Distance measurement device, distance measurement method, and distance measurement system

Abstract

A distance measurement device (3) comprises: a signal acquisition unit (31) that, when a signal has been emitted from a signal source (1) at the surface of an examination target (4), acquires received signals that include a first reflected signal that has been reflected at the surface of the examination target (4), a second reflected signal that has been reflected at the surface of a liquid film that is adhered to the surface of the examination target 4, and a third reflected signal that has been reflected multiple times between the surface of the examination target 4 and the surface of the liquid film; and a distance calculation unit (32) that calculates the distance from the signal source (1) to the surface of the examination target (4) on the basis of the received signals acquired by the signal acquisition unit (31) and a constraint condition that is that the intervals between the frequencies that correspond to a plurality of peak spectra that are included in distance spectra for the received signals are equal.

Description

Distance Measuring Device, Distance Measuring Method, and Distance Measuring System

[0001] The present disclosure relates to a distance measuring device, a distance measuring method, and a distance measuring system.

[0002] There is a distance measuring device that calculates the distance from a signal source to the surface of an inspection object. As such a distance measuring device, for example, in Patent Document 1, the time from when an optical signal is emitted until the reflected signal of the optical signal reflected by the inspection object is detected is detected, and based on the detected time, a distance measuring sensor that measures the distance from the signal source to the inspection object is disclosed.

[0003] International Publication No. 2019 / 186742

[0004] The distance measuring sensor disclosed in Patent Document 1 has a problem that when a liquid film adheres to the surface of the inspection object, not only the reflected signal reflected from the surface of the inspection object but also the reflected signal reflected from the surface of the liquid film is received, so that the distance from the signal source to the inspection object may not be measured.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to obtain a distance measuring device that can calculate the distance from a signal source to the surface of an inspection object even when a liquid film adheres to the surface of the inspection object.

[0006] The distance measuring device according to the present disclosure includes a signal acquisition unit that acquires a received signal including a first reflected signal reflected from the surface of the inspection object, a second reflected signal reflected from the surface of a liquid film adhering to the surface of the inspection object, and a third reflected signal multiply reflected between the surface of the inspection object and the surface of the liquid film when a signal is radiated from the signal source toward the surface of the inspection object, and based on the received signal acquired by the signal acquisition unit and a constraint condition that the intervals between the frequencies corresponding to a plurality of peak spectra included in the distance spectrum of the received signal are equal intervals, a distance calculation unit that calculates the distance from the signal source to the surface of the inspection object.

[0007] According to the present disclosure, even when a liquid film adheres to the surface of the inspection object, the distance from the signal source to the surface of the inspection object can be calculated.

[0008] This is a configuration diagram showing a distance measuring system including a distance measuring device 3 according to Embodiment 1. This is a hardware configuration diagram showing the hardware of the distance measuring device 3 according to Embodiment 1. This is a hardware configuration diagram of a computer when the distance measuring device 3 is implemented by software or firmware, etc. This is a flowchart showing the distance measuring method, which is the processing procedure of the distance measuring device 3. This is an explanatory diagram showing an example of a first reflection signal reflected from the surface of the object to be inspected 4, a second reflection signal reflected from the surface of the liquid film, and a third reflection signal multiple reflections between the surface of the object to be inspected 4 and the surface of the liquid film. This is an explanatory diagram showing an example of the distance spectrum of a received signal x. This is an explanatory diagram showing an example of the distance spectrum of a received signal x when N=3. This is a configuration diagram showing a distance measuring system including a distance measuring device 3 according to Embodiment 2. This is a hardware configuration diagram showing the hardware of the distance measuring device 3 according to Embodiment 2.

[0009] To provide a more detailed explanation of this disclosure, the forms for implementing this disclosure will be described below with reference to the attached drawings.

[0010] Embodiment 1. Figure 1 is a configuration diagram showing a distance measuring system including a distance measuring device 3 according to Embodiment 1. Figure 2 is a hardware configuration diagram showing the hardware of the distance measuring device 3 according to Embodiment 1. The distance measuring system shown in Figure 1 is a system that calculates the distance from a signal source 1 to the surface of an object to be inspected 4, and comprises a signal source 1, a receiving unit 2, and a distance measuring device 3.

