Controller and optical interferometric distance measuring sensor

Abstract

To sample signals generated by a main interferometer at appropriate timing.SOLUTION: A controller 110 comprises: a light source 140; a main interferometer 150 that generates a main interference signal; a sub-interferometer 160 that generates a sub-interference signal; a variable delay amount generation unit that generates a variable delay amount; a correction signal generation unit 171 that generates a correction signal to correct the sampling period of the main interference signal on the basis of the sub-interference signal and the variable delay amount; a processing unit 118 that measures the distance to a measurement object T on the basis of the main interference signal and the correction signal; and a variable delay amount setting unit 195 that sets a variable delay amount on the basis of a peak in the signal based on the digital signal of the main interference signal having been sampled on the basis of the correction signal and / or a peak in the signal based on the digital signal of the reflection signal generated by the main interferometer 150 and having been sampled on the basis of the correction signal.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a controller and an optical interferometric distance measuring sensor. [Background technology]

[0002] In recent years, optical distance measuring sensors that measure the distance to a measurement object without contact have become widespread. For example, an optical interferometric distance measuring sensor is known that generates interference light based on a reference light and a measurement light from light projected from a wavelength swept light source and measures the distance to the measurement object based on the interference light.

[0003] Conventionally, this type of optical frequency domain reflectometry measurement device includes a swept light source, an auxiliary interferometer that applies a predetermined delay time difference to a portion of the output light from the swept light source to cause interference and outputs an auxiliary interference signal, a measurement interferometer that inputs a portion of the output light from the swept light source into an optical fiber under test and causes reflected light from the optical fiber under test and a portion of the output light from the swept light source to interfere with each other and outputs a measurement interference signal, a linearization unit that uses the auxiliary interference signal to correct nonlinearity of the wavelength sweep of the swept light source for the measurement interference signal, and a Fourier transform unit that Fourier transforms the output signal from the linearization unit to output a frequency domain signal, in which the linearization unit has multiple linearization units each with a different delay time, and the Fourier transform unit has a weighted sum / Fourier transform unit that assigns different weights to the output signals of the multiple linearization units, adds them, and outputs the Fourier transformed result (see Patent Document 1). This optical frequency domain reflectometry measurement device corrects nonlinearity of the wavelength sweep over a wide range of the optical fiber under test. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-181115 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, in an optical interferometer ranging sensor that includes a controller and an optical fiber cable including an optical fiber connecting the controller and a sensor head, when the length of the optical fiber is changed, the optical path length of the light that propagates from the main interferometer to the sensor head via the optical fiber and from the sensor head to the main interferometer also becomes longer, which can cause a timing discrepancy between the signal generated by the main interferometer and the signal generated by the secondary interferometer to correct the sampling period.

[0006] Furthermore, if the distance from the sensor head to the measurement object is long compared to the length of the optical fiber, the round-trip time of the light that is irradiated from the sensor head to the measurement object, reflected by the measurement object, and returned to the sensor head becomes long, so in this case too, a timing discrepancy can occur between the signal generated by the main interferometer and the signal generated by the secondary interferometer for correcting the sampling period. As a result, the signal from the main interferometer cannot be sampled accurately, and an error can occur in the distance to the measurement object.

[0007] The present invention has been made in consideration of the above circumstances, and one of its objects is to provide a controller and an optical interferometric distance measuring sensor that can sample the signal generated by the main interferometer at an appropriate timing. [Means for solving the problem]

[0008] a main interferometer connected to the sensor head via an optical fiber cable, the main interferometer receiving the light projected from the light source and generating a main interference signal based on measurement light irradiated onto the measurement object by the sensor head and reflected therefrom, and reference light that follows an optical path at least partially different from that of the measurement light; a sub-interferometer receiving the light projected from the light source and generating a sub-interference signal based on two lights that follow different optical paths; a variable delay amount generator that generates a variable delay; a correction signal generator that generates a correction signal based on the sub-interference signal and the variable delay amount, the correction signal generator generating a correction signal that corrects a sampling period of the main interference signal based on the sub-interference signal and the variable delay; a processing unit that measures the distance to the measurement object based on the main interference signal and the correction signal; and a variable delay amount setting unit that sets the variable delay based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of a reflection signal generated by the main interferometer and based on the digital signal sampled based on the correction signal.

[0009] According to this aspect, the variable delay amount is set based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of the reflected signal generated by the main interferometer and sampled based on the correction signal. This makes it possible to set a variable delay amount that reduces a timing shift that may occur between the main interference signal, the reflected signal, and the secondary interference signal. Here, by setting the variable delay amount based on a peak in a signal based on a digital signal of the reflected signal sampled based on the correction signal, it is possible to set the variable delay amount even in the absence of a measurement object. Furthermore, by setting the variable delay amount based on a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal, it is possible to set a variable delay amount that reduces a timing shift that may occur due to the round-trip time it takes light to travel that distance when the distance from the sensor head to the measurement object is long compared to the length of the optical fiber. Therefore, the signal generated by the main interferometer can be sampled at an appropriate timing using a correction signal based on the secondary interference signal and the variable delay amount, thereby enabling the distance to the measurement object to be measured with high accuracy.

[0010] In the above aspect, the variable delay amount setting unit may set the variable delay amount based on at least one of a peak intensity in a signal based on a digital signal of the main interference signal and a peak intensity in a signal based on a digital signal of the reflected signal.

[0011] According to this aspect, the variable delay amount is set based on at least one of the peak intensity of the signal based on the digital signal of the main interference signal and the peak intensity of the signal based on the digital signal of the reflected signal, which makes it possible to easily set the variable delay amount that reduces a timing difference that may occur between the main interference signal, the reflected signal, and the secondary interference signal.

[0012] In the above aspect, the variable delay amount setting unit may set the variable delay amount based on at least one of a maximum value of peak intensities in a signal based on digital signals of a plurality of main interference signals and a maximum value of peak intensities in a signal based on digital signals of a plurality of reflected signals.

[0013] According to this aspect, the variable delay amount is set based on at least one of the maximum value of peak intensities in a signal based on digital signals of a plurality of main interference signals and the maximum value of peak intensities in a signal based on digital signals of a plurality of reflected signals. As a result, the variable delay amount is set based on the maximum value of the plurality of peak intensities, so it is possible to set a variable delay amount that further reduces a timing shift that may occur between the main interference signal, the reflected signal, and the secondary interference signal, compared to when the variable delay amount is set based on the peak intensities in a signal based on digital signals of one main interference signal or one reflected signal.

[0014] In the above aspect, the variable delay amount setting unit may set the variable delay amount based on at least one of a predetermined peak value width in a signal based on a digital signal of the main interference signal and a predetermined peak value width in a signal based on a digital signal of the reflected signal.

[0015] According to this aspect, the variable delay amount is set based on at least one of the predetermined peak value width of the signal based on the digital signal of the main interference signal and the predetermined peak value width of the signal based on the digital signal of the reflected signal, thereby making it possible to easily set the variable delay amount that reduces a timing difference that may occur between the main interference signal, the reflected signal, and the secondary interference signal.

[0016] In the above aspect, the variable delay amount setting unit may set the variable delay amount based on at least one of the minimum value of the peak predetermined value width in the signal based on the digital signals of the plurality of main interference signals and the minimum value of the peak predetermined value width in the signal based on the digital signals of the plurality of reflected signals.

[0017] According to this aspect, the variable delay amount is set based on at least one of the minimum value of the peak half widths in the signal based on the digital signals of the plurality of main interference signals and the minimum value of the peak half widths in the signal based on the digital signals of the plurality of reflected signals. As a result, the variable delay amount is set based on the minimum value of the plurality of predetermined peak widths, so it is possible to set a variable delay amount that further reduces a timing shift that may occur between the main interference signal, the reflected signal, and the secondary interference signal, compared to when the variable delay amount is set based on the predetermined peak width in the signal based on the digital signal of one main interference signal or the predetermined peak width in the signal based on the digital signal of one reflected signal.

[0018] In the above aspect, the variable delay amount setting unit may set the variable delay amount so that at least one of the number of measurement points included in the predetermined peak value width in the signal based on the digital signal of the main interference signal and the number of measurement points included in the predetermined peak value width in the signal based on the digital signal of the reflected signal is less than a predetermined number.

[0019] According to this aspect, the variable delay amount is set so that at least one of the number of measurement points included in the predetermined peak value width in the signal based on the digital signal of the main interference signal and the number of measurement points included in the predetermined peak value width in the signal based on the digital signal of the reflected signal is less than a predetermined number. This makes it possible to easily set the variable delay amount that reduces a timing difference that may occur between the main interference signal, the reflected signal, and the secondary interference signal.

[0020] In the above aspect, the reflected signal may be generated by a part of light projected from the light source and supplied to the main interferometer being reflected by a member having a reflecting surface formed in the main interferometer.

[0021] According to this aspect, the reflected signal is generated when a part of the light projected from the light source and supplied to the main interferometer is reflected by a member having a reflecting surface formed in the main interferometer. As a result, even when the measurement object is not present and the main interference signal cannot be obtained, the reflected signal can be obtained from the reflecting surface of the main interferometer, so that the variable delay amount can be set without preparing the measurement object.

[0022] In the above aspect, the variable delay amount generating unit may include a variable delay line that generates a delay in the time axis direction according to the variable delay amount in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and outputs the delay to the correction signal generating unit.

[0023] According to this aspect, the variable delay amount generation unit includes a variable delay line that generates a delay in the time axis direction according to the variable delay amount in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal and outputs the delay to the correction signal generation unit. As a result, by outputting the sub-interferometer signal in which the electrical delay has been generated, the correction signal generation unit can easily generate the correction signal, which is an electrical signal.

[0024] In the above aspect, the correction signal generating unit may generate a pulse signal that is a correction signal based on a signal in which a delay corresponding to a variable delay amount is generated in the time axis direction in a sub-interferometer signal obtained by converting a sub-interference signal into an electrical signal.

[0025] According to this aspect, a pulse signal, which is a correction signal, is generated based on a signal in which a delay according to a variable delay amount is generated in the time axis direction in the sub interferometer signal obtained by converting the sub interference signal into an electrical signal, thereby making it possible to easily match (synchronize) the sampling timing of the main interference signal.

[0026] The above aspect may further comprise an AD converter that samples a main interferometer signal, obtained by converting the main interference signal into an electrical signal, based on the correction signal and converts the sampled signal into a digital signal.

[0027] According to this aspect, the main interferometer signal is converted into an electrical signal, and the main interferometer signal is sampled based on the correction signal and converted into a digital signal, which can easily realize a configuration in which the main interferometer signal is converted into a digital signal with a corrected sampling period.

[0028] An optical interferometric distance measuring sensor according to one aspect of the present disclosure is an optical interferometric distance measuring sensor including a controller and an optical fiber cable connected to the controller, wherein the controller includes a light source that projects light while changing the wavelength, and a main interferometer connected to a sensor head via an optical fiber included in the optical fiber cable, the main interferometer being supplied with light projected from the light source and generating a main interference signal based on measurement light that is irradiated onto a measurement object and reflected by the sensor head, and reference light that follows at least a part of an optical path different from that of the measurement light, and the main interferometer being supplied with light projected from the light source and generating a sub-interference signal based on two lights that follow different optical paths. a variable delay amount generating unit that generates a variable delay amount; a correction signal generating unit that generates a correction signal that corrects the sampling period of the main interference signal based on the sub-interference signal and the variable delay amount; a processing unit that measures the distance to the measurement object based on the main interference signal and the correction signal; and a variable delay amount setting unit that sets the variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of a reflected signal generated by the main interferometer and based on a digital signal sampled based on the correction signal.

