Distance measuring device

Abstract

Provided is a distance measuring device capable of simultaneously achieving a longer length measurement range and higher length measurement accuracy. A distance measuring device is provided with: 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; an optical unit that interferes and detects the plurality of light beams incident on the optical unit, and outputs a signal corresponding to the result of the interference of the plurality of light beams; and a processing circuit that processes the signal. The set frequency of the first single-wavelength laser light and the set frequency of the second single-wavelength laser light are fixed during the measurement period. The light source unit includes a frequency stabilized laser that emits a first single wavelength laser.

Description

Technical Field

[0001] The present disclosure relates to a distance measuring device. Background Art

[0002] Optical interference using lasers is widely used as a means of obtaining information indicating the distance and / or shape of an object in a non-contact manner. As an example, LiDAR (Light Detection And Ranging) using the frequency modulated continuous wave radar (FMCW) method is well known as a three-dimensional measurement device with millimeter accuracy. In addition, optical interference using Optica coherence tomography (OCT) or optical comb is well known as a means of measuring with micron accuracy. They are widely used in the medical field and / or industrial field.

[0003] In addition, by controlling the light interference phenomenon with higher precision, it is possible to measure with nanometer precision. For example, the Michelson interferometer using a single wavelength laser is a method of measuring the difference in distance in nanometer units as light intensity.

[0004] Nano-precision optical measurement, represented by homodyne interferometry, can perform high-precision measurements in a non-contact manner, but has the problem that the measurement range is limited to half the wavelength, that is, sub-micrometer units. Therefore, it is difficult to measure samples that have both nanometer-level structures and tens of micrometer-level structures.

[0005] As a method to solve this problem, multi-wavelength interference, which uses optical interference of two or more single-wavelength lasers, is expected. Multi-wavelength interference can eliminate the trade-off between the length measurement range and the length measurement accuracy, which is a conventional problem, and simultaneously achieve a longer length measurement range and higher length measurement accuracy.

[0006] For example, in Patent Document 1, by combining the optical interference results of laser beams with different wavelengths, the trade-off between the conventional length measurement range and the length measurement accuracy can be eliminated, thereby achieving a longer length measurement range and higher length measurement accuracy.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: German Patent Invention No. 102015209567 Utility Model Content

[0010] Issues to be solved by utility models

[0011] In the distance measuring device using the principle of multi-wavelength interference (MWI) disclosed in Patent Document 1, two or more single-wavelength lasers having different wavelengths are required. At this time, when the frequency stability of the two or more single-wavelength lasers is different from each other, the distance measurement accuracy may be reduced depending on the combination method of the wavelengths used in distance calculation.

[0012] Therefore, the present disclosure provides a distance measuring device that can simultaneously achieve a longer length measuring range and a higher length measuring accuracy.

[0013] Means for solving problems

[0014] A distance measuring device according to one aspect of the present disclosure comprises: a light source unit that emits a first single wavelength laser having a first wavelength and a second single wavelength laser having a second wavelength different from the first wavelength; an optical unit that detects interference of a plurality of lights incident on the optical unit and outputs a signal corresponding to the result of interfering the plurality of lights; and a processing circuit that processes the signal. 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. The light source unit includes a frequency stabilized laser that emits the first single wavelength laser.

[0015] Utility Model Effect

[0016] According to the present disclosure, a longer length measurement range and a higher length measurement accuracy can be achieved simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 2 It is a block diagram showing the configuration of a light source unit of the distance measuring device according to the embodiment.

[0019] Figure 3 It is a diagram showing a specific configuration of an optical unit of the distance measuring device according to the embodiment.

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

[0021] Figure 5 This is a diagram for explaining the principle of the second measurement using a plurality of single-wavelength laser beams by the distance measuring device according to the embodiment.

[0022] Figure 6 It is a diagram showing the length measurement range and the length measurement accuracy of two measurements by the distance measurement device according to the embodiment.

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

[0024] Figure 8 This is a flowchart showing an example of the operation of the distance measuring device according to the embodiment.

[0025] Fig. 9 This is a flowchart showing another example of the operation of the distance measuring device according to the embodiment.

[0026] Fig.10 It is a block diagram showing the configuration of a light source unit of a distance measuring device according to a modified example of the embodiment.

[0027] Description of Reference Numerals

[0028] 1Distance measuring device

[0029] 10. 10A light source

[0030] 11a, 11b, 11c laser light source

[0031] 12 Wavelength Synthesis System

[0032] 20 Optical units

[0033] 30 Processing circuit

[0034] 40 Interference optical system

[0035] 41 Beam splitter

[0036] 42, 52 Reflector

[0037] 50 Light receiving optical system

[0038] 51 dichroic mirror

[0039] 53, 54 Photodetector

[0040] 90, 90a, 90b, 90c Object DETAILED DESCRIPTION

[0041] (Overview of the present disclosure)

[0042] First, definitions of important terms used in this specification are shown below.

[0043] "Measurement accuracy" refers to the degree of accuracy when measuring distance. In other words, measurement accuracy is a measure of how accurately distance information can be obtained. Therefore, it can be said that the higher the measurement accuracy, the more accurate the measurement can be.

[0044] The "distance measurement range" indicates a range in the distance direction in which unique distance information can be obtained. In other words, the distance measurement range indicates a range in which distance measurement can be performed.

[0045] In this specification, the length measurement accuracy and the length measurement range are expressed in the same dimension as the distance. Specifically, the units of the length measurement accuracy and the length measurement range are expressed in nanometers (nm), micrometers (μm), millimeters (mm), etc. Therefore, "higher length measurement accuracy" is synonymous with "shorter length measurement accuracy" expressed in the dimension of distance. "Lower length measurement accuracy" is synonymous with "longer length measurement accuracy" expressed in the dimension of distance. In addition, in this specification, the length measurement accuracy is sometimes recorded simply as "accuracy". Sometimes the length measurement range is recorded simply as "range".

[0046] Distance measurement within the measurement range is called “absolute distance measurement.” For example, distance measurement with an accuracy of 10 nm and a measurement range of 1 mm is absolute distance measurement that can distinguish a difference of 10 nm within a range of 1 mm.

[0047] A plurality of aspects of the distance measuring device disclosed herein are as follows.

[0048] The first embodiment of the present invention discloses a distance measuring device comprising: a light source unit that emits a first single wavelength laser having a first wavelength and a second single wavelength laser having a second wavelength different from the first wavelength; an optical unit that interferes and detects a plurality of lights incident on the optical unit and outputs a signal corresponding to the result of interfering the plurality of lights; and a processing circuit that processes the signal. 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. The light source unit includes a frequency stabilized laser that emits the first single wavelength laser.

[0049] This can suppress frequency fluctuations during the measurement period, thereby improving measurement accuracy.

