Distance measuring device

Abstract

The distance measuring device includes: a light source unit that emits a first single-wavelength laser beam having a first wavelength and a second single-wavelength laser beam having a second wavelength different from the first wavelength; and an optical unit that interferes the plurality of light beams incident on the optical unit, detects a first light component having a first wavelength in interference light generated by the interference of the plurality of light beams, outputs a first signal corresponding to a result of detecting the first light component, and detects a second light component having a second wavelength in the interference light, and outputs a second signal corresponding to a result of detecting the second light component. Outputting a second signal corresponding to a result of detecting the second light component; and a processing circuit that processes the first signal and the second signal. The processing circuit calculates a first distance within a first range with a first precision based on the first signal, and calculates a second distance within a second range with a second precision based on the first signal and the second signal. The first precision is higher than the second precision, and the second range is longer than the first range. The stability of the frequency of the first single-wavelength laser light is higher than the stability of the frequency of the second single-wavelength laser light.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a distance measuring apparatus. BACKGROUND

[0002] Optical interference using a laser is widely used as a means capable of non-contact acquisition of information indicating a distance and / or shape of an object, and the like. As an example thereof, a LiDAR (Light Detection And Ranging) of a frequency modulated continuous wave radar (FMCW) system is known as a three-dimensional measuring apparatus of millimeter precision. In addition, optical interference using optical coherence tomography (OCT) or an optical comb is known as a means capable of measurement with micrometer precision. These are widely utilized in the medical field and / or the industrial field.

[0003] In addition, by controlling the optical interference phenomenon with higher precision, measurement with nanometer precision is possible. For example, a Michelson interferometer using a single-wavelength laser is one method of measuring a difference in distance in the nanometer unit as an optical intensity.

[0004] Nanometer-precision optical measurement typified by homodyne optical interference enables high-precision measurement in a non-contact manner, and on the other hand, there is a problem that the measurement range is limited to half the wavelength, i.e., the sub-micrometer unit. Therefore, in measurement of a sample having a structure in the nanometer unit and a structure in the tens of micrometer unit, there is a case where it is difficult to measure.

[0005] As a method of solving this problem, optical interference using two or more single-wavelength lasers, i.e., multi-wavelength interference, is expected. Multi-wavelength interference can solve the trade-off between the measurement range and the measurement precision, which is a problem of the related art, and realize a longer measurement range and higher measurement precision at the same time.

[0006] For example, in Patent Literature 1, by combining optical interference results of lasers having different wavelengths, the trade-off between the measurement range and the measurement precision, which is a problem of the related art, can be solved, and a longer measurement range and higher measurement precision can be realized.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: German Patent Application No. 102015209567 Specification SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] In a distance measuring device using the principle of multi-wavelength interference (MWI) disclosed in Patent Document 1, two or more single-wavelength lasers having mutually different wavelengths are required. At this time, in a case where the stabilities of the frequencies of the two or more single-wavelength lasers are different from each other, depending on the combination of the wavelengths used at the time of calculating the distance, the distance measuring accuracy sometimes decreases.

[0012] Therefore, the present disclosure provides a distance measuring device capable of taking into account both a longer distance measuring range and higher distance measuring accuracy.

[0013] Means for solving the problem

[0014] A distance measuring device of one embodiment of the present application includes a light source section that emits first single-wavelength laser light having a first wavelength and second single-wavelength laser light having a second wavelength different from the first wavelength; an optical unit that causes a plurality of lights incident to the optical unit to interfere with each other, detects a first light component having the first wavelength among interference light generated by the interference of the plurality of lights, outputs a first signal corresponding to a result of detecting the first light component, and detects a second light component having the second wavelength among the interference light, and outputs a second signal corresponding to a result of detecting the second light component; and a processing circuit that processes the first signal and the second signal. The processing circuit calculates a first distance in a first range at a first accuracy based on the first signal, and calculates a second distance in a second range at a second accuracy based on the first signal and the second signal, the first accuracy is higher than the second accuracy, the second range is longer than the first range, and the stability of the frequency of the first single-wavelength laser light is higher than the stability of the frequency of the second single-wavelength laser light.

[0015] Effects of the Invention

[0016] According to the present disclosure, both a longer distance measuring range and higher distance measuring accuracy can be taken into account. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a block diagram showing the structure of a distance measuring device of an embodiment.

[0018] Figure 2 is a block diagram showing the structure of a light source section of a distance measuring device of an embodiment.

[0019] Figure 3 is a diagram showing a specific structure of an optical unit of a distance measuring device of an embodiment.

[0020] Figure 4 is a diagram for explaining the principle of first measurement using single-wavelength laser light of a distance measuring device of an embodiment.

[0021] Figure 5 is a diagram for explaining the principle of a second measurement of the distance measuring apparatus of the embodiment using multiple single-wavelength lasers.

[0022] Figure 6 is a diagram showing the measurement range and the measurement accuracy of two measurements of the distance measuring apparatus of the embodiment.

[0023] Figure 7 is a diagram for explaining the stability of the frequency of a single-wavelength laser.

[0024] Figure 8 is a flowchart showing an example of the operation of the distance measuring apparatus of the embodiment.

[0025] Figure 9 is a flowchart showing another example of the operation of the distance measuring apparatus of the embodiment.

[0026] Figure 10 is a block diagram showing the structure of the light source section of the distance measuring apparatus to which the modification of the embodiment pertains. DETAILED DESCRIPTION

[0027] (SUMMARY OF THE DISCLOSURE)

[0028] First, the definitions of important terms used in the present specification are shown below.

[0029] "Measurement accuracy" indicates the degree of accuracy at the time of distance measurement. That is, the measurement accuracy is a scale for judging to what extent distance information can be accurately obtained. Therefore, it can be said that the higher the measurement accuracy, the more accurate the measurement can be performed.

[0030] "Measurement range" indicates the range of the distance direction in which unique distance information can be obtained. That is, the measurement range indicates the range in which distance measurement can be performed.

[0031] In the present specification, both the measurement accuracy and the measurement range are indicated by the same dimension as the distance. Specifically, both the unit of the measurement accuracy and the unit of the measurement range are indicated by nanometers (nm), micrometers (pm), millimeters (mm), or the like. Therefore, "high measurement accuracy" is synonymous with "short measurement accuracy" indicated by the dimension of the distance. "Low measurement accuracy" is synonymous with "long measurement accuracy" indicated by the dimension of the distance. In the present specification, the measurement accuracy is sometimes simply referred to as "accuracy". The measurement range is sometimes simply referred to as "range".

[0032] Distance measurement in the measurement range is referred to as "absolute distance measurement". For example, distance measurement in the case where the accuracy is 10 nm and the measurement range is 1 mm is absolute distance measurement in which a difference of 10 nm can be distinguished within a range of 1 mm.

[0033] The distance measurement apparatuses according to the present disclosure include the following modes.

[0034] The distance measurement apparatus according to the first mode of the present disclosure includes a light source unit, an optical unit, and a processing circuit. The light source unit emits first single-wavelength laser light having a first wavelength and second single-wavelength laser light having a second wavelength different from the first wavelength. The optical unit interferes a plurality of lights incident to the optical unit, detects a first light component having the first wavelength among interference light generated by the interference of the plurality of lights, outputs a first signal corresponding to a result of detecting the first light component, and detects a second light component having the second wavelength among the interference light, and outputs a second signal corresponding to a result of detecting the second light component. The processing circuit processes the first signal and the second signal. The processing circuit calculates a first distance within a first range with a first accuracy based on the first signal, and calculates a second distance within a second range with a second accuracy based on the first signal and the second signal. The first accuracy is higher than the second accuracy. The second range is longer than the first range. The stability of the frequency of the first single-wavelength laser light is higher than the stability of the frequency of the second single-wavelength laser light.