[0029] According to this aspect, the variable delay amount is set based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of the reflected signal generated by the main interferometer and sampled based on the correction signal. This makes it possible to set a variable delay amount that reduces a timing shift that may occur between the main interference signal, the reflected signal, and the secondary interference signal. Here, by setting the variable delay amount based on a peak in a signal based on a digital signal of the reflected signal sampled based on the correction signal, it is possible to set the variable delay amount even in the absence of a measurement object. Furthermore, by setting the variable delay amount based on a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal, it is possible to set a variable delay amount that reduces a timing shift that may occur due to the round-trip time it takes light to travel that distance when the distance from the sensor head to the measurement object is long compared to the length of the optical fiber. Therefore, the signal generated by the main interferometer can be sampled at an appropriate timing using a correction signal based on the secondary interference signal and the variable delay amount, thereby enabling the distance to the measurement object to be measured with high accuracy. [Effects of the Invention]

[0030] According to the present invention, the signal generated by the main interferometer can be sampled at an appropriate timing. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a schematic view showing an outline of a displacement sensor 10 according to the present disclosure. [Figure 2] 1 is a flowchart showing a procedure for measuring a measurement object T by a displacement sensor 10 according to the present disclosure. [Figure 3] 1 is a functional block diagram showing an overview of a sensor system 1 in which a displacement sensor 10 according to the present disclosure is used. [Figure 4]1 is a flowchart showing a procedure for measuring a measurement object T by a sensor system 1 using a displacement sensor 10 according to the present disclosure. [Figure 5A] 1 is a diagram for explaining the principle of measurement of a measurement object T by a displacement sensor 10 according to the present disclosure. [Figure 5B] 10A and 10B are diagrams for explaining another principle by which the measurement object T is measured by the displacement sensor 10 according to the present disclosure. [Figure 6A] FIG. 2 is a perspective view showing a schematic configuration of a sensor head 20. [Figure 6B] FIG. 2 is a schematic diagram showing the internal structure of the sensor head 20. [Figure 7] FIG. 2 is a block diagram for explaining signal processing in a controller 30. [Figure 8] 10 is a flowchart showing a method for calculating a distance to a measurement object T, which is executed by a processing unit 59 in the controller 30. [Figure 9A] FIG. 1 is a diagram showing how a waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency). [Figure 9B] FIG. 10 is a diagram showing how a spectrum (voltage vs. frequency) is distance-transformed into a spectrum (voltage vs. distance). [Figure 9C] FIG. 10 is a diagram showing how a peak is detected based on a spectrum (voltage vs. distance) and a corresponding distance value is calculated. [Figure 10] 1 is a schematic diagram showing the general configuration of an optical interferometric distance measuring sensor 100 according to an embodiment of the present invention. [Figure 11] FIG. 10 is a schematic diagram showing a specific example of a configuration for generating reflected waves in the main interferometer 150. [Figure 12] 10A and 10B are diagrams for explaining the relationship between the peaks in a signal based on a digital signal of a main interference signal and the peaks in a signal based on a digital signal of a reflected signal and the variable delay amount. [Figure 13] 10 is a diagram for explaining the relationship between the peak half width in a signal based on a digital signal of a main interference signal and the peak half width in a signal based on a digital signal of a reflected signal and the FFT conditions. FIG. [Figure 14] 10 is a flowchart illustrating an example of a processing procedure performed by a controller 110 according to an embodiment. [Figure 15] 10 is a flowchart illustrating another example of the processing procedure performed by the controller 110 in an embodiment. [Figure 16] 10 is a flowchart illustrating yet another example of the processing procedure performed by the controller 110 in an embodiment. [Figure 17] FIG. 1 is a schematic diagram showing an outline of the configuration of another optical interferometric distance measuring sensor 101 according to an embodiment of the present invention. [Figure 18] 10A and 10B are diagrams showing variations of an interferometer that generates interference light using measurement light and reference light. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that each embodiment described below is merely a specific example for carrying out the present invention and is not intended to limit the scope of the present invention. Furthermore, to facilitate understanding of the description, the same components in each drawing will be designated by the same reference numerals wherever possible, and duplicate descriptions may be omitted.

[0033] [Displacement sensor overview] First, an overview of the displacement sensor according to the present disclosure will be described. 1 is a schematic external view showing an overview of a displacement sensor 10 according to the present disclosure. As shown in Fig. 1, the displacement sensor 10 includes a sensor head 20 and a controller 30, and measures the displacement of a measurement object T (the distance to the measurement object T).

[0034] The sensor head 20 and the controller 30 are connected by an optical fiber 40, and an objective lens 21 is attached to the sensor head 20. The controller 30 also includes a display unit 31, a setting unit 32, an external interface (I / F) unit 33, an optical fiber connection unit 34, and an external storage unit 35, and further includes a measurement processing unit 36 ​​inside.

[0035] The sensor head 20 irradiates the measurement object T with light output from the controller 30 and receives the light reflected from the measurement object T. The sensor head 20 has an internal reference surface that reflects the light output from the controller 30 and received via the optical fiber 40 and causes it to interfere with the light reflected from the measurement object T described above.

[0036] The sensor head 20 is provided with an objective lens 21, which is detachable. The objective lens 21 can be replaced with an objective lens having an appropriate focal length depending on the distance between the sensor head 20 and the measurement target T, or a variable-focus objective lens may be used.

[0037] Furthermore, when installing the sensor head 20, guide light (visible light) may be irradiated onto the measurement object T, and the sensor head 20 and / or the measurement object T may be installed so that the measurement object T is appropriately positioned within the measurement area of ​​the displacement sensor 10.

[0038] The optical fiber 40 is connected to and extends from an optical fiber connection unit 34 arranged in the controller 30, connecting the controller 30 and the sensor head 20. As a result, the optical fiber 40 is configured to guide light emitted from the controller 30 to the sensor head 20, and further guide return light from the sensor head 20 to the controller 30. The optical fiber 40 is detachable from the sensor head 20 and the controller 30, and various optical fibers having different lengths, thicknesses, characteristics, etc. can be used.

[0039] The display unit 31 is configured with, for example, a liquid crystal display or an organic EL display, etc. The display unit 31 displays the set value of the displacement sensor 10, the amount of received return light from the sensor head 20, and measurement results such as the displacement of the measurement object T measured by the displacement sensor 10 (the distance to the measurement object T).

[0040] The setting unit 32 performs settings necessary for measuring the measurement target T, for example, by a user operating a mechanical button, a touch panel, or the like. All or part of these necessary settings may be set in advance, or may be set from an externally connected device (not shown) connected to the external I / F unit 33. The externally connected device may be connected by wire or wirelessly via a network.

[0041] Here, the external I / F unit 33 is configured with, for example, Ethernet (registered trademark), RS232C, analog output, etc. The external I / F unit 33 may be connected to another connected device so that necessary settings can be made from the external connected device, or the measurement results measured by the displacement sensor 10, etc., may be output to the external connected device.

[0042] Furthermore, the controller 30 may perform settings necessary for measuring the measurement object T by importing data stored in the external storage unit 35. The external storage unit 35 is, for example, an auxiliary storage device such as a USB (Universal Serial Bus) memory, and stores settings and the like necessary for measuring the measurement object T in advance.

[0043] The measurement processing unit 36 ​​in the controller 30 includes, for example, a wavelength swept light source that emits light while continuously changing the wavelength, a light receiving element that receives the returned light from the sensor head 20 and converts it into an electrical signal, and a signal processing circuit that processes the electrical signal. The measurement processing unit 36 ​​performs various processes using a control unit, a memory unit, etc., based on the returned light from the sensor head 20 so that the displacement of the measurement object T (the distance to the measurement object T) is ultimately calculated. These processes will be described in detail later.

[0044] 2 is a flowchart showing a procedure for measuring the measurement target T by the displacement sensor 10 according to the present disclosure. As shown in FIG. 2, the procedure includes steps S11 to S14.

[0045] In step S11, the sensor head 20 is installed. For example, guide light is irradiated from the sensor head 20 onto the measurement target T, and the sensor head 20 is installed in an appropriate position based on the guide light.

[0046] Specifically, the amount of received light returning from the sensor head 20 is displayed on the display unit 31 of the controller 30, and the user may adjust the orientation of the sensor head 20 and the distance (height position) from the measurement object T while checking the amount of received light. Basically, if the light from the sensor head 20 can be irradiated perpendicularly to the measurement object T (at an angle closer to perpendicular), the amount of reflected light from the measurement object T will be large and the amount of received light returning from the sensor head 20 will also be large.

[0047] Furthermore, depending on the distance between the sensor head 20 and the object T to be measured, the objective lens 21 may be replaced with one having an appropriate focal length.

[0048] Furthermore, if appropriate settings cannot be made when measuring the measurement object T (for example, the amount of light received required for measurement cannot be obtained, or the focal length of the objective lens 21 is inappropriate), an error or incomplete settings may be displayed on the display unit 31 or output to an externally connected device to notify the user.

[0049] In step S12, various measurement conditions are set when measuring the measurement object T. For example, the user sets the inherent calibration data (such as a function for correcting linearity) of the sensor head 20 by operating the setting unit 32 in the controller 30.

[0050] Various parameters may also be set. For example, a sampling time, a measurement range, and a threshold for determining whether a measurement result is normal or abnormal may be set. Furthermore, a measurement cycle may be set according to the characteristics of the measurement object T, such as the reflectance and material of the measurement object T, and a measurement mode may be set according to the material of the measurement object T.

[0051] These measurement conditions and various parameters are set by operating the setting unit 32 in the controller 30, but they may also be set from an externally connected device or by importing data from the external memory unit 35.

[0052] In step S13, the sensor head 20 installed in step S11 measures the measurement target T in accordance with the measurement conditions and various parameters set in step S12.

[0053] Specifically, in the measurement processing unit 36 ​​of the controller 30, light is projected from the wavelength swept light source, and the light returning from the sensor head 20 is received by a light receiving element, and frequency analysis, distance conversion, peak detection, etc. are performed by a signal processing circuit to calculate the displacement of the measurement object T (the distance to the measurement object T). Specific details of the measurement processing will be described later.

[0054] In step S14, the measurement results measured in step S13 are output. For example, the displacement of the measurement object T (distance to the measurement object T) measured in step S13 is displayed on the display unit 31 of the controller 30 or output to an externally connected device.

[0055] In addition, whether the displacement of the measurement object T (distance to the measurement object T) measured in step S13 is within a normal range or abnormal based on the threshold set in step S12 may also be displayed or output as a measurement result. Furthermore, the measurement conditions, various parameters, measurement mode, etc. set in step S12 may also be displayed or output.

[0056] [System overview including displacement sensors] Fig. 3 is a functional block diagram showing an overview of a sensor system 1 that uses a displacement sensor 10 according to the present disclosure. As shown in Fig. 3, the sensor system 1 includes the displacement sensor 10, a control device 11, a control signal input sensor 12, and an external connection device 13. Note that the displacement sensor 10 is connected to the control device 11 and the external connection device 13 by, for example, a communication cable or an external connection cord (including, for example, an external input line, an external output line, a power line, etc.), and the control device 11 and the control signal input sensor 12 are connected by a signal line.

[0057] 1 and 2, the displacement sensor 10 measures the displacement of the measurement object T (the distance to the measurement object T). The displacement sensor 10 may then output the measurement results and the like to the control device 11 and the externally connected device 13.

[0058] The control device 11 is, for example, a PLC (Programmable Logic Controller), and gives various instructions to the displacement sensor 10 when the displacement sensor 10 measures the measurement target T.

[0059] For example, the control device 11 may output a measurement timing signal to the displacement sensor 10 based on an input signal from a control signal input sensor 12 connected to the control device 11, or may output a zero reset command signal (a signal for setting the current measurement value to 0) or the like to the displacement sensor 10.

[0060] The control signal input sensor 12 outputs an on / off signal to the control device 11, which indicates the timing at which the displacement sensor 10 measures the measurement object T. For example, the control signal input sensor 12 may be installed near a production line on which the measurement object T moves, and may output an on / off signal to the control device 11 upon detecting that the measurement object T has moved to a predetermined position.

[0061] The externally connected device 13 is, for example, a PC (Personal Computer), and various settings can be made to the displacement sensor 10 by the user operating it.

[0062] As specific examples, the measurement mode, operation mode, measurement period, material of the measurement object T, etc. are set.

[0063] The measurement mode can be set to either an "internal synchronous measurement mode" in which measurement is started periodically within the control device 11, or an "external synchronous measurement mode" in which measurement is started in response to an input signal from outside the control device 11, or the like.

[0064] As the setting of the operation mode, an "operation mode" in which the measurement object T is actually measured, or an "adjustment mode" in which measurement conditions for measuring the measurement object T are set, etc., can be selected.

[0065] The measurement period is the period for measuring the measurement object T, and can be set according to the reflectance of the measurement object T. However, even if the reflectance of the measurement object T is low, the measurement object T can be measured appropriately by lengthening the measurement period and setting the measurement period appropriately.

[0066] For the measurement object T, a "rough surface mode" suitable for when diffuse reflection is a relatively large component of the reflected light, a "specular surface mode" suitable for when specular reflection is a relatively large component of the reflected light, or a "standard mode" that is intermediate between these two is selected.

[0067] In this way, by making appropriate settings depending on the reflectance and material of the measurement object T, the measurement object T can be measured with higher accuracy.

[0068] 4 is a flowchart showing a procedure for measuring a measurement target T by the sensor system 1 that uses the displacement sensor 10 according to the present disclosure. As shown in FIG. 4, this procedure is a procedure for the external synchronization measurement mode described above, and includes steps S21 to S24.

[0069] In step S21, the sensor system 1 detects a measurement target T, which is an object to be measured. Specifically, the control signal input sensor 12 detects that the measurement target T has moved to a predetermined position on the production line.

