Distance measurement system

Abstract

To provide a distance measuring system that can easily evaluate if a light source is in a normal frequency sweep state.SOLUTION: A distance measuring system comprises: a light source that outputs FM light; a measurement optical system that divides one of the rays of FM light, which has been divided into two by a beam splitter, further into two, and outputs a measurement beat signal; a reference optical system that divides the other of the rays of FM light, which has been divided into two by the beam splitter, further into two, and outputs a reference beat signal; and an arithmetic unit that performs arithmetic processing on the measurement beat signal and reference beat signal. The arithmetic unit has a distance measuring unit that calculates the distance to an object to be measured based on the measurement beat signal, a beat signal processing unit that processes the reference beat signal to generate a desired signal, and a determination processing unit that compares the desired signal with a reference value to determine an abnormality in the light source.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a distance measuring system that measures the distance to an object without contact. [Background technology]

[0002] As a non-contact method for measuring the distance to an object, the Frequency Modulated Continuous Waves (FMCW) method is known, which indirectly measures the distance to the object by irradiating the object with frequency-swept FM light and analyzing the interference beat signal generated by the interference of the irradiated light and reflected light. An example of a distance measurement system using the FMCW method is the technology described in Patent Document 1.

[0003] For example, paragraphs 0034, 0035, and 0037 of Patent Document 1 state, "Figure 2 is a diagram illustrating the principle of the FMCW method." "As shown in the figure, there is a time difference Δt between the timing when the reference light 201 arrives at the receiver 107 and the timing when the measurement light 202 arrives at the receiver 109. During this time difference Δt, the optical frequency of the FM light from the laser light source 101 changes, so the distance measuring unit 116 sets a beat frequency f equal to the frequency difference due to the change in optical frequency." b The target measurement beat signal is detected. If the frequency sweep width is Δν and the time required to modulate by Δν is T, the time difference Δt is expressed by the following equation (1). "Then, since the distance L1 to the object 113 is half the distance that light travels during the time difference Δt, the distance L1 can be calculated using the speed of light c in the atmosphere as shown in the following equation (2)." [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-025952 [Overview of the project] [Problems that the invention aims to solve]

[0005] The technology described in Patent Document 1 above allows for non-contact measurement of the distance to the object being measured. However, it has the problem that it is difficult to detect abnormalities in the distance measurement value, such as when noise is superimposed on the frequency sweep signal supplied to the light source, or when the frequency sweep width of the measurement light changes due to damage to the light source. Furthermore, it is difficult to identify the cause of the abnormality (such as noise superimposition on the frequency sweep signal or damage to the light source) from the change in the distance measurement value.

[0006] To address this challenge, for example, it is possible to evaluate the variation in the frequency sweep width of the measurement light by splitting the measurement light and inputting it into an optical spectrum analyzer. However, this introduces a new challenge: the size of the equipment becomes larger. Furthermore, there is the challenge of directly observing the characteristics of frequency changes during frequency sweeping.

[0007] The present invention has been made in view of the above points, and aims to provide a distance measurement system that can easily evaluate whether the frequency sweep state of the light source is normal while non-contact measuring the distance to the object to be measured. [Means for solving the problem]

[0008] To solve the above problems, a distance measuring system according to one aspect of the present invention is a distance measuring system for measuring the distance to a measurement target object in a non-contact manner, comprising: a light source that outputs FM light whose optical frequency is periodically swept; a beam splitter that splits the FM light into two; a measuring optical system that further splits one of the FM lights split by the beam splitter into two and outputs a measurement beat signal based on the frequency difference between the reflected light and the other FM light when one of the FM lights is irradiated onto the measurement target object; a reference optical system that further splits the other of the FM lights split by the beam splitter into two and inputs both of the further split FM lights to an interferometer with a known optical path length difference, and outputs a reference beat signal based on the frequency difference between the FM lights output by the interferometer; and a computing device that performs calculations on the measurement beat signal and the reference beat signal, wherein the computing device comprises: a distance measuring unit that calculates the distance to the measurement target object based on the measurement beat signal; a beat signal processing unit that processes the reference beat signal to generate a desired signal; and a determination processing unit that determines an abnormality of the light source by comparing the desired signal with a reference value. [Effects of the Invention]

[0009] According to the distance measurement system of the present invention, it is possible to easily evaluate whether the frequency sweep state of the light source is normal while non-contact measuring the distance to the object to be measured. Other issues, configurations, and effects not mentioned above will be clarified by the following embodiments. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram showing an example configuration of the distance measurement system in Example 1. [Figure 2] Functional block diagram of the arithmetic unit of Example 1. [Figure 3] Diagram illustrating the distance measurement principle of the FMCW method. [Figure 4] An explanatory diagram of a method for determining the reflection position on an object based on its reflection intensity profile. [Figure 5] This figure shows the details of the frequency processing and phase analysis processing of the reference beat signal in Example 1. [Figure 6A]Explanation diagram of the evaluation process of the reference beat signal in Example 1 (normal state). [Figure 6B] Explanation diagram of the evaluation process of the reference beat signal in Example 1 (abnormal state). [Figure 7] Flowchart of the evaluation process of the reference beat signal in Example 1. [Figure 8] Example of the GUI screen displayed on the display device during the abnormality determination in Example 1. [Figure 9] Flowchart of the evaluation process of the reference beat signal in Example 2. [Figure 10] Explanation diagram of the evaluation process of the reference beat signal in Example 3. [Figure 11A] Explanation diagram of the evaluation process of the reference beat signal in Example 4. [Figure 11B] Explanation diagram of the evaluation process of the reference beat signal in Example 4. [Figure 11C] Explanation diagram of the evaluation process of the reference beat signal in Example 4.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the distance measurement system according to the present invention will be described based on the drawings. In each of the following embodiments, the same members are given the same reference numerals in principle, and repeated explanations thereof are omitted. Also, in each embodiment, it is needless to say that the constituent elements (including element steps, etc.) are not necessarily essential except in cases where it is particularly明示した場合および原理的に明らかに必須であると考えられる場合等. Also, when it is said that "consisting of A", "comprising A", "having A", "including A", etc., it is needless to say that other elements are not excluded except in cases where it is particularly明示した場合等 that only that element is involved. Similarly, in each embodiment, when referring to the shape, positional relationship, etc., of the constituent elements, etc., it is assumed to include those that are substantially approximated or similar to the shape, etc., except in cases where it is particularly明示した場合および原理的に明らかにそうでないと考えられる場合等.