[0035] Thus, the first measurement can be performed based on the first single-wavelength laser light having high stability of the frequency, and thus, a longer measurement range and higher measurement accuracy can be achieved. In addition, laser light sources having high stability of the frequency are generally expensive. According to the present mode, the stability of the frequency of laser light other than the first single-wavelength laser light emitted by the light source can be low. Thus, for example, a cheap light source can be used as a light source that emits the second single-wavelength laser light, and thus, cost reduction is expected.

[0036] The distance measurement apparatus according to the second mode of the present disclosure can be such that the second accuracy is also below the first range in the distance measurement apparatus according to the first mode.

[0037] Thus, the first distance based on the first measurement and the second distance based on the second measurement can be appropriately combined, and thus, higher measurement accuracy can be achieved.

[0038] The distance measurement apparatus according to the third mode of the present disclosure can be such that the processing circuit can further calculate a distance from the distance measurement apparatus to an object based on the first distance and the second distance in the distance measurement apparatus according to the second mode.

[0039] Thus, the processing circuit calculates the distance from the distance measurement apparatus to the object, and thus, for example, a user does not need to calculate the distance by hand or the like, and thus, the convenience of the user is improved.

[0040] The distance measuring device according to the fourth aspect of the present application can calculate an absolute distance from the distance measuring device to the object in addition to the distance measuring device according to the third aspect of the present application.

[0041] Thus, the absolute distance from the distance measuring device to the object can be calculated, and the distance measuring device is useful in, for example, inspection of the surface shape of the object and the like.

[0042] The distance measuring device according to the fifth aspect of the present application can include the first single-wavelength laser, the second single-wavelength laser, the first reflected light, and the second reflected light in addition to the distance measuring device according to any one of the first to fourth aspects of the present application, and the optical unit can output the first signal by causing the first single-wavelength laser to interfere with the first reflected light and detecting, and output the second signal by causing the second single-wavelength laser to interfere with the second reflected light and detecting.

[0043] Thus, the intensity signal of the interference light can be simply obtained for each wavelength using homodyne interference.

[0044] The distance measuring device according to the sixth aspect of the present application can include the beam splitter, the first light detector, and the second light detector in addition to the distance measuring device according to the fifth aspect of the present application, the beam splitter can split the first single-wavelength laser from the light source section into the first reference light and the first detection light, and split the second single-wavelength laser from the light source section into the second reference light and the second detection light, the first reflected light can be light generated by reflection of the first detection light on the object, the second reflected light can be light generated by reflection of the second detection light on the object, the first light detector can output the first signal by detecting the first light component generated by interference of the first reference light and the first reflected light, and the second light detector can output the second signal by detecting the second light component generated by interference of the second reference light and the second reflected light.

[0045] Thus, interference can be caused by the beam splitter, and the interference signal for each wavelength can be obtained with high precision by two light detectors.

[0046] The distance measurement device according to the seventh aspect of the present invention, in the distance measurement device according to the sixth aspect of the present invention, the optical unit can further include an optical element that causes the first reference light and the second reference light to be incident on the beam splitter, and a wavelength separation element that separates the incident light into the first wavelength light and the second wavelength light, and the beam splitter can cause at least a portion of each of the first reflected light and the second reflected light from the object and at least a portion of each of the first reference light and the second reference light from the optical element to be emitted toward the wavelength separation element.

[0047] Thus, a Michelson interferometer is configured, and the configuration of the optical path of each laser light becomes easy, and distance measurement can be performed with high accuracy.

[0048] The distance measurement device according to the eighth aspect of the present invention, in the distance measurement device according to any one of the fifth aspect to the seventh aspect of the present invention, the processing circuitry can correct the second signal based on the first signal.

[0049] Thus, the accuracy of the second measurement can be improved.

[0050] The distance measurement device according to the ninth aspect of the present invention, in the distance measurement device according to any one of the first aspect to the eighth aspect of the present invention, the set frequency of the first single-wavelength laser light and the set frequency of the second single-wavelength laser light can be fixed during measurement.

[0051] Thus, the variation in frequency during measurement is suppressed, and the measurement accuracy can be improved.

[0052] The distance measurement device according to the tenth aspect of the present invention, in the distance measurement device according to any one of the first aspect to the ninth aspect of the present invention, the light source unit can further emit third single-wavelength laser light having a third wavelength different from the first wavelength and the second wavelength.

[0053] Thus, by using three wavelengths, the measurement range can be further extended. In addition, four or more wavelengths can be used, and the measurement range can be further extended.

[0054] The distance measurement device according to the eleventh aspect of the present invention, in the distance measurement device according to the tenth aspect of the present invention, the first single-wavelength laser light has the highest stability of frequency among all the single-wavelength laser light emitted by the light source unit.

[0055] Thus, the measurement with the highest accuracy can be achieved among the combinations of the wavelengths of the laser light that can be emitted.

[0056] The distance measurement device according to the twelfth aspect of the present invention can further detect a third light component having the third wavelength from the interference light and output a third signal corresponding to the detection result of the third light component, and the processing circuitry can further calculate a third distance within a third range with a third accuracy based on the first signal and the third signal, the third accuracy can be lower than the second accuracy, and the third range can be longer than the second range.

[0057] Thus, the measurement range can be further extended. Therefore, both a longer measurement range and a higher measurement accuracy can be achieved.

[0058] The distance measurement device according to the thirteenth aspect of the present invention can calculate the phase of the beat wavelength of the first wavelength and the second wavelength based on the first signal and the second signal, and calculate the second distance.

[0059] Thus, the distance within a longer measurement range can be calculated based on the beat wavelength.

[0060] The distance measurement device according to the fourteenth aspect of the present invention can calculate the first distance by calculating the phase of the first wavelength based on the first signal, and calculate the absolute distance from the distance measurement device to the object by combining the first distance and the second distance.

[0061] Thus, the absolute distance from the distance measurement device to the object can be calculated, and therefore the distance measurement device is useful in, for example, the inspection of the surface shape of the object.

[0062] The distance measurement device according to the fifteenth aspect of the present invention can include a first laser light source that emits the first single-wavelength laser light and a second laser light source that emits the second single-wavelength laser light.

[0063] Thus, by providing the laser light sources for each wavelength, the plurality of single-wavelength laser lights can be emitted simply.

[0064] Hereinafter, the embodiments will be described with reference to the drawings.

[0065] Further, the embodiments described below are merely examples and are not intended to limit the present disclosure. Numerical values, shapes, materials, component configurations, component arrangement positions, connection methods, steps, sequences of steps, and the like shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, components not recited in the independent claims among the components of the following embodiments are described as arbitrary components.

[0066] Further, each drawing is a schematic view and is not necessarily strictly illustrated. Therefore, for example, the scale and the like are not necessarily consistent in each drawing. In addition, in each drawing, the same reference numerals are assigned to substantially the same structures, and repetitive explanation is omitted or simplified.

[0067] Further, in the present specification, terms indicating relationships between elements, such as parallel or perpendicular, and terms indicating shapes of elements, and numerical ranges are not merely expressions of strict meanings, but also expressions including substantially equivalent ranges, such as a difference of several percent or so.

[0068] Further, in the present specification, ordinal terms, such as "first" and "second", do not mean a number or order of the components, but are used for the purpose of avoiding confusion with the same components and making a distinction.