[0011] The signal source 1 comprises a laser light source 11, a sweeping unit 12, a branching unit 13, an optical circulator 14, an optical system 15, and a delay adjustment unit 16. The signal source 1 emits a signal toward the surface of the object to be inspected 4. The laser light source 11 oscillates laser light and outputs the laser light to the sweeping unit 12. The laser light is, for example, infrared light. The sweeping unit 12 outputs the laser light output from the laser light source 11 as sweep light to the branching unit 13. The sweep light is, for example, wavelength sweep light. The branching unit 13 splits the sweep light output from the sweeping unit 12 into two, outputting one of the sweep light to the optical circulator 14 and the other sweep light to the delay adjustment unit 16.

[0012] The optical circulator 14 outputs the swept light output from the branching unit 13 to the optical system 15, and outputs the reflected light output from the optical system 15 to the receiving unit 2. The optical system 15 includes, for example, an optical fiber and a collimating lens, and irradiates the surface of the object to be inspected 4 with the swept light output from the optical circulator 14. The swept light output from the optical circulator 14 is a signal emitted from the signal source 1. The optical system 15 receives reflected light that includes a first swept light reflected from the surface of the object to be inspected 4, a second swept light reflected from the surface of a liquid film adhering to the surface of the object to be inspected 4, and a third swept light that is multiple-reflected between the surface of the object to be inspected 4 and the surface of the liquid film. The liquid film is a thin film of liquid such as water or processing oil. The optical system 15 outputs the received reflected light to the optical circulator 14. The delay adjustment unit 16 delays the swept light output from the branching unit 13 and outputs the delayed swept light to the receiving unit 2. The delay time of the swept light by the delay adjustment unit 16 is approximately equivalent to the time from when the swept light is emitted from the optical system 15 until the reflected light is received by the optical system 15.

[0013] The receiving unit 2 comprises an optical interference unit 21, a photoelectric conversion unit 22, and a digital conversion unit 23. The receiving unit 2 receives the reflected light output from the signal source 1 and the delayed swept light output from the signal source 1, and outputs the interference signal between the reflected light and the delayed swept light as a received signal to the distance measuring device 3. The first swept light contained in the reflected light output from the signal source 1 corresponds to the first reflected signal reflected from the surface of the object to be inspected 4, and the second swept light contained in the reflected light corresponds to the second reflected signal reflected from the surface of the liquid film. Furthermore, the third swept light contained in the reflected light corresponds to the third reflected signal that is multiple reflected between the surface of the object to be inspected 4 and the surface of the liquid film.

[0014] The optical interference unit 21 interferes the reflected light output from the optical circulator 14 with the delayed swept light output from the delay adjustment unit 16, and outputs the interference signal of the reflected light and the delayed swept light to the photoelectric conversion unit 22. The photoelectric conversion unit 22 converts the interference signal output from the optical interference unit 21 from an optical signal to an electrical signal and outputs the electrical signal to the digital conversion unit 23. The digital conversion unit 23 converts the electrical signal output from the photoelectric conversion unit 22 from an analog signal to a digital signal and outputs the digital signal as a received signal to the distance measuring device 3.

[0015] The distance measuring device 3 comprises a signal acquisition unit 31 and a distance calculation unit 32. The distance measuring device 3 is a device that calculates the distance from the signal source 1 to the surface of the object to be inspected 4. The signal acquisition unit 31 is implemented, for example, by the signal acquisition circuit 41 shown in Figure 2. The signal acquisition unit 31 acquires a received signal from the receiving unit 2. The signal acquisition unit 31 outputs the received signal to the distance calculation unit 32.

[0016] The distance calculation unit 32 is implemented, for example, by the distance calculation circuit 42 shown in Figure 2. The distance calculation unit 32 acquires the received signal from the signal acquisition unit 31. Based on the received signal acquired by the signal acquisition unit 31 and the constraint that the intervals between the frequencies corresponding to multiple peak spectra included in the distance spectrum of the received signal are equal, the distance calculation unit 32 calculates the distance from the signal source 1 to the surface of the object to be inspected 4.

[0017] In Figure 1, it is assumed that the signal acquisition unit 31 and the distance calculation unit 32, which are components of the distance measuring device 3, are each implemented by dedicated hardware as shown in Figure 2. That is, it is assumed that the distance measuring device 3 is implemented by a signal acquisition circuit 41 and a distance calculation circuit 42. The signal acquisition circuit 41 and the distance calculation circuit 42 can be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof.