[0050] The second mode of distance measuring device disclosed in the present invention is that, in the distance measuring device of the first mode, the optical unit can also detect the first light component having the first wavelength in the interference light generated by the interference of the multiple lights, and output a first signal corresponding to the result of detecting the first light component, and detect the second light component having the second wavelength in the interference light, and output a second signal corresponding to the result of detecting the second light component, the processing circuit can also calculate the first distance within the first range with a first accuracy based on the first signal, and calculate the second distance within the second range with a second accuracy based on the first signal and the second signal, the first accuracy can also be higher than the second accuracy, the second range can also be longer than the first range, and the frequency stability of the first single wavelength laser can also be higher than the frequency stability of the second single wavelength laser.

[0051] Thus, the first measurement can be performed based on the first single wavelength laser with higher frequency stability, so that a longer length measurement range and a higher length measurement accuracy can be achieved at the same time. In addition, laser light sources with higher frequency stability are usually expensive. According to this method, the frequency stability of lasers other than the light source emitting the first single wavelength laser can also be lower. Therefore, for example, a cheap light source can be used as the light source emitting the second single wavelength laser, so low cost can also be expected.

[0052] A distance measurement device according to a third aspect of the present disclosure may be, in the distance measurement device according to the second aspect, wherein the second accuracy is equal to or less than the first range.

[0053] 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 length measurement accuracy can be achieved.

[0054] A distance measurement device according to a fourth aspect of the present disclosure may be the distance measurement device according to the third aspect, wherein the processing circuit further calculates a distance from the distance measurement device to an object based on the first distance and the second distance.

[0055] Thus, the processing circuit calculates the distance from the distance measuring device to the object, so that, for example, the user does not need to perform the calculation by manual calculation, and user convenience is improved.

[0056] A distance measuring device according to a fifth aspect of the present disclosure may be the distance measuring device according to the fourth aspect, wherein the processing circuit calculates an absolute distance from the distance measuring device to the object.

[0057] This makes it possible to calculate the absolute distance from the distance measuring device to the object, and thus the distance measuring device is useful in, for example, inspection of the surface shape of the object.

[0058] The sixth mode of the distance measuring device disclosed in the present invention is that in the distance measuring device of any one of the second mode to the fifth mode, the multiple lights may also include the first single wavelength laser, the second single wavelength laser, the first reflected light generated by the reflection of the first single wavelength laser in the object, and the second reflected light generated by the reflection of the second single wavelength laser in the object, and the optical unit may also output the first signal by causing the first single wavelength laser to interfere with the first reflected light and detect the interference, and output the second signal by causing the second single wavelength laser to interfere with the second reflected light and detect the interference.

[0059] This makes it possible to easily obtain an intensity signal of interference light for each wavelength using homodyne interference.

[0060] The seventh mode of the distance measuring device disclosed in the present invention is that in the sixth mode of the distance measuring device, the optical unit may also include a beam splitter, a first light detector, and a second light detector, the beam splitter may also split the first single wavelength laser from the light source unit into a first reference light and a first detection light, and split the second single wavelength laser from the light source unit into a second reference light and a second detection light, the first reflected light is the light generated by the first detection light being reflected in the object, the second reflected light is the light generated by the second detection light being reflected in the object, the first light detector may also output the first signal by detecting the first light component generated by interference between the first reference light and the first reflected light, and the second light detector may output the second signal by detecting the second light component generated by interference between the second reference light and the second reflected light.

[0061] Thus, interference is caused by the beam splitter, and interference signals for each wavelength can be obtained with high accuracy by two photodetectors.

[0062] The eighth mode of the distance measuring device disclosed in the present invention is that in the seventh mode of the distance measuring device, the optical unit may also include an optical element that allows 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, and the beam splitter may also emit 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 toward the wavelength separation element.

[0063] Thus, since a Michelson interferometer is constructed, the configuration of the optical path of each laser beam becomes easy, and distance measurement can be performed with high accuracy.

[0064] A distance measurement device according to a ninth aspect of the present disclosure may be the distance measurement device according to any one of the sixth to eighth aspects, wherein the processing circuit corrects the second signal based on the first signal.

[0065] This can improve the accuracy of the second measurement.

[0066] The distance measuring device of the tenth aspect of the present disclosure may be the distance measuring device of any one of the second to ninth aspects, wherein the light source unit further emits a third single wavelength laser having a third wavelength different from both the first wavelength and the second wavelength.

[0067] Thus, by using three wavelengths, the length measurement range can be further extended. Alternatively, four or more wavelengths may be used to further extend the length measurement range.

[0068] The distance measuring device according to an eleventh aspect of the present disclosure may be the distance measuring device according to the tenth aspect, wherein the frequency stability of the first single wavelength laser light is the highest among all the single wavelength laser lights emitted by the light source unit.

[0069] This makes it possible to achieve the highest-precision measurement among the combinations of wavelengths of laser light that can be emitted.

[0070] The twelfth mode of the distance measuring device disclosed in the present invention is that in the tenth mode or the eleventh mode of the distance measuring device, the optical unit may also detect a third light component having the third wavelength in the interference light, and output a third signal corresponding to the result of detecting the third light component. The processing circuit may also calculate a third distance within a third range with a third accuracy based on the first signal and the third signal. The third accuracy may also be lower than the second accuracy, and the third range may also be longer than the second range.

[0071] Thus, the length measuring range can be further extended. Thus, a longer length measuring range and higher length measuring accuracy can be achieved at the same time.

[0072] The distance measuring device of the thirteenth aspect of the present disclosure may be a distance measuring device of any one of the second aspect to the twelfth aspect, wherein the processing circuit calculates the second distance by calculating the phase of the beat wavelength of the first wavelength and the second wavelength based on the first signal and the second signal.

[0073] Thus, the distance within a longer measurement range can be calculated based on the beat frequency wavelength.

[0074] The fourteenth mode of the distance measuring device disclosed in the present invention is that, in the thirteenth mode of the distance measuring device, the processing circuit can also calculate the first distance by calculating the phase of the first wavelength based on the first signal, and can also calculate the absolute distance from the distance measuring device to the object by combining the first distance and the second distance.

[0075] This makes it possible to calculate the absolute distance from the distance measuring device to the object, and thus the distance measuring device is useful in, for example, inspecting the surface shape of the object.

[0076] A distance measuring device according to a fifteenth aspect of the present disclosure may be the distance measuring device according to any one of the first to fourteenth aspects, wherein the light source unit further includes a laser light source that emits the second single wavelength laser light.

[0077] Thus, by providing a laser light source for each wavelength, a plurality of single-wavelength laser lights can be easily emitted.

[0078] Below, while referring to the attached Figure 1 The implementation method will be specifically described.

[0079] In addition, the embodiments described below are used to represent general or specific examples. The numerical values, shapes, materials, components, configuration positions of components, connection methods, steps, and the order of steps shown in the following embodiments are examples and are not intended to limit the present disclosure. In addition, the components in the following embodiments that are not recorded in the independent claims are described as arbitrary components.