[0069] (Embodiment)

[0070] [1. Structure of distance measuring device]

[0071] First, the structure of the distance measuring device of the embodiment will be described. Figure 1 The structure of the distance measuring device 1 of the embodiment will be described. Figure 1 is a block diagram showing the structure of the distance measuring device 1 of the present embodiment.

[0072] Figure 1 The distance measuring device 1 shown in the drawing is a device that measures a distance from the distance measuring device 1 to an object 90. Specifically, the distance measuring device 1 is capable of obtaining information showing a surface shape of the object 90 by measuring a distance of each portion of the object 90. The distance measuring device 1 can be used for appearance inspection of a product or the like, for example.

[0073] As shown in Figure 1 , the distance measuring device 1 is provided with a light source section 10, an optical unit 20, and a processing circuit 30. In addition, although not shown, the distance measuring device 1 can be provided with a support section that supports the object 90. The support section can include a driving section such as a motor, a piezoelectric element, and the like, and is capable of changing a posture and / or a position of the object 90.

[0074] The light source section 10 emits a plurality of single-wavelength lasers. Figure 2is a block diagram showing the structure of the light source section 10 of the distance measuring apparatus 1 of the present embodiment. As shown in Figure 2 , the light source section 10 includes laser light sources 11a and 11b and a wavelength combining system 12.

[0075] The laser light sources 11a and 11b each emit single-wavelength laser light of a different wavelength. The laser light sources 11a and 11b are, for example, semiconductor laser elements that emit laser light of a prescribed single wavelength when supplied with electric current.

[0076] The laser light source 11a is an example of a first laser light source that emits laser light L1 having a wavelength λ1. The wavelength λ1 is an example of a first wavelength, and the laser light L1 is an example of first single-wavelength laser light.

[0077] The laser light source 11b is an example of a second laser light source that emits laser light L2 having a wavelength λ2. The wavelength λ2 is an example of a second wavelength, and the laser light L2 is an example of second single-wavelength laser light. The wavelength λ2 is a different wavelength from the wavelength λ1. In the present embodiment, the wavelength λ2 is longer than the wavelength λ1.

[0078] The wavelength combining system 12 combines the laser light L1 and L2 emitted from the two laser light sources 11a and 11b, respectively. The light L emitted from the wavelength combining system 12 is coupled with the interference optical system 40. The wavelength combining system 12 is, for example, a DWDM (Dense Wavelength Division Multiplexing) element or a holographic optical element.

[0079] The optical unit 20 is an example of an optical unit that detects light that has been incident to the optical unit 20 by causing the light to interfere and outputs a signal corresponding to the result of the interference. The laser light L1 and L2 from the light source section 10, first reflected light that has been generated by the laser light L1 being reflected by the object 90, and second reflected light that has been generated by the laser light L2 being reflected by the object 90 are incident to the optical unit 20. As shown in Figure 1 , the optical unit 20 includes an interference optical system 40 and a light-receiving optical system 50. The specific structures of the interference optical system 40 and the light-receiving optical system 50 will be described later. Figure 3

[0080] ​The processing circuit 30 is a signal processing circuit that processes the signal output from the optical unit 20. Specifically, the processing circuit 30 calculates the distance from the distance measuring apparatus 1 to the object 90. For example, the processing circuit 30 processes the signal based on the interference result output from the optical unit 20 based on a prescribed algorithm, thereby acquiring the position of the object 90 as phase information. As a representative algorithm of phase estimation, a 4-step phase-shifting algorithm or the like can be used. The processing circuit 30 can calculate the distance from the distance measuring apparatus 1 to the object 90 based on the phase information.

[0081] Specifically, the processing circuit 30 calculates the first distance in the first distance measuring range with the first distance measuring accuracy based on the interference result corresponding to the wavelength λ1. In addition, the processing circuit 30 calculates the second distance in the second distance measuring range with the second distance measuring accuracy based on the interference result corresponding to the wavelengths λ1 and λ2. The processing circuit 30 calculates the distance from the distance measuring apparatus 1 to the object 90 based on the first distance and the second distance. The processing circuit 30 calculates the absolute distance from the distance measuring apparatus 1 to the object 90.

[0082] Here, the first distance measuring accuracy is higher than the second distance measuring accuracy. In addition, the second distance measuring range is longer than the first distance measuring range. Thus, simply put, the processing circuit 30 calculates the distance in the shorter distance measuring range with higher distance measuring accuracy based on the interference result corresponding to one wavelength. The processing circuit 30 calculates the distance in the longer distance measuring range with lower distance measuring accuracy based on the interference result corresponding to two wavelengths. The specific distance calculating method will be described later.

[0083] The processing circuit 30 is realized by an integrated circuit such as an LSI (Large Scale Integration). For example, the processing circuit 30 can also be realized by a dedicated hardware structure, and calculate the distance from the distance measuring apparatus 1 to the object 90. Alternatively, the processing circuit 30 can include a processor and a memory, and calculate the distance from the distance measuring apparatus 1 to the object 90 by causing the processor to execute a program stored in the memory. Specifically, the processing circuit 30 can include a nonvolatile memory in which a program is stored, a volatile memory as a temporary storage area for executing the program, an input / output port, a processor that executes the program, and the like. Alternatively, the processing circuit 30 can be a programmable FPGA (Field Programmable Gate Array), or a reconfigurable processor that can reconfigure the connection and setting of the circuit units within the LSI.

[0084] [1.1. Specific structure of optical unit]

[0085] Next, the specific structure of the optical unit 20 will be described. As described above, the optical unit 20 includes the interference optical system 40 and the light-receiving optical system 50. Hereinafter, the specific structure of the optical unit 20 will be described using the drawings. Figure 3 The specific structure of the optical unit 20 of the distance measuring apparatus 1 according to the present embodiment will be described with reference to FIG. 2. Figure 3

[0086] In the present embodiment, the interference optical system 40 is an optical system that utilizes Michelson interference. As shown in FIG. 1, the interference optical system 40 includes a beam splitter 41 and a mirror 42. Figure 3

[0087] The beam splitter 41 is an optical element that splits light incident on the beam splitter 41 into a plurality of lights in terms of intensity and causes the plurality of lights to be emitted in different directions, respectively. The beam splitter 41 is, for example, a half mirror that splits light incident on the beam splitter 41 into transmitted light and reflected light so that the intensities of the respective lights are the same. Note that the intensity ratio of the transmitted light and the reflected light can not be 1:1.

[0088] Specifically, the beam splitter 41 splits laser light L1 from the light source section 10 into first detection light and first reference light, and splits laser light L2 from the light source section 10 into second detection light and second reference light. The first detection light and the second detection light are emitted toward the object 90. The first reference light and the second reference light are emitted toward the mirror 42.

[0089] The mirror 42 is an example of an optical element that causes the first reference light and the second reference light from the beam splitter 41 to be incident on the beam splitter. Specifically, the mirror 42 causes light incident on the mirror 42 to be specularly reflected. The higher the reflectivity, the less the loss of light, and thus the detection accuracy can be improved.

[0090] In the example shown in FIG. 3, the combined light L of the laser light from the light source section 10, i.e., the laser light L1 and L2, is incident on the beam splitter 41. The beam splitter 41 transmits a part of the combined light L as the transmitted light Lt and reflects the other part as the reflected light Lr. The transmitted light Lt includes the first detection light and the second detection light, and is irradiated to the object 90. The reflected light Lr includes the first reference light and the second reference light, and is irradiated to the mirror 42. Figure 3 The transmitted light Lt irradiated to the object 90 is reflected by the object 90 and is incident on the beam splitter 41 again. A part of the transmitted light Lt incident on the beam splitter 41 again is reflected toward the light-receiving optical system 50. The transmitted light Lt incident on the beam splitter 41 again includes a reflected light (i.e., first reflected light) generated by reflection of the first detection light, which is a part of the laser light L1, at the object 90 and a reflected light (i.e., second reflected light) generated by reflection of the second detection light, which is a part of the laser light L2, at the object 90.