[0012] Furthermore, each embodiment is an example for illustrating the present invention, and has been omitted and simplified as appropriate for clarity of explanation. The present invention can also be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0013] The positions, sizes, shapes, and ranges of the components shown in the drawings may not represent their actual positions, sizes, shapes, and ranges in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, and ranges disclosed in the drawings.

[0014] Examples of various types of information may be described using terms such as "table," "list," and "queue," but these types of information may also be represented using other data structures.

[0015] When there are multiple components with the same or similar function, they may be described using the same symbol but with different subscripts. Furthermore, when it is not necessary to distinguish between these multiple components, the subscripts may be omitted in the description.

[0016] In each embodiment, the processing performed by executing the program may be described. Here, the computer executes the program using a processor (e.g., CPU, GPU) and performs the processing defined by the program using memory resources (e.g., memory) and interface devices (e.g., communication ports). Therefore, the main entity performing the processing by executing the program may be the processor. Similarly, the main entity performing the processing by executing the program may be a controller, device, system, computer, or node having a processor. The main entity performing the processing by executing the program may be an arithmetic unit, and may include dedicated circuits that perform specific processing. Here, dedicated circuits include, for example, FPGAs (Field Programmable Gate Arrays), ASICs (Application Specific Integrated Circuits), CPLDs (Complex Programmable Logic Devices), etc.

[0017] The program may be installed on the computer from the program source. The program source may be, for example, a program distribution server or a storage medium readable by the computer. If the program source is a program distribution server, the program distribution server includes a processor and storage resources for storing the program to be distributed, and the processor of the program distribution server may distribute the program to other computers. In addition, in the embodiment, two or more programs may be implemented as one program, or one program may be implemented as two or more programs. [Examples]

[0018] The distance measurement system 1 according to Embodiment 1 of the present invention will be described below with reference to Figures 1 to 8.

[0019] Figure 1 is a schematic diagram showing an example configuration of the distance measuring system 1 of Embodiment 1. The distance measuring system 1 of this embodiment uses a distance measuring device 10 and a computer 20 to measure the distance L to the object to be measured 30 in a non-contact manner. Although not shown in Figure 1, the distance measuring system 1 may also include a measuring light scanning mechanism 40.

[0020] The measuring light scanning mechanism 40 is a mechanism that scans the irradiation position of the measuring light emitted by the distance measuring device 10, and can use mechanisms such as a galvanometer mirror, MEMS mirror, polygon mirror, linear stage, and rotary stage. For example, if one galvanometer mirror is used, the irradiation position of the measuring light can be scanned in one dimension, and if two galvanometer mirrors are used, the irradiation position of the measuring light can be scanned in two dimensions. Therefore, by equipping the distance measuring system 1 with the measuring light scanning mechanism 40, the irradiation position of the measuring light on the surface of the object to be measured 30 can be scanned appropriately, and the surface shape of the object to be measured 30 can be measured continuously and accurately.

[0021] <Distance measurement device 10> As shown in Figure 1, the distance measuring device 10 of this embodiment includes an oscillator 11, a light-emitting unit 12, an optical fiber 13, an optical fiber coupler 14, an optical circulator 15, a light-receiving unit 16, a lens 17, and a distance measuring control unit 18. Each component will be described in order below.

[0022] The oscillator 11 injects a periodically modulated current, such as a sawtooth wave, triangular wave current, or sine wave, based on a command (sweep waveform signal) from the distance measuring control unit 18, thereby modulating the drive current supplied to the light-emitting unit 12. The waveform of the modulated current is not limited to the above; for example, a modulated current may be generated such that the output optical frequency sweep is approximately linear, after understanding the characteristics of the current value injected into the light-emitting unit 12 and the output optical frequency.

[0023] The light-emitting unit 12 generates frequency-modulated (FM) light that is frequency-swept over time at a constant modulation rate using a drive current modulated by the oscillator unit 11, and outputs it to the optical fiber coupler 14a via the optical fiber 13. Alternatively, the light-emitting unit 12 may be configured as a semiconductor laser device with an external resonator, and the resonant wavelength of the light-emitting unit 12 may be changed by a control signal from the oscillator unit 11. In this case as well, the light-emitting unit 12 can generate frequency-swept FM light.

[0024] The optical fiber coupler 14a is a beam splitter that splits the incident FM light into two, outputting one portion of the FM light to the measurement optical system (14b, 13a, 15, 14c, 16a, 17) and the other portion of the FM light to the reference optical system (14d, 13b, 14e, 16b). As is obvious from this configuration, in the distance measurement system 1 of this embodiment, processing based on the output of the measurement optical system and processing based on the output of the reference optical system can be performed in parallel.

