Shape measuring device and shape measuring method

Abstract

Provided are a shape measuring device and a shape measuring method capable of reducing errors in a measured shape of a surface to be measured. The shape measuring device comprises: a relative movement unit (14) for scanning measurement light (LA) over a surface to be measured (W), by causing a probe (24) to move relatively along the surface to be measured (W); a detecting unit (light detector (28)) for repeatedly detecting combined light (LC) generated by a light combining unit (beam splitter (22)), for each of a plurality of measurement points (Pm) on the surface to be measured (W) on which the measurement light (LA) is incident, during the relative movement; a distance calculating unit (32) for detecting a beat frequency from a detection signal (29) of the combined light (LC) detected by the detecting unit for each measurement point (Pm), and calculating a distance from the probe (24) to the measurement point (Pm) on the basis of the beat frequency; a position calculating unit (34) for calculating a position of each measurement point (Pm); and a position adjusting unit (38) for adjusting the position of the measurement point (Pm) on the basis of a Doppler shift amount (fd) of the measurement light (LA) reflected by the measurement point (Pm), for each measurement point (Pm).

Description

Shape measuring device and shape measuring method

[0001] The present invention relates to a shape measuring apparatus and a shape measuring method for measuring the shape of a surface to be measured using a wavelength swept light source.

[0002] A scanning measurement device that performs scanning measurement is known as a shape measuring device that measures the shape (surface shape, contour shape, etc.) of a measurement surface of a measurement target in a non-contact manner (see Patent Document 1). This scanning measurement device measures the shape of the measurement surface by moving a probe of a non-contact distance meter relatively along the measurement surface while maintaining a gap between the probe and the measurement surface, and repeatedly detecting the distance from the probe to each of a plurality of measurement points on the measurement surface and detecting the position of the measurement point based on the distance detection result.

[0003] A known non-contact rangefinder is a wavelength-swept non-contact rangefinder that uses a wavelength-swept light source (see Patent Document 2). The wavelength-swept non-contact rangefinder splits wavelength-swept light emitted from the wavelength-swept light source into measurement light and reference light, emits the measurement light from the probe toward the surface to be measured, and emits the reference light toward the reference surface. The wavelength-swept non-contact rangefinder detects, with a photodetector, a combined light of the measurement light reflected by the surface to be measured and incident on the probe and the reference light reflected by the reference surface. At this time, a difference in wavelength (frequency) between the measurement light and the reference light occurs on the photodetector due to a difference in arrival times between the measurement light and the reference light from the wavelength-swept light source to the photodetector. The photodetector detects the frequency difference between the measurement light and the reference light as a beat frequency. The wavelength-swept non-contact rangefinder then frequency-analyzes the detection signal detected by the photodetector to detect the beat frequency, and calculates the distance from the probe to the surface to be measured based on the beat frequency.

[0004] JP 2020-56637 A JP 2021-32734 A

[0005] When performing the scanning measurement described in Patent Document 1 using the wavelength-sweeping non-contact range finder described in Patent Document 2, if the surface to be measured is non-horizontal, such as a curved surface, the measurement light from the probe is incident on the surface at an angle rather than perpendicularly. Moving the probe relative to the surface in this state causes a Doppler shift, in which the frequency of the measurement light reflected at the measurement point on the surface is shifted due to the Doppler effect. In a wavelength-sweeping non-contact range finder, if the frequency of the measurement light changes independently due to factors other than the distance between each measurement point and the probe, errors occur in the distance measurement results from the probe to each measurement point, and therefore in the position detection results for each measurement point. Therefore, scanning measurements of a surface to be measured using a wavelength-sweeping non-contact range finder may result in errors in the measured shape of the surface to be measured.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a shape measuring device and a shape measuring method that can reduce errors in the measured shape of a surface to be measured due to Doppler shift.

[0007] A shape measuring device for achieving the object of the present invention includes a wavelength swept light source, a light splitting unit that splits light emitted from the wavelength swept light source into measurement light and reference light, a probe that emits the measurement light split by the light splitting unit toward a surface to be measured and into which the measurement light reflected by the surface to be measured is incident, a reference surface that reflects the reference light split by the light splitting unit, a multiplexing unit that generates multiplexed light of the measurement light reflected by the surface to be measured and incident on the probe and the reference light reflected by the reference surface, and a relative movement detector that moves the probe along the surface to be measured at a distance from the surface to scan the surface to be measured with the measurement light. a detection unit that repeatedly detects the combined light generated by the combining unit at each of a plurality of measurement points on the surface to be measured where the measurement light is incident while the relative movement is being performed; a distance calculation unit that detects a beat frequency from a detection signal of the combined light detected by the detection unit for each measurement point and calculates the distance from the probe to the measurement point based on the beat frequency; a position calculation unit that calculates the position of each measurement point based on the calculation result of the distance calculation unit corresponding to the measurement point; and a position correction unit that corrects the position of the measurement point calculated by the position calculation unit based on the amount of Doppler shift of the measurement light reflected at the measurement point for each measurement point.