[0080] In addition, each figure is a schematic diagram and is not necessarily a strict illustration. Therefore, for example, the scales and the like are not necessarily the same in each figure. In addition, in each figure, substantially the same components are marked with the same reference numerals, and repeated descriptions are omitted or simplified.

[0081] In the present specification, words such as parallel or perpendicular indicating the relationship between elements, words indicating the shape of an element, and numerical ranges do not mean expressions in a strict sense, but refer to substantially equivalent ranges, for example, expressions including a difference of about several percent.

[0082] In addition, in this specification, unless otherwise specified, ordinal numbers such as “first” and “second” do not refer to the number or order of components, but are used to distinguish between components of the same kind to avoid confusion.

[0083] (Implementation Method)

[0084] [1. Configuration of distance measuring device]

[0085] First, use Figure 1 The configuration of the distance measuring device according to the embodiment will be described. Figure 1 It is a block diagram showing the configuration of the distance measuring device 1 according to the present embodiment.

[0086] Figure 1 The distance measuring device 1 shown is a device for measuring the distance from the distance measuring device 1 to the object 90. Specifically, the distance measuring device 1 can obtain information indicating the surface shape of the object 90 by measuring the distance of each part of the object 90. The distance measuring device 1 can be used, for example, for appearance inspection of products.

[0087] like Figure 1 As shown, the distance measuring device 1 includes a light source unit 10, an optical unit 20, and a processing circuit 30. Although not shown, the distance measuring device 1 may also include a support unit for supporting the object 90. The support unit may include a driving unit such as a motor or a piezoelectric element, and may be capable of changing the posture and / or position of the object 90.

[0088] The light source unit 10 emits a plurality of single-wavelength laser beams. Figure 2 1 is a block diagram showing the structure of the light source unit 10 of the distance measuring device 1 according to the present embodiment. Figure 2 As shown, the light source unit 10 includes laser light sources 11 a and 11 b and a wavelength synthesis system 12 .

[0089] The laser light sources 11a and 11b emit single-wavelength laser beams having different wavelengths, respectively. The laser light sources 11a and 11b are, for example, semiconductor laser elements, and emit laser beams having a predetermined single wavelength when current is supplied thereto.

[0090] The laser light source 11 a is an example of a first laser light source, and 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 a first single-wavelength laser light.

[0091] The laser light source 11b is an example of a second laser light source, and 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 a second single wavelength laser. The wavelength λ2 is a wavelength different from the wavelength λ1. In this embodiment, the wavelength λ2 is longer than the wavelength λ1.

[0092] The wavelength synthesis system 12 combines the laser light L1 and laser light L2 emitted from the two laser light sources 11a and 11b, respectively. The light L emitted from the wavelength synthesis system 12 is coupled by the interference optical system 40. The wavelength synthesis system 12 is, for example, a DWDM (Dense Wavelength Division Multiplexing) element or a holographic optical element.

[0093] The optical unit 20 is an example of an optical unit that interferes with and detects light incident to the optical unit 20 and outputs a signal corresponding to the interference result. The laser lights L1 and L2 from the light source unit 10, the first reflected light generated by the laser light L1 reflected by the object 90, and the second reflected light generated by the laser light L2 reflected by the object 90 are incident on the optical unit 20. Figure 1 As shown, the optical unit 20 includes an interference optical system 40 and a light receiving optical system 50. Figure 3 The specific configurations of the interference optical system 40 and the light receiving optical system 50 will be described.

[0094] 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 device 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 predetermined algorithm, thereby obtaining the position of the object 90 as phase information. As a representative phase estimation algorithm, a 4-step phase-shifting algorithm can be used. The processing circuit 30 can calculate the distance from the distance measuring device 1 to the object 90 based on the phase information.

[0095] Specifically, the processing circuit 30 calculates a first distance within a first measurement range with a first measurement accuracy based on the interference result corresponding to the wavelength λ1. In addition, the processing circuit 30 calculates a second distance within a second measurement range with a second measurement accuracy based on the interference result corresponding to the wavelength λ1 and the wavelength λ2. The processing circuit 30 calculates the distance from the distance measuring device 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 device 1 to the object 90.

[0096] Here, the first length measurement accuracy is higher than the second length measurement accuracy. In addition, the second length measurement range is longer than the first length measurement range. Therefore, to put it another way, the processing circuit 30 calculates the distance within the shorter length measurement range with a higher length measurement accuracy based on the interference result of one wavelength. The processing circuit 30 calculates the distance within the longer length measurement range with a lower length measurement accuracy based on the interference result of two wavelengths. The specific distance calculation method is described later.

[0097] The processing circuit 30 is implemented by an integrated circuit such as LSI (Large Scale Integration). For example, the processing circuit 30 may also be implemented by a dedicated hardware configuration to calculate the distance from the distance measuring device 1 to the object 90. Alternatively, the processing circuit 30 may also include a processor and a memory, and the distance from the distance measuring device 1 to the object 90 is calculated by causing the processor to execute a program stored in the memory. Specifically, the processing circuit 30 may also include a non-volatile memory storing a program, a temporary storage area for executing the program, i.e., a volatile memory, an input / output port, a processor for executing the program, etc. Alternatively, the processing circuit 30 may also be a programmable FPGA (Field Programmable Gate Array), or a reconfigurable processor capable of reconfiguring the connection and settings of the circuit units within the LSI.

[0098] [1.1. Specific structure of the optical unit]

[0099] Next, the specific structure of the optical unit 20 is described. As described above, the optical unit 20 includes the interference optical system 40 and the light receiving optical system 50. Figure 3 Each structure will be described in sequence. Figure 3 It is a diagram showing a specific configuration of the optical unit 20 of the distance measuring device 1 according to the present embodiment.

[0100] In this embodiment, the interference optical system 40 is an optical system using Michelson interference. Figure 3 As shown, the interference optical system 40 includes a beam splitter 41 and a reflection mirror 42 .

[0101] The beam splitter 41 is an optical element that splits the intensity of light incident to the beam splitter 41 into a plurality of lights and emits the plurality of lights in different directions. The beam splitter 41 is, for example, a half-transparent half-reflective mirror, and splits the light incident to the beam splitter 41 into transmitted light and reflected light in such a manner that the light has the same intensity. In addition, the intensity ratio of the transmitted light to the reflected light may not be 1:1.

[0102] Specifically, the beam splitter 41 splits the laser light L1 from the light source unit 10 into the first detection light and the first reference light, and splits the laser light L2 from the light source unit 10 into the second detection light and the 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 reflector 42.

[0103] The reflector 42 is an example of an optical element that allows the first reference light and the second reference light from the beam splitter 41 to enter the beam splitter. Specifically, the reflector 42 specularly reflects the light incident on the reflector 42. The higher the reflectivity, the less the light loss, and thus the detection accuracy can be improved.

[0104] exist Figure 3 In the example shown, the laser light from the light source unit 10, that is, the synthesized light L of the laser light L1 and the laser light L2, is incident on the beam splitter 41. The beam splitter 41 transmits a part of the synthesized 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 toward the object 90. The reflected light Lr includes the first reference light and the second reference light, and is irradiated toward the reflector 42.