[0018] The components of the distance measuring device 3 are not limited to those implemented by dedicated hardware; the distance measuring device 3 may also be implemented by software, firmware, or a combination of software and firmware. The software or firmware is stored as a program in the computer's memory. The computer refers to the hardware that executes the program, and includes, for example, a CPU (Central Processing Unit), GPU (Graphics Processing Unit), central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor).

[0019] Figure 3 is a hardware configuration diagram of a computer when the distance measuring device 3 is implemented by software or firmware. When the distance measuring device 3 is implemented by software or firmware, a program that causes the computer to execute the respective processing procedures in the signal acquisition unit 31 and the distance calculation unit 32 is stored in the memory 51. The computer's processor 52 then executes the program stored in the memory 51.

[0020] Furthermore, Figure 2 shows an example in which each component of the distance measuring device 3 is implemented by dedicated hardware, and Figure 3 shows an example in which the distance measuring device 3 is implemented by software or firmware, etc. However, this is only one example, and some components of the distance measuring device 3 may be implemented by dedicated hardware, while the remaining components may be implemented by software or firmware, etc.

[0021] Next, the operation of the distance measuring system shown in Figure 1 will be explained. Figure 4 is a flowchart of the distance measuring method, which is the processing procedure of the distance measuring device 3. Figure 5 is an explanatory diagram showing an example of a first reflected signal reflected from the surface of the object to be inspected 4, a second reflected signal reflected from the surface of the liquid film, and a third reflected signal that is multiplely reflected between the surface of the object to be inspected 4 and the surface of the liquid film.

[0022] The laser light source 11 oscillates laser light and outputs the laser light to the sweeping unit 12. The sweeping unit 12 outputs the laser light output from the laser light source 11 as sweep light to the branching unit 13. The branching unit 13 splits the sweep light output from the sweeping unit 12 into two. The branching unit 13 outputs one of the swept light after splitting to the optical circulator 14 and outputs the other swept light to the delay adjustment unit 16.

[0023] When the optical circulator 14 outputs sweep light from the branching section 13, it outputs the sweep light to the optical system 15. When the optical system 15 receives the sweep light output from the optical circulator 14, it irradiates the surface of the object to be inspected 4 with the sweep light. If a liquid film is attached to the surface of the object to be inspected 4, as shown in Figure 5, the sweep light is reflected from the surface of the object to be inspected 4, as well as from the surface of the liquid film. In addition, the sweep light is multiple-reflected between the surface of the object to be inspected 4 and the surface of the liquid film. As a result, the first sweep light reflected from the surface of the object to be inspected 4, the second sweep light reflected from the surface of the liquid film, and the third sweep light multiple-reflected between the surface of the object to be inspected 4 and the surface of the liquid film all return to the optical system 15. Figure 5 shows an example where the sweep light is reflected twice from the surface of the object to be inspected 4. However, this is only one example, and the sweep light may be reflected more than twice from the surface of the object to be inspected 4.

[0024] The optical system 15 receives reflected light including the first sweep light, the second sweep light, and the third sweep light. The optical system 15 outputs the received reflected light to the optical circulator 14. The optical circulator 14 outputs the reflected light output from the optical system 15 to the optical interference unit 21. The delay adjustment unit 16 delays the sweep light output from the branching unit 13 and outputs the delayed sweep light to the optical interference unit 21.

[0025] The optical interference unit 21 interferes the reflected light output from the optical circulator 14 with the delayed swept light output from the delay adjustment unit 16. The optical interference unit 21 outputs the interference signal of the reflected light and the delayed swept light to the photoelectric conversion unit 22. The photoelectric conversion unit 22 converts the interference signal output from the optical interference unit 21 from an optical signal to an electrical signal. The photoelectric conversion unit 22 outputs the electrical signal to the digital conversion unit 23. The digital conversion unit 23 converts the electrical signal output from the photoelectric conversion unit 22 from an analog signal to a digital signal. The digital conversion unit 23 outputs the digital signal as a received signal x to the signal acquisition unit 31 of the distance measuring device 3.

[0026] The signal acquisition unit 31 acquires the received signal x from the receiving unit 2 (step ST1 in Figure 4). The signal acquisition unit 31 outputs the received signal x to the distance calculation unit 32.