[0070] In step S22, the sensor system 1 issues a measurement instruction to measure the measurement object T detected in step S21 using the displacement sensor 10. Specifically, the control signal input sensor 12 outputs an on / off signal to the control device 11 to instruct the timing of measuring the measurement object T detected in step S21, and the control device 11 outputs a measurement timing signal to the displacement sensor 10 based on the on / off signal to instruct the displacement sensor 10 to measure the measurement object T.

[0071] In step S23, the measurement object T is measured by the displacement sensor 10. Specifically, the displacement sensor 10 measures the measurement object T based on the measurement instruction received in step S22.

[0072] In step S24, the sensor system 1 outputs the measurement result obtained in step S23. Specifically, the displacement sensor 10 displays the result of the measurement process on the display unit 31, or outputs the result to the control device 11 or the externally connected device 13 via the external I / F unit 33.

[0073] 4, the procedure for the external synchronization measurement mode in which the measurement object T is measured by detecting the measurement object T with the control signal input sensor 12 has been described, but the present invention is not limited to this. For example, in the internal synchronization measurement mode, instead of steps S21 and S22, a measurement timing signal is generated based on a preset cycle to instruct the displacement sensor 10 to measure the measurement object T.

[0074] Next, the principle of measurement of the measurement target T by the displacement sensor 10 according to the present disclosure will be described. 5A is a diagram illustrating the principle of measurement of a measurement target T by a displacement sensor 10 according to the present disclosure. As shown in FIG. 5A, the displacement sensor 10 includes a sensor head 20 and a controller 30. The sensor head 20 includes an objective lens 21 and a plurality of collimating lenses 22a to 22c, and the controller 30 includes a wavelength swept light source 51, an optical amplifier 52, a plurality of isolators 53 and 53a to 53b, a plurality of optical couplers 54 and 54a to 54e, an attenuator 55, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balanced detector 60, and a correction signal generation unit 61.

[0075] The wavelength swept light source 51 emits a laser beam with a swept wavelength. For example, if a method of modulating a VCSEL (Vertical Cavity Surface Emitting Laser) with current is applied as the wavelength swept light source 51, mode hopping is unlikely to occur due to a short cavity length, wavelength change is easy, and it can be realized at low cost.

[0076] The optical amplifier 52 amplifies the light emitted from the wavelength swept light source 51. The optical amplifier 52 may be, for example, an erbium-doped fiber amplifier (EDFA), and may be, for example, an optical amplifier dedicated to 1550 nm.

[0077] The isolator 53 is an optical element that transmits incident light in one direction, and may be disposed immediately after the wavelength swept light source 51 to prevent the influence of noise caused by returning light.

[0078] In this way, the light emitted from the wavelength swept light source 51 is amplified by the optical amplifier 52, passes through the isolator 53, and is branched to the main interferometer and the sub interferometer by the optical coupler 54. For example, the proportion of the light branched to the main interferometer and the sub interferometer by the optical coupler 54 may be set to 90% or more on the main interferometer side.

[0079] The light branched to the main interferometer is further branched by the first-stage optical coupler 54a into the direction of the sensor head 20 and the direction of the second-stage optical coupler 54b.

[0080] The light branched by the first-stage optical coupler 54a toward the sensor head 20 passes from the tip of the optical fiber through the collimator lens 22a and the objective lens 21 in the sensor head 20 and is irradiated onto the measurement object T. Then, the tip (end face) of the optical fiber serves as a reference surface, and the light reflected by the reference surface interferes with the light reflected by the measurement object T, generating interference light that returns to the first-stage optical coupler 54a and is then received by the light-receiving element 56a and converted into an electrical signal.

[0081] The light branched by the first-stage optical coupler 54a toward the second-stage optical coupler 54b travels through the isolator 53a to the second-stage optical coupler 54b, and is further branched by the second-stage optical coupler 54b toward the sensor head 20 and the third-stage optical coupler 54c. As in the first stage, the light branched from the optical coupler 54b toward the sensor head 20 passes from the tip of the optical fiber in the sensor head 20 through the collimator lens 22b and the objective lens 21 and is irradiated onto the measurement object T. The tip (end face) of the optical fiber serves as a reference surface, and the light reflected by the reference surface and the light reflected by the measurement object T interfere with each other to generate interference light. The interference light returns to the second-stage optical coupler 54b, and is branched by the optical coupler 54b toward the isolator 53a and the light receiving element 56b, respectively. The light branched from the optical coupler 54b toward the light-receiving element 56b is received by the light-receiving element 56b and converted into an electrical signal. On the other hand, the isolator 53a transmits light from the upstream optical coupler 54a to the downstream optical coupler 54b and blocks light from the downstream optical coupler 54b to the upstream optical coupler 54a, so the light branched from the optical coupler 54b toward the isolator 53a is blocked.

[0082] The light branched by the second-stage optical coupler 54b toward the third-stage optical coupler 54c travels through the isolator 53b to the third-stage optical coupler 54c, where it is further branched by the third-stage optical coupler 54c toward the sensor head 20 and the attenuator 55. As in the first and second stages, the light branched from the optical coupler 54c toward the sensor head 20 passes from the tip of the optical fiber through the collimator lens 22c and the objective lens 21 in the sensor head 20, and is then irradiated onto the measurement object T. The tip (end face) of the optical fiber serves as a reference surface, and the light reflected by the reference surface and the light reflected by the measurement object T interfere with each other to generate interference light, which returns to the third-stage optical coupler 54c and is branched by the optical coupler 54c toward the isolator 53b and the light receiving element 56c, respectively. The light branched from the optical coupler 54c toward the light-receiving element 56c is received by the light-receiving element 56c and converted into an electrical signal. On the other hand, the isolator 53b transmits light from the upstream optical coupler 54b to the downstream optical coupler 54c and blocks light from the downstream optical coupler 54c to the upstream optical coupler 54b, so that the light branched from the optical coupler 54c toward the isolator 53b is blocked.

[0083] In addition, since the light branched in a direction other than the sensor head 20 by the third-stage optical coupler 54c is not used to measure the measurement object T, it is preferable to attenuate it by an attenuator 55 such as a terminator to prevent it from being reflected back.

[0084] In this way, the main interferometer has three optical paths (three channels), each with an optical path length difference that is twice the distance (round trip) from the tip (end face) of the optical fiber of the sensor head 20 to the object to be measured T, and generates three interference lights corresponding to the optical path length difference.

[0085] As described above, the light receiving elements 56a to 56c receive the interference light from the main interferometer and generate electrical signals according to the amount of light received.

[0086] The amplifier circuits 57a to 57c amplify the electrical signals output from the light receiving elements 56a to 56c, respectively.

[0087] The AD conversion units 58a to 58c receive the electrical signals amplified by the amplifier circuits 57a to 57c, respectively, and convert the electrical signals from analog to digital (AD conversion). Here, the AD conversion units 58a to 58c perform AD conversion based on the correction signal from the correction signal generation unit 61 in the sub-interferometer.

[0088] In order to correct the nonlinearity of the wavelength when the wavelength swept light source 51 is swept, the secondary interferometer acquires an interference signal and generates a correction signal called a K clock.

[0089] Specifically, the light branched to the sub-interferometer by optical coupler 54 is further branched by optical coupler 54d. Here, the optical paths of the branched light are configured to have an optical path length difference, for example, by using optical fibers of different lengths between optical coupler 54d and optical coupler 54e, and interference light corresponding to the optical path length difference is output from optical coupler 54e. Then, balance detector 60 receives the interference light from optical coupler 54e and amplifies the optical signal and converts it into an electrical signal while removing noise by taking the difference with a signal of the opposite phase.

[0090] The optical coupler 54d and the optical coupler 54e may both branch light at a ratio of 50:50.

[0091] The correction signal generator 61 determines the nonlinearity of the wavelength during the sweep of the wavelength swept light source 51 based on the electrical signal from the balance detector 60, generates a K clock according to the nonlinearity, and outputs it to the AD converters 58a to 58c.

[0092] Due to the nonlinearity of the wavelength during the sweep of the wavelength swept light source 51, the waves of the analog signals input to the AD converters 58a to 58c in the main interferometer are not spaced at equal intervals. The AD converters 58a to 58c perform AD conversion (sampling) by correcting the sampling time based on the K clock described above so that the waves are spaced at equal intervals.

[0093] As described above, the K clock is a correction signal used to sample the analog signal of the main interferometer, and therefore needs to be generated at a higher frequency than the analog signal of the main interferometer. Specifically, the optical path length difference between the optical couplers 54d and 54e in the sub interferometer may be made longer than the optical path length difference between the tip (end face) of the optical fiber in the main interferometer and the measurement object T, or the frequency may be multiplied (e.g., eight times) by the correction signal generator 61 to increase the frequency.

[0094] The processing unit 59 acquires the digital signals that have been AD converted while the nonlinearity has been corrected by the AD conversion units 58a to 58c, and calculates the displacement of the measurement object T (the distance to the measurement object T) based on the digital signals. Specifically, the processing unit 59 converts the frequencies of the digital signals using a fast Fourier transform (FFT), and calculates the distance by analyzing the converted signals. The detailed processing in the processing unit 59 will be described later.

[0095] Since the processing unit 59 is required to perform high-speed processing, it is often realized by an integrated circuit such as an FPGA (field-programmable gate array).

[0096] Also, here, three optical paths are provided in the main interferometer, and the sensor head 20 irradiates measurement light from each optical path onto the measurement object T, and based on the interference light (return light) obtained from each, the distance to the measurement object T and the like are measured (multi-channel). The number of channels in the main interferometer is not limited to three, and may be one, two, or four or more.

[0097] 5B is a diagram illustrating another principle by which the measurement target T is measured by the displacement sensor 10 according to the present disclosure. As shown in FIG. 5B, the displacement sensor 10 includes a sensor head 20 and a controller 30. The sensor head 20 includes an objective lens 21 and a plurality of collimating lenses 22a to 22c, and the controller 30 includes a wavelength swept light source 51, an optical amplifier 52, a plurality of isolators 53 and 53a to 53b, a plurality of optical couplers 54 and 54a to 54j, an attenuator 55, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balanced detector 60, and a correction signal generation unit 61. The displacement sensor 10 shown in FIG. 5B differs from the configuration of the displacement sensor 10 shown in FIG. 5A mainly in that it includes optical couplers 54f to 54j. The principle of this different configuration will be described in detail below in comparison with FIG. 5A.

[0098] The light emitted from the wavelength swept light source 51 is amplified by an optical amplifier 52, passes through an isolator 53, and is branched by an optical coupler 54 to the main interferometer side and the sub-interferometer side. The light branched to the main interferometer side is further branched by an optical coupler 54f into measurement light and reference light.

[0099] As described in FIG. 5A, the measurement light is passed through the collimator lens 22a and the objective lens 21 by the first-stage optical coupler 54a, irradiated onto the measurement object T, and reflected by the measurement object T. Here, in FIG. 5A, the tip (end face) of the optical fiber is used as a reference surface, and light reflected from the reference surface interferes with light reflected by the measurement object T to generate interference light, but in FIG. 5B, no reference surface is provided for reflecting light. That is, in FIG. 5B, no light is reflected by the reference surface as in FIG. 5A, and therefore the measurement light reflected by the measurement object T returns to the first-stage optical coupler 54a.

[0100] Similarly, light branched from the first-stage optical coupler 54a toward the second-stage optical coupler 54b passes through the collimator lens 22b and the objective lens 21 by the second-stage optical coupler 54b, is irradiated onto the measurement object T, is reflected by the measurement object T, and returns to the second-stage optical coupler 54b. Light branched from the second-stage optical coupler 54b toward the third-stage optical coupler 54c passes through the collimator lens 22c and the objective lens 21 by the third-stage optical coupler 54c, is irradiated onto the measurement object T, is reflected by the measurement object T, and returns to the third-stage optical coupler 54c.

[0101] On the other hand, the reference light split by the optical coupler 54f is further split by the optical coupler 54g to optical couplers 54h, 54i, and 54j.

[0102] In the optical coupler 54h, the measurement light output from the optical coupler 54a and reflected by the measurement object T interferes with the reference light output from the optical coupler 54g, generating interference light that is received by the light-receiving element 56a and converted into an electrical signal. In other words, the measurement light and the reference light are split by the optical coupler 54f, and interference light is generated according to the difference in optical path length between the optical path of the measurement light (the optical path from the optical coupler 54f, via the optical coupler 54a, the collimator lens 22a, and the objective lens 21, reflected by the measurement object T, and reaching the optical coupler 54h) and the optical path of the reference light (the optical path from the optical coupler 54f, via the optical coupler 54g, to reach the optical coupler 54h). The interference light is received by the light-receiving element 56a and converted into an electrical signal.