[0105] The transmitted light Lt irradiated to the object 90 is reflected by the object 90 and enters the beam splitter 41 again. A part of the transmitted light Lt that enters the beam splitter 41 again is reflected and moves toward the light receiving optical system 50. The transmitted light Lt that enters the beam splitter 41 again includes reflected light (i.e., first reflected light) generated by the first detection light that is a part of the laser light L1 reflected on the object 90 and reflected light (i.e., second reflected light) generated by the second detection light that is a part of the laser light L2 reflected on the object 90.

[0106] Similarly, the reflected light Lr incident on the reflector 42 is reflected by the reflector 42 and incident on the beam splitter 41 again. A part of the reflected light Lr incident on the beam splitter 41 again is transmitted toward the light receiving optical system 50. The reflected light Lr incident on 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.

[0107] In other words, when the combined light L from the light source unit 10 is split into the transmitted light Lt and the reflected light Lr by the beam splitter 41 , the transmitted light Lt may be irradiated to the reflector 42 , and the reflected light Lr may be irradiated to the object 90 .

[0108] In addition, the interference optical system 40 is not limited to an optical system using Michelson interference, and the interference optical system 40 may be an optical system using Fizeau interference or Mach-Zehnder interference.

[0109] The light receiving optical system 50 is an optical system using homodyne interference. Figure 3 As shown, the light receiving optical system 50 includes a dichroic mirror 51 , a reflecting mirror 52 , and photodetectors 53 and 54 .

[0110] The dichroic mirror 51 is an example of a wavelength separation element that separates the light incident on the dichroic mirror 51 into light of wavelength λ1 and light of wavelength λ2. Specifically, the dichroic mirror 51 performs wavelength separation on the light incident from the beam splitter 41 to the light receiving optical system 50. In the present embodiment, the light of wavelength λ1 on the dichroic mirror 51 is emitted toward the photodetector 53, and the light of wavelength λ2 is emitted toward the photodetector 54. In the present embodiment, the reflector 52 is provided to adjust the optical path.

[0111] The reflector 52 reflects the light of wavelength λ2 separated by the dichroic mirror 51 and makes it incident on the photodetector 54. Alternatively, the reflector 52 may not be provided and the photodetector 54 may be arranged at the position of the reflector 52. Alternatively, the reflector 52 may be provided for the purpose of adjusting the optical path of the light of wavelength λ1.

[0112] The photodetectors 53 and 54 each include a photoelectric conversion element that generates an electrical signal corresponding to the intensity of the incident light. The photodetector 53 is an example of a first photodetector, and has sensitivity to at least the wavelength λ1, and performs photoelectric conversion on the light of the wavelength λ1, and outputs a first signal having a signal level corresponding to the intensity thereof to the processing circuit 30. The first signal is a signal obtained by detecting interference light between the laser light L1 reflected by the reflector 42 and the reflected light of the laser light L1 caused by the reflection on the object 90.

[0113] The photodetector 54 is an example of a second photodetector, has sensitivity to at least the wavelength λ2, and performs photoelectric conversion on the light of the wavelength λ2, and outputs a second signal having a signal level corresponding to the intensity thereof to the processing circuit 30. The second signal is a signal obtained by interfering and detecting the laser light L2 reflected by the reflector 42 with the reflected light of the laser light L2 caused by the reflection on the object 90.

[0114] In addition, as long as it is possible to receive light of each wavelength, the structure of the light receiving optical system 50 is not limited to the above example. For example, after the intensity of the light from the beam splitter 41 to the light receiving optical system 50 is split into two lights, the two split lights are respectively passed through a filter having a transmission band for a specific wavelength component. The filter can be, for example, a bandpass filter, but it can also be a low-pass filter, a high-pass filter, etc.

[0115] In addition, the light receiving optical system 50 may not be an optical system using homodyne interference. The light receiving optical system 50 may also be an optical system using heterodyne interference. In this case, the light receiving optical system 50 may not include the dichroic mirror 51 for wavelength division of light, and the number of photodetectors may be one.

[0116] [2. Principle of distance measurement]

[0117] Next, the principle of distance measurement by the distance measurement device 1 of the present embodiment will be described.

[0118] In the distance measuring device 1 of the present embodiment, distance measurement is performed based on multi-wavelength interferometry (MWI) using multiple single-wavelength lasers. MWI can eliminate the trade-off between the length measurement range and the length measurement accuracy, which is a conventional problem, by combining the interference results of multiple single-wavelength lasers with different wavelengths, and achieve a longer length measurement range and higher length measurement accuracy. The principle of multi-wavelength interferometry is described below.

[0119] [2.1. First measurement (using one wavelength)]

[0120] First, the first measurement using a single wavelength laser will be described.

[0121] If used Figure 3 As described above, in homodyne interferometry, a single wavelength laser is split by a beam splitter 41 and irradiated to a reflector 42 functioning as a reference surface and an object 90 to be measured as a distance. The beam splitter 41 causes the reflected light from the reflector 42 and the object 90 to interfere with each other. When the interfering light is detected by the photodetector 53, the intensity P of the signal output from the photodetector 53 is PD It is represented by the following formula (1).

[0122]

Formula 1

[0123]

[0124] In formula (1), L － =L x -L y .L x L is the distance from the beam splitter 41 to the reflecting surface of the reflecting mirror 42. y is the distance from the beam splitter 41 to the object 90. k is the wavelength of the single-wavelength laser. Here, k = 1. L x and k are all known values ​​to the processing circuit 30. Therefore, the processing circuit 30 can calculate the signal strength P based on the signal strength P. PD Calculate the distance L to the object 90 y .

[0125] In the first measurement, there is a problem that the measuring range is relatively short. Figure 4 , illustrating the relationship between the position of the object 90 and the length measuring range.

[0126] Figure 41 is a diagram for explaining the principle of the first measurement using a single wavelength laser of the distance measuring device 1 of the present embodiment. Figure 4 In the figure, objects 90a, 90b and 90c respectively represent Figure 1 as well as Figure 3 The object 90 shown is located at different positions. When there is no need to distinguish the position, it will be described as "the object 90".

[0127] exist Figure 4 In FIG. 1 , the following graph is shown: the horizontal axis represents the distance to the object 90 with the predetermined position as the reference point, and the vertical axis represents the distance calculated by the processing circuit 30, that is, the calculated distance. Figure 4 As shown, the processing circuit 30 can calculate the distance to the object 90 within a predetermined measuring range. As can be seen from equation (1), when the wavelength of the single-wavelength laser is λ1, the measuring range is half its wavelength (λ1 / 2).

[0128] In the first measurement, if the distance measurement range is exceeded, the absolute distance from the distance measurement device 1 to the object 90 cannot be calculated. Figure 4 In the example shown, all of the objects 90a, 90b, and 90c are calculated as having the same distance.

