Object shape measurement device

Abstract

To provide an object shape measurement device capable of performing measurement with high accuracy in a short time.SOLUTION: An object shape measurement device includes: a laser light source capable of emitting laser light whose frequency can be swept; a distributor that divides the laser light into reference light and signal light; a mirror that changes the traveling direction of the signal light and irradiates an object with the signal light; a generation unit that generates an interference signal of the reflected light and the reference light from the object of the signal light; and a measurement unit that specifies the shape of the object from the frequency of the interference signal. The mirror is configured to be rotatable so that the signal light scans the surface of the object. In sweeping of the frequency, a raising section where the frequency is raised while rotating the mirror at a constant speed and a lowering section where the frequency is lowered are alternately repeated. The raising section and the lowering section are classified into a low-speed region and a high-speed region that is swept in a shorter time relative to the low-speed region. In each section, at least one of the adjacent sections on both sides belongs to a different region. The measurement unit uses the interference signal in the high-speed region as the interference signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an object shape measuring device. [Background technology]

[0002] As a distance measuring device, a device that measures the distance to an object by a frequency modulated continuous wave (FMCW) method is known (see JP 2017-181115 A).

[0003] In this distance measuring device, a laser beam with a swept frequency is irradiated onto an object, and the reflected light is made to interfere with a reference beam similarly split from the laser beam. Since the frequency of the laser beam is swept, light of different frequencies interferes depending on the optical path difference between the reflected light and the reference light, and the optical path difference can be determined by observing the interference light. Since the optical path length of the reference light is known, this optical path difference is due to the optical path length of the reflected light, i.e., the distance to the object.

[0004] If the optical path difference is obtained by changing the measurement position of the object, the difference in the optical path difference represents the unevenness of the surface of the object, and therefore the shape of the object can be specified. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-181115 A Summary of the Invention [Problem to be solved by the invention]

[0006] As a method for changing the measurement position of the object, for example, a method using a galvanometer mirror can be adopted. The galvanometer mirror reciprocates so as to rotate within a certain angle range. This changes the angle of incidence of the laser light on the mirror surface, allowing the surface of the object to be scanned.

[0007] Here, since it is better not to change the measurement position during distance measurement, the rotation angle of the galvanometer mirror is controlled to change in steps. In other words, the distance is measured with the galvanometer mirror fixed at a certain angle, then the rotation angle of the galvanometer mirror is slightly changed and fixed again, and then the distance is measured again. This measurement is repeated.

[0008] When using this type of measurement method, the galvanometer mirror rotates and stops repeatedly, and it takes time for the mirror angle to stabilize. The measurement time for the target object can be shortened by shortening the period for sweeping the laser light, but if the period is shorter than the time it takes for the mirror angle to stabilize, an error will occur in the distance measurement. For example, in the case of a galvanometer mirror, the modulation frequency (the reciprocal of the period for sweeping the laser light) at which high-precision measurement is possible is low, at 1.4 kHz or less, making it difficult to measure with high precision in a short time.

[0009] The present disclosure has been made in light of the above-mentioned circumstances, and aims to provide an object shape measuring device capable of performing measurements with high accuracy and in a short time while utilizing FMCW distance measurement. [Means for solving the problem]

[0010] An object shape measuring device according to one aspect of the present disclosure is an object shape measuring device that measures the shape of an object using laser light, and includes a laser light source capable of irradiating laser light whose frequency can be swept, a distributor that distributes the laser light into reference light and signal light, a mirror that changes the direction of travel of the signal light and irradiates the signal light to the object, a generation unit that generates an interference signal of the reflected light of the signal light from the object and the reference light, and a measurement unit that identifies the shape of the object from the frequency of the interference signal, wherein the mirror is configured to be rotatable such that the signal light scans the surface of the object, and the frequency sweep is performed by alternately repeating an increase section in which the frequency is increased and a decrease section in which the frequency is decreased while rotating the mirror at a constant speed, the increase section and the decrease section are classified into a low speed region and a high speed region that is swept in a shorter time than the low speed region, and in each section, at least one of the sections adjacent to both sides belongs to a different region, and the measurement unit uses the interference signal in the high speed region as the interference signal. Effect of the Invention