[0103] Similarly, in the optical coupler 54i, interference light is generated according to the difference in optical path length between the optical path of the measurement light (the optical path from the optical coupler 54f, through the optical couplers 54a and 54b, the collimator lens 22b, and the objective lens 21, reflected by the measurement object T, and reaching the optical coupler 54i) and the optical path of the reference light (the optical path from the optical coupler 54f, through the optical coupler 54g, and reaching the optical coupler 54i), and the interference light is received by the photodetector 56b and converted into an electrical signal.

[0104] In the optical coupler 54j, interference light is generated according to the difference in optical path length between the optical path of the measurement light (the optical path from the optical coupler 54f, through the optical couplers 54a, 54b, and 54c, the collimator lens 22c, and the objective lens 21, reflected by the measurement target T, and reaching the optical coupler 54j) and the optical path of the reference light (the optical path from the optical coupler 54f, through the optical coupler 54g, and reaching the optical coupler 54j), and the interference light is received by the light-receiving element 56c and converted into an electrical signal. Note that the light-receiving elements 56a to 56c may be, for example, balanced photodetectors.

[0105] In this way, the main interferometer has three optical paths (three channels) and generates three interference lights according to the optical path length difference between the measurement light reflected by the measurement object T and input to the optical couplers 54h, 54i, and 54j, and the reference light input to the optical couplers 54h, 54i, and 54j, respectively, via the optical couplers 54f and 54g.

[0106] The optical path length difference between the measurement light and the reference light may be set to be different for each of the three channels, for example, the optical path lengths of the optical coupler 54g and the optical couplers 54h, 54i, and 54j may be set to be different.

[0107] Then, based on the interference light obtained from each, the distance to the measurement object T and the like are measured (multi-channel).

[0108] [Sensor head structure] Here, the structure of the sensor head used in the displacement sensor 10 will be described. FIG. 6A is a perspective view showing a schematic configuration of the sensor head 20, and FIG. 6B is a schematic view showing the internal structure of the sensor head.

[0109] 6A, the sensor head 20 has the objective lens 21 and the collimator lens stored in the lens holder 23. For example, the size of the lens holder 23 is such that the length of one side surrounding the objective lens 21 is about 20 mm, and the length in the optical axis direction is about 40 mm.

[0110] 6B, one objective lens 21 and three collimating lenses 22a to 22c are stored in the lens holder 23. Light from the optical fiber is guided to the three collimating lenses 22a to 22c via the optical fiber array 24, and the light that has passed through the three collimating lenses 22a to 22c is irradiated onto the measurement object T via the objective lens 21.

[0111] In this way, these optical fibers, collimator lenses 22a to 22c, and optical fiber array 24, together with the objective lens 21, are held by the lens holder 23 to form the sensor head 20.

[0112] Furthermore, the lens holder 23 constituting the sensor head 20 may be made of a metal (for example, A2017) that is strong and can be processed with high precision.

[0113] Fig. 7 is a block diagram for explaining signal processing in the controller 30. As shown in Fig. 7, the controller 30 includes a plurality of light receiving elements 71a to 71e, a plurality of amplifier circuits 72a to 72c, a plurality of AD conversion units 74a to 74c, a processing unit 75, a differential amplifier circuit 76, and a correction signal generation unit 77.

[0114] As shown in Figure 5A, the controller 30 splits the light emitted from the wavelength swept light source 51 into a main interferometer and a sub interferometer using an optical coupler 54, and calculates the distance to the measurement object T by processing the main interference signal and the sub interferometer signal obtained from each.

[0115] The plurality of light receiving elements 71a to 71c correspond to the light receiving elements 56a to 56c shown in FIG. 5A, and receive the main interference signal from the main interferometer and output it as a current signal to the amplifier circuits 72a to 72c, respectively.

[0116] The plurality of amplifier circuits 72a to 72c convert the current signals into voltage signals (IV conversion) and amplify them.

[0117] The AD conversion units 74a to 74c correspond to the AD conversion units 58a to 58c shown in FIG. 5A, and convert the voltage signal into a digital signal (AD conversion) based on K clocks from a correction signal generation unit 77, which will be described later.

[0118] Processing unit 75 corresponds to processing unit 59 shown in FIG. 5A, converts the digital signals from AD conversion units 74a to 74c into frequencies using FFT, analyzes them, and calculates the distance value to measurement object T.

[0119] The multiple light receiving elements 71d to 71e and the differential amplifier circuit 76 correspond to the balanced detector 60 shown in Figure 5A, and each receive the interference light in the sub-interferometer, one of which outputs an interference signal with an inverted phase, and by taking the difference between the two signals, noise is removed, while the interference signal is amplified and converted into a voltage signal.

[0120] 5A, the correction signal generator 77 binarizes the voltage signal using a comparator, generates a K clock, and outputs it to the AD converters 74a to 74c. Since the K clock needs to be generated at a higher frequency than the analog signal of the main interferometer, the correction signal generator 77 may multiply the frequency (for example, by 8) to increase the frequency.

[0121] 8 is a flowchart showing a method for calculating the distance to the measurement object T, which is executed by the processing unit 59 in the controller 30. As shown in FIG. 8, the method includes steps S31 to S34.

[0122] In step S31, processing unit 59 performs frequency conversion on the waveform signal (voltage vs. time) into a spectrum (voltage vs. frequency) using the following FFT: Fig. 9A is a diagram showing how the waveform signal (voltage vs. time) is frequency converted into a spectrum (voltage vs. frequency).

number

[0123] In step S32, the processing unit 59 performs distance conversion on the spectrum (voltage vs. frequency) to convert it into a spectrum (voltage vs. distance). Fig. 9B is a diagram showing how the spectrum (voltage vs. frequency) is converted into a spectrum (voltage vs. distance).

[0124] In step S33, processing unit 59 calculates distance values ​​corresponding to the peaks based on the spectrum (voltage vs. distance). Fig. 9C is a diagram showing how peaks are detected based on the spectrum (voltage vs. distance) and distance values ​​corresponding to the peaks are calculated. As shown in Fig. 9C, peaks are detected based on the spectrum (voltage vs. distance) for each of the three channels, and distance values ​​corresponding to the peaks are calculated.

[0125] In step S34, the processing unit 59 averages the distance values ​​calculated in step S33. Specifically, since peaks have been detected in each of the three channels based on the spectrum (voltage vs. distance) in step S33 and the corresponding distance values ​​have been calculated, the processing unit 59 averages these and outputs the averaged calculation result as the distance to the measurement object T.

[0126] In step S34, when averaging the distance values ​​calculated in step S33, the processing unit 59 preferably averages distance values ​​whose SNR is equal to or greater than a threshold value. For example, if a peak is detected based on the spectrum (voltage vs. distance) of one of the three channels but the SNR is less than the threshold value, the distance value calculated based on that spectrum is determined to be unreliable and is not adopted.

[0127] Next, the present disclosure will be described in detail as a specific embodiment, focusing on its more characteristic configurations, functions, and properties. Note that the optical interferometric distance measuring sensor shown below corresponds to the displacement sensor 10 described with reference to Figures 1 to 9, and all or part of the basic configurations, functions, and properties included in the optical interferometric distance measuring sensor are common to the configurations, functions, and properties included in the displacement sensor 10 described with reference to Figures 1 to 9.

[0128] <One embodiment> [Configuration of optical interferometric ranging sensor] Fig. 10 is a schematic diagram showing the general configuration of an optical interferometric distance measuring sensor 100 according to one embodiment of the present invention. As shown in Fig. 10, the optical interferometric distance measuring sensor 100 includes a controller 110 and an optical fiber cable 130 that connects the controller 110 and a sensor head 121. The optical interferometric distance measuring sensor 100 may further include a sensor head 121.

[0129] The controller 110 includes a wavelength swept light source 140, an optical branching unit 111, a main interferometer 150, a sub interferometer 160, a first photodiode (PD) 112, an amplifier circuit 114, a second photodiode (PD) 116, a variable delay line 191, a correction signal generating unit 171, an AD conversion unit 181, a processing unit 118, and a variable delay amount setting unit 195.

[0130] The optical fiber cable 130 is an optical fiber group composed of one or more optical fibers. The optical fiber cable 130 is configured to be detachable, that is, to be able to be attached and detached to and from each of the controller 110 and the sensor head 121. The optical fiber cable 130 is configured to include, for example, an optical fiber 131. The optical fiber 131 has an optical path length that is proportional to its length, and the length of the optical fiber 131 is set based on the distance to the measurement object T.

[0131] The swept light source 140 emits light while continuously changing its wavelength. That is, the wavelength of the light emitted from the swept light source 140 is continuously changing. The light emitted from the swept light source 140 is then supplied to the main interferometer 150 and the sub interferometer 160 via an optical branching unit 111, which is configured, for example, by an optical coupler. The swept light source 140 continuously controls the wavelength by changing the magnitude of the input current. A triangular wave or a sawtooth wave is typically used as the input current waveform.

[0132] The main interferometer 150 is connected to the optical fiber 131 of the optical fiber cable 130, and supplies light emitted from the wavelength swept light source 140 to the sensor head 121 via the optical fiber 131, and further guides the returning light from the sensor head 121 to the first photodiode 112.

[0133] Specifically, the light guided from the main interferometer 150 to the sensor head 121 is irradiated as measurement light onto the measurement object T via, for example, a collimator lens or an objective lens arranged in the sensor head 121. Then, the light reflected by the measurement object T returns to the sensor head 121.

[0134] Furthermore, a portion of the light guided from the main interferometer 150 to the sensor head 121 is reflected as reference light by, for example, a reference surface provided at the tip of the optical fiber 131. Then, the measurement light and the reference light interfere with each other to generate interference light (also referred to as a "main interference signal") corresponding to the optical path length difference between the measurement light and the reference light.

[0135] In this way, the main interferometer 150 is supplied with light projected from the swept light source 140, and generates a main interference signal based on the measurement light that is irradiated onto the measurement object T and reflected by the sensor head 121, and the reference light that follows an optical path that is at least partially different from that of the measurement light. Note that, because the main interferometer 150 is supplied with light projected from the swept light source and generates a main interference signal, the main interferometer 150 including the sensor head 121 can also be called the main interferometer.

[0136] The first photodiode 112 receives the main interference signal generated by the main interferometer 150 and converts it into an electrical signal. The electrical signal converted by the first photodiode 112 is, for example, a current signal.

[0137] The amplifier circuit 114 amplifies the electrical signal input from the first photodiode 112 with a predetermined gain (also referred to as "gain"). When a current signal is input from the first photodiode 112, the amplifier circuit 114 converts the current signal into a voltage signal (also referred to as "IV conversion") and amplifies the voltage signal. The amplified electrical signal is output to the AD conversion unit 181.

[0138] The sub-interferometer 160 receives light emitted from the wavelength swept light source 140, split by the optical splitter 111, and generates a sub-interference signal based on two beams of light traveling along optical paths with different optical lengths. Specifically, the first optical coupler 161 splits the light into two beams of light traveling along optical paths with different optical lengths, and the second optical coupler 162 then combines and interferes with the two beams to generate a sub-interference signal based on the difference in optical path length. The sub-interference signal propagates through an optical fiber 163 and is guided to the second photodiode 116. Meanwhile, the remaining port of the second optical coupler 162 is connected to an optical fiber equipped with a coreless fiber termination or to an attenuator.

[0139] The second photodiode 116 receives the secondary interference signal propagated through the optical fiber 163 of the secondary interferometer 160 and converts it into an electrical signal (hereinafter also referred to as a "secondary interferometer signal"). The electrical signal converted by the second photodiode 116 is, for example, a current signal.

[0140] The electrical signals output from the second photodiodes 116 may be amplified at a predetermined gain by an amplifier circuit (not shown). In this case, the amplifier circuit outputs the amplified electrical signals to the variable delay line 191.

[0141] The variable delay line 191 is configured to generate a variable delay amount. The variable delay line 191 of this embodiment corresponds to an example of the "variable delay amount generating section" of the present invention.

[0142] More specifically, the variable delay line 191 is configured to generate a delay in the time axis direction according to the variable delay amount in a sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and output the delay to the correction signal generation unit 171. The variable delay amount of the variable delay line 191 is generated according to a control signal input from a variable delay amount setting unit described later.

[0143] The variable delay line 191 is an electronic component that delays the propagation of an electrical signal and includes a component that allows the delay to be changed, such as a programmable delay line. Note that the electronic component of the variable delay line 191 is not limited to a programmable delay line, and may be any other electronic component that generates a changeable delay (delay) in the electrical signal according to a variable delay amount. Furthermore, the variable delay line 191 may have any structure, type, number, etc.

[0144] In this way, the variable delay line 191 generates a delay in the time axis direction according to the variable delay amount in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and outputs the signal to the correction signal generation unit 171. By outputting the sub-interferometer signal in which an electrical delay has been generated, the correction signal generation unit 171 can easily generate the correction signal, which is an electrical signal.