[0025] Light incident on the reference optical system is further split into two by the optical fiber coupler 14d, then combined by the optical fiber coupler 14e, and received by the light receiving unit 16b. Of the two optical fibers 13 connecting the optical fiber coupler 14d and the optical fiber coupler 14e, one is a relatively longer optical fiber 13b, and a predetermined optical path difference is provided with respect to the other. Therefore, the reference optical system functions as a Mach-Zehnder interferometer with a known optical path length difference, and the light receiving unit 16b detects a constant beat signal (hereafter referred to as the reference beat signal) proportional to the optical path difference. The reference beat signal detected by the reference optical system is transmitted to the distance measuring control unit 18 and the computer 20.

[0026] Furthermore, the light incident on the measurement optical system is further split into two by the optical fiber coupler 14b. One portion is emitted to the optical fiber 13a as reference light, and the other passes through the optical circulator 15 and is emitted to the lens 17, illuminating the object to be measured 30. The light reflected or scattered by the object to be measured 30 (hereinafter referred to as measurement light) is guided to the optical fiber coupler 14c via the lens 17 and the optical circulator 15. This measurement light is combined with the reference light that has passed through the optical fiber 13a at the optical fiber coupler 14c and received by the light receiving unit 16a. The light receiving unit 16a detects a beat signal (hereinafter referred to as measurement beat signal) generated by the interference of the reference light and the measurement light. The measurement beat signal detected by the measurement optical system is transmitted to the distance measuring control unit 18 and the computer 20. Note that the configuration of the measurement optical system is not limited to the above. For example, instead of using an optical fiber coupler 14b, an optical fiber 13a, and an optical fiber coupler 14c as a means of splitting the light incident on the measurement optical system into two and generating a measurement beat signal, a partial reflective surface may be provided between the optical path from the optical circulator 15 to the object to be measured 30, and the measurement beat signal may be generated by interference between the reflected light from the partial reflective surface (hereinafter referred to as partial reflected light) and the measurement light (i.e., the measurement beat signal is generated by splitting the light into two on the same optical axis, as in a Fizeau interferometer). Fresnel reflected light generated at the end face of the optical fiber between the optical circulator 15 and the lens 17, or at the surface of the lens 17, may be used as the partial reflected light. Depending on the configuration of the optical system, the light receiving units 16a and 16b may use a balanced photodetector equipped with two photodetectors, or a photodetector equipped with one photodetector.

[0027] <Calculator 20> The computer 20 in this embodiment includes an arithmetic unit 21 that processes measurement beat signals and reference beat signals transmitted from the distance measuring device 10, and a display device 22 (for example, a liquid crystal display) that displays the calculation results of the arithmetic unit 21.

[0028] Figure 2 is a functional block diagram of the arithmetic unit 21. As shown here, the arithmetic unit 21 is equipped with the functional units of a beat signal processing unit 21a, a determination processing unit 21b, and a storage unit 21c, and is communicated with the distance measuring device 10, the display device 22, the measuring light scanning mechanism 40, etc. Figure 2 illustrates a configuration in which the functional units such as the beat signal processing unit 21a are mounted on the arithmetic unit 21, but these functional units may also be mounted on the distance measuring control unit 18 of the distance measuring device 10. Conversely, the functions of the distance measuring control unit 18 in this embodiment may also be implemented in the arithmetic unit 21.

[0029] Specifically, the arithmetic unit 21 is a computer equipped with hardware such as a CPU and other arithmetic units, a memory device such as semiconductor memory, and a communication device. The arithmetic unit then executes a predetermined program to realize each functional unit such as the beat signal processing unit 21a. In the following explanation, such well-known technologies will be omitted as appropriate.

[0030] <Distance measurement method based on measurement beat signal> In the distance measurement system 1 of this embodiment, FMCW (Frequency Modulated Continuous Waves) or SS-OCT (Swept-Source Optical Coherence Tomography) (or wavelength-swept OCT) is used as the distance measurement method for the distance L to the object to be measured 30. Although the principles of FMCW and SS-OCT are the same, FMCW is a distance measurement method mainly used for long-distance measurements using a light source with a long coherence distance, while SS-OCT is a distance measurement method mainly used for measuring fine structures using a light source with a short coherence distance.

[0031] Figure 3 is an explanatory diagram of the distance measurement principle of the FMCW method. In the measurement optical system, there is a time difference Δt between the arrival timing of the measurement light and the reference light at the light receiving unit 16a due to the optical path difference between the measurement light and the reference light. In this embodiment, the light emission unit 12 changes its optical frequency during this time difference Δt, so the light receiving unit 16a detects a measurement beat signal with a beat frequency fb equal to the frequency difference between the measurement light and the reference light. For example, if the modulation by the oscillator 11 is sawtooth wave frequency modulation, and the lowest frequency of the light emitted by the light emission unit 12 is ν0, the frequency sweep width is Δν, and the time required to modulate by Δν is T, then the following relationship (Equation 1) holds.

[0032]

number

[0033] The distance L to the object 30 being measured is half the distance light travels during the time difference Δt calculated by (Equation 1). Therefore, the distance L can be calculated using the speed of light c in the atmosphere by the following (Equation 2).

[0034]

number

[0035] The distance L and the beat frequency fb have a linear relationship. Therefore, by performing an FFT (First Fourier Transform) on the measurement signal obtained from the light receiving unit 16a and determining the peak position and magnitude, the reflection position and amount of reflected light of the object being measured 30 can be determined.

[0036] Figure 4 illustrates an example of a method for determining the reflection position on the surface of the object 30 from the reflection intensity profile. In this figure, the horizontal axis represents the FFT frequency, and the vertical axis represents the reflection intensity. As shown in the figure, the data near the peak of the reflection intensity is discrete. The interval between points, i.e., the distance resolution, is c / 2Δν.