[0011] The object shape measuring device disclosed herein is capable of performing measurements with high accuracy and in a short time while utilizing FMCW distance measurement. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic block diagram showing the device configuration of an object shape measuring device according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a graph showing a frequency sweep pattern of the laser light of FIG. [Diagram 3] FIG. 3 is a schematic diagram showing the configuration of a galvanometer mirror used as the mirror in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of a polygon mirror used as the mirror in FIG. [Diagram 5] FIG. 5 is a graph illustrating an interference signal generated by the generating unit in FIG. [Figure 6] FIG. 6 is a graph illustrating the operation of the auxiliary interferometer. [Figure 7] FIG. 7 is a schematic block diagram showing the configuration of an object shape measuring apparatus according to an embodiment different from that shown in FIG. [Figure 8] FIG. 8 is a graph showing a frequency sweep pattern of the laser light of FIG. [Figure 9] FIG. 9 is a graph illustrating the interference signal generated by the generation unit in FIG. [Figure 10] FIG. 10 is an explanatory diagram showing the occurrence of the Doppler effect. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [Description of the embodiments of the present disclosure] (1) An object shape measuring device according to one aspect of the present disclosure is an object shape measuring device that measures the shape of an object using laser light, the object shape measuring device comprising: a laser light source capable of irradiating a laser light capable of sweeping a frequency; a distributor that distributes the laser light into a reference light and a signal light; a mirror that changes the direction of travel of the signal light and irradiates the signal light to the object; a generation unit that generates an interference signal of the reflected light of the signal light from the object and the reference light; and a measurement unit that identifies the shape of the object from the frequency of the interference signal, the mirror is configured to be rotatable such that the signal light scans the surface of the object, the frequency sweep is performed by alternately repeating an increase section in which the frequency is increased and a decrease section in which the frequency is decreased while rotating the mirror at a constant speed, the increase section and the decrease section are classified into a low speed region and a high speed region that is swept in a shorter time than the low speed region, and in each section, at least one of the sections adjacent to both sides belongs to a different region, and the measurement unit uses the interference signal in the high speed region as the interference signal.

[0014] In this object shape measuring device, the mirror is rotated at a constant speed when the frequency of the laser light is swept, so the mirror is in a steady state and the induction of measurement errors due to the response of the mirror can be suppressed. In addition, in this object shape measuring device, an interference signal in a high-speed region that is swept in a short time is used for measurement, so movement of the measurement position on the surface of the target object during measurement can be suppressed. This makes it possible to suppress a decrease in measurement accuracy due to movement of the measurement position. Therefore, this object shape measuring device can perform measurements with high precision and in a short time.

[0015] (2) In the object shape measuring device described in (1) above, the mirror may be a galvanometer mirror. A galvanometer mirror can control the tilt in two axial directions of X and Y, and is unlikely to experience a temperature rise due to resonance or the like. For this reason, by using a galvanometer mirror as the mirror, controllability can be improved.

[0016] (3) In the object shape measuring device described in (1) above, the mirror may be a polygon mirror. A polygon mirror can rotate at high speed in the same rotation direction. Therefore, by using a polygon mirror as the mirror, it is possible to perform measurement in a shorter time.

[0017] (4) In the object shape measuring device according to any one of (1) to (3) above, it is preferable that the number of sections included in the low speed region and the high speed region is one each. By limiting the number of sections included in the low speed region and the high speed region to one each in this manner, the time for each region can be shortened. Reducing the time for the low speed region means reducing the distance between adjacent measurement points on the object surface, improving the resolution. Reducing the time for the high speed region also reduces the distance that the measurement position on the object surface moves during measurement. In either case, the measurement accuracy can be improved.

[0018] (5) In the object shape measuring device according to any one of (1) to (3) above, it is preferable that the number of sections included in the low speed region and the high speed region is two each. If the number of sections included in the low speed region and the high speed region is two each in this way, then an increase section for increasing the frequency and a decrease section for decreasing the frequency are included during one measurement. By including an increase section and a decrease section during one measurement, the Doppler effect caused by the rotation of the mirror can be compensated for, and measurement accuracy can be improved.

[0019] (6) In the object shape measuring device according to any one of (1) to (5) above, the scanning distance of the signal light on the surface of the object in the high-speed region is preferably 20 μm or less. By setting the scanning distance of the signal light on the surface of the object in the high-speed region to be equal to or less than the upper limit in this manner, it is possible to further prevent a decrease in measurement accuracy due to movement of the measurement position. Note that the scanning distance refers to the distance in a planar view.

