Ps and the reference light Pr, and the phase difference between modes between adjacent modes. Are calculated, and the calculated phase difference between the modes is subjected to statistical processing (calculation of mean μ and variance σ ² and creation of existence probability distribution N). Then, this step is repeated a plurality of times (J times), and the phase difference having the highest appearance probability is calculated from the J existence probability distributions N, which is caused by either or both of the direct reflected light 301 and the diffused light 302a. And the distance to the workpiece 150 is obtained based on the signal component.

With reference to FIG. 5, described of determining the direct reflection light 301 and / or based on the diffused light 302a between the modes of the formula 4 phase difference ^{_{Δθ k + 1 b-a -Δθ}} k b-a. Hereinafter, in order to simplify the description, the inter-mode phase difference “Δθ _{k + 1} ba ⁻ Δθ _k ^b−a ” is represented by “ΔΦ” and is determined between the modes to be determined to obtain the distance to the workpiece 150. Let the phase difference be “ΔΦ _D ”. That is, ΔΦ _D is a phase difference corresponding to the left side of Equation 4 determined from a signal component caused by either or both of the directly reflected light 301 and the diffused light 302a. Further, it is assumed that the interference light detected by the optical frequency comb laser device 110 includes 0th to nth modes, and k is an integer of 0 to n.

  The optical frequency comb laser device 110 irradiates the surface of the workpiece 150 with the measurement light Ps, and detects the interference light between the measurement light Ps reflected from the workpiece 150 and the reference light reflected from the reference surface 116 by the detector 118b. Detect with. The waveform detected by the detector 118b includes components of the direct reflected light 301 and the indirectly reflected light 302 if reflected from the flat surface 150f, and the component of the indirectly reflected light 302 if reflected from the inclined surface 150c. However, the component of the direct reflected light 301 is hardly included.

  As shown in FIG. 5, based on the detection data from the detectors 118a and 118b, phase spectra 501a and 501b are generated in the FFT units 119a and 119b, respectively, and stored in the storage unit 131 of the arithmetic processing unit 130.

Thereafter, the phase determination unit 133 of the arithmetic processing unit 130 calculates Δθ _k ^b−a in Expression 3. That is, the phase determination unit 133, the detector from the phase of each mode _F 0 to F _n of the phase spectrum 501b about the detected interference light 118b, the corresponding mode of the phase spectrum 501a regarding detected by the detector 118a interference light The phase spectrum 502 of Δθ _k ^b−a is calculated by subtracting the phases of F _{0 to} F _n and stored in the storage unit 131.

Thereafter, the phase determination unit 133, a plurality of inter-mode phase difference ^{_{ΔΦ k + 1 = Δθ k +}} 1 b-a -Δθ k b-a between adjacent modes of the phase spectrum 502 (up to n) is calculated (503), storage Stored in the unit 131. The phase determination unit 133 calculates the average μ and the variance σ ² of the phase difference ΔΦ between the modes from the values of the plurality of phase differences ΔΦ ₁ , ΔΦ ₂ ,..., And calculates the existence probability distribution N (ΔΦ) of ΔΦ. Formula 5:
And is stored in the storage unit 131. Here, the distribution of a plurality of inter-mode phase differences ΔΦ ₁ , ΔΦ ₂ ,... Follows the normal distribution N (ΔΦ | μ, σ), but is not limited to this, and other statistical distributions (for example, chi- Square distribution, t distribution, F distribution, etc.) may be used.

  Thereafter, the phase determination unit 133 repeats the steps from the detection of the interference light to the creation of the existence probability distribution N (ΔΦ) J times, and causes the storage unit 131 to store the J existence probability distributions 504. Here, J is an integer of 2 or more, and is a value that is appropriately adjusted in consideration of the time taken for measuring the shape of one workpiece 150. The greater the value of J, the better the distance accuracy.

Then, the phase determination unit 133 applies Equation 6 to the _J existence probability distributions 504 ₁ (N ₁ (ΔΦ)) to 504 _J (N _J (ΔΦ)):
Or Equation 7:
Based on, the phase difference ΔΦ _D between the modes having the highest appearance probability is calculated, and it is determined that the phase is caused by either or both of the direct reflected light 301 and the diffused light 302a. In other words, the inter-mode phase difference ΔΦ taking the maximum value of the function obtained by multiplying the _J existence probability distributions 504 _{1 to} 504 _J with each other or the function obtained by adding each other is determined as ΔΦ _D. Yes. Therefore, the influence of the signal component due to the multiple reflected light 302b is greatly reduced in the determined inter-phase phase difference ΔΦ _D.