[0145] The correction signal generating unit 171 is configured to generate a correction signal (also referred to as a "K clock signal" or simply a "K clock") based on the secondary interference signal and the variable delay amount. The correction signal is a signal that corrects the sampling period of the primary interference signal generated by the primary interferometer 150. Since the secondary interference signal is nonlinear like the primary interference signal due to the nonlinearity of the wavelength during sweeping, the correction signal generating unit 171 can generate a correction signal, i.e., a K clock signal, for appropriately sampling and AD converting the analog signal of the primary interference signal by grasping the nonlinearity of the wavelength during sweeping based on the secondary interference signal.

[0146] In order for the correction signal generating unit 171 to generate an appropriate correction signal, it is necessary for the correction signal generating unit 171 to properly grasp the nonlinearity of the main interference signal received by the first photodiode 112. To this end, it is preferable to match the characteristics (nonlinearity) of the main interference signal and the sub-interference signal, in other words, to synchronize the main interference signal and the sub-interference signal in terms of time.

[0147] More specifically, the correction signal generating unit 171 is configured to generate a correction signal based on a delayed sub-interferometer signal. That is, the correction signal is generated based on a signal obtained by converting the sub-interferometer signal into an electrical signal and delaying it in the time axis direction. The delay is a time corresponding to the variable delay amount described above.

[0148] Furthermore, the correction signal generator 171 may generate a pulse signal as a correction signal based on a signal obtained by converting the secondary interference signal into an electrical signal and delaying the secondary interferometer signal in the time axis direction according to the variable delay amount described above. This makes it possible to easily synchronize the sampling timing of the primary interference signal.

[0149] The AD converter 181 is configured to sample the main interferometer signal, which is obtained by converting the main interference signal into an electrical signal, based on the correction signal and convert it into a digital signal. The main interference signal input to the AD converter 181 is an analog signal whose wave intervals are not equal. The AD converter 181 samples and AD-converts the analog signal of the main interference signal at a sampling period (sampling interval) based on the above-mentioned correction signal, i.e., the K clock signal, so that the wave intervals in the main interference signal become equal.

[0150] In this way, the AD conversion unit 181 converts the main interference signal into an electrical signal, and the main interferometer signal is sampled based on the correction signal and converted into a digital signal, thereby easily realizing a configuration in which the main interferometer signal is converted into a digital signal with a corrected sampling period.

[0151] The processing unit 118 is configured to calculate the distance to the measurement object T based on the main interference signal generated by the main interferometer 150 and the secondary interference signal generated by the secondary interferometer 160.

[0152] More specifically, the processing unit 118 is configured to calculate the distance to the measurement object T based on the main interference signal received by the first photodiode 112 and amplified by the amplifier circuit 114, and a correction signal generated based on the sub-interference signal received by the second photodiode 116 and the variable delay amount generated by the variable delay line 191.

[0153] Specifically, in the AD conversion unit 181, a nonlinear analog signal based on the main interference signal is converted into a digital signal at a sampling period corrected by a correction signal based on the sub-interference signal and a variable delay amount, and the processing unit 118 converts the digital signal into a frequency using FFT or the like, analyzes them, and calculates the distance value to the measurement object T.

[0154] The variable delay amount setting unit 195 is configured to set the variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a signal based on a digital signal of the reflected signal generated by the main interferometer and sampled based on the correction signal.

[0155] More specifically, the AD converter 181 converts the signal into a digital signal, and the processing unit 118 converts the digital signal into a frequency using FFT, and the resulting signal is input to the variable delay setting unit 195. The variable delay setting unit 195 is configured to set a variable delay based on this signal. The signal input to the variable delay setting unit 195 is, for example, a signal obtained by converting the digital signal of the main interference signal into a frequency using FFT, and a signal obtained by converting the digital signal of the reflected signal into a frequency using FFT. Alternatively, the signal input to the variable delay setting unit 195 may be a signal obtained by converting the digital signal of the main interference signal into a power spectrum for each measurement point (number of data points) using FFT, and a signal obtained by converting the digital signal of the reflected signal into a power spectrum for each measurement point (number of data points) using FFT. The variable delay set by the variable delay setting unit 195 is the variable delay generated by the variable delay line 191 described above.

[0156] Here, the reflected signal generated by the main interferometer 150 will be described.

[0157] Fig. 11 is a schematic diagram showing a specific example of a configuration for generating a reflected wave in the main interferometer 150. As shown in Fig. 11, the main interferometer 150 has a reflecting surface 126a that reflects light. Specifically, the sensor head 121 has an objective lens 126 that irradiates the measurement object T with light, and a collimating lens 127 that is arranged between the tip of the optical fiber 131 and the objective lens 126. The reflecting surface 126a is formed on the back surface of the objective lens 126 in the sensor head 121 (the surface of the sensor head 121 that faces the optical fiber 131).

[0158] The sensor head 121 may not have the collimator lens 127 between the tip of the optical fiber 131 and the objective lens 126, or may have only the collimator lens 127 without the objective lens 126. In this case, the reflecting surface may be formed on the collimator lens 127.

[0159] As described above, a portion of the light input to the sensor head 121 via the optical fiber 131 is irradiated onto the measurement object T as measurement light and reflected by the measurement object. Another portion of the light input to the sensor head 121 is reflected as reference light by a reference surface 131a provided at the tip of the optical fiber 131. A main interference signal (interference light) is generated based on the measurement light and the reference light, and the distance from the sensor head 121 to the measurement object T is detected as a peak in the signal frequency-converted by FFT.

[0160] Another part of the light input to the sensor head 121 via the optical fiber 131 is reflected by a reflecting surface 126a formed on the objective lens 126. Then, a reflected signal (interference light) is generated based on the reflected light reflected by the reflecting surface 126a and the above-mentioned reference light, and the position of the objective lens 126 in the sensor head 121, specifically the position of the reflecting surface 126a, is detected as a peak in the signal frequency-converted by FFT.

[0161] In this way, the reflected signal is generated when a portion of the light projected from the wavelength swept light source 140 and supplied to the main interferometer 150 is reflected by a member having the reflecting surface 126a formed in the main interferometer 150. This makes it possible to obtain a reflected signal from the reflecting surface of the main interferometer even when the measurement object T is not present and a main interference signal cannot be obtained, so that the variable delay amount can be set without preparing (readying) a measurement object.

[0162] The reflecting surface 126a formed on the objective lens 126 may be formed on the surface of the objective lens 126. The reflecting surface 126a may also be formed by applying a partial reflection coating to the objective lens 126, or may be formed by utilizing Fresnel reflection with a small reflectance (about 5% or less), for example.

[0163] The reflecting surface may also be formed on a component inside the sensor head 121. The component may be a part of the component that constitutes the sensor head 121, or may be a component that is separately arranged inside the housing for generating a reflected signal.

[0164] [Relationship between the peaks in the signal based on the digital signal of the main interference signal and the peaks in the signal based on the digital signal of the reflected signal and the variable delay amount] Fig. 12 is a diagram for explaining the relationship between the variable delay and peaks in a signal based on the digital signal of the main interference signal and the digital signal of the reflected signal. Fig. 13 is a diagram for explaining the relationship between the FFT conditions and peak half-widths in a signal based on the digital signal of the main interference signal and the digital signal of the reflected signal. Note that, in the following, unless explicitly stated, the digital signal of the reflected signal will be used for explanation, and explanations using the digital signal of the main interference signal will be omitted.

[0165] In conventional optical interferometer distance measuring sensors, when the length of the optical fiber in the optical fiber cable connecting the controller and the sensor head is changed, the optical path length of the light that propagates from the main interferometer to the sensor head via the optical fiber also becomes longer, which can cause a timing discrepancy between the main interference signal and reflected signal generated by the main interferometer and the correction signal generated by the secondary interferometer to correct the sampling period.

[0166] Furthermore, in conventional optical interferometric ranging sensors, if the distance from the sensor head to the object to be measured is long compared to the length of the optical fiber, the round-trip time of the light that is irradiated from the sensor head to the object to be measured, reflected by the object to be measured, and returned to the sensor head becomes long. Therefore, in this case too, a timing discrepancy may occur between the main interference signal and reflected signal generated by the main interferometer and the correction signal generated by the secondary interferometer to correct the sampling period.

[0167] Here, in a signal obtained by converting a digital signal into a frequency using FFT (hereinafter also referred to as a "frequency signal"), an ideal frequency signal without the timing deviation described above has a predetermined peak, for example, a peak intensity (peak signal intensity) of a predetermined value PI and a peak half-width of a predetermined value PHW, as shown in FIG.

[0168] As described above, in the optical interferometric ranging sensor 100 of this embodiment, the reflected signal and main interference signal generated by the main interferometer 150 are each converted into a digital signal by the AD conversion unit 181, and the digital signal is converted into a frequency signal using FFT by the processing unit 118, and these frequency signals are each input to the variable delay amount setting unit 195.

[0169] As described above, the optical interferometric ranging sensor 100 of this embodiment converts an analog signal based on the reflected signal or the main interference signal into a digital signal by correcting the sampling period using a correction signal based on the sub-interference signal and the variable delay amount in the AD conversion unit 181. Therefore, by setting an appropriate variable delay amount, it is possible to reduce (eliminate) the timing discrepancy, and the frequency signals of the digital signals of the reflected signal and the main interference signal will have peaks similar to the predetermined peaks in the ideal frequency signal shown in FIG.

[0170] More specifically, if the peak intensities of the frequency-converted signals of the digital signals of the reflected signal and the main interference signal are high, for example, if the peak intensities are equal to or greater than a predetermined value PI, it can be determined that the set variable delay amount is appropriate. In other words, the peak intensities of the frequency-converted signals of the digital signals of the reflected signal and the main interference signal are an indicator of an appropriate variable delay amount.

[0171] Furthermore, if the peak half-width in the frequency-converted signals of the digital signals of the reflected signal and the main interference signal is small (narrow), for example, the peak half-width is less than or approximately equal to the predetermined value PHW, the set variable delay amount can be determined to be appropriate. In other words, the peak half-width in the frequency-converted signals of the digital signals of the reflected signal and the main interference signal is an index of an appropriate variable delay amount. Note that the peak half-width may be generalized as an index of an appropriate variable delay amount, and a width of a predetermined value relative to the peak value (hereinafter also referred to as "peak predetermined value width"). In this case, the predetermined value may be half the value of the peak value, or may be, for example, 1 / e, 1 / e 2 Similarly, when the peak half width is used, if the peak predetermined value width is small (narrow), for example, the peak predetermined value width is less than or approximately the same as a predetermined value, the set variable delay amount can be determined to be appropriate.

[0172] As described above, in the optical interferometric ranging sensor 100 of this embodiment, the variable delay amount setting unit 195 sets the variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on a correction signal and a peak in a signal based on a digital signal of the reflected signal generated by the main interferometer and sampled based on a correction signal.

[0173] In this way, by using at least one of the peaks in the signal based on the digital signal of the main interference signal sampled based on the correction signal and the peaks in the signal based on the digital signal of the reflected signal generated by the main interferometer and sampled based on the correction signal, it is possible to set a variable delay amount that reduces a timing shift that may occur between the main interference signal, the reflected signal, and the secondary interference signal. Here, by using the peaks in the signal based on the digital signal of the reflected signal sampled based on the correction signal, it is possible to set a variable delay amount even when the measurement object T is not present. Furthermore, by using the peaks in the signal based on the digital signal of the main interference signal sampled based on the correction signal, it is possible to set a variable delay amount that reduces a timing shift that may occur due to the round-trip time it takes for light to travel that distance when the distance from the sensor head 121 to the measurement object T is long compared to the length of the optical fiber 131. Therefore, the signal generated by the main interferometer can be sampled at an appropriate timing using the correction signal based on the secondary interference signal and the variable delay amount, and the distance to the measurement object T can be measured with high accuracy.

[0174] Furthermore, the variable delay amount setting unit 195 sets the variable delay amount based on at least one of the peak intensity of the signal based on the digital signal of the main interference signal and the peak intensity of the signal based on the digital signal of the reflected signal, thereby making it possible to easily set the variable delay amount that reduces a timing difference that may occur between the main interference signal, the reflected signal, and the secondary interference signal.

[0175] Furthermore, the variable delay amount setting unit 195 sets the variable delay amount based on at least one of the predetermined peak value width in the signal based on the digital signal of the main interference signal and the predetermined peak value width in the signal based on the digital signal of the reflected signal, thereby making it possible to easily set the variable delay amount that reduces a timing difference that may occur between the main interference signal, the reflected signal, and the secondary interference signal.