[0008] This shape measuring device can correct errors in the positions of the measurement points due to Doppler shift.

[0009] In a form measuring instrument according to another aspect of the present invention, a relative movement unit moves a probe relatively along a surface to be measured, with a fixed gap therebetween, based on pre-created shape data of the surface to be measured, thereby making it possible to detect an error between the ideal shape of the surface to be measured, which is assumed in the shape data, and the actual shape of the surface to be measured.

[0010] In a form measuring device according to another aspect of the present invention, the probe causes measurement light to be incident on the surface to be measured from an oblique direction, thereby making it possible to correct errors in the position of each measurement point due to Doppler shift.

[0011] In another aspect of the shape measuring device of the present invention, a scanning direction vector calculation unit is provided that calculates, for each measurement point, the magnitude of a scanning direction vector of the measurement light that scans the surface to be measured and that is parallel to the tangent direction of the surface to be measured at the measurement point, and when the direction of the measurement light between the probe and the measurement point is defined as the measurement light direction, a position correction unit calculates, for each measurement point, the amount of Doppler shift based on the component of the scanning direction vector calculated by the scanning direction vector calculation unit that is parallel to the measurement light direction and the wavelength or frequency of the measurement light.

[0012] A shape measurement method for achieving the object of the present invention includes a light splitting step of splitting light emitted from a wavelength swept light source into measurement light and reference light, and emitting the measurement light from a probe toward a surface to be measured and the reference light toward the reference surface; a combining step of generating combined light of the measurement light reflected by the surface to be measured and incident on the probe and the reference light reflected by the reference surface; a relative movement step of moving the probe along the surface to be measured while keeping a gap therebetween and scanning the surface to be measured with the measurement light; and a relative movement step of scanning multiple points on the surface to be measured onto which the measurement light is incident during the relative movement step. The method includes a detection step for repeatedly detecting the combined light generated in the combining step for each measurement point, a distance calculation step for detecting a beat frequency from a detection signal of the combined light detected in the detection step for each measurement point and calculating a distance from the probe to the measurement point based on the beat frequency, a position calculation step for calculating a position of the measurement point for each measurement point based on the calculation result of the distance calculation step corresponding to the measurement point, and a position correction step for correcting the position of the measurement point calculated in the position calculation step for each measurement point based on the Doppler shift amount of the measurement light reflected at the measurement point.

[0013] The present invention can reduce errors in the measured shape of the measurement target surface due to Doppler shift.

[0014] 7 is a schematic diagram of a scanning measurement device that performs non-contact scanning measurement of a curved measurement surface of an object to be measured. It is a schematic diagram showing the optical configuration of a wavelength scanning interferometer. It is a functional block diagram of a control device. It is an explanatory diagram for explaining issues when performing non-contact scanning measurement of a curved measurement surface to be measured. It is an explanatory diagram for explaining calculation of a scanning direction vector by a scanning direction vector calculation unit. It is a flowchart showing the flow of scanning measurement processing of a measurement surface by a scanning measurement device. It is a diagram showing an example of a measurement surface on which scanning measurement is performed by a scanning measurement device. It is a graph comparing the positions of each measurement point and each correction measurement point obtained by scanning measurement of the measurement range of the measurement surface shown in FIG. 7 using a scanning measurement device with the positions of each measurement point obtained by measuring each measurement point with a contact-type rangefinder.

[0015] 1 is a schematic diagram of a scanning measurement apparatus 10 that performs non-contact scanning measurement of a curved (non-horizontal) measurement surface W of an object to be measured. In this embodiment, an airfoil surface will be used as an example of the measurement surface W. As shown in FIG. 1, the scanning measurement apparatus 10 corresponds to the shape measurement apparatus of the present invention and includes a wavelength-sweeping interferometer 12, a relative movement unit 14, and a control device 16.

[0016] 2 is a schematic diagram showing the optical configuration of the wavelength-swept interferometer 12. As shown in FIG. 2 and the previously described FIG. 1, the wavelength-swept interferometer 12, together with a control device 16 (described later), constitutes a wavelength-swept non-contact distance meter that measures the distances to a plurality of measurement points Pm on a measurement surface W in a non-contact manner. The wavelength-swept interferometer 12 includes a wavelength-swept light source 20, a beam splitter 22, a probe 24, a reference surface 26, and a photodetector 28.