[0037] When the ranging method is SS-OCT, a typical wavelength is, for example, 1300 nm, the sweep width is 100 nm, and the frequency sweep width Δν is 17.8 THz, so the distance resolution c / 2Δν is 8.4 μm. On the other hand, when the ranging method is FMCW, a typical wavelength is, for example, 1500 nm, the sweep width is 2 nm, and the frequency sweep width Δν is 267 GHz, so the distance resolution c / 2Δν is 0.56 mm.

[0038] In contrast, as shown in Figure 4, by fitting a quadratic function or Gaussian function to three or more points near the peak, and then interpolating using the values ​​near the peak of the fitted function, it is possible to increase the resolution to about 1 / 10.

[0039] While FFT was given as an example of beat frequency analysis, the maximum entropy method could also be used for beat frequency analysis. In this case, the peak position can be detected with higher resolution than with FFT.

[0040] <Overview of evaluation process based on reference beat signal> Next, an overview of the evaluation process based on the reference beat signal detected by the light-receiving unit 16b of the reference optical system will be explained using Figures 5 and 6A, 6B. In the following explanation, the evaluation process of the reference beat signal will be described assuming that it is performed by the arithmetic unit 21 of the computer 20 (see Figure 2). However, the same evaluation process may be performed by the distance measuring control unit 18 of the distance measuring device 10 and the evaluation result may be output to the computer 20. Alternatively, the same evaluation process may be performed in cooperation between the distance measuring control unit 18 and the arithmetic unit 21.

[0041] First, the beat signal processing unit 21a of the arithmetic unit 21 creates a signal (C(t) in Figure 5(b)) with a phase shift of π / 2 by performing a Hilbert transform on the original reference beat signal (B(t) in Figure 5(a)) obtained during the measurement period.

[0042] Next, the beat signal processing unit 21a calculates the instantaneous phase θ(t) of the signal from the reference beat signals B(t) and C(t) before and after the Hilbert transform, based on (Equation 3) (Figure 5(c)).

[0043]

number

[0044] Furthermore, the beat signal processing unit 21a sequentially connects the calculated instantaneous phases to determine the time change of the phase Φ(t) of the reference beat signal during the measurement period (Figure 5(d)).

[0045] Subsequently, the judgment processing unit 21b of the arithmetic unit 21 evaluates the quality of the reference beat signal based on the change in phase Φ(t) after phase connection. Specifically, it compares the maximum value of phase Φ(t) obtained during the measurement period with a threshold Th1 registered in the storage unit 21c. This threshold Th1 is a variable that depends on the characteristics of the reference optical system, and an appropriate value according to the specifications of the distance measuring device 10 is pre-registered in the storage unit 21c. The same applies to the various thresholds described later.

[0046] Then, as shown in Figure 6A, if the maximum value of the phase change is greater than the threshold Th1, the judgment processing unit 21b determines that the reference beat signal is normal. As a result, the judgment processing unit 21b can also determine that the distance L calculated based on the measurement beat signal of the same measurement period is also normal.

[0047] On the other hand, as shown in Figure 6B, if the maximum value of the phase change is less than or equal to the threshold Th1, the judgment processing unit 21b determines that the reference beat signal is abnormal. In this case, the judgment processing unit 21b determines that the reliability of the distance L calculated based on the measurement beat signal of the same measurement period is low.

[0048] For example, if the frequency sweep signal of the oscillator 11 is inappropriate and the frequency sweep width decreases, or if the light-emitting unit 12 malfunctions, the frequency of the reference beat signal will drop lower than expected, and the maximum value of the phase change will decrease. Therefore, as shown in Figure 6B, the abnormal state of the oscillator 11 or light-emitting unit 12 can be evaluated by comparing the maximum value of the phase change of the reference beat signal with the threshold Th1.

[0049] In addition to the evaluation process described above, a similar effect can be achieved by maintaining a table of phase changes acquired in advance when the device is in a normal state, and comparing the difference in phase changes obtained by processing a reference beat signal against the maintained table with a threshold value. In this case, it is possible to evaluate changes in frequency sweep characteristics and jitter during frequency sweep.

[0050] <Details of the evaluation process based on the reference beat signal> Next, the evaluation process of the reference beat signal described above will be explained in more detail using the flowchart in Figure 7. As mentioned above, in the distance measurement system 1 of this embodiment, processing based on the output of the measurement optical system and processing based on the output of the reference optical system can be performed in parallel. Therefore, Figure 7 illustrates a situation in which both processes are performed in parallel. However, if the system is specialized for evaluation processing, it is sufficient to process only the output of the reference optical system.

[0051] The process shown in Figure 7 is initiated in response to a predetermined operation input from the user to the computer 20. Examples of predetermined operation inputs include the operation to start the control program when the computer 20 is started, and the operation to start the measurement of the object to be measured 30.

[0052] First, in step S1, the distance measuring device 10 and computer 20, etc., which constitute the distance measuring system 1 are started. Specifically, the distance measuring control unit 18 of the distance measuring device 10 is put into a standby state where it can send and receive signals, and the arithmetic unit 21 of the computer 20 is also put into a standby state where it can send and receive signals.

[0053] Next, in step S2, the oscillator 11 outputs a modulated current based on a command (swept waveform signal) from the distance measurement control unit 18, and the light-emitting unit 12 outputs FM light while modulating the optical frequency based on the modulated current from the oscillator 11. As a result, as explained in Figure 1, FM light from the light-emitting unit 12 is incident on both the measurement optical system and the reference optical system.