[0129] 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 wavelength band of about 700 nm or more and about 2500 nm or less. The visible light band is a wavelength band of about 380 nm or more and about 780 nm or less. In this case, the length measurement range in the first measurement becomes about 190 nm or more and about 1250 nm or less. That is, the length measurement range in the first measurement becomes a size of several hundred nanometers to several micrometers. In this way, the length measurement range of the first measurement is relatively narrow compared to the second measurement described later.

[0130] [2.2. Second measurement (using two wavelengths)]

[0131] Next, use Figure 3 as well as Figure 5 A second measurement using two single-wavelength laser beams having wavelengths different from each other will be described. This second measurement is for solving the problem of the short length measuring range that is a problem of the first measurement.

[0132] like Figure 3 As shown, in the distance measuring device 1 of this embodiment, the light interfered by the beam splitter 41 is separated into each wavelength by the dichroic mirror 51, and detected by two photodetectors 53 and 54. As a result, signals corresponding to the results of homodyne light interference of each corresponding wavelength are output from the photodetectors 53 and 54. The processing circuit 30 can calculate the distance to the object 90 based on the two signals.

[0133] In the second measurement, the measurement range is extended by combining the two signals. Figure 5 , illustrating the relationship between the position of the object 90 and the length measuring range.

[0134] Figure 5 1 is a diagram for explaining the principle of the second measurement using two single-wavelength lasers of the distance measuring device 1 of this embodiment. Figure 5 In the figure, objects 90a, 90b and 90c respectively represent Figure 1 as well as Figure 3 The object 90 shown is located at different positions. When there is no need to distinguish the position, it will be described as "the object 90".

[0135] exist Figure 5 , two graphs are shown, wherein the horizontal axis represents the distance to the object 90 with the predetermined position as the reference point, and the vertical axis represents the distance calculated by the processing circuit 30, that is, the calculated distance. Figure 4 The graphs shown are the same, and show the distance calculated based on the signal obtained from one of the two photodetectors 53 and 54. The lower graph of the two graphs shows the distance calculated based on the signal obtained from the other of the two photodetectors 53 and 54.

[0136] By using the two graphs separately, the length measuring range is λ1 / 2 or λ2 / 2, respectively, so the level of the length measuring range is almost the same as that of the first measurement. In the second measurement, by combining the two graphs, the length measuring range can be extended.

[0137] Specifically, for each of the objects 90a, 90b, and 90c, the distances calculated corresponding to the upper graph are substantially the same. However, the distances calculated corresponding to the lower graph are different. Therefore, by combining the two calculation results, the distance can be calculated within the measurement range longer than both λ1 / 2 and λ2 / 2. Specifically, the processing circuit 30 can calculate 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.

[0138] The measuring range 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, then the beat wavelength Λ 12 It is represented by the following formula (2).

[0139]

Formula 2

[0140]

[0141] Based on the beat frequency wavelength Λ 12The light interference can be equivalent to the beat frequency wavelength Λ 12 For example, when λ1 and λ2 are 1550nm and 1551nm respectively, the beat frequency wavelength Λ 12 The length measurement range is 2.4 mm and 1.2 mm. The length measurement range of single wavelength interference is about 775 nm, which is nanometer level, while the length measurement range of MWI is extended to millimeter level.

[0142] [2.3 Length measurement accuracy]

[0143] Next, the length measurement accuracy of each of the first measurement and the second measurement will be described.

[0144] The length measurement accuracy depends on the wavelength of the single-wavelength laser used for measurement. Specifically, the shorter the wavelength of the single-wavelength laser, the higher the length measurement accuracy (i.e., the smaller in the dimension of distance), and the longer the wavelength of the single-wavelength laser, the lower the length measurement accuracy (i.e., the longer in the dimension of distance).

[0145] When two single-wavelength lasers are used as in the second measurement, the length measurement accuracy depends on the beat wavelength. Specifically, the shorter the beat wavelength, the higher the length measurement accuracy (i.e., the smaller it is in the dimension of distance), and the longer the beat wavelength, the lower the length measurement accuracy (i.e., the longer it is in the dimension of distance).

[0146] Since the beat frequency wavelength is longer than the wavelength of the single wavelength laser, the length measurement accuracy in the second measurement is lower than that in the first measurement. 12 Thus, only using the second measurement cannot eliminate the trade-off between the length measurement range and the length measurement accuracy.

[0147] In order to eliminate this trade-off, in MWI, both a long measuring range and a high measuring accuracy are achieved by combining the first measurement and the second measurement. That is, by combining the first measurement with a short measuring range but a high measuring accuracy and the second measurement with a low measuring accuracy but a long measuring range, both a long measuring range and a high measuring accuracy are achieved.

[0148] Figure 6 2 is a diagram showing the measuring range and the measuring accuracy of two measurements of the distance measuring device 1 of this embodiment. Figure 6 As shown in FIG. 1 , the length measurement accuracy (second length measurement accuracy) in the second measurement is set to Am, and the length measurement range (second length measurement range) in the second measurement is set to Rm. In addition, the length measurement accuracy (first length measurement accuracy) in the first measurement is set to As, and the length measurement range (first length measurement range) in the first measurement is set to Rs. The length measurement range and the length measurement accuracy are both expressed in the dimension of distance, so they can be compared.

[0149] As mentioned above, in addition, Figure 6 As 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 less than the length measurement range Rs of the first measurement. Thus, the combination of the first measurement and the second measurement can be uniquely performed, so that the distance measurement can be performed with a higher length measurement accuracy than the length measurement accuracy of the second measurement.

[0150] Here, in order to achieve higher length measurement accuracy, it is important to select a single wavelength laser for the first measurement. The inventors of the present application have conducted in-depth research and found that in order to improve the length measurement accuracy, the frequency stability of the single wavelength laser becomes important. The relationship between frequency stability and length measurement accuracy is described below.

[0151] [3. Relationship between frequency stability and length measurement accuracy]

[0152] The frequency of the single wavelength laser is adjusted by a control unit (not shown) to maintain a predetermined set value. Specifically, the frequency is kept constant by adjusting the current supplied to the laser light source and / or the temperature of the laser light source. In this embodiment, the set frequency of the light source unit 10 is controlled to be fixed during the measurement period.

[0153] However, due to the characteristics of laser light sources, it is impossible to keep the frequency constant. Figure 7 As shown, the frequency of a single wavelength laser changes over time, that is, fluctuates. In addition, Figure 7 This is a graph used to illustrate the frequency stability of a single wavelength laser. Figure 7 In the figure, the horizontal axis represents time and the vertical axis represents the frequency of a single wavelength laser.

[0154] The wavelength of a single wavelength laser k It is expressed as the speed of light ÷ frequency. Since the speed of light can be considered constant, when the frequency fluctuates, the wavelength λ k According to the above formula (1), if the wavelength λ k If the frequency fluctuates, the wavelength of the single-wavelength laser used for measurement will deviate from the calculated wavelength. Therefore, the calculated distance value will deviate, and the length measurement accuracy will deteriorate. In this way, the frequency fluctuation is correlated with the length measurement accuracy. Specifically, the smaller the fluctuation, the better the length measurement accuracy.