[0091] The transmitted light Lt irradiated to the object 90 is reflected by the object 90 and is incident on the beam splitter 41 again. A part of the transmitted light Lt incident on the beam splitter 41 again is reflected toward the light-receiving optical system 50. The transmitted light Lt incident on the beam splitter 41 again includes a reflected light (i.e., first reflected light) generated by reflection of the first detection light, which is a part of the laser light L1, at the object 90 and a reflected light (i.e., second reflected light) generated by reflection of the second detection light, which is a part of the laser light L2, at the object 90.​​

[0092] Likewise, the reflected light Lr that is irradiated to the mirror 42 is reflected by the mirror 42 to be incident to the beam splitter 41 again. A part of the reflected light Lr that is incident to the beam splitter 41 again is transmitted to be directed toward the light-receiving optical system 50. The reflected light Lr that is incident to the beam splitter 41 again includes the first reference light of the laser light L1 and the second reference light of the laser light L2.

[0093] Further, the configuration of the mirror 42 and the object 90 can be exchanged. That is, it can also be that, in a case where the synthesized light L from the light source section 10 is split into the transmitted light Lt and the reflected light Lr by the beam splitter 41, the transmitted light Lt is irradiated to the mirror 42 and the reflected light Lr is irradiated to the object 90.

[0094] In addition, the interference optical system 40 is not limited to an optical system that utilizes Michelson interference. The interference optical system 40 can also be an optical system that utilizes Fizeau interference or Mach-Zehnder interference, or the like.

[0095] The light-receiving optical system 50 is an optical system that utilizes homodyne interference. As shown in FIG. 5, the light-receiving optical system 50 includes a dichroic mirror 51, a mirror 52, and photodetectors 53 and 54. Figure 3

[0096] The dichroic mirror 51 is an example of a wavelength separation element that separates light incident to the dichroic mirror 51 into light of wavelength λ1 and light of wavelength λ2. Specifically, the dichroic mirror 51 wavelength-separates light incident to the light-receiving optical system 50 from the beam splitter 41. In the present embodiment, the dichroic mirror 51 causes light of wavelength λ1 to be emitted toward the photodetector 53 and causes light of wavelength λ2 to be emitted toward the photodetector 54. In the present embodiment, the mirror 52 is provided for the purpose of optical path adjustment.

[0097] The mirror 52 causes light of wavelength λ2 that is separated by the dichroic mirror 51 to be incident to the photodetector 54 by mirror reflection. Further, the mirror 52 can not be provided, and the photodetector 54 can be disposed at the position of the mirror 52. Alternatively, the mirror 52 can be provided for the purpose of adjusting the optical path of light of wavelength λ1.

[0098] The photodetectors 53 and 54 each include a photoelectric conversion element that generates an electric signal corresponding to the intensity of incident light. The photodetector 53 is an example of a first photodetector that has at least sensitivity to wavelength λ1, and outputs a first signal having a signal level corresponding to the intensity of light of wavelength λ1 by photoelectric conversion of the light of wavelength λ1 to the processing circuit 30. The first signal is a signal obtained by detecting interference light of reflected light of the laser light L1 that is reflected by the mirror 42 and the laser light L1 that is reflected by the object 90.

[0099] ​The light detector 54 is an example of a second light detector having at least sensitivity to the wavelength λ2, and outputs a second signal having a signal level corresponding to the intensity of the light of the wavelength λ2 to the processing circuit 30 by photoelectrically converting the light of the wavelength λ2. The second signal is a signal obtained by causing the laser light L2 reflected by the mirror 42 to interfere with the reflected light of the laser light L2 reflected by the object 90 and detecting the interference.

[0100] Further, the configuration of the light-receiving optical system 50 is not limited to the above-described example as long as light of each wavelength can be received. For example, after splitting the light from the beam splitter 41 toward the light-receiving optical system 50 into two lights in terms of intensity, the two split lights can each pass through a filter having a transmission band for a specific wavelength component. The filter is, for example, a band-pass filter, but can also be a low-pass filter, a high-pass filter, or the like.

[0101] In addition, the light-receiving optical system 50 can not be an optical system using homodyne interference. The light-receiving optical system 50 can also be an optical system using heterodyne interference. In this case, the light-receiving optical system 50 can not have the dichroic mirror 51 that splits light by wavelength, and the number of light detectors can be one.

[0102] [2. Principle of distance measurement]

[0103] Next, the principle of distance measurement of the distance measurement apparatus 1 of the present embodiment will be described.

[0104] In the distance measurement apparatus 1 of the present embodiment, distance measurement based on multiwavelength interferometry (MWI) using a plurality of single-wavelength lasers is performed. The MWI can solve the trade-off between the measurement range and the measurement accuracy, which is a problem in the related art, by combining the interference results of a plurality of single-wavelength lasers having mutually different wavelengths, and achieve a longer measurement range and a higher measurement accuracy. Hereinafter, the principle of multiwavelength interferometry will be described.

[0105] [2.1. First measurement (using one wavelength)]

[0106] First, the first measurement using one single-wavelength laser will be described.

[0107] As used in the above description, the single-wavelength laser is a laser light having a single wavelength. The single-wavelength laser is, for example, a laser light having a wavelength of 532 nm. Figure 3 As described above, in homodyne light interference, the single-wavelength laser is branched by the beam splitter 41, and is irradiated to the mirror 42 that functions as a reference surface and the object 90 that is the object of measurement of distance. The reflected lights of the mirror 42 and the object 90 are interfered with each other by the beam splitter 41. The intensity P of the signal output from the light detector 53 when the light of the interference is detected by the light detector 53 is represented by the following formula (1). PD The intensity P of the signal output from the light detector 53 when the light of the interference is detected by the light detector 53 is represented by the following formula (1).

[0108] [Number 1]

[0109] (1)

[0110] In equation (1), L - =L x -L y L x L is the distance from beam splitter 41 to the reflecting surface of mirror 42. y λ is the distance from beam splitter 41 to object 90. k This refers to the wavelength of a single-wavelength laser. Here, k = 1. L x and λ k These are all values ​​known to the processing circuit 30. Therefore, the processing circuit 30 can process signals based on the signal strength P. PD To calculate the distance L to object 90 y .

[0111] In the first measurement, there was a problem with a relatively short measurement range. The following will use... Figure 4 Explain the relationship between the position of object 90 and the measurement range.

[0112] Figure 4 This diagram illustrates the principle of the first measurement using a single-wavelength laser in the distance measuring device 1 of this embodiment. Figure 4 In the diagram, objects 90a, 90b, and 90c represent respectively... Figure 1 as well as Figure 3 The objects 90 shown are located in different positions. Where it is not necessary to distinguish their positions, they will be described as "object 90".

[0113] exist Figure 4 The diagram shows the horizontal axis representing the distance from the object 90 to the specified position as a reference point, and the vertical axis representing the distance calculated by the processing circuit 30, i.e., the calculated distance. Figure 4 As shown, the processing circuit 30 can calculate the distance to the object 90 within a specified length measurement range. As can be seen from equation (1), when the wavelength of a single-wavelength laser is set to λ1, the length measurement range is half of its wavelength (λ1 / 2).

[0114] In the first measurement, when the distance exceeds the measuring range, it is impossible to calculate the absolute distance from the distance measuring device 1 to the object 90. For example, in Figure 4 In the example shown, objects 90a, 90b, and 90c are all calculated to have the same distance.