Therefore, the distance calculation unit 134 of the arithmetic processing unit 130 determines the value of the phase difference ΔΦ _D between the modes caused by either or both of the directly reflected light 301 and the diffused light 302a determined in this way as the value on the left side of Equation 4. Used as “Δθ _{k + 1} ^b−a −Δθ _k ^b−a ”. Thereby, the distance calculation part 134 can calculate the distance to the workpiece | work 150 more correctly by reducing the influence of the multiple reflected light 302b with respect to phase difference (DELTA) (PHI) between modes used for calculating a distance.

  The information on the distance to the workpiece 150 calculated in this manner is stored in the storage unit 131 in association with the position information regarding the measurement target point of the workpiece 150, that is, the point irradiated with the irradiation light Ps. Then, the image generation unit 135 generates a three-dimensional distance image related to the shape of the workpiece 150 using the information.

FIG. 6 is a flowchart of the shape measuring method according to this embodiment. In step S601, the workpiece 150 is placed on the position adjuster 140, and operating conditions and the like of various devices of the shape measuring apparatus 100 are set. For example, adjustment of the output of the laser light source 111, adjustment of the modulation frequencies f _m1 and f _m2 of the OFCGs 113a and 113b, adjustment of the modulation frequency f _α of the frequency shifter 114, and the like.

  In step S602, the position controller 132 of the arithmetic processing unit 130 outputs a control signal to the position adjuster 140, and the position adjuster 140 moves the workpiece 150 to a predetermined position accordingly. The position information of the workpiece 150 at this time is stored in the storage unit 131. This position information is information relating to the point where the measurement light Ps on the surface of the workpiece 150 is irradiated, and is stored in the storage unit 131 in association with the distance information acquired in step S611.

  In step S603, the arithmetic processing unit 130 operates the optical frequency comb laser device 110, and detects interference light between the measurement light Ps and the reference light Pr in each of the detectors 118a and 118b. Detectors 118a and 118b output interference signals based on the detected interference light to FFTs 119a and 119b, respectively. In response thereto, the FFTs 119a and 119b perform FFT processing on the interference signals, and store amplitude information, beat frequency (mode) information, phase information for each mode (θ-F phase spectrum), and the like in the storage unit 131.

In step S604, the phase determination unit 133 of the arithmetic processing device 130 subtracts the phase of the corresponding mode of the phase spectrum output from the FFT 119a from the phase of each mode of the phase spectrum output from the FFT 119b, and Δθ _{k of} Expression 3 ^The phase spectrum related to ^b−a is calculated and stored in the storage unit 131.

In step S605, the phase determination unit 133, a plurality of inter-mode phase difference ^{_{ΔΦ k + 1 = Δθ k +}} 1 b-a -Δθ k b-a between adjacent modes of the phase spectrum calculated (up to n) calculated in step S604 And stored in the storage unit 131.

In step S606, the phase determination unit 133 calculates the average μ of ΔΦ and the variance σ ² from the values of the plurality of inter-mode phase differences ΔΦ calculated in step S605. In step S <b> 607, the existence probability distribution N _i (ΔΦ) of the phase difference ΔΦ between the modes is created based on Expression 5 of the normal distribution and stored in the storage unit 131. Here, i is an integer of 1 to J, and the initial value is 1.

  In step S608, the phase determination unit 133 determines whether steps S603 to S607 have been performed a predetermined number of times (J times). If not performed (No in step S608), steps S603 to S607 are repeated.

In step S609, the phase determination unit 133 performs “argmax 、 N (ΔΦ)” processing of Expression 6 or “argmaxΣN (ΔΦ) of Expression 7 for the _J existence probability distributions N ₁ (ΔΦ) to N _J (ΔΦ). ”Processing (processing for obtaining the inter-mode phase difference ΔΦ that maximizes the function obtained by multiplying the J existence probability distributions with each other or the function obtained by adding each other), and the mode position with the highest appearance probability. The phase difference ΔΦ _D is calculated. In step 610, the phase determination unit 133 determines that the phase difference ΔΦ _D calculated in step S609 is a phase related to the direct reflected light 301 and / or the diffused light 302a.