[0054] In step S3, the distance measuring control unit 18 of the distance measuring device 10 receives a measurement beat signal from the light receiving unit 16a of the measurement optical system and a reference beat signal from the light receiving unit 16b of the reference optical system. The distance measuring control unit 18 also transmits the received measurement beat signal and reference beat signal to the arithmetic unit 21 of the computer 20.

[0055] In step S4, the distance measurement control unit 18 analyzes the measurement beat signal to calculate the distance L to the object to be measured 30, as explained in Figures 3 and 4. The beat signal processing unit 21a of the calculation unit 21 performs a Hilbert transform on the reference beat signal, then obtains the instantaneous phase θ(t), as explained in Figure 5, and then obtains the time change of the phase Φ(t) of the reference beat signal by sequentially connecting the instantaneous phases.

[0056] In step S5, the determination processing unit 21b of the arithmetic unit 21 performs determination processing of the reference beat signal. Specifically, as illustrated in Figures 6A and 6B, the determination processing unit 21b compares the threshold Th1 obtained from the storage unit 21c with the magnitude of the reference beat signal.

[0057] In step S6, the determination processing unit 21b determines whether the reference beat signal is normal based on the comparison result in step S5. If the requirements are met, the process shown in Figure 7 is terminated; otherwise, the process proceeds to step S7.

[0058] Furthermore, if the requirements of step S6 are met, that is, if the maximum value of the phase Φ(t) of the reference beat signal is greater than the threshold Th1 and the reference beat signal can be determined to be normal, then there is no abnormality in the system and the distance L calculated based on the measured beat signal can also be determined to be normal. In this case, even after the reference beat signal determination process is completed, the measurement process based on the measured beat signal can be continued.

[0059] On the other hand, in step S7, the display device 22 displays an error to inform the user of a system abnormality. If the requirements of step S6 are not met and the system proceeds to step S7, that is, if the maximum value of the phase Φ(t) of the reference beat signal is less than or equal to the threshold Th1 and the reference beat signal can be determined to be abnormal, the distance L calculated based on the measurement beat signal acquired in the same measurement period can also be determined to be abnormal, and the subsequent measurement process is interrupted to avoid measuring an incorrect distance L.

[0060] <How to display errors> Next, Figure 8 will be used to specifically explain how errors are displayed in step S7. This figure shows an example of the GUI screen displayed on the display device 22 when the reference beat signal is determined to be abnormal in step S6 and the process proceeds to step S7.

[0061] The GUI screen shown here displays an error code display field 22a, an error details display field 22b, a countermeasure display field 22c, and a confirmation button 22d. The error code display field 22a displays the code number assigned according to the evaluation content in step S6. The error details display field 22b displays the details of the error content corresponding to each code number. The countermeasure display field 22c displays the countermeasure content corresponding to the error content. Pressing the confirmation button 22d interrupts the display of the GUI screen. The error codes, error details, and countermeasure content displayed here can be those that have been pre-registered in the memory unit 21c.

[0062] Note that the GUI screen display is not limited to what is shown in Figure 11; only a portion may be displayed. For example, the error details display field 22b may not display the details of the error, but only the corrective action. Also, when the confirmation button 22d is pressed, the measurement operation may be interrupted and the device may be shut down, or other incidental information such as the time of occurrence may be displayed.

[0063] Furthermore, as another method of notifying the user of the evaluation results, an alarm light or buzzer may be provided to activate when an abnormal condition is detected. Additionally, a lamp indicating a healthy state may be provided on the screen of the distance measuring device 10 or the display device 22, which will light up when the evaluation result is determined to be normal. Moreover, a log file recording the status of the device may be maintained, recording the evaluation result, the evaluated value, and the date together, or it may be recorded in the header area when saving distance measurement data as a file. Furthermore, the arithmetic unit 21 may be provided with an external output terminal to output a signal to an external device during interruption processing.

[0064] Furthermore, the threshold Th used in the evaluation process may be made modifiable through a parameter setting screen provided in the GUI. The values ​​of each threshold may be saved in a threshold setting file, and the threshold setting file may be loaded when the program starts.

[0065] According to the distance measurement system of this embodiment described above, it is possible to easily evaluate whether the frequency sweep state of the light source is normal while non-contact measuring the distance to the object to be measured. [Examples]

[0066] Next, the distance measurement system 1 according to Embodiment 2 of the present invention will be explained using the flowchart in Figure 9. Note that common points with Embodiment 1 will be omitted from the explanation.

[0067] In the flowchart of Figure 7 of Example 1, if the requirements of step S6 were not met, the system immediately proceeded to step S7 (error display). However, in the flowchart of Figure 9 of this example, if the requirements of step S6 were not met, the system proceeded to step S6a. If the requirements of step S6a were met, the system was improved in step S8. Only if the requirements of step S6a were also not met did the system proceed to step S7 (error display). The significance of steps S6a and S8 added in this example will be explained below.

[0068] In step S6a, the distance measuring control unit 18 determines whether the current value of the modulated signal output from the oscillator unit 11 is within the acceptable range, that is, whether there is room to improve the reference beat signal by changing the current value of the modulated signal. If the requirements are met (there is room for improvement), the system proceeds to step S8; otherwise, it proceeds to step S7 (error display) as described above. In the latter case, the error display should indicate that automatic recovery is not possible.

[0069] In step S8, the distance measuring control unit 18 updates the command (sweep waveform signal) to be transmitted to the oscillator unit 11. More specifically, for example, by increasing the amplitude and DC (Direct Current) component of the waveform of the modulated signal output from the oscillator unit 11 by a certain amount, the unit attempts to increase the optical frequency modulation width and optical frequency of the output light, thereby increasing the maximum phase value of the reference beat signal.