[0155] Therefore, in the first measurement requiring high-precision measurement, the single-wavelength laser with the smaller frequency fluctuation of the two single-wavelength lasers is used. In other words, the single-wavelength laser with the higher frequency stability of the two single-wavelength lasers is used.

[0156] The frequency stability is represented by a value having a negative correlation with the fluctuation of the laser frequency corresponding to the time change. Specifically, the smaller the fluctuation, the higher the frequency stability, and the larger the fluctuation, the lower the frequency stability.

[0157] Fluctuation, for example Figure 7 The standard deviation σ shown is represented by the standard deviation σ. The standard deviation σ can be statistically calculated relative to the average value (central value) of the frequency of the laser within a limited time. In addition, the frequency fluctuation can also be expressed in wavelength units instead of frequency units, or in units that are correlated with other frequencies.

[0158] In the present embodiment, λ1<λ2, and the fluctuation of the frequency of the laser light L1 is smaller than the fluctuation of the frequency of the laser light L2. Therefore, in the first measurement, the laser light L1 having the wavelength λ1 can be used.

[0159] In addition, the laser light source 11a that emits the laser L1 is a frequency stabilized laser. As the laser light source 11a that emits the laser L1, a distributed feedback (DFB) laser light source having a high frequency stability characteristic or a light source device that combines the absorption line of a gas cell and a semiconductor laser as a reference frequency can be used.

[0160] [4. Calculation of absolute distance]

[0161] An example of a method of calculating the absolute distance to the object 90 by MWI using two single-wavelength lasers will be described below.

[0162] In the second assay, based on Figure 3 The phase of each wavelength is calculated by using the signals of the two photodetectors 53 and 54 shown in FIG. 1 , and the difference is obtained as the beat frequency wavelength Λ 12 When the conditions for performing the above-mentioned MWI are met, according to the beat frequency wavelength Λ 12 The wave number N of the wavelength λ1 of the laser L1 is determined by dividing the rough distance calculated from the phase of the laser L1 by the wavelength λ1 of the laser L1 with less frequency fluctuation. Figure 3 The phase φ of a single wavelength is calculated from the signal of one of the two photodetectors 53 and 54 (photodetector 53 in this case). Based on the above results, the absolute distance x is calculated using the following equation (3).

[0163]

Formula 3

[0164]

[0165] The main reason for the fluctuation component of the calculated distance x is φ, which is caused by the fluctuation of the frequency of the first single-wavelength laser. Therefore, the best wavelength combination is that the laser used in the first measurement has the smallest frequency fluctuation, that is, the laser with the highest frequency stability. Although the details are described later, the method of the present disclosure can also be applied in the same order when the number of wavelengths is 3 or more.

[0166] [5. Action (distance measurement method)]

[0167] Next, use Figure 8 The operation of the distance measuring device 1 according to this embodiment will be described.

[0168] Figure 8 This is a flowchart showing an example of the operation of the distance measurement device 1 according to the present embodiment.

[0169] First, the processing circuit 30 determines the laser with the highest frequency stability, that is, the smallest frequency fluctuation, among the multiple single-wavelength lasers used in the MWI, and reflects the information indicating the determined laser to the measurement algorithm (S10). The standard deviation σ indicating the frequency fluctuation is, for example, information contained in a data sheet or specification sheet of the light source. By reading the corresponding information of each light source, the processing circuit 30 can determine the laser with the smallest frequency fluctuation. The information indicating the determined laser is input into the measurement algorithm.

[0170] In addition, the information on the fluctuation of the frequency of the single wavelength laser can be obtained, for example, by measuring the fluctuation of the frequency over time for all the single wavelength lasers using an optical wavelength meter, etc. This information can be evaluated in advance and read before the measurement, or the fluctuation of the frequency can be evaluated in parallel with the distance measurement, and the single wavelength laser with the least fluctuation can be determined in real time.

[0171] Then, the processing circuit 30 obtains interference signals of each wavelength of the plurality of single-wavelength laser beams by measuring MWI ( S20 ). Specifically, the light source unit 10 emits a plurality of single-wavelength laser beams and outputs signals corresponding to the light intensities detected by the photodetectors 53 and 54 .

[0172] Next, the processing circuit 30 calculates the absolute distance by an absolute distance calculation algorithm in a manner that determines the accuracy of the absolute distance based on the interference result of the single wavelength laser with the highest frequency stability (S30). Specifically, the processing circuit 30 uses the interference signal of the wavelength of the single wavelength laser with the highest frequency stability, that is, the smallest frequency fluctuation, 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 with the smallest frequency fluctuation and the interference signal of the wavelength of other single wavelength lasers for the second measurement to calculate the second distance. The processing circuit 30 calculates the absolute distance from the distance measuring device 1 to the object 90 based on the first distance and the second distance.

[0173] If the distance measurement is continued (S40: No), the process returns to step S20 to obtain interference signals for each wavelength. For example, if the purpose is to obtain the surface shape of the object 90, the interference signal may be obtained after changing the posture and / or position of the object 90.

[0174] When the distance measurement is completed (S40: Yes), the distance measurement device 1 ends the measurement. The distance measurement device 1 may output the measurement result to a display or the like for display.

[0175] in addition, Figure 8 The action shown is just an example. Fig. 9 Another operation example of the distance measuring device 1 will be described.

[0176] Fig. 9 FIG. 1 is a flowchart showing another example of the operation of the distance measuring device 1 according to the present embodiment. Fig. 9 In the action shown, Figure 8 The operation shown in FIG. 2 is different in that, after obtaining the interference signal and before calculating the absolute distance, the processing circuit 30 performs correction of the interference signal ( S25 ).

[0177] Specifically, the processing circuit 30 corrects other interference signals based on the interference result of the laser with the highest frequency stability, that is, the smallest frequency fluctuation. For example, the processing circuit 30 corrects the second signal output from the photodetector 54 detecting the light of wavelength λ2 based on the first signal output from the photodetector 53 detecting the light of wavelength λ1. As an example, the processing circuit 30 infers the fluctuation of wavelength λ2 by comparing the intensity of the signal of wavelength λ1 with the intensity of the signal of wavelength λ2. By inferring the fluctuation of wavelength λ2, the value of the wavelength used for distance calculation can be changed to a value close to the actual wavelength. Therefore, the accuracy of the calculated distance can be further improved.

[0178] [6. Modifications]

[0179] Next, modifications of the embodiment will be described.

[0180] This modification is different from the embodiment mainly in that the number of wavelengths of the single-wavelength laser light used for distance measurement is three. The following description will focus on the differences from the embodiment, and the description of the common points will be omitted or simplified.

[0181] Fig.10 FIG. 1 is a block diagram showing the structure of a light source unit 10A of the distance measuring device according to this modification. Fig.10 As shown, the light source unit 10A includes three laser light sources 11a, 11b, and 11c and a wavelength synthesis system 12. The laser light sources 11a and 11b are the same as those in the embodiment, and thus description thereof is omitted.