[0027] The distance calculation unit 32 acquires the received signal x from the signal acquisition unit 31. Figure 6 is an explanatory diagram showing an example of the distance spectrum of the received signal x. As shown in Figure 6, the distance from the reference position in space to the surface of the object to be inspected 4 is D. ｗ When the thickness of the liquid film attached to the surface of the object to be inspected 4 is ΔD, and the swept light is reflected twice by the surface of the object to be inspected 4, the received signal x is expressed by the following equation (1). In the example in Figure 6, the spatial reference position is located to the left of the surface opposite to the surface of the object to be inspected 4. The distance L from the spatial reference position to the optical system 15 is known in the distance measuring device 3.

[0028] In equation (1), a(D ｗ ) is the distance mode vector. １ s is the amplitude of the first reflected signal. ２ s is the amplitude of the second reflected signal. ３ n is the amplitude of the third reflected signal. n is the unknown observed noise vector.

[0029] By, for example, performing FFT (Fast Fourier Transform) on the received signal x, if the distance spectrum of the received signal x is calculated, the distance spectrum will be as shown in FIG. 6. The distance spectrum includes a plurality of peak spectra as shown in FIG. 6. The plurality of peak spectra include the peak spectrum related to the distance D from the reference position in space to the surface of the inspection object 4, the peak spectrum related to the distance D ｗ + ΔD from the reference position in space to the surface of the liquid film, and the peak spectrum related to the distance D ｗ - ΔD when the scanning light is reflected twice on the surface of the inspection object 4. ｗ

[0030] The distance D ｗ and the distance D ｗ - ΔD have an interval of ΔD, and the distance D ｗ and the distance D ｗ + ΔD have an interval of ΔD. Therefore, the intervals between the distance D ｗ - ΔD, the distance D ｗ and the distance D ｗ + ΔD are all equal. Since the distance and the frequency are proportional, the interval between the frequency corresponding to the distance D ｗ and the frequency corresponding to the distance D ｗ - ΔD is Δf, and the interval between the frequency corresponding to the distance D ｗ and the frequency corresponding to the distance D ｗ + ΔD is Δf. Therefore, the intervals between the frequency corresponding to the distance D ｗ - ΔD, the frequency corresponding to the distance D ｗ and the frequency corresponding to the distance D ｗ + ΔD are all equal.

[0031] The distance calculation unit 32 calculates the distance L - D from the signal source 1 to the surface of the inspection object 4 based on the received signal x and the constraint condition that the interval Δf between the frequencies corresponding to the plurality of peak spectra included in the distance spectrum of the received signal x is equal (step ST2 in FIG. 4). Hereinafter, the calculation process of the distance L - D ｗ by the distance calculation unit 32 will be specifically described. ｗ

[0032] Here, since the right-hand side of equation (1) is unknown, the distance D is calculated from the observed value, the received signal x, on the left-hand side. ｗ Let's consider the problem of estimating the distance ΔD. The distance calculation unit 32 uses a first parameter d, which indicates the distance from a reference position in space to the surface of the object to be inspected 4. ｗ An evaluation function P(d) has a second parameter Δd that indicates the distance corresponding to the frequency interval Δf. ｗ Construct the evaluation function P(d). ｗ Δd) is the first parameter d ｗ The distance indicated is distance D ｗ The evaluation value is maximized when it matches the second parameter and the distance Δd indicated by the second parameter matches the interval ΔD. The distance calculation unit 32 calculates the evaluation function P(d ｗ The first parameter d when the evaluation value of Δd) reaches its maximum value. ｗ By searching for the second parameter Δd, the distance D from the reference position in space to the surface of the object being inspected 4 is determined. ｗ The distance calculation unit 32 then calculates the distance D from the distance L from the reference position in space to the optical system 15. ｗ By subtracting this, the distance L-D from the optical system 15 to the surface of the object being inspected 4 is obtained. ｗ Calculate.

[0033] The above distance D ｗ The distance ΔD is the distance between three distances d ｗ d ｗ +Δd, d ｗ The output power P shown in equation (2) below is minimized such that the received signal x is minimized while retaining the signal from -Δd. ＯＵＴ It can be found by calculating it.

[0034] In equation (2), R ｘｘ (=xx Ｈ ) is the correlation matrix, and w(d ｗ Δd) is the weight vector.

[0035] Output power P ＯＵＴ The weight vector w(d) that minimizes ｗThe output power P(Δd) can be calculated analytically using the principles of the known CAPON method. ＯＵＴ The weight vector w(d) that minimizes ｗ Using Δd, the evaluation function P(d) can be expressed as shown in equation (3) below. ｗ The evaluation function P(d) can be constructed. ｗ When the evaluation value of Δd) is maximized, d ｗ distance D ｗ The interval ΔD can be calculated as the value of Δd when the evaluation value is maximized.