[0020] [Details of the embodiment of the present disclosure] Below, an object shape measuring apparatus according to each embodiment of the present disclosure will be described.

[0021] [First embodiment] 1 is an object shape measuring apparatus that uses laser light L1 to measure the shape of an object S. The object shape measuring apparatus 1 includes a laser light source 10, a first distributor 20, a second distributor 30, a circulator 40, a lens 50, a mirror 60, a generating unit 70, a measuring unit 80, and an auxiliary interferometer 90.

[0022] <Laser light source> The laser light source 10 can emit laser light L1 whose frequency can be swept. For example, a semiconductor laser can be used as the laser light source 10. In the case of a semiconductor laser, the frequency of the oscillating light can be swept by modulating the current injected therein with a triangular wave or a sawtooth wave.

[0023] The frequency sweep is an alternating repeat of an up section DU in which the frequency is increased and a down section DD in which the frequency is decreased, as shown in Fig. 2. It is preferable that the frequency sweeps of the up section DU and the down section DD have the same sweep pattern (the frequency response waveform with respect to time is the same).

[0024] In addition, the rising section DU and the falling section DD are classified into a low speed region RL and a high speed region RH that is swept in a time shorter than the low speed region RL, and in each section, at least one of the sections adjacent to both sides belongs to a different region. In FIG. 2, the sections adjacent to both sides of each section belong to different regions, and the number of sections included in the low speed region RL and the high speed region RH is one each. Specifically, the falling section DD belongs to the low speed region RL, and the rising section DU belongs to the high speed region RH. In the following, in the first embodiment, a case where the sweep of the frequency of the laser light L1 has the waveform of FIG. 2 will be described.

[0025] <1st distributor, 2nd distributor> The first distributor 20 distributes the laser light L1 and extracts a part of the distributed light as an auxiliary reference light L2. The second distributor 30 distributes the laser light L1 into a reference light L3 and a signal light L4.

[0026] Known optical distributors, for example, a 1×2 optical fiber coupler, can be used as the first distributor 20 and the second distributor 30. In the object shape measuring device 1, the first distributor 20 is disposed upstream of the second distributor 30, but this order does not matter and may be reversed.

[0027] <Circulator> The circulator 40 transmits the signal light L4, changes the traveling direction of reflected light L5 of the signal light L4 from the object S, and extracts the reflected light L5.

[0028] As the circulator 40, a known optical circulator can be used.

[0029] <Lens> The lens 50 collects the signal light L4 and the reflected light L5 and focuses them on the object S and the generator 70.

[0030] <mirror> The mirror 60 changes the direction of travel of the signal light L4 and irradiates the signal light L4 onto the object S. The mirror 60 is configured to be rotatable so that the signal light L4 scans the surface of the object S. In the object shape measuring device 1, the frequency is swept while rotating the mirror 60 at a constant speed. Note that, even if there is a mechanical control error or the like, or if there is an unavoidable speed fluctuation when the direction of rotation is changed for an object that performs a reciprocating rotational motion, it is considered to be rotating at a "constant speed."

[0031] As the mirror 60, a galvanometer mirror 61 shown in FIG. 3, a polygon mirror 62 shown in FIG. 4, or the like can be used.

[0032] (Galvano mirror) The galvanometer mirror 61 is a plate-shaped component that reflects laser light. The galvanometer mirror 61 rotates back and forth within a certain range of angle θ shown in FIG. 3. The angular velocity (absolute value) of this rotational motion is constant. In FIG. 3, one of the rotations of this rotational motion is indicated by an arrow. As a result, the signal light L4 scans the surface of the target S along the scan direction SD shown in FIG. 3.

[0033] As will be described later, in the object shape measuring device 1, the distance to the object S is measured in the high speed region RH, and the shape of the object is found based on this distance. As shown in Fig. 3, since the high speed region RH and the low speed region RL appear alternately, the measurement points P appear discretely on the surface of the object S as shown in Fig. 3. Also, since the time to pass through the high speed region RH is shorter than the time to pass through the low speed region RL, the scan distance of the measurement points P is smaller than the interval between adjacent measurement points P.