[0017] Under the control of the control device 16, the swept light source 20 emits swept light L toward the beam splitter 22. The swept light L is, for example, light whose wavelength changes sinusoidally over time at a constant wavelength sweep period (constant wavelength sweep frequency) and within a constant wavelength band.

[0018] A half mirror, for example, is used as the beam splitter 22. The beam splitter 22 splits the wavelength swept light L input from the wavelength swept light source 20 into measurement light LA ​​and reference light LB, and emits the measurement light LA ​​toward the input / output end 24a of the probe 24, while emitting the reference light LB toward the reference surface 26. In this case, the beam splitter 22 functions as a light splitting unit of the present invention.

[0019] The probe 24 (also referred to as a measurement head) has an incident / exit end 24a that emits the measurement light LA ​​split by the beam splitter 22 toward the measurement surface W while scanning measurement of the measurement surface W is being performed. The measurement light LA ​​reflected on the measurement surface W is incident on the incident / exit end 24a. Note that at least one of the beam splitter 22, the reference surface 26, and the photodetector 28 may be housed inside the probe 24.

[0020] The reference surface 26 is, for example, a reflecting mirror, and reflects the reference light LB incident from the beam splitter 22 toward the beam splitter 22 .

[0021] The beam splitter 22 generates a combined light LC (interference light) from the measurement light LA, which is reflected by the measurement surface W and then incident on the input / output end 24a of the probe 24, and the reference light LB, which is reflected by the reference surface 26, and outputs this combined light LC to the photodetector 28. In this case, the beam splitter 22 functions as a combining section of the present invention.

[0022] The photodetector 28 corresponds to the detection unit of the present invention, and may be, for example, a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) image sensor, a silicon photodiode, an InGaAs (Indium Gallium Arsenide) photodiode, etc. Under the control of the control device 16, the photodetector 28 detects the combined light LC input from the beam splitter 22, i.e., converts and amplifies the combined light LC into an electrical signal, and outputs a detection signal 29 of the combined light LC to the control device 16.

[0023] The relative moving unit 14 is composed of various actuators such as a motor-driven mechanism (for example, an actuator capable of five-axis operation), and is capable of displacing the position and orientation of the probe 24. Under the control of the control device 16, the relative moving unit 14 displaces the position and orientation of the probe 24, thereby moving the probe 24 relative to the measurement surface W along the measurement path 15 shown in FIG. 1 at a substantially constant interval from the measurement surface W. As a result, the measurement surface W is scanned with the measurement light LA, and the detection of the combined light LC by the photodetector 28 and the output of an interference signal 29 from the photodetector 28 are repeatedly performed for each of a plurality of measurement points Pm on the measurement surface W.

[0024] In addition, instead of displacing the position and posture of the probe 24, the relative movement unit 14 may move the probe 24 relatively along the measurement path 15 by displacing the position and posture of the stage supporting the measurement surface W (measurement object).

[0025] The control device 16 comprehensively controls the scanning measurement of the measurement surface W by the wavelength-swept interferometer 12 and the relative movement unit 14, and the shape calculation of the measurement surface W. The control device 16 includes an arithmetic circuit configured with various processors, memories, etc. The various processors include a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), and a programmable logic device (e.g., a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). The various functions of the control device 16 may be realized by a single processor or by multiple processors of the same or different types.

[0026] 3 is a functional block diagram of the control device 16. As shown in FIG. 3, the control device 16 is connected to the components of the wavelength-swept interferometer 12 and the relative movement unit 14, and is also provided with a storage unit 17. This storage unit 17 stores a control program (not shown) for the control device 16, shape calculation results for the measurement surface W, and CAD data 17a, which is shape data of the measurement surface W (object) created in advance using CAD (Computer Aided Design). The CAD data 17a may be stored on an external server on the Internet. Shape data in a format other than CAD may also be stored in the storage unit 17, as long as it is data indicating the shape of the measurement surface W.

[0027] The control device 16 functions as a measurement control unit 30, a distance calculation unit 32, a position calculation unit 34, a scanning direction vector calculation unit 36, a position correction unit 38, and a shape calculation unit 40 by executing a control program (not shown) in the memory unit 17.

[0028] The measurement control unit 30 controls the scanning measurement operation of the measurement surface W by the wavelength-swept interferometer 12 and the relative movement unit 14. Specifically, in response to a measurement start operation for scanning measurement of the measurement surface W, the measurement control unit 30 starts emitting the wavelength-swept light L from the wavelength-swept light source 20 and repeatedly causes the photodetector 28 to detect the combined light LC and output the detection signal 29.