[0182] The laser light source 11c is, for example, a semiconductor laser element, which emits a laser of a specified single wavelength when supplied with an electric current. The laser light source 11c is an example of a third laser light source, and emits a laser L3 having a wavelength λ3. The wavelength λ3 is an example of a third wavelength, and the laser L3 is an example of a third single wavelength laser. 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 also be set to be more than 10 times the difference between the wavelength λ2 and the wavelength λ1. By setting a larger difference in the difference between the two wavelengths, the difference between the beat wavelength between the wavelength λ3 and the wavelength λ1 and the beat wavelength between the wavelength λ2 and the wavelength λ1 can be increased. As a result, the length measurement range and the length measurement accuracy can be set in stages, so that the absolute distance can be measured with high precision.

[0183] The wavelength synthesis system 12 combines laser beams L1, L2 and L3 emitted from three laser light sources 11a, 11b and 11c respectively. Light L emitted from the wavelength synthesis system 12 is coupled by the interference optical system 40. The wavelength synthesis system 12 is, for example, a DWDM element or a holographic optical element.

[0184] The configuration of the distance measuring device of this modification example other than the light source unit 10A is similar to Figure 1 The configuration of the distance measuring device 1 shown is the same. The light receiving optical system 50 of the optical unit 20 includes a photodetector for detecting light of wavelength λ3. Alternatively, the light receiving optical system 50 of the optical unit 20 may detect the beat light by heterodyne interference.

[0185] As in this modification, when three single-wavelength lasers having different wavelengths can be used, there are three combinations of two single-wavelength lasers. Therefore, the second measurement can be performed based on at least one of the three combinations. Specifically, the beat frequency wavelength λ caused by the interference of the laser L1 having a wavelength λ1 and the laser L2 having a wavelength λ2 can be measured. 12, the beat frequency wavelength Λ caused by the interference of the laser L1 with wavelength λ1 and the laser L3 with wavelength λ3 13 , and the beat frequency wavelength Λ caused by the interference of the laser light L3 with the wavelength λ3 and the laser light L2 with the wavelength λ2 23 The length measurement accuracy corresponding to at least one of the above and the second measurement within the length measurement range.

[0186] In addition, the beat frequency wavelength Λ 12 It is expressed by formula (2). In addition, the beat frequency wavelength Λ 13 And Λ 23 They are represented by the following equations (4) and (5), respectively.

[0187]

Formula 4

[0188]

[0189]

[0190] In this modification, 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 frequency wavelength Λ 12 and the beat frequency wavelength Λ 13 For example, λ1, λ2, and λ3 are set to 1550nm, 1551nm, and 1600nm, respectively. At this time, according to equations (2) and (4), the beat frequency wavelength Λ 12 About 2.4mm, beat frequency wavelength Λ 13 is about 50μm. In addition, since λ1≒λ2, the beat frequency wavelength Λ 13 and the beat frequency wavelength Λ 23 Roughly equal.

[0191] The processing circuit 30 of this modification example uses the beat frequency wavelength Λ 12 ,Λ 13 And Λ 23 The processing circuit 30 performs a second measurement on two of the first and second distances obtained by the second measurement, and combines the result with the first measurement to calculate the distance from the distance measuring device 1 to the object 90. Specifically, the processing circuit 30 calculates the absolute distance from the distance measuring device 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.

[0192] The processing circuit 30 uses the beat wavelength obtained based on the laser light with the smallest frequency fluctuation among all the single-wavelength laser lights emitted from the light source unit 10A. Here, since the frequency fluctuation of the laser light L1 is the smallest, the beat wavelength Λ is used. 13 and the beat frequency wavelength Λ 12In the first measurement, the processing circuit 30 also uses the interference result of the laser light with the smallest frequency fluctuation among all the single-wavelength laser lights emitted from the light source unit 10A.

[0193] Here, if the absolute distance from the probe to the measurement object is x, the absolute distance x is expressed by the following equation (6).

[0194] (6) x=(A×Λ 13 +B×λ1+θ i ×λ1) / 2

[0195] A and B are the absolute distances x to the part 91 in the object 90. i The beat frequency wavelength Λ 13 and the wave number of wavelength λ1. In addition, θ i The phases of the interference results based on the wavelength λ1 obtained by the first measurement are expressed corresponding to the positions of the parts 91, 92, and 93 in the object 90. In addition, the equation (6) is equivalent to the expansion of the equation (3) to three wavelengths.

[0196] The second measurement is performed with the combination with the longest beat frequency wavelength. The distance calculated by the second measurement is an example of a third distance calculated with the third length measurement accuracy within the third length measurement range. In addition, the third length measurement accuracy is lower than the second length measurement accuracy and the first length measurement accuracy. The third length measurement range is longer than the second length measurement range and the first length measurement range. In short, the second measurement is performed with the combination with the longest length measurement range.

[0197] Here, the processing circuit 30 determines the beat frequency wavelength λ based on the combination of the wavelength λ1 and the wavelength λ2. 12 The processing circuit 30 is based on the determined beat frequency wavelength Λ 12 The phase of the second measured beat frequency wavelength Λ 13 Specifically, the wave number A is counted based on the beat frequency wavelength Λ 12 The calculated distance is divided by the beat frequency wavelength Λ 13 The components of the quotient obtained are used to calculate the beat frequency wavelength Λ 13 The wave number A.

[0198] Then, the processing circuit 30 determines the beat frequency wavelength λ based on the combination of the wavelength λ1 and the wavelength λ3 as the next second measurement. 13 The processing circuit 30 is based on the determined beat frequency wavelength Λ 13 Specifically, the phase of the beat frequency wavelength Λ 13 The calculated distance is divided by the wavelength λ1, thereby calculating the wave number B of the wavelength λ1.

[0199] Finally, the processing circuit 30 determines the phase θ1 of the wavelength λ1 as a first measurement. The processing circuit 30 can calculate the absolute distance x based on the wave numbers A and B and the phase θ1 of the wavelength λ1 using the above equation (6): i .

[0200] As described above, by performing a plurality of second measurements using a plurality of beat frequency wavelengths, the length measurement range can be further expanded.

[0201] In addition, the absolute distance may be calculated by other methods than those described above. For example, the excess fraction method (decimal superposition method) may be used to calculate the absolute distance by combining the phases of all wavelengths of the laser light used.

[0202] (Other embodiments)

[0203] The above describes one or more distance measuring devices based on the embodiments, but the present disclosure is not limited to these embodiments. As long as it does not deviate from the main purpose of the present disclosure, various deformation methods that can be thought of by those skilled in the art to implement the present embodiment and the methods constructed by combining the constituent elements in different embodiments are also included in the scope of the present disclosure.