[0034] After rotating to a certain angle, the galvanometer mirror 61 starts to rotate in the opposite direction to the arrow in FIG. 3, and scanning is performed in the opposite direction to the scanning direction SD in FIG. 3. At this time, the scanning direction SD is the same except that it is reversed. For example, by rotating the galvanometer mirror 61 in a direction perpendicular to the paper surface of FIG. 3 each time the scanning direction SD changes, a row of measurement points P different from the row that has already been measured can be measured. In this way, the three-dimensional shape of the target S can be measured. Alternatively, a configuration may be adopted in which the galvanometer mirror 61, including the optical system, is moved as a whole in the direction perpendicular to the paper surface of FIG. 3 to measure a different row.

[0035] The galvanometer mirror 61 can control the tilt in two axial directions of the X and Y axes, and the temperature does not increase much due to resonance, etc. Therefore, by using the galvanometer mirror 61 instead of the mirror 60, the controllability can be improved.

[0036] (Polygon mirror) The polygon mirror 62 is a rotating polygonal mirror that can rotate in one direction at high speed. The polygon mirror 62 is in the shape of a polygonal prism having a central axis in a direction perpendicular to the plane of the paper in Fig. 4. Although the polygon mirror 62 is in the shape of a hexagonal prism in Fig. 4, it is not limited to a hexagonal prism, and may be in another polygonal prism shape such as an octagonal prism or a decagonal prism.

[0037] The other configuration is similar to that of the galvanometer mirror 61, so a detailed description will be omitted.

[0038] The polygon mirror 62 can rotate at high speed in the same direction, so by using the polygon mirror 62 instead of the mirror 60, measurement can be completed in a shorter time.

[0039] <Generation part> The generation unit 70 generates an interference signal L6 of the reflected light L5 of the signal light L4 from the object S and the reference light L3. The generation unit 70 includes a first merging / distributing unit 71 and a first detector 72.

[0040] The first integrating / distributing device 71 integrates the reflected light L5 and the reference light L3, and splits them into two lights having the same DC component and opposite AC components. The AC components correspond to interference light. A 2×2 optical fiber coupler can be used as the first integrating / distributing device 71.

[0041] The first detector 72 takes the difference between the two lights split by the first multiplexer / distributor 71 and converts it into an electrical signal (interference signal L6). When the difference between the two lights split by the first multiplexer / distributor 71 is taken in this way, the DC component is subtracted and becomes zero, and the amplitude of the AC component is doubled, improving the S / N ratio of the interference signal L6.

[0042] The waveform observed by the generating unit 70 will be described with reference to Fig. 5. For simplicity, Fig. 5 illustrates a case where the laser light L1 has the waveform of Fig. 2.

[0043] In the object shape measuring device 1, it is preferable that the frequency of the laser light L1 is swept linearly. The following description will be given taking as an example a case where the frequency is swept linearly. Generally, it is difficult to perform the frequency sweep linearly, and the frequency may deviate from the linearity. In such a case, it is possible to obtain the same effect as when the frequency is swept linearly by the auxiliary interferometer 90 described later.

[0044] The reference light L3 and the reflected light L5 are observed to have the same waveform as the laser light L1, except for the occurrence of a phase delay. Here, the reflected light L5 is light reflected on the surface of the object S, and reaches the first merging and dividing device 71 through a longer optical path than the reference light L3. If the optical path from the second dividing device 30 to the first merging and dividing device 71 and the optical path from the circulator 40 to the first merging and dividing device 71 are designed to be equal in length, this optical path difference is 2L, which is the distance traveled back and forth along the optical path (optical path length L) from the circulator 40 to the surface of the object S. At this time, assuming that the speed of light is c, the reflected light L5 has a waveform delayed by τ=2L / c with respect to the reference light L3. Generally, 2L<<c, so as shown in FIG. 5, the reflected light L5 has a waveform slightly delayed with respect to the reference light L3. Note that this delay amount can be adjusted to a desired value, for example, because the length of L can be changed by adjusting the position of the mirror 60, etc.

[0045] In the object shape measuring device 1, measurement is performed by a measuring unit 80, which will be described later, using an interference signal L6 in the high-speed region RH. In the high-speed region RH, as shown in Fig. 5, except for parts at both ends, the reference light L3 and the reflected light L5 are swept with a constant frequency difference Δf with the reference light L3 on the high-frequency side. At this time, when the two are superimposed, an interference signal L6 is generated in which the intensity changes at the frequency Δf (see the lower graph in Fig. 5).