[0176] Furthermore, in a signal obtained by converting the digital signals of the reflected signal and the main interference signal into a power spectrum for each number of measurement points (number of data points) using an FFT, the number of samples (also referred to as the "number of measurement points" or "number of data points") included in the range of the predetermined peak value width in the signal depends on the FFT conditions, such as whether or not zero-padding is used, whether or not a window function is used, and the type of window function. In other words, once the FFT conditions are determined, ideally, the number of measurement points included in the range of the predetermined peak value width in the signal converted into a power spectrum for each number of measurement points will be a predetermined number (hereinafter also referred to as the "predetermined number"). Zero-padding is a common technique for improving frequency resolution by adding zeros to measurement data. For example, if the number of measurement points is doubled by adding the same number of zeros as the number of measurement points, the frequency resolution will be doubled. In this application, "Npad" (Npad is a positive integer) is used as a coefficient to determine how many times the number of actual measurement points should be multiplied by zero-padding. Specifically, when Npad = 2, 5,000 zero data points are added to the 5,000 measurement points, resulting in 10,000 points. Also, when Npad = 3, 10,000 zero data points are added to the 5,000 measurement points, resulting in 15,000 points. Therefore, the number of measurement points when zero-padded with the actual number of measurement points N is N x Npad.

[0177] For example, as shown by the dashed-dotted line in Figure 13, when an ideal noise-free sine wave is converted into a power spectrum for each measurement point using an FFT without a window function, i.e., a rectangular window with no zero-padding, the number of measurement points included in the range of the predetermined peak value of the signal, for example, the peak half-width, is one. Also, as shown by the solid line in Figure 13, when the above-mentioned sine wave is converted into a power spectrum for each measurement point using an FFT with a general window function, for example, a Hamming window with no zero-padding, the number of measurement points included in the range of the peak half-width of the signal is two, due to the specification of the window function itself. Note that, even when a window function other than a Hamming window, such as a Hann window or a Gaussian window, is used in the FFT, the number of measurement points included in the range of the peak half-width is two, with some exceptions. Furthermore, as shown by the dashed line in Fig. 13, when the above-mentioned sine wave is converted into a power spectrum for each measurement point using FFT with a Hamming window and zero padding (Npad=2), the number of measurement points included in the range of the peak half-width of the signal is 2 due to the specification of the window function itself, and 4 because the number of data points is doubled by zero padding. Note that in the graph in Fig. 13, the intensity values ​​on the vertical axis are normalized.

[0178] In this way, when the digital signals of an ideal reflected signal and a main interference signal are converted into a power spectrum for each measurement point using an FFT that assumes a window function such as a Hamming window (with some exceptions), the number of measurement points included in the range of the peak half-width of the signal will be two, and when the signals are further converted into a power spectrum for each measurement point using an FFT that performs zero padding, the number of measurement points included in the range of the peak half-width of the signal can be expressed as 2 × Npad.

[0179] In reality, due to the influence of jitter, noise, and the like during data acquisition, the number of measurement points included in the range of the peak half-width in the signal converted into a power spectrum for each measurement point may expand by about one point on either side. Taking this into consideration, if the number of measurement points included in the range of the peak half-width in the signal converted into a power spectrum for each measurement point is less than 2×Npad+2, the digital signals of the reflected signal and the main interference signal can be considered ideal, that is, with small timing deviations. Furthermore, by extending this to the specified peak width, if the number of measurement points included in the range of the specified peak width in the signal converted into a power spectrum for each measurement point is less than a specified number, the digital signals of the reflected signal and the main interference signal can be considered to be in an ideal state with small timing deviations.

[0180] In this embodiment, in Fig. 12 and Fig. 13, the peak half width is the full width at half maximum, but this is not limited thereto. The peak half width may be the half width at half maximum. Similarly, the peak predetermined value width may be the full width at half maximum or the half width at half maximum.

[0181] [Variable delay setting procedure] Fig. 14 is a flowchart for explaining an example of a processing procedure performed by the controller 110 in an embodiment. Fig. 15 is a flowchart for explaining another example of a processing procedure performed by the controller 110 in an embodiment. Fig. 16 is a flowchart for explaining yet another example of a processing procedure performed by the controller 110 in an embodiment.

[0182] In the following explanation, it is assumed that values ​​are stored in the maximum number max (max is an integer greater than or equal to 2) and max delay amounts Dn (n=1, 2, ..., max) and that these values ​​are stored in advance in a storage means such as a memory.

[0183] (Example 1: Processing procedure of variable delay amount setting process S210) In the variable delay amount setting process S210, the variable delay amount is set based on the maximum value among the multiple peak intensities.

[0184] 14, first, the variable delay amount setting unit 195 sets "1" to the subscript n (S211). The subscript n indicates one of the max delay amounts. Each delay amount Dn stores a value representing a different delay time, and the values ​​are arranged, for example, in ascending or descending order.

[0185] Next, the variable delay amount setting unit 195 reads out the delay amount Dn corresponding to the subscript n from among the max delay amounts stored in advance, and sets the read delay amount Dn as the variable delay amount (S212). Specifically, the variable delay amount setting unit 195 generates a control signal based on the delay amount Dn read out in step S212, and outputs the control signal to the variable delay line 191. This sets the variable delay amount generated by the variable delay line 191.

[0186] Next, the wavelength swept light source 140 emits light, and the reflected signal generated by the main interferometer 150 is converted into a digital signal by the AD converter 181, and a frequency signal is obtained by converting the digital signal using FFT by the processor 118 (S213). When the reflected signal is converted into a digital signal in step S213, the sampling period is corrected by a correction signal based on the variable delay amount set in step S212. Similarly, in the case of the main interference signal, whose description is omitted, the sampling period is corrected by a correction signal based on the variable delay amount set in step S212.

[0187] Next, the variable delay amount setting unit 195 analyzes the frequency signal obtained in step S213 to detect peak intensity, and stores the value of the detected peak intensity in the intensity In corresponding to the subscript n (S214). The stored value of the intensity In is stored in a storage means such as a memory. This allows the value of the peak intensity when the delay amount Dn is set to be obtained.

[0188] Next, the variable delay amount setting unit 195 determines whether the subscript n is equal to the maximum number max (S215).

[0189] If the result of the determination in step S215 is that the subscript n is not equal to the maximum number max, the variable delay amount setting unit 195 adds "1" to the subscript n (step S216) and returns to step S212. Then, steps S212 to S215 are repeated until the subscript n becomes equal to the maximum number max.

[0190] On the other hand, if the result of the determination in step S215 is that the subscript n is equal to the maximum number max, the digital signals of the reflected signals have been converted into frequency signals using FFT for all max delay amounts, and the peak intensities of the frequency signals have been detected. In this case, the maximum of the max intensities In detected and stored in S214 is considered to be the peak intensity of the frequency signal converted using FFT for the digital signal of the reflected signal with the smallest timing deviation. Therefore, the variable delay amount setting unit 195 searches for the maximum intensity In from the stored max intensities In (S217).

[0191] Then, the variable delay amount setting unit 195 reads out the delay amount Dn corresponding to the subscript n of the intensity In found in step S217, and sets the read delay amount Dn as the variable delay amount (S218). Specifically, similar to step S212, the variable delay amount setting unit 195 generates a control signal based on the delay amount Dn read out in step S217, and outputs the control signal to the variable delay line 191. As a result, the variable delay amount generated by the variable delay line 191 is set to a delay amount at which the peak intensity becomes maximum in the frequency signal converted from the digital signal of the reflected signal.

[0192] In this way, the variable delay amount setting unit 195 sets the variable delay amount based on at least one of the maximum value of peak intensities in the signal based on the digital signals of the multiple main interference signals and the maximum value of peak intensities in the signal based on the digital signals of the multiple reflected signals. As a result, the variable delay amount is set based on the maximum value of the multiple peak intensities, so it is possible to set a variable delay amount that further reduces timing deviation that may occur between the main interference signal, the reflected signal, and the secondary interference signal, compared to when the variable delay amount is set based on the peak intensities in the signal based on the digital signal of one main interference signal or the peak intensities in the signal based on the digital signal of one reflected signal.

[0193] (Example 2: Processing procedure of variable delay amount setting process S230) In the variable delay amount setting process S230, the variable delay amount is set based on the minimum value among a plurality of peak predetermined value widths. In the example shown in Fig. 15, a case will be described in which the peak half width is used as the peak predetermined value width.

[0194] Note that steps S231 to S233 of the variable delay amount setting process S230 are the same or substantially the same as steps S211 to S213 of the variable delay amount setting process S210 described above, and therefore a description thereof will be omitted.

[0195] 15, after step S233, the variable delay amount setting unit 195 analyzes the frequency signal obtained in step S233 to detect a peak (S234). The detected peak is the peak whose peak intensity is the maximum value in the frequency signal.

[0196] Next, the variable delay amount setting unit 195 calculates the peak half width for the peak detected in step S234, and stores the calculated value of the peak half width in the half width FWHMn corresponding to the subscript n (S235). The calculated peak half width is, for example, the full width at half maximum (FWHM). The stored value of the half width FWHMn is stored in a storage means such as a memory. This allows the value of the peak half width when the delay amount Dn is set to be obtained.

[0197] Next, the variable delay amount setting unit 195 determines whether the subscript n is equal to the maximum number max (S236).

[0198] If the result of the determination in step S236 is that the subscript n is not equal to the maximum number max, the variable delay amount setting unit 195 adds "1" to the subscript n (step S237) and returns to step S232. Then, steps S232 to S236 are repeated until the subscript n becomes equal to the maximum number max.

[0199] On the other hand, if the result of the determination in step S236 is that the subscript n is equal to the maximum number max, then for all max delay amounts, the digital signal of the reflected signal has been converted into a frequency signal using FFT, the peaks of the frequency signal have been detected, and the peak half-widths have been calculated. In this case, the one that shows the smallest value among the max half-widths FWHMn calculated and stored in step S235 is considered to be the peak half-width of the frequency signal converted using FFT for the digital signal of the reflected signal with the smallest timing shift. Therefore, the variable delay amount setting unit 195 searches for the half-width FWHMn that shows the smallest value from the stored max half-widths FWHMn (S238).

[0200] Then, the variable delay amount setting unit 195 reads out the delay amount Dn corresponding to the subscript n of the half width FWHMn found in step S238, and sets the read delay amount Dn as the variable delay amount (S239). Specifically, similar to step S232, the variable delay amount setting unit 195 generates a control signal based on the delay amount Dn read out in step S238, and outputs the control signal to the variable delay line 191. As a result, the variable delay amount generated by the variable delay line 191 is set to a delay amount at which the peak half width is minimum in the frequency signal converted from the digital signal of the reflected signal.

[0201] In this way, the variable delay amount setting unit 195 sets the variable delay amount based on at least one of the minimum value of the predetermined peak value widths in the signal based on the digital signals of the multiple main interference signals and the minimum value of the predetermined peak value widths in the signal based on the digital signals of the multiple reflected signals. As a result, the variable delay amount is set based on the minimum value of the multiple predetermined peak value widths, so it is possible to set a variable delay amount that further reduces a timing shift that may occur between the main interference signal, the reflected signal, and the secondary interference signal, compared to when the variable delay amount is set based on the predetermined peak value width in the signal based on the digital signal of one main interference signal or the predetermined peak value width in the signal based on the digital signal of one reflected signal.

[0202] (Example 3: Processing procedure of variable delay amount setting process S250) In the variable delay setting process S250, the variable delay is set so that the number of measurement points included in the peak predetermined value width of the frequency signal is less than a predetermined number. In the example shown in Fig. 16, the peak half width is used as the peak predetermined value width, and 2 × Npad + 2 is used as the predetermined number.

[0203] Note that steps S251 to S252 of the variable delay amount setting process S250 are the same or substantially the same as steps S231 to S232 of the variable delay amount setting process S230 described above, and therefore a description thereof will be omitted.

[0204] 16, after step S252, the wavelength swept light source 140 emits light, and the reflected signal generated by the main interferometer 150 is converted into a digital signal by the AD converter 181, and the signal is converted into a power spectrum for each measurement point (number of data points) using FFT by the processor 118 (S253). When the reflected signal in step S253 is converted into a digital signal, the sampling period is corrected by a correction signal based on the variable delay amount set in step S252. Similarly, in the case of the main interference signal, whose description is omitted, the sampling period is corrected by a correction signal based on the variable delay amount set in step S252.

[0205] Next, the variable delay amount setting unit 195 analyzes the signal converted into the power spectrum for each measurement point obtained in step S252 and detects a peak (S254). The detected peak is the peak in the signal that exhibits the maximum peak intensity.

[0206] Next, the variable delay amount setting unit 195 calculates the peak half width for the peak detected in step S254, and stores the number of measurement points included in the calculated range of the peak half width in the half width FWHMn corresponding to the subscript n (S255). The calculated peak half width is, for example, the full width at half maximum (FWHM). The half width FWHMn containing the number of measurement points is stored in a storage means such as a memory. This allows the number of measurement points included in the range of the peak half width when the delay amount Dn is set to be obtained.