[0115] The wavelength of the single-wavelength laser is, for example, a wavelength in the near-infrared light band or the visible light band. The near-infrared light band is a band of about 700 nm or more and about 2500 nm or less. The visible light band is a band of about 380 nm or more and about 780 nm or less. In this case, the measurement length range in the first measurement is about 190 nm or more and about 1250 nm or less. That is, the measurement length range in the first measurement is in the order of several hundred nm to several μm. Thus, the measurement length range in the first measurement is relatively small compared to the second measurement described later.

[0116] [2.2. Second measurement (using two single-wavelength lasers having mutually different wavelengths)]

[0117] Next, the second measurement using two single-wavelength lasers having mutually different wavelengths for solving the problem of the short measurement length range as the first measurement will be described using Figure 3 and Figure 5 .

[0118] As shown in Figure 3 , in the distance measurement apparatus 1 according to the present embodiment, the light interfered by the beam splitter 41 is split by the dichroic mirror 51 by each wavelength and detected by the two photodetectors 53 and 54. As a result, a signal corresponding to the result of the homodyne interference of each corresponding wavelength is output from each of the photodetectors 53 and 54. The processing circuit 30 can calculate the distance to the object 90 based on the two signals.

[0119] In the second measurement, the measurement length range is lengthened by combining the two signals. Hereinafter, the relationship between the position of the object 90 and the measurement length range will be described using Figure 5 .

[0120] Figure 5 is a view for explaining the principle of the second measurement of the distance measurement apparatus 1 according to the present embodiment using two single-wavelength lasers. In Figure 5 , the objects 90a, 90b, and 90c respectively represent the object 90 shown in Figure 1 and Figure 3 . In cases where it is not necessary to distinguish the positions, the objects 90 are described as "the object 90".

[0121] In Figure 5 , the horizontal axis represents the distance to the object 90 with a prescribed position as a reference point, and the vertical axis represents a graph of the distance calculated by the processing circuit 30, i.e., the calculated distance. In the two graphs, the upper graph is the same as the graph shown in Figure 4 , and represents the distance calculated based on the signal obtained from one of the two photodetectors 53 and 54. In the two graphs, the lower graph represents the distance calculated based on the signal obtained from the other of the two photodetectors 53 and 54.

[0122] By using the two graphs separately, the range of the length measurement is λ1 / 2 or λ2 / 2, respectively, and thus the order of the range of the length measurement hardly changes from the first measurement. In the second measurement, by combining the two graphs, it is possible to extend the range of the length measurement.

[0123] Specifically, the distance calculated in correspondence with the upper graph is substantially the same for each of the objects 90a, 90b, 90c. However, the distance calculated in correspondence with the lower graph is different from each other. Thus, by combining the two calculation results, it is possible to calculate the distance with a range of the length measurement longer than either of λ1 / 2 and λ2 / 2. Specifically, the processing circuit 30 calculates the absolute distance to the object 90 by combining the first distance obtained by the first measurement and the second distance obtained by the second measurement.

[0124] The range of the length measurement in the second measurement is half of the beat wavelength of the two single-wavelength lasers. For example, if the wavelengths of the two single-wavelength lasers are λ1 and λ2, the beat wavelength Λ 12 is expressed by the following equation (2).

[0125] [Equation 2]

[0126] (2)

[0127] By the light interference based on the beat wavelength Λ 12 , it is possible to perform the distance measurement in the range of the length measurement corresponding to half of the beat wavelength Λ 12 . For example, in the case where λ1 and λ2 are 1550 nm and 1551 nm, respectively, the beat wavelength Λ 12 is 2.4 mm, and the range of the length measurement is 1.2 mm. In the case of the single-wavelength interference, the range of the length measurement is about 775 nm and is in the order of nanometers, and in contrast to this, the range of the length measurement of the MWI is extended to the order of millimeters.

[0128] [2.3 Measurement accuracy]

[0129] Next, the measurement accuracy of each of the first measurement and the second measurement will be described.

[0130] The measurement accuracy depends on the wavelength of the single-wavelength laser used for the measurement. Specifically, the shorter the wavelength of the single-wavelength laser, the higher the measurement accuracy (i.e., the smaller in the dimension of the distance), and the longer the wavelength of the single-wavelength laser, the lower the measurement accuracy (i.e., the larger in the dimension of the distance).

[0131] In the case of using two single-wavelength lasers as in the second measurement, the measurement accuracy depends on the beat wavelength. Specifically, the shorter the beat wavelength, the higher the measurement accuracy (i.e., the smaller in the dimension of the distance), and the longer the beat wavelength, the lower the measurement accuracy (i.e., the larger in the dimension of the distance).

[0132] Since the beat wavelength is longer than the wavelength of the single-wavelength laser, the length measurement accuracy is lower in the second measurement than in the first measurement. That is, the length measurement accuracy of the second measurement is degraded due to the beat wavelength Λ 12 Thus, only with the second measurement, the trade-off between the length measurement range and the length measurement accuracy has not been resolved.

[0133] To resolve this trade-off, in the MWI, both the long length measurement range and the high length measurement accuracy are achieved by combining the first measurement and the second measurement. That is, by combining the first measurement with the short length measurement range but the high length measurement accuracy and the second measurement with the low length measurement accuracy but the long length measurement range, both the long length measurement range and the high length measurement accuracy are achieved.

[0134] Figure 6 is a graph showing the length measurement range and the length measurement accuracy of the two measurements of the distance measurement apparatus 1 of the present embodiment. As Figure 6 shown, the length measurement accuracy in the second measurement (second length measurement accuracy) is set to Am, and the length measurement range in the second measurement (second length measurement range) is set to Rm. In addition, the length measurement accuracy in the first measurement (first length measurement accuracy) is set to As, and the length measurement range in the first measurement (first length measurement range) is set to Rs. The length measurement range and the length measurement accuracy are both represented by the dimension of the distance, and thus can be compared.

[0135] As described above, in addition, as Figure 6 shown, Rm > Rs and Am > As hold. In addition, in the present embodiment, Am < Rs holds. That is, the length measurement accuracy Am of the second measurement is equal to or lower than the length measurement range Rs of the first measurement. Thereby, the combination of the first measurement and the second measurement can be uniquely made, and thus the distance measurement can be made with the length measurement accuracy higher than the length measurement accuracy of the second measurement.

[0136] Here, to achieve higher length measurement accuracy, it is important to select the single-wavelength laser for the first measurement. The present inventors have found through intensive studies that, to improve the length measurement accuracy, the stability of the frequency of the single-wavelength laser becomes important. Hereinafter, the relationship between the stability of the frequency and the length measurement accuracy will be described.

[0137] [3. Relationship between the stability of the frequency and the length measurement accuracy]

[0138] The frequency of the single-wavelength laser is adjusted by a control section not shown to maintain a predetermined set value. Specifically, the frequency is kept constant by adjusting the amount of current supplied to the laser light source and / or the temperature of the laser light source. In the present embodiment, the set frequency of the light source section 10 is controlled to be fixed during the measurement period.

[0139] However, on the characteristics of the laser light source, it is not possible to completely keep the frequency constant. As Figure 7As shown, the frequency of the single-wavelength laser fluctuates with time. In addition, Figure 7 is a graph for explaining the stability of the frequency of the single-wavelength laser. In Figure 7 , the horizontal axis represents time, and the vertical axis represents the frequency of the single-wavelength laser.