[0046] <Measurement section> The measurement unit 80 identifies the shape of the target object S from the frequency of the interference signal L6. The measurement unit 80 uses the interference signal L6 in the high speed region RH as the interference signal L6. The measurement unit 80 also includes an AD converter 81 and a computer .

[0047] The AD converter 81 samples and digitizes the interference signal L6. In the object shape measuring device 1, the interference signal L6 is discretely digitized by a sampling signal CK supplied from an auxiliary interferometer 90, which will be described later. Depending on the timing of this sampling signal CK, even if the sweep of the frequency of the laser light L1 is nonlinear, it is possible to obtain the same effect as if it were swept linearly.

[0048] The calculator 82 is configured by, for example, a personal computer, a microcontroller board, a microcontroller unit, etc., and specifies the shape of the target object S by calculating the change in the above-mentioned optical path length L. The principle thereof will be described below.

[0049] First, the frequency Δf of the interference signal L6 in the high speed region RH is identified from the digital data of the interference signal L6 obtained by the AD converter 81. This Δf is calculated by using the width ΔF of the swept frequency, the time tu required to sweep the frequency in the rising section DU, and the delay time τ of the reflected light L5 with respect to the reference light L3, as follows: Δf=ΔF×τ / tu=ΔF×2L / c / tu ···1 Because we can write L=1 / 2×(Δf / ΔF)×(c×tu) ···2 It can be expressed as:

[0050] As described above, the measurement points P at which the distance to the object S is measured in the high speed region RH are discrete. For example, when the optical path length L calculated at the first measurement point P is used as a reference and a difference ΔL between the optical path length calculated at another measurement point P is calculated, this ΔL represents the unevenness of the surface of the object S. Furthermore, by controlling the position and inclination of the mirror 60, etc. as described above, it is possible to measure a row different from the row of measurement points P that have already been measured, so that the object shape measuring device 1 can identify the shape of the object S.

[0051] The object shape measuring device 1 determines the optical path length L while rotating the mirror 60 at a constant speed, so that the measurement point P moves a constant distance even in the high-speed region RH where the measurement of the optical path length L is performed. The upper limit of the scanning distance of the signal light L4 on the surface of the object S in the high-speed region RH is preferably 10 μm, more preferably 5 μm. If the scanning distance is long, the fluctuation of the optical path length L during measurement may become large due to, for example, the unevenness of the object S, leading to a measurement error. By setting the scanning distance to the upper limit or less, it is easy to prevent measurement errors caused by the movement of the measurement position. On the other hand, the scanning distance is not particularly limited as long as the time required to identify the frequency Δf of the interference signal L6 in the high-speed region RH can be secured, and although the smaller the scanning distance, the better, it is usually set to 1 μm or more.

[0052] The lower limit of the ratio of the high speed region RH to the repetition period of the region that is the sum of one section of the continuous low speed region RL and one section of the high speed region RH is preferably 5%, more preferably 10%. On the other hand, the upper limit of the ratio of the high speed region RH is preferably 40%, more preferably 30%. By setting the ratio of the high speed region RH to the lower limit or more, it is easy to secure the time required to identify the frequency Δf of the interference signal L6 in the high speed region RH. In addition, the frequency of the laser light can be easily swept. By setting the ratio of the high speed region RH to the upper limit or less, it is easy to prevent measurement errors caused by movement of the measurement position. In addition, by setting the ratio of the high speed region RH to a low value in this way, measurement errors can be further reduced even with the same repetition period.

[0053] From the viewpoint of measurement time, the lower limit of the repetition frequency (the reciprocal of the repetition period) between the low speed region RL and the high speed region RH is preferably 2 kHz, more preferably 10 kHz, further preferably 50 kHz, and particularly preferably 200 kHz. On the other hand, if the repetition frequency is large, the time of the high speed region RH becomes short, and it may become difficult to secure the time required to identify the frequency Δf of the interference signal L6 in the high speed region RH. From this viewpoint, the upper limit of the repetition frequency is preferably 50 MHz, and more preferably 30 MHz.

[0054] <Auxiliary interferometer> The auxiliary interferometer 90 generates sampling timing for canceling the nonlinearity of the sweep of the frequency of the laser light L1. The auxiliary interferometer 90 includes a third distributor 91, a second merging and distributor 92, and a second detector 93.