[0029] In addition, the measurement control unit 30 drives the relative movement unit 14 to move the probe 24 along the measurement path 15 shown in Figure 1, i.e., to move it relatively along the measurement surface W while maintaining an approximately constant gap from the measurement surface W.

[0030] Specifically, based on the CAD data 17a of the measurement surface W obtained from the memory unit 17, the measurement control unit 30 determines a measurement path 15 that follows the measurement surface W while leaving a certain distance from the measurement surface W assumed in this CAD data 17a (ideal measurement surface W).

[0031] The measurement control unit 30 then drives the relative movement unit 14 to align the probe 24 to the measurement start position of the determined measurement path 15, and then moves the probe 24 along this measurement path 15. As a result, the probe 24 is moved relatively along the actual measurement surface W while maintaining a substantially constant gap from the measurement surface W, and the measurement surface W is scanned with the measurement light LA. Note that the method of moving the probe 24 relative to the measurement surface W during scanning measurement is a well-known technique, and therefore a detailed description thereof will be omitted here.

[0032] In this way, in the scanning measurement of the measurement surface W, the measurement light LA ​​is scanned over the measurement surface W while the probe 24 is relatively moved along the measurement path 15, and the photodetector 28 repeatedly detects the combined light LC, thereby detecting the combined light LC by the photodetector 28 and outputting a detection signal 29 for each of the plurality of measurement points Pm on the measurement surface W. As a result, in the scanning measurement of the measurement surface W in this embodiment, the error between the ideal shape of the measurement surface W assumed in the CAD data 17a and the actual shape of the measurement surface W is detected.

[0033] While the probe 24 is moving relatively along the measurement path 15, the distance calculation unit 32 calculates the distance from the probe 24 to the measurement point Pm (hereinafter referred to as the measurement distance) for each measurement point Pm based on the detection signal 29 input from the photodetector 28.

[0034] Specifically, the distance calculation unit 32 performs frequency analysis on the detection signal 29 (beat signal) detected by the photodetector 28 to detect the beat frequency, which is the frequency difference between the measurement light LA ​​and the reference light LB. Since the method for detecting the beat frequency is a well-known technique, a detailed description thereof will be omitted here. The beat frequency and the difference in arrival times of the measurement light LA ​​and the reference light LB from the wavelength swept light source 20 to the photodetector 28 are proportional to the measurement distance. Therefore, the distance calculation unit 32 calculates the measurement distance based on the detection result of the beat frequency, with reference to the following equation (1). Note that "Df" in equation (1) is a conversion coefficient. This conversion coefficient Df is set in advance by conducting experiments or simulations.

[0035] [Equation 1] Measurement distance = Df × beat frequency

[0036] Similarly, the distance calculation unit 32 performs frequency analysis of the detection signal 29 (detection of beat frequency) and calculation of the measured distance using the above formula (1) for each measurement point Pm.

[0037] For each measurement point Pm, the position calculation unit 34 calculates the position of the measurement point Pm based on the calculation result of the distance calculation unit 32 corresponding to the measurement point Pm and the position (position of the reference point Ph described below, see Figure 4) and attitude (angle) of the probe 24 corresponding to the measurement point Pm.

[0038] 4 is an explanatory diagram illustrating the issues that arise when performing non-contact scanning measurement of a curved measurement surface W. The symbol Ph in the figure denotes a predetermined reference point within the probe 24. The distance calculation unit 32 described above calculates the distance between the reference point Ph and the measurement point Pm as the measurement distance. The symbol Vm in the figure denotes a measurement light vector directed from the reference point Ph to the measurement point Pm. The symbol N in the figure denotes the normal direction of the measurement surface W at the measurement point Pm. The symbol Vs in the figure denotes a scanning direction vector (velocity vector) of the measurement light LA ​​that scans the measurement surface W and is parallel to the tangent direction of the measurement surface W at the measurement point Pm.

[0039] 4, when scanning measurement of a curved measurement surface W, the angle of incidence of the measurement light LA ​​incident on each measurement point Pm from the probe 24 (one measurement point Pm is shown as a representative example in the figure) is not perpendicular (parallel to the normal direction N) due to the curvature of the measurement surface W and constraints imposed by the method of holding the probe 24 by the relative moving unit 14. In this case, the scanning direction vector Vs also has a component (hereinafter referred to as measurement light direction component Vd) in the direction of the measurement light vector Vm (corresponding to the measurement light direction of the present invention). This measurement light direction component Vd is expressed by the following equation (2), where θ is the angle formed between the scanning direction vector Vs and the measurement light vector Vm.