[0070] As a result of steps S6a and S8 described above, even if the reference beat signal is determined to be abnormal in step S6, a processing path is added to restart modulation with the updated modulation signal (step S2) and re-evaluate the reference beat signal (steps S5, S6). Therefore, according to the distance measurement system of this embodiment, a normal measurement beat signal can be detected by changing the system control to improve the reference beat signal that was determined to be abnormal. [Examples]

[0071] Next, the distance measurement system 1 according to Embodiment 3 of the present invention will be described using Figure 10. Note that common points with the above embodiment will be omitted from the explanation.

[0072] In steps S5 and S6 of Example 1, the quality of the reference beat signal was determined based on the phase Φ of the reference beat signal. However, in steps S5 and S6 of this embodiment, the quality of the reference beat signal is determined by calculating the rate of change of the phase Φ of the reference beat signal over time (hereinafter referred to as the phase change rate) and comparing it with a predetermined threshold. Alternatively, instead of calculating the phase change rate per unit of time, the phase change rate per unit of sampling rate when acquiring the reference beat signal may be calculated.

[0073] Specifically, in the beat signal processing unit 21a and the determination processing unit 21b of the arithmetic unit 21 of this embodiment, the maximum value of the phase change rate of the reference beat signal (ΔΦ / Δt) max And the minimum value of the phase change rate (ΔΦ / Δt) min We find (ΔΦ / Δt) max -(ΔΦ / Δt) min The width of the phase change rate obtained is compared with a predetermined threshold Th, and if the width of the phase change rate is greater than or equal to the threshold Th, it is judged to be abnormal.

[0074] Alternatively, the beat signal processing unit 21a and the judgment processing unit 21b can achieve a similar effect by analyzing the frequency of the reference beat signal using FFT, comparing the spread of the frequency spectrum (e.g., full width at half maximum) with a threshold Th, and determining that an abnormality exists if the spread is greater than or equal to the threshold Th.

[0075] When the nonlinearity of frequency modulation is high, the difference in magnitude of the phase change rate increases. Therefore, by evaluating the nonlinearity of the frequency sweep characteristics in this embodiment, it is possible to evaluate the deterioration of the frequency analysis accuracy of the measured beat signal.

[0076] Furthermore, as shown in Figure 10, the determination processing unit 21b determines the minimum value of the phase change rate (ΔΦ / Δt) min Alternatively, the value can be compared with the threshold Th2, and if it falls below the threshold Th2, it may be judged as abnormal, or the maximum value of the phase change rate (ΔΦ / Δt) can be used. max You can also compare this to the threshold Th3 and determine if it exceeds the threshold Th3 as abnormal.

[0077] When performing the resampling process described below, if a beat signal with an excessively small phase change rate or an excessively large beat signal is included during the measurement period, variations will occur in the density of the interpolation points generated during the resampling process, which may lead to a decrease in the throughput of the resampling process or a decrease in the measurement accuracy. To avoid this, the minimum value of the phase change rate (ΔΦ / Δt) min or the maximum value of the phase change rate (ΔΦ / Δt) max can be compared with a threshold value to evaluate whether the resampling process can be executed normally.

[0078] In addition to the above evaluation process, a phase change rate table Φ’(t) acquired in advance when the device is in a normal state can be retained, and the difference in the phase change rate Φ(t) - Φ’(t) obtained by processing the reference beat signal with respect to the retained table can be compared with a threshold value. In this case, it is possible to evaluate changes in the frequency sweep characteristics and jitter during frequency sweeping.

[0079] <Resampling Process by Distance Measurement Control Unit 18> Here, a method for performing a resampling process on the measurement beat signal obtained by the light receiving unit 16a of the measurement optical system using the reference beat signal obtained by the light receiving unit 16b of the reference optical system will be described.

[0080] The distance measurement control unit 18 samples the reference beat signal and the measurement beat signal with a sampling clock at regular time intervals. By performing a Hilbert transform on the reference beat signal and obtaining the phase change of the reference beat signal, it is possible to obtain the timing at which the reference beat signal has a constant phase. In accordance with this timing, the measurement beat signal is resampled. That is, based on the phase change of the reference beat signal, the measurement beat signal is resampled at regular intervals of the phase change. Note that the distance measurement control unit 18 can also sample and A / D convert the measurement beat signal using the reference beat signal as a sampling clock by means of the built-in AD / DA converter, achieving the same effect. An FFT is performed on the measurement beat signal after the resampling process to estimate the beat frequency and obtain the distance L to the measurement object 30.

[0081] As described above, by resampling the measured beat signal using a reference beat signal, a measured beat signal with suppressed frequency sweep nonlinearity can be obtained, thereby improving the accuracy of frequency estimation. Furthermore, since both this resampling process and the evaluation of the reference beat signal use the same hardware configuration and the result of the Hilbert transform of the reference beat signal, both processes can be implemented simultaneously. [Examples]

[0082] Next, the distance measurement system 1 according to Embodiment 4 of the present invention will be described using Figures 11A to 11C. Note that common points with the above embodiments will be omitted from the explanation.

[0083] In steps S5 and S6 of Example 1, the quality of the reference beat signal was determined based on the phase Φ of the reference beat signal. However, in steps S5 and S6 of this embodiment, the envelope A(t) of the reference beat signal is determined, and the quality of the reference beat signal is determined based on this envelope A(t).

[0084] Therefore, in the beat signal processing unit 21a of this embodiment, first, the original reference beat signal obtained during the measurement period (B(t) in Figure 4A) is subjected to a Hilbert transform to create a signal (C(t) in Figure 4B) with a phase shift of π / 2.