In step S611, the distance calculation unit 134 of the processor 130 uses the phase difference .DELTA..PHI _D determined in step S610 as the value of the value of the left side of the formula 4 ^{_{"Δθ k + 1 b-a -Δθ}} k b-a " The distance to the workpiece 150 is calculated. The calculated distance information is stored in the storage unit 131 in association with the position information of the workpiece 150 output in step S602.

  In step S612, the arithmetic processing unit 130 determines whether there is another position to be measured within the range to be measured on the surface of the workpiece 150. If there are other positions to be measured (Yes in step S612), steps S602 to S612 are repeated.

  In step S613, the image generation unit 135 of the arithmetic processing device 130 determines the color information determined according to the distance information for each pixel of the image according to the position information, based on the distance information associated with the position information. By assigning (shading), a three-dimensional distance image is generated.

  As described above, the shape measuring apparatus and the shape measuring method according to the present embodiment more accurately reduce the distance from the reference point RP to the workpiece 150 by greatly reducing the influence of the multiple reflected light 302b on the phase difference ΔΦ between modes. Can be measured.

(Example)
As an example of the present invention, using the shape measuring apparatus 100 according to the first embodiment, the distance to the vehicle component 701 as the workpiece 150 was obtained, and a three-dimensional shape image 703 of the vehicle component 701 was generated. FIG. 7 is an actual photograph of the vehicle component 701, and FIG. 8 shows a three-dimensional distance image 703 of the range 702 to be measured of the vehicle component 701.

  The points A, B, and C corresponding to the inclined surface of the vehicle component 701 in the three-dimensional distance image 703 are directed to the drawing by 4 °, 30 °, and 60 ° with respect to the flat surface F of the vehicle component 701, respectively. It is inclined to the back side. In this measurement, when the inclination exceeds 3 °, the direct reflected light 301 could hardly be detected. Therefore, the results regarding the points A to C are almost based on the indirect reflected light 302.

  FIG. 9 shows the result of obtaining the distance accuracy (μm) for the points A to C. The distance accuracy here is obtained by calculating the distance a plurality of (several tens) times for each of the points A to C by the method of the present invention and the prior art (Patent Document 2), and the average value and standard of the distance from the distribution of the distances. The deviation σ is obtained, and is a value of reproducibility (variation) (3σ) obtained therefrom.

  The distance accuracy (3σ) was 5, 6, 35 (μm) at points A to C for the present invention, and 27, 45, 123 (μm) at points A to C for the conventional technology, respectively. As described above, in the prior art, the value is greatly different every time the distance is measured with respect to the same point due to the influence of the multiple reflected light, the reproducibility is poor, in other words, the variation in each measurement is large. However, since the present invention reduces the influence of multiple reflected light, the reproducibility is good, in other words, the variation between measurements is small.

[Second Embodiment]
FIG. 10A is a block diagram of a shape measuring apparatus 1000 according to the second embodiment of the present invention, and FIG. 10B is a view of the lens 120 and the workpiece 150 as viewed from the optical frequency comb laser 110 side. . The configurations of the optical frequency comb laser device 110, the lens 120, the arithmetic processing device 130, and the position adjuster 140 are the same as those described above, and a description thereof will be omitted.

  The shape measuring apparatus 1000 further includes an irradiation angle changer 1001 that changes the direction of the measurement light Ps irradiated from the optical frequency comb laser apparatus 110 to the lens 120, and the center of the irradiation angle changer 1001 is on the central axis 1010 of the lens 120. It is in. The lens 120 of the present embodiment irradiates the work 150 with the measurement light Ps from the optical frequency comb laser device 110 as parallel light 1021 and 1022, and condenses the reflected light from the work 150 on the irradiation angle changer 1001. In response to this, the irradiation angle changer 1001 irradiates the optical frequency comb laser device 110 with the reflected light from the workpiece 150.

  The irradiation angle changer 1001 includes a mirror and a power mechanism for driving the mirror, and the measurement light Ps irradiated toward the lens 120 according to a control signal from the optical path control unit 136 of the arithmetic processing unit 130. The irradiation angle (x, y) is changed. Here, x is an angle with respect to the central axis 1010, and y is an angle with respect to an axis perpendicular to the central axis.