[0040] [Math. 2] Vd=-Vm / |Vm|×|Vs|×COS(θ)

[0041] When the measurement light direction component Vd is generated in this way, even though the measurement distance |Pm-Ph| is constant, each measurement point Pm (measurement surface W) is in the same state as approaching the probe 24 by the measurement light direction component Vd shown in the above [Equation 2]. This causes a Doppler shift, in which the frequency of the measurement light LA ​​reflected at each measurement point Pm is shifted due to the Doppler effect. As a result, an error occurs in the measurement distance for each measurement point Pm calculated by the distance calculation unit 32, and therefore an error also occurs in the position for each measurement point Pm calculated by the position calculation unit 34.

[0042] Therefore, in this embodiment, the position of the measurement point Pm calculated by the position calculation unit 34 is corrected for each measurement point Pm based on the Doppler shift amount of the measurement light LA. Specifically, in this embodiment, the calculation of the scanning direction vector Vs by the scanning direction vector calculation unit 36 ​​and the position correction of the measurement point Pm by the position correction unit 38 are repeatedly performed for each measurement point Pm. Note that, since the position measurement of the first measurement point Pm in this embodiment is performed while the probe 24 is stationary with respect to the measurement surface W, no Doppler shift of the measurement light LA ​​occurs. Therefore, the calculation of the scanning direction vector Vs and the position correction of the measurement point Pm are repeatedly performed for each measurement point Pm from the second measurement point Pm onwards.

[0043] FIG. 5 is an explanatory diagram for explaining the calculation of the scanning direction vector Vs by the scanning direction vector calculation unit 36. As shown in FIG. 5 and the previously described FIG. 3, the scanning direction vector calculation unit 36 ​​calculates the magnitude of the scanning direction vector Vs for each measurement point Pm from the second onward. For example, the scanning direction vector calculation unit 36 ​​approximately calculates the scanning direction vector Vs using the following formula (3), assuming that the most recent measurement point Pm is Pm(n), the previous measurement point Pm is Pm(n-1), and the scanning time of the measurement light LA ​​from Pm(n-1) to Pm(n) is "T." The scanning direction vector calculation unit 36 ​​then performs the calculation process of formula (3) for each measurement point Pm to calculate the scanning direction vector Vs for each measurement point Pm from the second onward.

[0044] [Math. 3] Vs (mm / s) = [Pm (n-1) - Pm (n)] / T

[0045] For each measurement point Pm from the second onward, the position correction unit 38 corrects the position of the measurement point Pm calculated by the position calculation unit 34 based on the amount of Doppler shift in the frequency of the measurement light LA ​​reflected at the measurement point Pm. Specifically, if the measurement point Pm after position correction is referred to as a "corrected measurement point Pmc," the position of the corrected measurement point Pmc is expressed by the following equation (4) based on the position of the measurement point Pm before correction, the conversion coefficient Df described above, and the measurement light direction component Vd and Doppler shift amount [fd (Hz)] corresponding to the measurement point Pm before correction.

[0046] [Math. 4] Pmc=Pm+Df×fd×Vd / |Vd|

[0047] Here, the Doppler shift amount [fd (Hz)] is expressed by the following [Equation 5] when the wavelength of the measurement light LA ​​is "λ (μm)". Therefore, the above [Equation 4] can be transformed into the following [Equation 6] based on [Equation 5]. Note that although [Equation 5] uses the wavelength λ of the measurement light LA ​​as a variable, the frequency v (v = C / λ) of the measurement light LA ​​may also be used as a variable instead of the wavelength λ.

[0048] [Math. 5] fd (Hz) = 2 x | Vd | (mm / s) / [λ (μm) x 0.001]

[0049] [Math. 6] Pmc=Pm+Df×{2×|Vd|(mm / s) / [λ(μm)×0.001]}×Vd / |Vd| =Pm+Df×2×Vd(mm / s) / [λ(μm)×0.001]

[0050] In addition, in the above [Equation 6], the measurement light direction component Vd (mm / s) is expressed by the above [Equation 2]. Therefore, the above [Equation 6] can be transformed into the following [Equation 7] based on the [Equation 2].