[0085] Next, the beat signal processing unit 21a determines the envelope A(t) of the reference beat signal from the reference beat signals B(t) and C(t) before and after the Hilbert transform, based on the following equation (4). This allows us to obtain the envelope A(t) shown in Figures 11A and 11B. Note that in Figures 11A and 11B, the illustration of the reference beat signal C(t) after the Hilbert transform is omitted for simplification.

[0086]

number

[0087] Subsequently, the determination processing unit 21b performs a high-pass filter on the obtained envelope A(t) and compares it with the threshold Th4 (Figure 11C).

[0088] Here, as shown in Figure 11A, if no noise is superimposed on the reference beat signal B(t), the envelope A(t) can be obtained as a nearly smooth curve. Therefore, the curve after high-pass filtering will not exceed the threshold Th4 described later.

[0089] On the other hand, as shown in Figure 11B, if noise is superimposed on the reference beat signal B(t), then, as shown in Figure 11C, a sharp change occurs in the curve of the envelope A(t) after high-pass filtering at the location where the noise is superimposed, and the absolute value of this change exceeds the threshold Th4. Therefore, the determination processing unit 21b of this embodiment can evaluate, for example, the control current of the light-emitting unit 12 or the noise of the frequency sweep signal generated in the oscillator 11, based on observation of the reference beat signal.

[0090] Alternatively, instead of using a high-pass filter, this evaluation can be performed similarly by retaining the envelope table A'(t) obtained beforehand under normal conditions and comparing the calculation result of A(t)-A'(t) (i.e., the difference in the envelope waveform from the normal state) with the threshold Th4. In this case, it becomes possible to evaluate the change in the modulation characteristics of the output intensity during frequency sweep.

[0091] Furthermore, in the determination processing unit 21b of this embodiment, the maximum value A(t) of the envelope max The value may be compared with a threshold Th5, and if it falls below the threshold Th5, it may be determined to be abnormal. This evaluation process makes it possible to detect a decrease in the light intensity output from the light-emitting unit 12.

[0092] Furthermore, in the determination processing unit 21b of this embodiment, the maximum value A(t) of the envelope max This is compared with the threshold Th6, and the maximum value of the envelope A(t) is obtained. maxAn abnormality may be determined if the threshold Th6 or higher is reached. This evaluation process allows for, for example, determining whether excessive light intensity is causing the signal obtained by detector 16a or detector 16b to saturate.

[0093] In step S6 of this embodiment, the maximum value A(t) of the envelope of the reference beat signal max This is compared with the threshold Th6, and the maximum value of the envelope A(t) is obtained. max If an abnormality is determined when the threshold Th6 or higher, then in step S8 of this embodiment, in addition to updating the modulated signal, the control current value of the optical amplifier separately provided in the distance measuring device 10 and the control voltage value of the attenuator may be updated by a certain amount. More specifically, examples of such optical amplifiers include EDFA (Erbium Doped Fiber Amplifier), PDFA (Praseodymium Doped Fiber Amplifier), FRA (Fiber Raman Amplifier), or SOA (Semiconductor Optical Amplifier), and an attempt is made to increase the maximum value of the envelope A(t) by updating the control current value of these optical amplifiers by a certain amount. Such optical amplifiers should be selected appropriately depending on the wavelength band of the light-emitting unit 12. It can be said that similar processing is possible for any evaluation index that can be improved by adjusting the control parameters of the light-emitting unit 12.

[0094] Although each embodiment has been described above, the present invention is not limited to the embodiments described above and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and the present invention is not limited to having all the configurations described herein. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. In addition, some or all of the above configurations, functions, processing units, processing means, etc., may be realized in hardware, for example, by designing them as integrated circuits. Also, the control lines and information lines in the figures are shown only if they are considered necessary for explanation and do not necessarily show all of them. It can be assumed that almost all configurations are interconnected.

[0095] Furthermore, the above configuration can be further divided into many more components depending on the processing content. Alternatively, it can be divided so that a single component performs even more processing. [Explanation of Symbols]

[0096] 1. Distance measurement system, 10 ranging equipment; 11. Oscillator section, 12. Light-emitting part, 13 Optical fiber, 14 Fiber optic couplers, 15 Light circulator, 16 Light receiving section, 17 lenses 18 Distance control section, 20 calculator, 21 Computing equipment; 21a Beat signal processing unit, 21b Determination processing unit, 21c storage section, 22 display device; 30. Objects to be measured, 40 Measurement light scanning mechanism

Claims

1. A distance measuring system for measuring the distance to an object to be measured without contact, A light source that outputs FM light with a periodically swept optical frequency, A beam splitter that divides the aforementioned FM light into two, A measuring optical system that splits one of the FM beams, which has been split into two by the beam splitter, into two more, and outputs a measurement beat signal based on the frequency difference between the reflected light and the other FM beam when one of the FM beams is irradiated onto the object to be measured, A reference optical system that further divides the other half of the FM light split by the beam splitter, inputs both of the further divided FM light beams to an interferometer with a known path length difference, and outputs a reference beat signal based on the frequency difference between the FM light beams output by the interferometer, The system comprises a arithmetic unit that performs calculations on the measured beat signal and the reference beat signal, The computing device is A distance measuring unit that calculates the distance to the object to be measured based on the measurement beat signal, A beat signal processing unit that processes the aforementioned reference beat signal to generate a desired signal, A determination processing unit that determines an abnormality of the light source by comparing the desired signal with a reference value, It has, The beat signal processing unit generates the desired signal by sequentially connecting the instantaneous phases calculated from the reference beat signal for a certain period of time, thereby obtaining the time change in the phase of the reference beat signal. The distance measuring system is characterized in that the determination processing unit determines the light source to be abnormal when the maximum value of the time change in the phase of the reference beat signal is less than or equal to the reference value.