[0207] Next, the variable delay amount setting unit 195 determines whether the number of measurement points included in the range of the calculated peak half width stored in the half width FWHMn in step S255 is less than 2×Npad+2 (half width FWHMn<2×Npad+2) (S256).

[0208] If the result of the determination in step S256 is that the number of measurement points included in the range of the peak half width stored in the half width FWHMn is not less than 2×Npad+2, that is, the number of measurement points of the half width FWHMn is 2×Npad+2 or more (half width FWHMn≧2×Npad+2), the variable delay amount setting unit 195 determines whether the subscript n is equal to the maximum number max (S257).

[0209] If the result of the determination in step S257 is that the subscript n is not equal to the maximum number max, the variable delay amount setting unit 195 adds "1" to the subscript n (step S258) and returns to step S252. Then, steps S252 to S257 or step S258 are repeated until the number of measurement points included in the range of the peak half width stored in the half width FWHMn becomes less than 2×Npad+2, or until the subscript n becomes equal to the maximum number max.

[0210] On the other hand, if the result of the determination in step S257 is that the subscript n is equal to the maximum number max, then for all max delay amounts, there is no delay amount for which the number of measurement points included in the range of the peak half width stored in the half width FWHMn is less than 2×Npad+2. In this case, the variable delay amount setting process S250 is terminated. Then, since there is likely to be some cause in the hardware, such as the fiber being too long or the measurement target T being placed too far away, the controller 110 displays or outputs an error.

[0211] On the other hand, if the result of the determination in step S256 is that the number of measurement points included in the range of the peak half-width stored in the half-width FWHMn is less than 2×Npad+2, the number of measurement points for the half-width FWHMn stored in the most recent step S255 is considered to be the number of measurement points included in the range of the peak half-width of the signal converted into a power spectrum for each measurement point using FFT for a digital signal of a reflected signal whose timing shift is less than a predetermined value. Therefore, the variable delay setting unit 195 reads out the delay amount Dn corresponding to the subscript n of the half-width FWHMn calculated and stored in the most recent step S255, and sets the read delay amount Dn as the variable delay amount (S259). Specifically, as in step S252, the variable delay setting unit 195 generates a control signal based on the delay amount Dn read out in step S259 and outputs the control signal to the variable delay line 191. As a result, the variable delay amount generated by the variable delay line 191 is set to a delay amount such that the peak half width is less than a predetermined value in the frequency signal converted from the digital signal of the reflected signal.

[0212] In this way, the variable delay amount setting unit 195 sets the variable delay amount so that at least one of the number of measurement points included in the predetermined peak value width in the signal based on the digital signal of the main interference signal and the number of measurement points included in the predetermined peak value width in the signal based on the digital signal of the reflected signal is less than a predetermined number. This makes it possible to easily set the variable delay amount that reduces timing deviations that may occur between the main interference signal / reflected signal and the secondary interference signal.

[0213] The order of the sequences and flowcharts described in this embodiment may be changed as long as no contradiction occurs in the processing.

[0214] Furthermore, the processing described in this embodiment may be executed, for example, at the initial setting when the controller is powered on, or may be executed every time the distance to the measurement target T is measured.

[0215] Furthermore, the variable delay amount is not limited to being set by the procedure described in this embodiment. In addition to the above, the following procedure for setting the variable delay amount is also possible. For example, a peak corresponding to the position of the reflecting surface formed on the sensor head 121 is detected in a signal obtained by distance-transforming the digital signal of the reflected signal using FFT. Since the position of the peak in the digital signal of the reflected signal also changes when the length of the optical fiber 131 changes, the position of this peak may be linked to the length of the optical fiber 131 in advance, the length of the optical fiber 131 may be determined based on the position of the peak in the digital signal of the reflected signal, and the variable delay amount may be set based on the determined length of the optical fiber 131. Alternatively, the user may select one of a plurality of predetermined variable delay amounts based on the length of the optical fiber 131 and set the selected variable delay amount. Alternatively, the length of the optical fiber 131, the distance from the sensor head 121 to the measurement target T, and the variable delay amount may be linked in advance. The user may input the length of the optical fiber 131 and the approximate distance to the measurement target T, and set the variable delay amount based on the input length of the optical fiber 131 and the approximate distance to the measurement target T. Also, a dedicated ROM (Read Only Memory) specific to the length of the optical fiber 131 may be inserted into the controller 110, and a value read from the dedicated ROM may be set as the variable delay amount. Furthermore, a frequency signal may be displayed in the digital signal of the reflected signal on a display or other display means, and the user may select or input and set the variable delay amount by viewing the peaks of several frequency signals each with a different variable delay amount.

[0216] In the present embodiment, an example has been shown in which the optical interferometric ranging sensor 100 includes a controller 110 and an optical fiber cable including one optical fiber connecting one sensor head to the controller 110, but the present invention is not limited to this. The optical interferometric ranging sensor may also include a controller and an optical fiber cable including the same number of optical fibers as the number of sensor heads, which is connected to two or more sensor heads. For simplicity of explanation, the following describes a configuration in which the optical interferometric ranging sensor includes a controller and an optical fiber cable including two optical fibers connected to each of two sensor heads.

[0217] [Configuration of optical interferometric distance measuring sensor when connected to two sensor heads] Fig. 17 is a schematic diagram showing the outline of the configuration of an optical interferometric distance measuring sensor when connected to two sensor heads. In Fig. 17, the same or similar components as those in the optical interferometric distance measuring sensor 100 shown in Fig. 10 are denoted by the same or similar reference numerals, and their description will be omitted as appropriate. Furthermore, similar effects and advantages resulting from the same configuration as the optical interferometric distance measuring sensor 100 shown in Fig. 10 will not be mentioned again and again.

[0218] 17, the optical interferometric distance measuring sensor 101 includes a controller 110 and an optical fiber cable 130 that connects the controller 110 to the sensor head 121 and the sensor head 122. The optical fiber cable 130 shown in FIG. 17 differs from the optical fiber cable 130 shown in FIG. 10 in that it further includes an optical fiber 132. The controller 110 shown in FIG. 17 also differs from the controller 110 shown in FIG. 10 in that the main interferometer 150 includes a first main interferometer 151 and a second main interferometer 152, and further includes a first photodiode 113, an amplifier circuit 115, a variable delay line 192, a correction signal generator 172, and an AD converter 182.

[0219] The optical fiber cable 130 includes an optical fiber 131 and an optical fiber 132. The optical fiber cable 130 is detachable from the controller 110 and the sensor head 121 and the sensor head 122, i.e., configured to be attachable and detachable. The optical fiber 131 has a length L1, and the optical fiber 132 has a length L2. The length L1 of the optical fiber 131 is set based on the distance to the measurement object T1, and the length L2 of the optical fiber 132 is set based on the distance to the measurement object T2. The measurement object T2 is assumed to be an object located at a different distance from the measurement object T1, i.e., a farther distance in the example shown in FIG. 17 . Therefore, the length L2 of the optical fiber 132 is longer than the length L1 of the optical fiber 131 (length L2>length L1).

[0220] The main interferometer 150 has two optical paths (two channels), and is configured to include a first main interferometer 151 and a second main interferometer.

[0221] The first main interferometer 151 is connected to the optical fiber 131 of the optical fiber cable 130, and supplies light emitted from the wavelength swept light source 140 to the sensor head 121 via the optical fiber 131, and further guides the returning light from the sensor head 121 to the first photodiode 112.

[0222] Specifically, the light guided from the first main interferometer 151 to the sensor head 121 is irradiated as measurement light onto the measurement object T via, for example, a collimator lens or an objective lens arranged in the sensor head 121. Then, the light reflected by the measurement object T returns to the sensor head 121.

[0223] Furthermore, a portion of the light guided from the first main interferometer 151 to the sensor head 121 is reflected as reference light by, for example, a reference surface provided at the tip of the optical fiber 131. Then, the measurement light and the reference light interfere with each other to generate interference light (also referred to as a "main interference signal") corresponding to the optical path length difference between the measurement light and the reference light.

[0224] In this way, the first main interferometer 151 is supplied with light projected from the swept light source 140 and generates a main interference signal based on the measurement light that is irradiated onto the measurement object T and reflected by the sensor head 121, and the first reference light that follows an optical path at least partially different from that of the measurement light. Note that, since the first main interferometer 151 is supplied with light projected from the swept light source and generates a main interference signal, the first main interferometer 151 including the sensor head 121 can also be referred to as the first main interferometer. Similar to the main interferometer 150 shown in Fig. 10 , the first main interferometer also generates a reflection signal based on the light reflected by the reflecting surface and the reference light.

[0225] The second main interferometer 152 is connected to the optical fiber 132 of the optical fiber cable 130, and supplies light emitted from the wavelength swept light source 140 to the sensor head 122 via the optical fiber 132, and further guides the returning light from the sensor head 122 to the first photodiode 113.

[0226] Specifically, the light guided from the second main interferometer 152 to the sensor head 122 is irradiated as measurement light onto the measurement object T via, for example, a collimator lens or an objective lens arranged in the sensor head 122. Then, the light reflected by the measurement object T returns to the sensor head 122.

[0227] Furthermore, a portion of the light guided from the second main interferometer 152 to the sensor head 122 is reflected as reference light by, for example, a reference surface provided at the tip of the optical fiber 132. Then, the measurement light and the second reference light interfere with each other, generating interference light (also referred to as a "main interference signal") corresponding to the optical path length difference between the measurement light and the reference light.

[0228] In this way, the second main interferometer 152 is supplied with light projected from the swept light source 140 and generates a main interference signal based on the measurement light that is irradiated onto the measurement object T and reflected by the second sensor head 122, and the reference light that follows an optical path at least partially different from that of the measurement light. Note that, since the second main interferometer 152 is supplied with light projected from the swept light source and generates a main interference signal, the second main interferometer 152 including the sensor head 122 can also be referred to as the second main interferometer. Similar to the main interferometer 150 shown in Fig. 10 , the second main interferometer also generates a reflection signal based on the light reflected by the reflecting surface and the reference light.

[0229] The first photodiode 112 receives the main interference signal generated by the first main interferometer 151 and converts it into an electrical signal. The first photodiode 113 receives the main interference signal generated by the second main interferometer 152 and converts it into an electrical signal.

[0230] The amplifier circuit 115 amplifies the electrical signal input from the first photodiode 113 with a predetermined gain. When a current signal is input from the first photodiode 113, the amplifier circuit 115 converts the current signal into a voltage signal and amplifies it. The amplified electrical signal is output to the AD conversion unit 182.

[0231] The second photodiode 116 receives the secondary interference signal propagated through the optical fiber 163 of the secondary interferometer 160 and converts it into a secondary interferometer signal, which is an electrical signal. The second photodiode 116 outputs the converted electrical signal to the variable delay line 191 and the variable delay line 192. When the electrical signal output from the second photodiode 116 is branched to the variable delay line 191 and the variable delay line 192, impedance matching may be performed between the second photodiode 116 and the variable delay line 191 and the variable delay line 192 to prevent reflection.

[0232] The variable delay line 192 is configured to generate a variable delay amount. The variable delay line 192 of this embodiment corresponds to an example of the "variable delay amount generating section" of the present invention.

[0233] More specifically, the variable delay line 192 is configured to generate a delay in the time axis direction according to the variable delay amount in a sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and output the delay to the correction signal generation unit 171. The variable delay amount of the variable delay line 192 is generated in accordance with a control signal input from the variable delay amount setting unit 195. Therefore, the variable delay amount generated by the variable delay line 192 may be the same as the variable delay amount generated by the variable delay line 191 in some cases, or may be different.

[0234] The variable delay line 192 is an electronic component that delays the propagation of an electrical signal and is configured to include a component that allows the delay to be changed, such as a programmable delay line. Note that the electronic component of the variable delay line 191 is not limited to a programmable delay line, and may be any other electronic component that generates a changeable delay (delay) in the electrical signal according to the variable delay amount. Furthermore, the structure, type, number, etc. of the variable delay line 192 are not limited.

[0235] The correction signal generating unit 172 is configured to generate a correction signal (also referred to as a "K clock signal" or simply a "K clock") based on the secondary interference signal and the variable delay amount of the variable delay line 192. The correction signal is a signal that corrects the sampling period of the main interference signal generated by the second main interferometer 152. The secondary interference signal is nonlinear like the main interference signal of the second main interferometer 152 due to the nonlinearity of the wavelength during sweeping. Therefore, the correction signal generating unit 172 can generate a correction signal, i.e., a K clock signal, for appropriately sampling and AD converting the analog signal of the main interference signal of the second main interferometer 152 by grasping the nonlinearity of the wavelength during sweeping based on the secondary interference signal.