[0055] The third distributor 91 distributes the auxiliary reference light L2 into a first auxiliary reference light L7 and a second auxiliary reference light L8. Of these, the second auxiliary reference light L8 has an optical path length L1 longer than that of the first auxiliary reference light L7. A The optical path difference L between the first auxiliary reference light L7 and the second auxiliary reference light L8 is adjusted to be longer than the first auxiliary reference light L7 by 100% and is delayed from the first auxiliary reference light L7 when it reaches the second merging / distributing device 92. For example, this adjustment can be performed by changing the length of the optical fiber through which the first auxiliary reference light L7 and the second auxiliary reference light L8 pass. A must satisfy the sampling theorem. When the refractive index of the optical path (optical fiber) through which the second auxiliary reference light L8 passes is n, the optical path length L to be measured is nL A is required to be at least four times as large.

[0056] The second converging / distributing device 92 and the second detector 93 are similar to the first converging / distributing device 71 and the first detector 72 of the generation unit 70, respectively, and output a signal (sampling signal CK) determined by the frequency difference between the first auxiliary reference light L7 and the second auxiliary reference light L8 at the same time.

[0057] The auxiliary interferometer 90 is effective when the frequency sweep of the laser light L1 is nonlinear. As described above, it is preferable that the frequency sweep of the laser light L1 is linear. However, when a semiconductor laser is used, for example, the frequency response of the laser light source 10 lags behind the current change, so that the frequency sweep is likely to be nonlinear in practice as shown in FIG. 6 (FIG. 6 shows the relationship between the first auxiliary reference light L7 and the second auxiliary reference light L8 and the sampling signal CK, but the same is true for the relationship between the reference light L3 and the reflected light L5 and the interference signal L6). In the case of FIG. 6, the frequency of the interference signal L6 observed as the interference of these waveforms gradually increases. Since the above-mentioned formula 2 for calculating the optical path length L from the circulator 40 to the target S is based on the assumption of linear sweep, if it is applied as it is, an error will occur in the calculation of the optical path length L.

[0058] In contrast, in the object shape measuring device 1, the AD converter 81 of the measuring unit 80 samples and digitizes the interference signal L6, which is an analog signal, using the sampling signal CK generated by the auxiliary interferometer 90. With this configuration, the sampling interval is widened where the change in the swept frequency is small and narrowed where the change in frequency is large, so that the frequency changes at adjacent sampling points are corrected and optimized in a uniform direction. Therefore, the calculation error of the optical path length L can be reduced.

[0059] Furthermore, the digitized interference signal L6 is subjected to FFT analysis. If a peak appears in the Dth data in this FFT-analyzed beat spectrum, the optical path length L can be found by the following equation 3. In the following equation 3, N is the number of data used in the FFT analysis. Since the beat spectrum obtained by FFT is a discrete value, the distance found by equation 3 is also a discrete value. Therefore, it is advisable to estimate the optical path length L by performing a quadratic function approximation near the peak of the beat spectrum. L = {(n × L A ) / (2×N)}×D 3

[0060] <Advantages> In the object shape measuring apparatus 1, the mirror 60 is rotated at a constant speed when sweeping the frequency of the laser light L1, so that the mirror 60 is in a steady state and it is possible to prevent the induction of measurement errors due to the response of the mirror 60. Furthermore, in the object shape measuring apparatus 1, the interference signal L6 in the high-speed region RH that is swept in a short time is used for measurement, so it is possible to prevent the measurement position on the surface of the target object S from moving during measurement. This makes it possible to prevent a decrease in measurement accuracy due to movement of the measurement position. Therefore, the object shape measuring apparatus 1 can perform measurements with high accuracy and in a short time.

[0061] Furthermore, in the object shape measuring device 1, the number of sections included in the low speed region RL and the high speed region RH is each limited to one section, so the time for each region can be shortened. Reducing the time in the low speed region RL means reducing the distance between adjacent measurement points on the surface of the object S, improving the resolution. Reducing the time in the high speed region RH also reduces the distance that the measurement position on the surface of the object S moves during measurement. In either case, the measurement accuracy can be improved.