[0140] The wavelength λ of the single-wavelength laser k is represented by the speed of light ÷ frequency. Since the speed of light is regarded as constant, in the case where the frequency fluctuates, the wavelength λ k also fluctuates. As is clear from the above equation (1), if the wavelength λ k fluctuates, the wavelength of the single-wavelength laser actually used for measurement deviates from the wavelength in the calculation. Therefore, the value of the distance calculated deviates, and thus the length measurement accuracy deteriorates. In this way, the fluctuation of the frequency is related to the length measurement accuracy. Specifically, the smaller the fluctuation, the better the length measurement accuracy.

[0141] Therefore, in the first measurement in which high accuracy is required, the single-wavelength laser in which the fluctuation of the frequency is small is used out of the two single-wavelength lasers. In other words, the single-wavelength laser in which the stability of the frequency is high is used out of the two single-wavelength lasers.

[0142] In addition, the stability of the frequency is represented by a value having a negative correlation with the fluctuation of the frequency of the laser with respect to the change in time. Specifically, the smaller the fluctuation, the higher the stability of the frequency, and the larger the fluctuation, the lower the stability of the frequency.

[0143] The fluctuation is represented by, for example, the standard deviation σ as shown in Figure 7 . The standard deviation σ can be calculated statistically with respect to the average (median) of the frequency of the laser in a limited time. In addition, the fluctuation of the frequency can not be represented in the frequency unit, but can be represented in the wavelength unit, or can be represented in a unit other than the frequency unit having a correlation with the frequency.

[0144] In the present embodiment, λ1 < λ2, and the fluctuation of the frequency of the laser L1 is smaller than the fluctuation of the frequency of the laser L2. Therefore, the laser L1 of the wavelength λ1 can be used in the first measurement.

[0145] In addition, as the laser light source 11a that emits the laser L1, a Distributed Feedback (DFB) laser light source having a feature of high stability of the frequency, or a light source device in which an absorption line of a gas cell is combined with a semiconductor laser as a reference frequency, or the like can be used.

[0146] [4. Calculation of Absolute Distance]

[0147] Hereinafter, one example of a method of calculating an absolute distance to the object 90 by the MWI using the two single-wavelength lasers will be described.

[0148] In the second determination, based on from Figure 3 The signals from each of the two photodetectors 53 and 54 shown are used to calculate the phase of each wavelength, and the difference between them is obtained as the beat wavelength Λ. 12 The phase. Under the condition that the above-mentioned MWI is satisfied, according to the phase of the beat wavelength Λ. 12 The wavenumber N of laser L1 is determined by dividing the rough distance calculated from the phase by the quotient of the wavelength λ1 of laser L1 with minimal frequency fluctuation. Then, in the first measurement, based on the data from... Figure 3 The phase φ of a single wavelength is calculated from the signal of one of the two photodetectors 53 and 54 shown (here, photodetector 53). Based on the above results, the absolute distance x is calculated using the following equation (3).

[0149] [Number 3]

[0150] (3)

[0151] The primary cause of the fluctuation in the calculated distance x is φ, which arises from the frequency fluctuation of the first single-wavelength laser. Therefore, the optimal combination of wavelengths is the laser with the least frequency fluctuation, i.e., the highest frequency stability, used in the first measurement. Details will be explained later, but the method of this disclosure can be applied in the same manner even when the number of wavelengths is 3 or higher.

[0152] [5. Action (Distance Measurement Method)]

[0153] Next, use Figure 8 The operation of the distance measuring device 1 in this embodiment will be explained.

[0154] Figure 8 This is a flowchart illustrating an example of the operation of the distance measuring device 1 in this embodiment.

[0155] First, the processing circuit 30 determines the laser with the highest frequency stability, i.e., the smallest frequency fluctuation, among the multiple single-wavelength lasers used in the MWI, and reflects the information representing the determined laser into the measurement algorithm (S10). The standard deviation σ representing the frequency fluctuation is, for example, information contained in the light source's data sheet, specification sheet, etc. By reading this information for each light source, the processing circuit 30 can determine the laser with the smallest frequency fluctuation. The information representing the determined laser is then input into the measurement algorithm.

[0156] Further, information of fluctuation of the frequency of the single-wavelength laser light can be acquired, for example, by measuring the fluctuation of the frequency over time for all the single-wavelength laser lights using an optical wavemeter. The evaluation can be performed in advance, and the information can be read in before the measurement, or the fluctuation of the frequency can be evaluated in parallel with the distance measurement, and the single-wavelength laser light having the least fluctuation can be determined in real time.

[0157] After that, the processing circuit 30 acquires the interference signal of each wavelength of the plurality of single-wavelength laser lights by the measurement of the MWI (S20). Specifically, the light source section 10 emits the plurality of single-wavelength laser lights, and the photodetectors 53 and 54 each output a signal corresponding to the detected light intensity.

[0158] Next, the processing circuit 30 calculates the absolute distance by the calculation algorithm of the absolute distance in a manner that the precision of the absolute distance is decided based on the interference result of the single-wavelength laser light having the highest stability of the frequency (S30). Specifically, the processing circuit 30 uses the interference signal of the wavelength of the single-wavelength laser light having the highest stability of the frequency, i.e., the least fluctuation of the frequency, for the first measurement to calculate the first distance. In addition, the processing circuit 30 uses the interference signal of the wavelength of the single-wavelength laser light having the least fluctuation of the frequency and the interference signals of the wavelengths of the other single-wavelength laser lights for the second measurement to calculate the second distance. The processing circuit 30 calculates the absolute distance from the distance measurement apparatus 1 to the object 90 based on the first distance and the second distance.

[0159] In the case of continuing the measurement of the distance (S40: No), the step S20 is returned to, and the interference signal of each wavelength is acquired. For example, in the case of aiming at obtaining the surface shape of the object 90, the interference signal can be acquired after changing the posture and / or position of the object 90.

[0160] In the case of ending the measurement of the distance (S40: Yes), the distance measurement apparatus 1 ends the measurement. The distance measurement apparatus 1 can also output the measurement result to a display or the like to be displayed.

[0161] In addition, Figure 8 The illustrated action is only an example. Hereinafter, the action will be described using Figure 9 Another example of the action of the distance measurement apparatus 1 will be described.

[0162] Figure 9 is a flowchart showing another example of the action of the distance measurement apparatus 1 of the present embodiment. In Figure 9 In the illustrated action, the difference from the action shown in Figure 8 In the illustrated action, the difference from the action shown in

[0163] Specifically, the processing circuit 30 corrects the other interference signals based on the interference result of the laser light whose frequency is most stable, that is, whose fluctuation is smallest. For example, the processing circuit 30 corrects the second signal output from the photodetector 54 that detects light of the wavelength λ2 based on the first signal output from the photodetector 53 that detects light of the wavelength λ1. As an example, the processing circuit 30 estimates the fluctuation of the wavelength λ2 by comparing the intensity of the signal of the wavelength λ1 and the intensity of the signal of the wavelength λ2. By estimating the fluctuation of the wavelength λ

[0164] 2, it is possible to change the value of the wavelength used for calculating the distance to a value close to the actual wavelength. Therefore, it is possible to further improve the accuracy of the calculated distance.

[0165] [6. Modified Example]

[0166] Next, a modified example of the embodiment will be described.

[0167] In the present modified example, the main difference from the embodiment is that the number of wavelengths of the single-wavelength laser light used for distance measurement is three. Hereinafter, the description will be focused on the difference from the embodiment, and the description of the commonalities will be omitted or simplified.

[0168] Figure 10 is a block diagram showing the structure of the light source section 10A of the distance measurement apparatus to which the present modified example pertains. As shown in Figure 10 the light source section 10A is provided with three laser light sources 11a, 11b, and 11c and a wavelength combining system 12. The laser light sources 11a and 11b are the same as in the embodiment, and thus the description will be omitted.