[0036]

[0037] Up to this point, assuming that the swept light is reflected twice from the surface of the object being inspected 4, the distance L-D from the signal source 1 to the surface of the object being inspected 4 is considered. ｗ An example of calculating the following is shown. Assuming that the swept light is reflected N times from the surface of the object being inspected 4, the distance L-D from the signal source 1 to the surface of the object being inspected 4 is shown. ｗ Let's explain an example of how to calculate it. N is an integer greater than or equal to 2. In this case, the received signal x is expressed as shown in equation (6) below.

[0038]

[0039] For example, when N=3, the distance spectrum includes multiple peak spectra, as shown in Figure 7. The multiple peak spectra represent the distance D from a reference position in space to the surface of the object being inspected 4. ｗ The peak spectrum related to this, and the distance D from the spatial reference position to the surface of the liquid film. ｗ The peak spectrum related to +ΔD and the distance D when the swept light is reflected twice from the surface of the object being inspected 4. ｗ The peak spectrum related to -ΔD and the distance D when the swept light is reflected three times from the surface of the object being inspected 4. ｗ This is the peak spectrum related to -2ΔD. Figure 7 is an explanatory diagram showing an example of the distance spectrum of the received signal x when N=3.

[0040] If the swept light is reflected N times from the surface of the object being inspected 4, the distance D ｗ The distance ΔD is the distance between (N+1) distances d ｗ dｗ +Δd, d ｗ -Δd, ..., d ｗ P minimizes the output power shown in equation (7) below, such that the received signal x is minimized while retaining the signal from -(N-1)ΔdD. ＯＵＴ It can be found by calculating it.

[0041]

[0042] In the above embodiment 1, the distance measuring device 3 is configured to include a signal acquisition unit 31 that acquires a received signal including a first reflected signal reflected from the surface of the object to be inspected 4, a second reflected signal reflected from the surface of the liquid film adhering to the surface of the object to be inspected 4, and a third reflected signal that is multiple reflected between the surface of the object to be inspected 4 and the surface of the liquid film, when a signal is emitted from the signal source 1 toward the surface of the object to be inspected 4; and a distance calculation unit 32 that calculates the distance from the signal source 1 to the surface of the object to be inspected 4 based on the received signal acquired by the signal acquisition unit 31 and the constraint condition that the intervals between the frequencies corresponding to the multiple peak spectra included in the distance spectrum of the received signal are equal. Therefore, the distance measuring device 3 can calculate the distance from the signal source 1 to the surface of the object to be inspected 4 even if a liquid film is adhering to the surface of the object to be inspected 4.

[0043] Embodiment 2. In Embodiment 2, the distance calculation unit 33 calculates the distance D from a reference position in space to the surface of the object to be inspected 4. ｗ A first distance range including and a second distance range including a distance ΔL corresponding to the frequency interval are set, and within the first distance range, the first parameter d ｗ We will now describe a distance measuring device 3 that searches for a second parameter Δd within a second distance range.

[0044] Figure 8 is a configuration diagram showing a distance measuring system including a distance measuring device 3 according to Embodiment 2. In Figure 8, the same reference numerals as in Figure 1 indicate the same or corresponding parts, so a detailed explanation is omitted. Figure 9 is a hardware configuration diagram showing the hardware of the distance measuring device 3 according to Embodiment 2. In Figure 9, the same reference numerals as in Figure 2 indicate the same or corresponding parts, so a detailed explanation is omitted. The distance measuring system shown in Figure 8 is a system that calculates the distance from a signal source 1 to the surface of an object to be inspected 4, and comprises a signal source 1, a receiving unit 2, and a distance measuring device 3.

[0045] The distance measuring device 3 comprises a signal acquisition unit 31 and a distance calculation unit 33. The distance calculation unit 33 is implemented, for example, by the distance calculation circuit 43 shown in Figure 9. The distance calculation unit 33 acquires the received signal from the signal acquisition unit 31. Based on the received signal acquired by the signal acquisition unit 31 and the constraint that the intervals between the frequencies corresponding to multiple peak spectra included in the distance spectrum of the received signal are equal, the distance L-D from the signal source 1 to the surface of the object to be inspected 4 is calculated by the distance calculation unit 33. ｗ Calculate.