[0062] Second Embodiment An object shape measuring device 2 according to another embodiment of the present disclosure shown in FIG. 7 is an object shape measuring device that measures the shape of an object S using laser light L1, and includes a laser light source 10 that can irradiate laser light L1 whose frequency can be swept, a second distributor 30 that distributes the laser light L1 into reference light L3 and signal light L4, a mirror 60 that changes the traveling direction of the signal light L4 and irradiates the object S with the signal light L4, a generation unit 70 that generates an interference signal L6 of reflected light L5 of the signal light L4 from the object S and the reference light L3, and a measurement unit 80 that identifies the shape of the object S from the frequency of the interference signal L6, wherein the mirror 60: The object S is configured to be rotatable so that the signal light L4 scans the surface of the object S, and the frequency is swept by rotating the mirror 60 at a constant speed while alternating between an increase section DU in which the frequency is increased and a decrease section DD in which the frequency is decreased, and the increase section DU and the decrease section DD are classified into a low speed region RL and a high speed region RH which is swept in a shorter time than the low speed region RL, and in each section, at least one of the adjacent sections on both sides belongs to a different region, and the measurement unit 80 uses the interference signal L6 in the high speed region RH as the interference signal L6.

[0063] Moreover, the object shape measuring apparatus 2 further includes a first distributor 20, a circulator 40, a lens 50, and an auxiliary interferometer 90. The object shape measuring apparatus 2 is configured similarly to the object shape measuring apparatus 1 in the first embodiment, except for the fact that the sweep of the frequency of the laser light L1 is different, and therefore the same reference numerals are used and detailed description thereof will be omitted.

[0064] (Frequency Sweep) As shown in Fig. 3, the frequency sweep of the object shape measuring device 2 alternates between an ascending section DU and a descending section DD. The ascending section DU and the descending section DD are classified into a low speed region RL and a high speed region RH, and at least one of the sections adjacent to each side of each section belongs to a different region. In Fig. 3, one of the sections adjacent to each side of each section belongs to the same region and the other belongs to a different region, and the number of sections included in the low speed region RL and the high speed region RH is two each. Specifically, the descending section DD and the ascending section DU belong to the low speed region RL and the high speed region RH, respectively, in that order.

[0065] In the measurement section 80, the interference signal L6 in the high speed region RH is used as the interference signal L6, so that in the object shape measuring device 2, as shown in FIG. 9, an increase section DU in which the frequency is increased and a decrease section DD in which the frequency is decreased are included during one measurement.

[0066] If the influence of the Doppler effect described later is ignored, Δf1 in the descending section DD and Δf2 in the ascending section DU can be calculated by using the width ΔF of the swept frequency, the times td and tu required to sweep the frequency in the descending section DD and the ascending section DU, and the delay time τ of the reflected light L5 relative to the reference light L3, as follows: Δf1=ΔF×τ / tu=ΔF×2L / c / tu ···4 Δf2=ΔF×τ / td=ΔF×2L / c / td...5 This is expressed as:

[0067] Here, the influence of the Doppler effect will be explained. In the object shape measuring device 2, the mirror 60 is configured to be rotatable so that the signal light L4 scans the surface of the target object S. The above frequency sweep is performed while rotating the mirror 60 at a constant speed. At this time, as shown in FIG. 10, the optical path length of the signal light L4S at the starting point of the high speed region RH where the measurement is performed may differ from that of the signal light L4E at the end point of the high speed region RH. In FIG. 10, since the optical path length of the signal light L4S is longer, the optical path length becomes shorter as the signal light L4 is scanned. In this case, the same effect as when the target object S comes relatively closer is produced, and the Doppler effect occurs in the frequency of the light, causing the frequency to be higher by Δf than the actual frequency. d A frequency that is higher by only 100% is observed. This appears as a change in the frequency Δf of the interference signal L6. Therefore, if the influence of the Doppler effect cannot be ignored, the optical path length L calculated from the above formulas 4 and 5 will contain an error.

[0068] For example, in the case of FIG. 10, in the descending section DD, Δf1 is larger than that in the case without the Doppler effect due to the Doppler effect. d In the rising section DU, the frequency increases by Δf2. d Therefore, the relational expression that takes into account the Doppler effect is Δf1+Δf d =ΔF×τ / tu=ΔF×2L / c / tu ···6 Δf2-Δf d =ΔF×τ / td=ΔF×2L / c / td 7 In addition, when the optical path length is increased by scanning the signal light L4, the opposite effect occurs. d , -Δf d becomes the opposite.