[0051] [Math. 7] Pmc=Pm+Df×2×{-Vm / |Vm|×|Vs|×COS(θ)}(mm / s) / [λ(μm)×0.001]

[0052] Here, cos(θ) in equation (7) is expressed by the known definition of the inner product of a vector based on the scanning direction vector Vs and the measurement light vector Vm, as shown in equation (8) below. Note that the measurement light vector Vm can be calculated for each measurement point Pm based on the known position of the reference point Ph for each measurement point Pm and the position of the measurement point Pm calculated for each measurement point Pm by the position calculation unit 34.

[0053] [Math. 8] COS (θ)=Vs×(-Vm) / (|Vs||Vm|)

[0054] Therefore, for each measurement point Pm from the second onwards, the position correction unit 38 calculates the position of the corrected measurement point Pmc by substituting the calculation result of the scanning direction vector Vs by the scanning direction vector calculation unit 36, the calculation result of the measurement light vector Vm calculated by itself, for example, and the wavelength of the measurement light LA ​​obtained from the wavelength swept light source 20 into the above equations [7] and [8].

[0055] Alternatively, the position corrector 38 may first calculate the Doppler shift amount fd for each measurement point Pm from the second onward based on the above-mentioned [Equation 5] or the like, and then calculate the position of the corrected measurement point Pmc based on the above-mentioned [Equation 4]. In this case, the position corrector 38 functions as a Doppler shift amount calculator that calculates the Doppler shift amount fd.

[0056] The shape calculation unit 40 calculates the shape (surface shape, contour shape, etc.) of the measurement surface W based on the position of the first measurement point Pm calculated by the position calculation unit 34 and the positions of the second and subsequent corrected measurement points Pmc calculated by the position correction unit 38. Note that the shape calculation unit 40 may calculate the shape of the measurement surface W based only on the positions of the corrected measurement points Pmc.

[0057] 6 is a flowchart showing the flow of scanning measurement processing of the measurement surface W by the scanning measurement device 10 having the above configuration, according to the shape measurement method of the present invention. As shown in Fig. 6, when an examiner sets the measurement surface W (measurement object) on the scanning measurement device 10 and then performs a measurement start operation on an operation unit (not shown), the measurement control unit 30 acquires CAD data 17a of the measurement surface W from the storage unit 17 and determines the measurement path 15 based on this CAD data 17a (step S1).

[0058] Next, the measurement control unit 30 drives the relative movement unit 14 to perform alignment by moving the probe 24 to the measurement start position of the determined measurement path 15 (step S2). The measurement control unit 30 also starts emission of the wavelength swept light L from the wavelength swept light source 20 (step S3).

[0059] The wavelength-swept light L is split by the beam splitter 22 into a measurement light LA ​​and a reference light LB, and the measurement light LA ​​is incident on the first measurement point Pm on the measurement surface W, and the reference light LB is incident on the reference surface 26 (step S4, which corresponds to the light splitting step of the present invention). Then, the measurement light LA ​​reflected from the first measurement point Pm and the reference light LB reflected from the reference surface 26 are combined by the beam splitter 22, and the combined light LC of the measurement light LA ​​and the reference light LB is incident on the photodetector 28 (step S4, which corresponds to the combining step of the present invention).

[0060] Furthermore, the measurement control unit 30 starts detecting the combined light LC by the photodetector 28 and outputting the detection signal 29 in synchronization with the emission of the wavelength swept light L from the wavelength swept light source 20 (step S5).

[0061] When the photodetector 28 outputs the detection signal 29 corresponding to the first measurement point Pm, the distance calculation unit 32 performs frequency analysis of the detection signal 29 to detect a beat frequency, and calculates the measurement distance corresponding to the first measurement point Pm based on the beat frequency detection result using the above-mentioned [Equation 1] (step S6). Furthermore, the position calculation unit 34 calculates the position of the first measurement point Pm based on the distance detection result of the first measurement point Pm by the distance calculation unit 32 and the position and attitude (angle) of the reference point Ph of the probe 24 (step S7).

[0062] Next, the measurement control unit 30 drives the relative movement unit 14 to move the probe 24 along the measurement path 15. As a result, the probe 24 is moved relatively along the actual measurement surface W at a substantially constant interval from the measurement surface W, and the measurement surface W is scanned with the measurement light LA ​​(step S8, corresponding to the relative movement step of the present invention). When the measurement light LA ​​scans the measurement surface W a constant distance (scanning time T) from the first measurement point Pm and the measurement light LA ​​is incident on the second measurement point Pm, the measurement control unit 30 causes the photodetector 28 to detect the combined light LC and output a detection signal 29 (step S9, corresponding to the detection step of the present invention).