[0046] Specifically, the distance calculation unit 33 calculates the distance D from a reference position in space to the surface of the object to be inspected 4. ｗ The first distance range DRG including １ And a second distance range DRG including the distance ΔL corresponding to the frequency interval. ２ The distance calculation unit 33 sets the first distance range DRG １ The first parameter d within ｗ Explore the second distance range DRG ２ By searching for a second parameter Δd within the system, the distance D from the reference position in space to the surface of the object being inspected 4 is determined. ｗ The distance calculation unit 33 then calculates the distance D from the distance L from the reference position in space to the optical system 15. ｗ By subtracting this, the distance L-D from the optical system 15 to the surface of the object being inspected 4 is obtained. ｗ Calculate.

[0047] In Figure 8, it is assumed that the signal acquisition unit 31 and the distance calculation unit 33, which are components of the distance measuring device 3, are each implemented by dedicated hardware as shown in Figure 9. That is, it is assumed that the distance measuring device 3 is implemented by a signal acquisition circuit 41 and a distance calculation circuit 43. The signal acquisition circuit 41 and the distance calculation circuit 43 can be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof.

[0048] The components of the distance measuring device 3 are not limited to those implemented by dedicated hardware; the distance measuring device 3 may also be implemented by software, firmware, or a combination of software and firmware. When the distance measuring device 3 is implemented by software or firmware, a program that causes a computer to execute the respective processing procedures in the signal acquisition unit 31 and the distance calculation unit 33 is stored in the memory 51 shown in Figure 3. Then, the processor 52 shown in Figure 3 executes the program stored in the memory 51.

[0049] Furthermore, Figure 9 shows an example in which each component of the distance measuring device 3 is implemented by dedicated hardware, while Figure 3 shows an example in which the distance measuring device 3 is implemented by software or firmware, etc. However, this is merely one example, and some components of the distance measuring device 3 may be implemented by dedicated hardware, while the remaining components may be implemented by software or firmware, etc.

[0050] Next, the operation of the distance measuring system shown in Figure 8 will be explained. Except for the distance calculation unit 33, it is the same as the distance measuring system shown in Figure 1. Therefore, only the operation of the distance calculation unit 33 will be explained here.

[0051] The distance calculation unit 33, similar to the distance calculation unit 32 shown in Figure 1, uses an evaluation function P(d ｗ The first parameter d when the evaluation value of Δd) reaches its maximum value. ｗ By searching for the second parameter Δd, the distance D from the reference position in space to the surface of the object being inspected 4 is determined.ｗ Calculate it. However, the distance calculation unit 33 has a first parameter d that is different from the distance calculation unit 32 shown in FIG. 1. ｗ And in order to reduce the load of the search process by limiting the respective search ranges for the second parameter Δd and the first parameter d, the distance D ｗ A first distance range DRG including １ And a second distance range DRG including the distance ΔL ２ Is set.

[0052] The distance calculation unit 33 is the evaluation function P(d ｗ , Δd) when the evaluation value is at its maximum, the first parameter d ｗ And when searching for the second parameter Δd, within the first distance range DRG １ Search for the first parameter d within ｗ And search for the second parameter Δd within the second distance range DRG ２ The distance calculation unit 33 searches for the first parameter d and the second parameter Δd when the evaluation value is at its maximum, thereby determining the distance D from the reference position in space to the surface of the inspection object 4. ｗ Is calculated. Then, the distance calculation unit 33 subtracts the distance D ｗ From the distance L from the reference position in space to the optical system 15, thereby obtaining the distance L - D from the optical system 15 to the surface of the inspection object 4. ｗ Is calculated. ｗ

[0053] In the above-described second embodiment, the distance calculation unit 33 sets a first distance range including the distance from the reference position in space to the surface of the inspection object 4 and a second distance range including the distance corresponding to the frequency interval, and searches for the first parameter within the first distance range and searches for the second parameter within the second distance range, thus configuring the distance measuring device 3 shown in FIG. 8. Therefore, similar to the distance measuring device 3 shown in FIG. 1, the distance measuring device 3 shown in FIG. 8 can calculate the distance from the signal source 1 to the surface of the inspection object 4 even when a liquid film adheres to the surface of the inspection object 4, and can reduce the load of the search process compared to the distance measuring device 3 shown in FIG. 1.

[0054] ​Furthermore, this disclosure allows for free combination of each embodiment, modification of any component in each embodiment, or omission of any component in each embodiment.