2. A distance measuring system for measuring the distance to an object to be measured without contact, A light source that outputs FM light with a periodically swept optical frequency, A beam splitter that divides the aforementioned FM light into two, A measuring optical system that splits one of the FM beams, which has been split into two by the beam splitter, into two more, and outputs a measurement beat signal based on the frequency difference between the reflected light and the other FM beam when one of the FM beams is irradiated onto the object to be measured, A reference optical system that further divides the other half of the FM light split by the beam splitter, inputs both of the further divided FM light beams to an interferometer with a known path length difference, and outputs a reference beat signal based on the frequency difference between the FM light beams output by the interferometer, The system comprises a arithmetic unit that performs calculations on the measured beat signal and the reference beat signal, The computing device is A distance measuring unit that calculates the distance to the object to be measured based on the measurement beat signal, A beat signal processing unit that processes the aforementioned reference beat signal to generate a desired signal, A determination processing unit that determines an abnormality of the light source by comparing the desired signal with a reference value, It has, The beat signal processing unit generates the desired signal by sequentially connecting the instantaneous phases calculated from the reference beat signal for a certain period of time, and taking the difference between the maximum and minimum values ​​of the rate of change of the phase of the reference beat signal over time. The distance measurement system is characterized in that the determination processing unit determines the light source to be abnormal when the difference is greater than or equal to the reference value.

3. A distance measuring system for measuring the distance to an object to be measured without contact, A light source that outputs FM light with a periodically swept optical frequency, A beam splitter that divides the aforementioned FM light into two, A measuring optical system that splits one of the FM beams, which has been split into two by the beam splitter, into two more, and outputs a measurement beat signal based on the frequency difference between the reflected light and the other FM beam when one of the FM beams is irradiated onto the object to be measured, A reference optical system that further divides the other half of the FM light split by the beam splitter, inputs both of the further divided FM light beams to an interferometer with a known path length difference, and outputs a reference beat signal based on the frequency difference between the FM light beams output by the interferometer, The system comprises a arithmetic unit that performs calculations on the measured beat signal and the reference beat signal, The computing device is A distance measuring unit that calculates the distance to the object to be measured based on the measurement beat signal, A beat signal processing unit that processes the aforementioned reference beat signal to generate a desired signal, A determination processing unit that determines an abnormality of the light source by comparing the desired signal with a reference value, It has, The beat signal processing unit generates the desired signal by taking the width of the frequency spectrum obtained by FFT analysis of the frequency of the reference beat signal, The distance measurement system is characterized in that the determination processing unit determines the light source to be abnormal when the spread width of the frequency spectrum is greater than or equal to the reference value.

4. A distance measuring system for measuring the distance to an object to be measured without contact, A light source that outputs FM light with a periodically swept optical frequency, A beam splitter that divides the aforementioned FM light into two, A measuring optical system that splits one of the FM beams, which has been split into two by the beam splitter, into two more, and outputs a measurement beat signal based on the frequency difference between the reflected light and the other FM beam when one of the FM beams is irradiated onto the object to be measured, A reference optical system that further divides the other half of the FM light split by the beam splitter, inputs both of the further divided FM light beams to an interferometer with a known path length difference, and outputs a reference beat signal based on the frequency difference between the FM light beams output by the interferometer, The system comprises a arithmetic unit that performs calculations on the measured beat signal and the reference beat signal, The computing device is A distance measuring unit that calculates the distance to the object to be measured based on the measurement beat signal, A beat signal processing unit that processes the aforementioned reference beat signal to generate a desired signal, A determination processing unit that determines an abnormality of the light source by comparing the desired signal with a reference value, It has, The beat signal processing unit generates the desired signal by sequentially connecting the instantaneous phases calculated from the reference beat signal for a certain period of time, and determining the minimum value of the rate of change of the phase of the reference beat signal over time. The distance measurement system is characterized in that the determination processing unit determines the light source to be abnormal when the minimum value falls below the reference value.

5. A distance measuring system for measuring the distance to an object to be measured in a non-contact manner, A light source that outputs FM light with a periodically swept optical frequency, A beam splitter that divides the aforementioned FM light into two, A measuring optical system that splits one of the FM beams, which has been split into two by the beam splitter, into two more, and outputs a measurement beat signal based on the frequency difference between the reflected light and the other FM beam when one of the FM beams is irradiated onto the object to be measured, A reference optical system that further divides the other half of the FM light split by the beam splitter, inputs both of the further divided FM light beams to an interferometer with a known path length difference, and outputs a reference beat signal based on the frequency difference between the FM light beams output by the interferometer, The system comprises a arithmetic unit that performs calculations on the measured beat signal and the reference beat signal, The computing device is A distance measuring unit that calculates the distance to the object to be measured based on the measurement beat signal, A beat signal processing unit that processes the aforementioned reference beat signal to generate a desired signal, A determination processing unit that determines an abnormality of the light source by comparing the desired signal with a reference value, It has, The beat signal processing unit generates the desired signal by sequentially connecting instantaneous phases calculated from the reference beat signal for a certain period of time, and taking the maximum value of the rate of change of the phase of the reference beat signal over time. The distance measurement system is characterized in that the determination processing unit determines the light source to be abnormal when the maximum value exceeds the reference value.

6. In the distance measuring system according to any one of claims 1 to 5, Furthermore, it is equipped with a display device, A distance measurement system characterized in that, when the judgment processing unit determines an abnormality, the display device displays either an error code, an error description, or a countermeasure.

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