[0063] When the detection signal 29 corresponding to the second measurement point Pm is output from the photodetector 28, the distance calculation unit 32 calculates the measurement distance corresponding to the second measurement point Pm (step S10), and the position calculation unit 34 calculates the position of the second measurement point Pm (step S11), in the same manner as when the position of the first measurement point Pm was detected. Note that step S10 corresponds to the distance calculation step of the present invention, and step S11 corresponds to the position calculation step of the present invention.

[0064] When the calculation of the position of the second measurement point Pm is completed, the scanning direction vector calculation unit 36 ​​calculates the scanning direction vector Vs corresponding to the second measurement point Pm using the above formula 3 based on the position of the previous first measurement point Pm, the position of the second measurement point Pm, and the scanning time T between the two (step S12).

[0065] Next, the position corrector 38 calculates a measurement light vector Vm corresponding to the second measurement point Pm based on the position of the reference point Ph corresponding to the second measurement point Pm and the position of the second measurement point Pm determined by the position calculator 34. The position corrector 38 also acquires the wavelength λ (or frequency v) of the measurement light LA ​​corresponding to the second measurement point Pm from the swept light source 20.

[0066] Then, the position correction unit 38 calculates the position of the corrected measurement point Pmc using the above-mentioned [Equation 7] and [Equation 8] based on the calculation result of the scanning direction vector Vs corresponding to the second measurement point Pm, the calculation result of the measurement light vector Vm, and the wavelength of the measurement light LA. This makes it possible to correct the position of the second measurement point Pm based on the Doppler shift amount of the measurement light LA ​​at the second measurement point Pm (step S13, corresponding to the position correction step of the present invention).

[0067] Thereafter, while the probe 24 is being moved relatively along the measurement path 15 (NO in step S14), the processes from step S9 to step S13 described above are repeatedly executed for each of the third and subsequent measurement points Pm. As a result, the positions of the third and subsequent measurement points Pm are corrected, and the positions of each of the third and subsequent corrected measurement points Pmc are calculated.

[0068] When the relative movement of the probe 24 is completed (YES in step S14), the shape calculation unit 40 calculates the shape of the measured surface W based on the position of the first measurement point Pm calculated in step S7 and the positions of each corrected measurement point Pmc calculated in step S9 (step S15).

[0069] [Effects of this embodiment] Fig. 7 is a diagram showing an example of a measurement surface W scanned by the scanning measurement apparatus 10 of this embodiment. Fig. 8 is a graph comparing the positions of each measurement point Pm and each correction measurement point Pmc obtained by scanning measurement of the measurement range R of the measurement surface W shown in Fig. 7 using the scanning measurement apparatus 10 with the positions of each measurement point Pm obtained by measuring each measurement point Pm with a contact-type range finder (not shown).

[0070] As shown in Fig. 7, a portion of the surface of a 25 mm diameter calibration sphere was used as the measurement surface W, and scanning measurement was performed by the scanning measurement device 10 of this embodiment along a measurement line C on this measurement surface W. The positions of each measurement point Pm measured by the scanning measurement device 10 were measured by a contact-type distance meter. As shown in Fig. 8, the positions of each measurement point Pm obtained by the scanning measurement by the scanning measurement device 10 deviate from the interpolation curve ML of each measurement point Pm measured by the contact-type scanning measurement device due to the influence of the Doppler shift.

[0071] In contrast, it has been confirmed that the positions of the corrected measurement points Pmc corrected by the position corrector 38 coincide with the above-mentioned interpolation curve ML regardless of the direction of the scanning measurement (forward or backward). Therefore, by correcting the positions of the measurement points Pm obtained by scanning measurement based on the amount of Doppler shift, as in this embodiment, it is possible to reduce errors in the measured shape of the measurement surface W due to the Doppler shift.

[0072] [Others] The wavelength-sweeping interferometer 12 used in the above embodiment is not limited to the one shown in FIG. 2, and the type thereof is not particularly limited.

[0073] In the above embodiment, the scanning measurement device 10 is used to perform scanning measurement of an airfoil surface and a spherical surface as the measurement surface W, but the present invention can also be applied to scanning measurement of non-horizontal surfaces such as curved surfaces and inclined surfaces.

[0074] In addition, the present invention is applicable to various shape measurement devices that measure the shape of the surface W to be measured by moving the probe 24 relative to the surface W to be measured, while irradiating the measurement light LA ​​from the probe 24 at an oblique angle onto the surface W to be measured, regardless of the shape of the surface W to be measured.