[0169] The laser light source 11c is, for example, a semiconductor laser element that emits laser light of a prescribed single wavelength when supplied with a current. The laser light source 11c is an example of a third laser light source that emits laser light L3 having a wavelength λ3. The wavelength λ3 is an example of a third wavelength, and the laser light L3 is an example of third single-wavelength laser light. The wavelength λ3 is a wavelength different from both the wavelength λ1 and the wavelength λ2. In the present embodiment, the wavelength λ3 is longer than both the wavelength λ1 and the wavelength λ2. At this time, for example, the difference between the wavelength λ3 and the wavelength λ1 can be 10 times or more the difference between the wavelength λ2 and the wavelength λ1. By setting a large difference between the two wavelengths, it is possible to increase the difference between the beat wavelength of the wavelength λ3 and the wavelength λ1 and the beat wavelength of the wavelength λ2 and the wavelength λ

[0170] 1. As a result, it is possible to set the measurement range and the measurement accuracy in stages, and thus it is possible to measure the absolute distance with high accuracy.

[0171] The wavelength combining system 12 combines the laser light L1, L2, and L3 emitted from the three laser light sources 11a, 11b, and 11c, respectively. The light L emitted from the wavelength combining system 12 is coupled with the interference optical system 40. The wavelength combining system 12 is, for example, a DWDM element or a holographic optical element.

[0172] The distance measuring apparatus according to the present variation has the same configuration as the distance measuring apparatus 1 shown in FIG. 1 except for the light source section 10A. Figure 1 The light receiving optical system 50 of the optical unit 20 has a light detector for detecting light of the wavelength λ3. Alternatively, the light receiving optical system 50 of the optical unit 20 can detect beat light by heterodyne interference.

[0173] As in the present variation, in a case where three single-wavelength laser lights having mutually different wavelengths can be used, there are three combinations of two single-wavelength laser lights. Therefore, the second measurement can be performed based on at least one of the three combinations. Specifically, at least one of the following can be performed: the second measurement at a length measurement accuracy and a length measurement range corresponding to the beat wavelength Λ 12 based on interference of the laser light L1 of the wavelength λ1 and the laser light L3 of the wavelength λ3, 13 the second measurement at a length measurement accuracy and a length measurement range corresponding to the beat wavelength Λ 23 based on interference of the laser light L3 of the wavelength λ3 and the laser light L2 of the wavelength λ2.

[0174] In addition, the beat wavelength Λ 12 is represented by Expression (2). Further, the beat wavelengths Λ 13 and Λ 23 are represented by Expressions (4) and (5), respectively.

[0175] [Num 4]

[0176] (4)

[0177] (5)

[0178] In the present variation, λ1 < λ2 < λ3 is satisfied. In addition, |λ1 - λ3| is set to be sufficiently larger than |λ1 - λ2|. In short, λ1 ≒ λ2 is set. As a result, the beat wavelength Λ 12 and the beat wavelength Λ 13 are made to be greatly different from each other. For example, λ1, λ2, and λ3 are set to 1550 nm, 1551 nm, and 1600 nm, respectively. At this time, according to Expressions (2) and (4), the beat wavelength Λ 12 is about 2.4 mm, and the beat wavelength Λ 13 is about 50 μm. In addition, since λ1 ≒ λ2, the beat wavelength Λ13 beat wavelength Λ 23 are substantially equal.

[0179] The processing circuit 30 calculates the distance from the distance measuring apparatus 1 to the object 90 by using the beat wavelength Λ 12 , Λ 13 , and Λ 23 in the second measurement and combining the result with that of the first measurement. Specifically, the processing circuit 30 calculates the absolute distance from the distance measuring apparatus 1 to the object 90 by combining the first distance obtained by the first measurement and the two second distances obtained by the second measurement.

[0180] The processing circuit 30 uses the beat wavelength Λ 12 based on the laser light whose frequency fluctuation is the smallest among the entire single-wavelength laser light emitted by the light source section 10A. Here, since the frequency fluctuation of the laser light L1 is the smallest, the beat wavelengths Λ 13 and Λ 12 are used. In addition, in the first measurement, the processing circuit 30 also uses the interference result of the laser light whose frequency fluctuation is the smallest among the entire single-wavelength laser light emitted by the light source section 10A.

[0181] Here, if the absolute distance from the probe to the measurement object is set as x, the absolute distance x is represented by the following equation (6).

[0182] (6) x = (A x Λ 13 + B x λ1 + θ i x λ1) / 2

[0183] A and B are the wave numbers of the beat wavelength Λ i and the wavelength λ1 included in the absolute distance x 13 to the portion 91 in the object 90, respectively. In addition, θ i indicates the phase based on the interference result of the wavelength λ1 obtained by the first measurement, corresponding to the respective positions of the portions 91, 92, and 93 in the object 90. In addition, equation (6) is equivalent to extending equation (3) to three wavelengths.

[0184] The second measurement is performed with the combination of the longest beat wavelength. The distance calculated in the second measurement is an example of a third distance calculated with a third measurement length accuracy in a third measurement length range. The third measurement length accuracy is lower than the second measurement length accuracy and the first measurement length accuracy. The third measurement length range is longer than the second measurement length range and the first measurement length range. In short, the second measurement is performed with the combination of the longest measurement length range.

[0185] Here, the processing circuit 30 determines the phase of the beat wavelength Λ 12 based on the combination of the wavelength λ1 and the wavelength λ2. The processing circuit 30 determines the beat wavelength Λ 12the beat wavelength Λ 13 the wave number A of the beat wavelength Λ 12 calculated. Specifically, the wave number B of the wavelength λ1 is calculated by dividing the distance calculated based on the beat wavelength Λ 13 by the wavelength λ1. 13

[0186] Further, as the second measurement next, the processing circuit 30 determines the phase of the beat wavelength Λ 13 based on the combination of the wavelength λ1 and the wavelength λ3. The processing circuit 30 counts the wave number B of the wavelength λ1 based on the phase of the beat wavelength Λ 13 determined. Specifically, the wave number B of the wavelength λ1 is calculated by dividing the distance calculated based on the beat wavelength Λ 13 by the wavelength λ1.

[0187] Finally, as the first measurement, the processing circuit 30 determines the phase θ1 of the wavelength λ1. The processing circuit 30 can calculate the absolute distance x i based on the wave numbers A and B and the phase θ1 of the wavelength λ1 by the above-described equation (6).

[0188] As described above, by performing a plurality of second measurements using a plurality of beat wavelengths, it is possible to further expand the range of the distance measurement.

[0189] In addition, the calculation of the absolute distance can also be performed in a manner other than the above. For example, an excess fraction method, which performs the calculation of the absolute distance using the combination of the phases of all the wavelengths of the laser used, can also be used.

[0190] (Other Embodiments)

[0191] The above describes a distance measurement apparatus according to one or more of the embodiments, but the present disclosure is not limited to these embodiments. As long as the gist of the present disclosure is not deviated from, a manner obtained by applying various modifications to the present embodiments that can be thought of by those skilled in the art, and a manner constructed by combining the constituent elements in different embodiments are also included in the scope of the present disclosure.

[0192] ​For example, in the above-described embodiments and modifications, an example in which the processing circuit 30 calculates the absolute distance from the distance measuring device 1 to the object 90 is shown, but the present application is not limited to this. The processing circuit 30 can also output the first distance and the second distance to another device after calculating them. For example, the processing circuit 30 can also transmit the first distance and the second distance to another computer, and calculate the absolute distance by the other computer. Alternatively, the processing circuit 30 can also transmit the first distance and the second distance to a display and display them on the display, or can output them to a printer and print them on a medium such as paper. Thus, the first distance and the second distance can be prompted to a user or the like, and thus the user can calculate the absolute distance by manual calculation. In this way, the processing circuit 30 can also not perform the calculation of the absolute distance.