[0069] Adding together both sides of the above formula 6 and formula 7, the following formula 8 is obtained, regardless of whether the optical path length becomes longer or shorter as the signal light L4 is scanned, and the influence of the Doppler effect can be offset. Specifically, the left side of the following formula 8 is equal to the sum of the frequencies of the interference signal L6 actually measured in the fall interval DD and the rise interval DU, regardless of whether the influence of the Doppler effect is present or not. Δf1+Δf2=ΔF×2L / c×(1 / tu+1 / td) ···8

[0070] <Advantages> In the object shape measuring apparatus 2, by including an ascending section DU and a descending section DD in one measurement, it is possible to compensate for the Doppler effect caused by the rotation of the mirror 60, and to improve the measurement accuracy.

[0071] [Other embodiments] The present disclosure is not limited to the above-described embodiment, and can be implemented in various forms including the above-described aspects, as well as aspects with various modifications and improvements.

[0072] In the above first embodiment, a case has been described in which the descending section belongs to the low speed region and the ascending section belongs to the high speed region, but the ascending section may belong to the low speed region and the descending section may belong to the high speed region. In this case, the shape of the object is measured in the descending section.

[0073] In the above second embodiment, a case has been described in which the descending section and the ascending section belong to the low speed region and the high speed region, respectively, in that order, but the ascending section and the descending section may also belong to the low speed region and the high speed region, respectively, in that order.

[0074] Furthermore, in each section, other patterns are possible as long as at least one of the sections adjacent to both sides belongs to a different region.

[0075] In the above embodiment, the generating unit and the auxiliary interferometer each have a junction / distributor and a detector, but the present invention is not limited to this configuration as long as it can generate an interference signal. Other known interferometers can also be used.

[0076] In the above embodiment, the object shape measuring device is described as being equipped with an auxiliary interferometer, but the auxiliary interferometer is not a required component, and for example, when the frequency sweep of the laser light source has high linearity, the auxiliary interferometer can be omitted. [Industrial Applicability]

[0077] The object shape measuring device disclosed herein is capable of performing measurements with high accuracy and in a short time while utilizing FMCW distance measurement. [Explanation of symbols]

[0078] 1, 2 Object shape measurement device 10 Laser light source 20 1st distributor 30 2nd distributor 40 Circulator 50 Lenses 60 mirror 61 Galvano Mirror 62 Polygon Mirror 70 Generation part 71 1st confluence distributor 72 Detector No. 1 80 Measuring part 81 A / D converter 82 Calculator 90 Auxiliary Interferometer 91 Third distributor 92 2nd confluence distributor 93 Second Detector DU rising section DD Descending section RL low speed area RH high speed region L1 Laser light L2 Auxiliary reference beam L3 Reference beam L4, L4S, L4E signal light L5 reflected light L6 Interfering Signal L7 1st auxiliary reference light L8 2nd auxiliary reference light CK Sampling Signal S Object SD Scan Direction P measurement point θ angle

Claims

1. An object shape measuring device that measures a shape of an object using laser light, A laser light source capable of emitting a laser light having a swept frequency; a distributor that distributes the laser light into a reference light and a signal light; a mirror that changes a traveling direction of the signal light and irradiates the signal light onto an object; a generating unit that generates an interference signal between the reflected light of the signal light from the object and the reference light; a measurement unit that identifies the shape of the object based on the frequency of the interference signal; Equipped with the mirror is configured to be rotatable so that the signal light scans a surface of the object; the frequency sweep is performed by alternately repeating an increase section in which the frequency is increased and a decrease section in which the frequency is decreased while rotating the mirror at a constant speed; The ascending section and the descending section are classified into a low speed region and a high speed region which is swept in a shorter time than the low speed region, and in each section, at least one of the sections adjacent to both sides belongs to a different region; The object shape measuring apparatus, wherein the measurement unit uses the interference signal in the high speed region as the interference signal.

2. 2. The object shape measuring apparatus according to claim 1, wherein the mirror is a galvanometer mirror.

3. 2. The object shape measuring apparatus according to claim 1, wherein the mirror is a polygon mirror.

4. The object shape measuring apparatus according to claim 1 , wherein the number of sections included in the low speed region and the high speed region is one section each.

5. The object shape measuring apparatus according to claim 1 , wherein the number of sections included in the low speed region and the high speed region is two, respectively.

6. 4. The object shape measuring apparatus according to claim 1, wherein a scanning distance of the signal light on the surface of the object in the high speed region is 20 [mu]m or less.

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