[0075] Furthermore, in the present invention, when the measurement light LA ​​is incident perpendicularly from the probe 24 onto the measurement surface W, cos(θ) in the above equation (2) becomes zero, and the measurement light direction component Vd (Doppler shift amount fd) also becomes zero. As a result, the corrected measurement point Pmc calculated by the position correction unit 38 coincides with the measurement point Pm before correction, so correction by the position correction unit 38 does not affect the shape measurement results of the measurement surface W. Therefore, the present invention is applicable to various shape measurement devices that measure the shape of the measurement surface W while moving the probe 24 relative to the measurement surface W, regardless of the incident direction of the measurement light LA ​​on the measurement surface W.

[0076] REFERENCE SIGNS LIST 10 Measurement device 12 Wavelength sweep interferometer 14 Relative movement unit 15 Measurement path 16 Control device 17 Memory unit 17a CAD data 20 Wavelength sweep light source 22 Beam splitter 24 Probe 24a Input / output end 26 Reference surface 28 Photodetector 29 Detection signal 30 Measurement control unit 32 Distance calculation unit 34 Position calculation unit 36 ​​Scanning direction vector calculation unit 38 Position correction unit 40 Shape calculation unit C Measurement line Df Conversion coefficient L Wavelength swept light LA ​​Measurement light LB Reference light LC Combined light ML Interpolation curve N Normal direction Ph Reference point Pm Measurement point Pmc Corrected measurement point R Measurement range T Scanning time Vd Measurement light direction component Vm Measurement light vector Vs Scanning direction vector W Measurement surface fd Doppler shift amount

Claims

1. A wavelength swept light source; a light splitting unit that splits light emitted from the wavelength swept light source into measurement light and reference light; a probe that emits the measurement light split by the light splitting unit toward a surface to be measured and into which the measurement light reflected by the surface to be measured is incident; a reference surface that reflects the reference light split by the light splitting unit; a multiplexing unit that generates multiplexed light of the measurement light reflected by the surface to be measured and incident on the probe, and the reference light reflected by the reference surface; a relative movement unit that moves the probe along the surface to be measured while keeping a gap with respect to the surface to scan the surface to be measured with the measurement light; and a detection unit that, while the relative movement is being performed, repeatedly detects the multiplexed light generated by the multiplexing unit for each of a plurality of measurement points on the surface to be measured into which the measurement light is incident. a distance calculation unit that detects a beat frequency from a detection signal of the combined light detected by the detection unit for each of the measurement points, and calculates a distance from the probe to the measurement point based on the beat frequency; a position calculation unit that calculates a position of each of the measurement points based on a calculation result of the distance calculation unit corresponding to the measurement point; and a position correction unit that corrects the position of the measurement point calculated by the position calculation unit for each of the measurement points based on a Doppler shift amount of the measurement light reflected at the measurement point.

2. A shape measuring device as described in claim 1, wherein the relative movement unit moves the probe relatively along the surface to be measured, keeping a fixed distance from the surface to be measured, based on shape data of the surface to be measured that has been created in advance.

3. A shape measuring device according to claim 1 or 2, wherein the probe directs the measurement light onto the surface to be measured from an oblique direction.

4. A shape measurement device according to any one of claims 1 to 3, further comprising a scanning direction vector calculation unit that calculates, for each measurement point, the magnitude of a scanning direction vector of the measurement light that scans the surface to be measured and that is parallel to the tangent direction of the surface to be measured at the measurement point, and when the direction of the measurement light between the probe and the measurement point is defined as the measurement light direction, the position correction unit calculates, for each measurement point, the amount of Doppler shift based on the component of the scanning direction vector calculated by the scanning direction vector calculation unit that is parallel to the measurement light direction and the wavelength or frequency of the measurement light.

5. A light splitting step of splitting light emitted from a wavelength swept light source into measurement light and reference light, and emitting the measurement light from the probe toward the surface to be measured and the reference light toward the reference surface; a combining step of generating combined light of the measurement light reflected by the surface to be measured and incident on the probe, and the reference light reflected by the reference surface; a relative movement step of moving the probe along the surface to be measured while maintaining a gap therebetween, and scanning the surface to be measured with the measurement light; a detection step of repeatedly detecting the combined light generated in the combining step for each of a plurality of measurement points on the surface to be measured at which the measurement light is incident during the relative movement step; a distance calculation step of detecting a beat frequency from a detection signal of the combined light detected in the detection step for each of the measurement points, and calculating the distance from the probe to each of the measurement points based on the beat frequency; and a position calculation step of calculating the position of each of the measurement points based on the calculation result of the distance calculation step corresponding to each of the measurement points. a position correcting step of correcting the positions of the measurement points calculated in the position calculating step, for each of the measurement points, based on the amount of Doppler shift of the measurement light reflected at the measurement point.

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