[0193] In addition, the wavelength of at least one of the two single-wavelength lasers can also be changed. For example, the wavelength of the laser whose frequency fluctuation is large can be made to be able to be scanned. Thus, the combination of the two wavelengths can be changed, and thus a measurement range and a measurement accuracy suitable for the object 90 can be achieved. In addition, compared to the case where three or more laser light sources are provided, the device can be made to be small.

[0194] In addition, one of the two single-wavelength lasers obtained by branching one single-wavelength laser into two and the laser whose frequency is shifted can also be used as the two single-wavelength lasers. As a unit that shifts the frequency, for example, an acousto-optic element (AOM: Acousto-Optic Modulator) can be used.

[0195] In addition, the frequency fluctuation can not be the standard deviation σ. For example, the frequency fluctuation can be 3σ. Alternatively, the frequency fluctuation can be the variance σ of the frequency of the laser within a limited time. 2 In addition, the frequency fluctuation can be the difference between the maximum value and the minimum value of the frequency of the laser within a limited time.

[0196] In addition, in the case where three or more laser light sources are provided in the light source unit, two of the laser light sources can also emit single-wavelength lasers of the same wavelength. In addition, the frequency fluctuation of the two single-wavelength lasers of the same wavelength can also be the same. One of the two single-wavelength lasers of the same wavelength can be used in the first measurement, and the other of the two single-wavelength lasers of the same wavelength can be used in the second measurement. In other words, the first single-wavelength laser used in each of the first measurement and the second measurement can be a laser emitted from a different laser light source.

[0197] In addition, the length measurement accuracy Am of the second measurement can be larger than the length measurement range Rs of the first measurement. In a case where Am > Rs, the distance measurement can be performed with substantially the same degree of accuracy as in a case where Am < Rs.

[0198] In addition, the entire or specific technical solutions of the present disclosure can also be implemented by a system, device, method, integrated circuit, or computer program. Alternatively, it can also be implemented by a computer-readable non-transitory recording medium such as an optical disc, HDD, or semiconductor memory, which stores the computer program. In addition, it can also be implemented by any combination of a system, device, method, integrated circuit, computer program, and recording medium.

[0199] In addition, each of the above-described embodiments can be variously changed, replaced, added, omitted, and the like within the scope of the claims or equivalents thereof.

[0200] Industrial applicability

[0201] The present disclosure can be used as a distance measurement device that can balance a longer length measurement range and higher length measurement accuracy, for example, can be used in a surface shape inspection device or the like.

[0202] Explanation of reference numerals:

[0203] 1 distance measurement device

[0204] 10, 10A light source unit

[0205] 11a, 11b, 11c laser light source

[0206] 12 wavelength combining system

[0207] 20 optical unit

[0208] 30 processing circuit

[0209] 40 interference optical system

[0210] 41 beam splitter

[0211] 42, 52 mirror

[0212] 50 light receiving optical system

[0213] 51 dichroic mirror

[0214] 53, 54 light detector

[0215] 90, 90a, 90b, 90c object

Claims

1. A distance measuring apparatus comprising: a light source section that emits first single-wavelength laser light having a first wavelength and second single-wavelength laser light having a second wavelength different from the first wavelength; an optical unit that causes a plurality of lights incident to the optical unit to interfere, detects a first light component having the first wavelength among interference light generated by the interference of the plurality of lights, outputs a first signal corresponding to a result of detecting the first light component, and detects a second light component having the second wavelength among the interference light, and outputs a second signal corresponding to a result of detecting the second light component; and a processing circuit that processes the first signal and the second signal, the processing circuit performing: calculation of a first distance within a first range with a first accuracy based on the first signal, calculation of a second distance within a second range with a second accuracy based on the first signal and the second signal, the first accuracy being higher than the second accuracy, the second range being longer than the first range, and the frequency stability of the first single-wavelength laser light being higher than the frequency stability of the second single-wavelength laser light. 2.The distance measuring apparatus according to claim 1, wherein the second accuracy is below the first range. 3.The distance measuring apparatus according to claim 2, wherein the processing circuit further calculates a distance from the distance measuring apparatus to an object based on the first distance and the second distance. 4.The distance measuring apparatus according to claim 3, wherein the processing circuit calculates an absolute distance from the distance measuring apparatus to the object. 5.The distance measuring apparatus according to any one of claims 1 to 4, wherein the plurality of lights include the first single-wavelength laser light, the second single-wavelength laser light, first reflected light generated by reflection of the first single-wavelength laser light at an object, and second reflected light generated by reflection of the second single-wavelength laser light at the object, the optical unit outputs the first signal by causing the first single-wavelength laser light and the first reflected light to interfere and detecting the interference, and outputs the second signal by causing the second single-wavelength laser light and the second reflected light to interfere and detecting the interference. 6.The distance measuring apparatus according to claim 5, wherein the optical unit includes a beam splitter, a first light detector, and a second light detector, the beam splitter splits the first single-wavelength laser light from the light source section into first reference light and first detection light, and splits the second single-wavelength laser light from the light source section into second reference light and second detection light, the first reflected light is light generated by reflection of the first detection light at the object, the second reflected light is light generated by reflection of the second detection light at the object, the first light detector outputs the first signal by detecting the first light component generated by interference of the first reference light and the first reflected light, and the second light detector outputs the second signal by detecting the second light component generated by interference of the second reference light and the second reflected light. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 7. The distance measuring apparatus according to claim 6, wherein the optical unit includes: an optical element that causes the first reference light and the second reference light to be incident on the beam splitter; and a wavelength separation element that separates the incident light into light of the first wavelength and light of the second wavelength, the beam splitter causes at least a portion of each of the first reflected light and the second reflected light from the object and at least a portion of each of the first reference light and the second reference light from the optical element to be emitted toward the wavelength separation element.

8. The distance measuring apparatus according to claim 5, wherein the processing circuit corrects the second signal based on the first signal.

9. The distance measuring apparatus according to any one of claims 1 to 4, wherein the set frequency of the first single-wavelength laser and the set frequency of the second single-wavelength laser are fixed during the measurement period.

10. The distance measuring apparatus according to any one of claims 1 to 4, wherein the light source section also emits a third single-wavelength laser having a third wavelength different from both the first wavelength and the second wavelength.

11. The distance measuring apparatus according to claim 10, wherein the first single-wavelength laser has the highest stability of frequency among all the single-wavelength lasers emitted by the light source section.

12. The distance measuring apparatus according to claim 10, wherein the optical unit also detects a third light component having the third wavelength in the interference light and outputs a third signal corresponding to a result of detecting the third light component, the processing circuit also calculates a third distance within a third range with a third precision based on the first signal and the third signal, the third precision is lower than the second precision, the third range is longer than the second range.

13. The distance measuring apparatus according to any one of claims 1 to 4, wherein the processing circuit calculates a phase of a beat wavelength of the first wavelength and the second wavelength based on the first signal and the second signal, thereby calculating the second distance.

14. The distance measuring apparatus according to claim 13, wherein the processing circuit performs: calculating the first distance based on the first signal, combining the first distance and the second distance, thereby calculating an absolute distance from the distance measuring apparatus to the object.

15. The distance measuring apparatus according to any one of claims 1 to 4, wherein the light source section includes: a first laser light source that emits the first single-wavelength laser; and a second laser light source that emits the second single-wavelength laser.

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