[0055] This disclosure enables the calculation of the distance from the signal source to the surface of the object being inspected, even if a liquid film is adhering to the surface of the object being inspected, and can be used in distance measuring devices, distance measuring methods, and distance measuring systems.

[0056] 1. Signal source, 2. Receiving unit, 3. Distance measuring device, 4. Object to be inspected, 11. Laser light source, 12. Sweeping unit, 13. Branching unit, 14. Optical circulator, 15. Optical system, 16. Delay adjustment unit, 21. Optical interference unit, 22. Photoelectric conversion unit, 23. Digital conversion unit, 31. Signal acquisition unit, 32, 33. Distance calculation unit, 41. Signal acquisition circuit, 42, 43. Distance calculation circuit, 51. Memory, 52. Processor.

Claims

1. A distance measuring device comprising: a signal acquisition unit that acquires a received signal including a first reflected signal reflected from the surface of an object to be inspected, a second reflected signal reflected from the surface of a liquid film adhering to the surface of the object to be inspected, and a third reflected signal multiple-reflected between the surface of the object to be inspected and the surface of the liquid film, when a signal is emitted from a signal source toward the surface of an object to be inspected; and a distance calculation unit that calculates the distance from the signal source to the surface of the object to be inspected based on the received signal acquired by the signal acquisition unit and the constraint condition that the intervals between frequencies corresponding to a plurality of peak spectra included in the distance spectrum of the received signal are equal.

2. The distance measuring device according to claim 1, wherein the distance calculation unit constructs an evaluation function having a first parameter and a second parameter, where the evaluation value is maximized when the distance indicated by the first parameter matches the distance from a reference position in space to the surface of the object to be inspected, and the distance indicated by the second parameter matches the distance corresponding to the frequency interval, and calculates the distance from the signal source to the surface of the object to be inspected by searching for the first parameter and the second parameter when the evaluation value is maximized.

3. The distance measuring device according to claim 2, characterized in that the distance calculation unit calculates the distance from the reference position in space to the surface of the object to be inspected by searching for the first parameter and the second parameter when the evaluation value reaches its maximum value, and calculates the distance from the signal source to the surface of the object to be inspected by subtracting the distance from the reference position in space to the surface of the object to be inspected from the distance from the reference position in space to the signal source.

4. The distance measuring device according to claim 2 or 3, characterized in that the distance calculation unit sets a first distance range including the distance from a reference position in space to the surface of the object to be inspected, and a second distance range including a distance corresponding to the interval of the frequencies, searches for the first parameter within the first distance range, and searches for the second parameter within the second distance range.

5. The distance measuring device according to any one of claims 1 to 4, characterized in that the signal acquisition unit acquires a received signal which includes the third reflected signal that has been reflected N times (where N is an integer of 2 or more) from the surface of the object to be inspected, as the third reflected signal which has been multiple reflected between the surface of the object to be inspected and the surface of the liquid film.

6. A distance measurement method comprising: a signal acquisition unit acquires a received signal that includes a first reflected signal reflected from the surface of the object to be inspected, a second reflected signal reflected from the surface of a liquid film adhering to the surface of the object to be inspected, and a third reflected signal that is multiple reflected between the surface of the object to be inspected and the surface of the liquid film, when a signal is emitted from a signal source toward the surface of the object to be inspected; and a distance calculation unit calculates the distance from the signal source to the surface of the object to be inspected based on the received signal acquired by the signal acquisition unit and the constraint that the intervals between the frequencies corresponding to a plurality of peak spectra included in the distance spectrum of the received signal are equal.

7. A distance measuring system comprising: a signal source that emits a signal toward the surface of an object to be inspected; a receiving unit that, when a signal is emitted from the signal source, receives a first reflected signal reflected from the surface of the object to be inspected, a second reflected signal reflected from the surface of a liquid film adhering to the surface of the object to be inspected, and a third reflected signal multiple-reflected between the surface of the object to be inspected and the surface of the liquid film, and outputs an interference signal of the signal including the first reflected signal, the second reflected signal, and the third reflected signal and the signal emitted from the signal source as a received signal; a signal acquisition unit that acquires the received signal output from the receiving unit; and a distance calculation unit that calculates the distance from the signal source to the surface of the object to be inspected based on the received signal acquired by the signal acquisition unit and the constraint condition that the intervals between frequencies corresponding to a plurality of peak spectra included in the distance spectrum of the received signal are equal.

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