[0204] For example, in the above-mentioned embodiments and variations, an example is shown in which the processing circuit 30 calculates the absolute distance from the distance measuring device 1 to the object 90, but the present invention is not limited thereto. The processing circuit 30 may also output the first distance and the second distance to other devices after calculating them. For example, the processing circuit 30 may also send the first distance and the second distance to other computers, and the other computers may calculate the absolute distance. Alternatively, the processing circuit 30 may also send the first distance and the second distance to a display and display them on the display, or may also 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 the user, so that the user can calculate the absolute distance by manual calculation. In this way, the processing circuit 30 may not calculate the absolute distance.

[0205] In addition, the wavelength of at least one of the two single-wavelength lasers may be changed. For example, the wavelength of the laser having a larger frequency fluctuation may be swept. Thus, the combination of the two wavelengths may be changed, so that a length measurement range and length measurement accuracy suitable for the object 90 may be achieved. In addition, compared with a case where three or more laser light sources are provided, the device may be miniaturized.

[0206] Alternatively, one laser beam obtained by splitting a single wavelength laser beam into two and the other laser beam obtained by frequency shifting the other laser beam may be used as two single wavelength laser beams. As a means for frequency shifting, for example, an acousto-optic element (AOM: Acousto-Optic Modulator) may be used.

[0207] In addition, the frequency fluctuation may not be the standard deviation σ. For example, the frequency fluctuation may be 3σ. Alternatively, the frequency fluctuation may be the variance σ of the frequency of the laser within a limited time. 2 Alternatively, the frequency fluctuation may be the difference between the maximum value and the minimum value of the frequency of the laser light within a finite time.

[0208] In addition, when the light source unit has three or more laser light sources, two of the laser light sources may also emit single-wavelength lasers of the same wavelength. In addition, the frequency fluctuations of the two single-wavelength lasers of the same wavelength may also be the same. It is also possible that one of the two single-wavelength lasers of the same wavelength is used in the first measurement, and the other of the two single-wavelength lasers of the same wavelength is used in the second measurement. In other words, the first single-wavelength laser used in each of the first measurement and the second measurement may also be a laser emitted from a different laser light source.

[0209] In addition, the second measurement length measurement accuracy Am may be greater than the first measurement length measurement range Rs. The difference between the second measurement length measurement accuracy Am and the first measurement length measurement range Rs is small, and in the case of Am>Rs, the distance can be measured with substantially the same degree of accuracy as in the case of Am≤Rs.

[0210] In addition, the whole or specific methods of the present disclosure may also be implemented by a system, device, method, integrated circuit or computer program. Alternatively, it may also be implemented by a non-temporary recording medium such as a CD, HDD or semiconductor memory storing the computer program and which can be read by a computer. In addition, it may also be implemented by any combination of a system, device, method, integrated circuit, computer program and recording medium.

[0211] In addition, various changes, substitutions, additions, omissions, etc. can be made to the above-mentioned embodiments within the scope of the claims or their equivalents.

[0212] Industrial Applicability

[0213] The present disclosure can be used as a distance measuring device that can simultaneously achieve a longer measuring range and higher measuring accuracy, and can be used, for example, in a surface shape inspection device.

Claims

1. A distance measuring device comprising: A light source unit that emits a first single-wavelength laser having a first wavelength and a second single-wavelength laser having a second wavelength different from the first wavelength; an optical unit configured to interfere and detect a plurality of lights incident on the optical unit, and output a signal corresponding to a result of interfering the plurality of lights; and a processing circuit for processing the signal, 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. The light source unit includes a frequency-stabilized laser that emits the first single-wavelength laser.

2. The distance measuring device according to claim 1, The optical unit, detecting a first light component having the first wavelength in the interference light generated by the interference of the plurality of lights, outputting a first signal corresponding to the result of detecting the first light component, and detecting a second light component having the second wavelength in the interference light, and outputting a second signal corresponding to a result of detecting the second light component, the processing circuit, calculating a first distance within a first range with a first accuracy based on the first signal, calculating a second distance within a second range with a second accuracy based on the first signal and the second signal, The first precision is higher than the second precision, The second range is longer than the first range, The frequency stability of the first single-wavelength laser is higher than the frequency stability of the second single-wavelength laser.

3. The distance measuring device according to claim 2, The second accuracy is below the first range.

4. The distance measuring device according to claim 3, The processing circuit further calculates a distance from the distance measuring device to an object based on the first distance and the second distance.

5. The distance measuring device according to claim 4, The processing circuit calculates an absolute distance from the distance measuring device to the object.

6. The distance measuring device according to any one of claims 2 to 5, The plurality of lights include the first single-wavelength laser light, the second single-wavelength laser light, a first reflected light generated by the first single-wavelength laser light being reflected from an object, and a second reflected light generated by the second single-wavelength laser light being reflected from the object, The optical unit, The first signal is output by causing the first single-wavelength laser to interfere with the first reflected light and detecting the interference. The second signal is output by causing the second single-wavelength laser light to interfere with and detect the second reflected light.

7. The distance measuring device according to claim 6, The optical unit includes a beam splitter, a first photodetector, and a second photodetector. The beam splitter splits the first single wavelength laser beam from the light source into a first reference beam and a first detection beam, and splits the second single wavelength laser beam from the light source into a second reference beam and a second detection beam. The first reflected light is light generated by reflection of the first detection light in the object. The second reflected light is light generated by the second detection light being reflected by the object. The first light detector detects the first light component generated by interference between the first reference light and the first reflected light, thereby outputting the first signal. The second photodetector detects the second light component generated by interference of the second reference light and the second reflected light, thereby outputting the second signal.

8. The distance measuring device according to claim 7, The optical unit comprises: causing the first reference light and the second reference light to be incident on an optical element of the beam splitter; and a wavelength separation element that separates incident light into light of the first wavelength and light of the second wavelength, The beam splitter emits 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 toward the wavelength separation element.

9. The distance measuring device according to claim 6, The processing circuit corrects the second signal based on the first signal.

10. The distance measuring device according to any one of claims 2 to 5, The light source unit further emits a third single-wavelength laser beam having a third wavelength different from both the first wavelength and the second wavelength.

11. The distance measuring device according to claim 10, The first single-wavelength laser light has the highest frequency stability among all the single-wavelength laser lights emitted from the light source unit.

12. The distance measuring device according to claim 10, The optical unit further detects a third light component having the third wavelength in the interference light, and outputs a third signal corresponding to the result of detecting the third light component. The processing circuit further calculates a third distance within a third range with a third accuracy 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 device according to any one of claims 2 to 5, The processing circuit calculates the second distance by calculating a phase of a beat wavelength of the first wavelength and the second wavelength based on the first signal and the second signal.

14. The distance measuring device according to claim 13, the processing circuit, by calculating the phase of the first wavelength based on the first signal, thereby calculating the first distance, By combining the first distance and the second distance, an absolute distance from the distance measuring device to the object is calculated.

15. The distance measuring device according to any one of claims 1 to 5, The light source unit further includes a laser light source that emits the second single-wavelength laser.

Images