By changing the irradiation angle (x, y), the position where the workpiece 150 is irradiated with the measurement light Ps can be adjusted to a predetermined position. For example, the measurement light Ps is irradiated to the point A _{1 of} the workpiece 150 at an irradiation angle (x ₁ , y ₁ ), and the point A _{2 of} the workpiece 150 is irradiated at an irradiation angle (x ₂ , y ₂ ).

  In this way, the optical path control unit 136 can irradiate the measurement light Ps to a predetermined position of the workpiece 150 by controlling the irradiation angle (x, y) of the measurement light Ps by the irradiation angle changer 1001.

As can be seen from FIG. 10, when the irradiation angle of the measurement light Ps is adjusted, the optical path 1021 is longer by ΔLs = Ls1−Ls0 = (1 / cosx ₁ −1) Ls0 than the optical path 1010 passing through the center of the lens 120. Will be. Here, Ls is an optical path length from the reference point RP of the measurement light Ps passing through the center of the lens 120 to the workpiece 150.

  Therefore, in this embodiment, the distance calculation unit 134 calculates the distance to the workpiece 150 by replacing Ls in the above-described Expression 3 and Expression 4 with “Ls + ΔLs” = “Ls + (1 / cosx−1) Ls0”. .

  In this embodiment, the irradiation position of the measurement light Ps can be changed without moving the workpiece 150, and the irradiation position of the measurement light Ps can be easily finely adjusted.

100: Shape measuring device,
113a: first optical frequency comb generator (OFCG) (first optical generator)
113b: second optical frequency comb generator (OFCG) (second optical generator)
116: Reference plane 118a: First detector 118b: Second detector 120: Lens 130: Arithmetic processing device 132: Position control unit 133: Phase determination unit 134: Distance calculation unit 135: Image generation unit 150: Workpiece ( Measurement object)

Claims (4)

A first light generator for generating first light having a mode of a first repetition frequency;
A second light generator for generating a second light having a second repetition frequency mode different from the first repetition frequency;
A first detector for detecting a first interference light between the first light and the second light emitted from the first and second light generators via a reference point;
A second detector for detecting a second interference light between the first light reflected from the measurement object and the second light reflected from the reference surface via the reference point;
Calculating a phase difference between said second interference light phase (θ _{k ^b)} and said first interference light phase _{^{(θ k a) (Δθ k}} b-a), the phase difference ([Delta] [theta] _k ^a plurality of phase differences (ΔΦ) between adjacent modes in ( ^b−a ) and a plurality of phase difference existence probability distributions (N (ΔΦ)) are generated a predetermined number of times. Repetitively, a phase determining unit that determines a phase difference (ΔΦ _D ) between modes that takes a maximum value of a function obtained by multiplying the predetermined number of the existence probability distributions with each other or a function obtained by adding to each other;
A shape measuring apparatus comprising: a distance calculating unit that calculates a distance from the reference point to the measurement object based on the determined phase difference between modes. A position control unit for controlling the position of the measurement object;
The shape measuring apparatus according to claim 1, further comprising: an image generation unit configured to generate a three-dimensional distance image of the measurement object based on the distance information associated with the position information of the measurement object. A lens,
An irradiation angle changer that makes the first light incident through the reference point and irradiates the first light to the lens at a predetermined irradiation angle;
The shape according to claim 1 or 2, wherein the phase determination unit calculates a distance from the reference point to the measurement object based on the determined phase difference between modes (ΔΦ _D ) and the irradiation angle. measuring device. A first step of detecting interference light having a mode of a predetermined repetition frequency;
A second step of calculating a plurality of phase differences (ΔΦ) between adjacent modes of the interference light;
A third step of creating an existence probability distribution (N (ΔΦ)) of the phase differences between the plurality of modes;
A phase difference between modes that takes a maximum value of a function obtained by repeating the first step to the third step a predetermined number of times and multiplying the predetermined number of the existence probability distributions with each other or adding each other. Determining (ΔΦ _D );
Calculating the distance from the reference point to the measurement object based on the determined inter-phase phase difference (ΔΦ _D ).