[0236] In order for the correction signal generating unit 172 to generate an appropriate correction signal, the correction signal generating unit 172 needs to properly grasp the nonlinearity of the main interference signal of the second main interferometer 152 received by the first photodiode 113. For this purpose, it is preferable to match the characteristics (nonlinearity) of the main interference signal and the sub-interference signal of the second main interferometer 152.

[0237] More specifically, the correction signal generating unit 172 is configured to generate a correction signal based on a delayed sub-interferometer signal. That is, the correction signal is generated based on a signal obtained by converting the sub-interferometer signal into an electrical signal and delaying it in the time axis direction. The delay is a time corresponding to the variable delay amount of the variable delay line 192 described above.

[0238] In addition, the correction signal generating unit 172 may generate a pulse signal that is a correction signal based on a signal in which a delay corresponding to the variable delay amount of the variable delay line 192 is generated in the time axis direction in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal.

[0239] The AD conversion unit 182 is configured to sample the main interferometer signal, obtained by converting the main interference signal of the second main interferometer 152 into an electric signal, based on the correction signal of the correction signal generation unit 172, and convert the signal into a digital signal. The main interference signal of the second main interferometer 152 that is input to the AD conversion unit 182 is an analog signal in which the wave intervals are not equal. The AD conversion unit 182 samples and AD converts the analog signal of the main interference signal at a sampling period (sampling interval) corrected based on the correction signal of the correction signal generation unit 172, i.e., the K clock signal, so that the wave intervals in the main interference signal become equal.

[0240] The variable delay amount setting unit 195 is configured to set the variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a signal based on a digital signal of the reflected signal generated by the main interferometer and sampled based on the correction signal.

[0241] The variable delay amount setting unit 195 receives as input a signal that has been converted into a digital signal by the AD conversion unit 181 and then converted into a frequency by the processing unit 118 using FFT, and a signal that has been converted into a digital signal by the AD conversion unit 182 and then converted into a frequency by the processing unit 118 using FFT. The variable delay amount setting unit 195 is configured to set the variable delay amount of the variable delay line 191 based on the signal that has been converted into a digital signal by the AD conversion unit 181 and then converted into a frequency by the processing unit 118 using FFT. The variable delay amount setting unit 195 is also configured to set the variable delay amount of the variable delay line 192 based on the signal that has been converted into a digital signal by the AD conversion unit 182 and then converted into a frequency by the processing unit 118 using FFT.

[0242] The signals input to the variable delay amount setting unit 195 are a signal obtained by converting the digital signal of the main interference signal of the first main interferometer 151 into a frequency by FFT, a signal obtained by converting the digital signal of the reflected signal of the first main interferometer 151 into a frequency by FFT, a signal obtained by converting the digital signal of the main interference signal of the second main interferometer 152 into a frequency by FFT, and a signal obtained by converting the digital signal of the reflected signal of the second main interferometer 152 into a frequency by FFT. Alternatively, the signal input to the variable delay amount setting unit 195 may be a signal obtained by converting the digital signal of the main interference signal of the first main interferometer 151 into a power spectrum for each measurement point (number of data points) using FFT, a signal obtained by converting the digital signal of the reflected signal of the first main interferometer 151 into a power spectrum for each measurement point (number of data points) using FFT, a signal obtained by converting the digital signal of the main interference signal of the second main interferometer 152 into a power spectrum for each measurement point (number of data points) using FFT, and a signal obtained by converting the digital signal of the reflected signal of the second main interferometer 152 into a power spectrum for each measurement point (number of data points) using FFT. Furthermore, the variable delay amounts set by the variable delay amount setting unit 195 are two variable delay amounts: a variable delay amount generated by the variable delay line 191 and a variable delay amount generated by the variable delay line 192.

[0243] The variable delay amount of the variable delay line 191 and the variable delay amount of the variable delay line 192 may be set by executing one of the variable delay amount setting processes shown in Fig. 14 to Fig. 16. Furthermore, the variable delay amount of the variable delay line 191 and the variable delay amount of the variable delay line 192 may be set in parallel or in series in a predetermined order.

[0244] In this way, even when the main interferometer 150 has two optical paths (two channels) and is connected to the sensor head 121 by an optical fiber cable 130 including two optical fibers 131 and 132, it is possible to set the variable delay amount of the variable delay line 191 to reduce the timing difference that may occur between the main interference signal and reflected signal of the first main interferometer 151 and the secondary interference signal, and the variable delay amount of the variable delay line 192 to reduce the timing difference that may occur between the main interference signal and reflected signal of the second main interferometer 152 and the secondary interference signal.

[0245] [Modified interferometer] In the above-described embodiment, the optical interferometer ranging sensors 100, 101 use a Fizeau interferometer in the main interferometer 150, which generates reference light by using the tip of an optical fiber as a reference surface, but the interferometer is not limited to this.

[0246] FIG. 18 shows variations of an interferometer that generates interference light using measurement light and reference light. In FIG. 18(a), interference light is generated based on the optical path difference between reference light, whose reference surface is the tip (end face) of an optical fiber, and measurement light that is irradiated from the sensor head and reflected by the measurement target T, in the optical path passing through the main interferometer 150. This is the configuration of the main interferometer 150 of the optical interferometer distance measuring sensors 100 and 101 according to the above-described embodiments (Fizeau interferometer), and the reference surface may be configured to reflect light due to the difference in refractive index between the optical fiber and air (Fresnel reflection). Alternatively, a reflective film may be coated on the tip of the optical fiber, or an anti-reflective coating may be applied to the tip of the optical fiber and a separate reflective surface such as a lens surface may be disposed on the tip.

[0247] 18(b), the optical path passing through the main interferometer 150 is formed with a measurement optical path Lm that guides measurement light to the measurement object T and a reference optical path Lr that guides reference light, and a reference surface is disposed at the end of the reference optical path Lr (a Michelson interferometer). The reference surface may be formed by coating a reflective film on the tip of an optical fiber, or by applying an anti-reflective coating to the tip of an optical fiber and disposing a separate mirror or the like on the tip. In this configuration, interference light is generated by providing an optical path length difference between the measurement optical path Lm and the reference optical path Lr.

[0248] 18(c), the optical path passing through the main interferometer 150 is formed with a measurement optical path Lm that guides measurement light to the measurement object T and a reference optical path Lr that guides reference light, and a balance detector is disposed in the reference optical path Lr (Mach-Zehnder interferometer). In this configuration, interference light is generated by providing an optical path length difference between the measurement optical path Lm and the reference optical path Lr.

[0249] As described above, the main interferometer is not limited to the Fizeau interferometer described in the embodiments, but may be, for example, a Michelson interferometer or a Mach-Zehnder interferometer. Any interferometer, or a combination thereof, or other configuration, may be used as long as it is possible to generate interference light by setting the optical path length difference between the measurement light and the reference light. Similarly, the secondary interferometer (not shown) may be a Fizeau interferometer, a Michelson interferometer, or a Mach-Zehnder interferometer. Any interferometer, or a combination thereof, or other configuration, may be used as long as it is possible to generate interference light by setting the optical path length difference between the measurement light and the reference light.

[0250] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. The present invention may be modified or improved without departing from its spirit, and equivalents are also included within the scope of the present invention. In other words, designs modified by those skilled in the art as appropriate are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention. For example, the elements of the embodiments, their arrangement, materials, conditions, shape, size, etc., are not limited to those illustrated and can be modified as appropriate. Furthermore, the embodiments are merely examples, and partial substitution or combination of the configurations shown in different embodiments is, of course, possible. These are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention.

[0251] [Appendix 1] A controller (110) connected via an optical fiber cable (130) to a sensor head (121) that irradiates a measurement object (T) with light, a light source (140) that emits light while changing the wavelength; a main interferometer (150) connected to the sensor head (121) via an optical fiber (131) included in the optical fiber cable (130), the main interferometer (150) receiving light projected from the light source (140) and generating a main interference signal based on measurement light irradiated onto the measurement target (T) and reflected by the sensor head (121) and reference light following an optical path at least partially different from that of the measurement light; a sub-interferometer (160) that receives light projected from a light source (140) and generates a sub-interference signal based on two lights that follow different optical paths; a variable delay amount generating unit that generates a variable delay amount; a correction signal generating unit (171) that generates a correction signal for correcting the sampling period of the main interference signal based on the secondary interference signal and the variable delay amount; a processing unit (118) for measuring a distance to a measurement object (T) based on the main interference signal and the correction signal; a variable delay amount setting unit (195) that sets a variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of a reflected signal generated by the main interferometer (150) that is based on a digital signal sampled based on the correction signal; Controller (110). [Appendix 11] An optical interferometric distance measuring sensor (100) including a controller (110) and a fiber optic cable (130) connected to the controller (110), The controller (110) a light source (140) that emits light while changing the wavelength; a main interferometer (150) connected to the sensor head (121) via an optical fiber (131) included in the optical fiber cable (130), the main interferometer (150) receiving light projected from the light source (140) and generating a main interference signal based on measurement light irradiated onto the measurement target (T) and reflected by the sensor head (121) and reference light following an optical path at least partially different from that of the measurement light; a sub-interferometer (160) that receives light projected from a light source (140) and generates a sub-interference signal based on two lights that follow different optical paths; a variable delay amount generating unit that generates a variable delay amount; a correction signal generating unit (171) that generates a correction signal for correcting the sampling period of the main interference signal based on the secondary interference signal and the variable delay amount; a processing unit (118) for measuring a distance to a measurement object (T) based on the main interference signal and the correction signal; a variable delay amount setting unit (195) that sets a variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of a reflected signal generated by the main interferometer (150) that is based on a digital signal sampled based on the correction signal; An optical interferometric ranging sensor (100). [Explanation of symbols]

[0252] 1...sensor system, 10...displacement sensor, 11...control device, 12...sensor for control signal input, 13...external connection device, 20...sensor head, 21...objective lens, 22a...collimating lens, 22b...collimating lens, 22c...collimating lens, 23...lens holder, 24...optical fiber array, 30...controller, 31...display unit, 32...setting unit, 33...external I / F unit, 34...optical fiber connection unit, 35...external memory unit, 36...measurement processing a processing unit, 40... optical fiber, 51... wavelength swept light source, 52... optical amplifier, 53, 53a, 53b... isolator, 54, 54a, 54b, 54c, 53d, 54e, 54f, 54g, 54h, 54i, 54j... optical coupler, 55... attenuator, 56a, 56b, 56c... light receiving element, 57a, 57b, 57c... amplifier circuit, 58a, 58b, 58c... AD conversion unit, 59... processing unit, 60... balance detector, 61... correction signal generation unit, 71a, 71b , 71c, 71d, 71e...light receiving element, 72a 72b, 72c...amplification circuit, 74a, 74b, 74c...AD conversion unit, 75...processing unit, 76...differential amplification circuit, 77...correction signal generation unit, 100, 101...optical interference distance measuring sensor, 110...controller, 111...optical branching unit, 112, 113...first photodiode, 114, 115...amplification circuit, 116...second photodiode, 118...processing unit, 121, 122...sensor head, 130...optical Fiber cable, 131, 132...optical fiber, 140...wavelength swept light source, 150...main interferometer, 151...first main interferometer, 152...second main interferometer, 160...sub-interferometer, 161...first optical coupler, 162...second optical coupler, 163...optical fiber, 171, 172...correction signal generation unit, 181, 182...AD conversion unit, 191, 192...variable delay line, 195...variable delay amount setting unit, Lm...measurement optical path, Lr...reference optical path, T, T1, T2...measurement object.

Claims

1. A controller connected via an optical fiber cable to a sensor head that irradiates a measurement object with light, a light source that projects light while changing the wavelength; a main interferometer connected to the sensor head via an optical fiber included in the optical fiber cable, the main interferometer receiving light projected from the light source and generating a main interference signal based on measurement light that is irradiated onto the measurement object and reflected by the sensor head, and reference light that follows an optical path at least partially different from that of the measurement light; a sub-interferometer that receives light projected from the light source and generates a sub-interference signal based on two lights that follow different optical paths; a variable delay amount generating unit that generates a variable delay amount; a correction signal generator that generates a correction signal for correcting a sampling period of the main interference signal based on the secondary interference signal and the variable delay amount; a processing unit that measures the distance to the measurement object based on the main interference signal and the correction signal; a variable delay amount setting unit that sets the variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of a reflected signal generated by the main interferometer and based on the digital signal sampled based on the correction signal. controller.

2. the variable delay amount setting unit sets the variable delay amount based on at least one of a peak intensity in a signal based on a digital signal of the main interference signal and a peak intensity in a signal based on a digital signal of the reflected signal. The controller of claim 1 .

3. the variable delay amount setting unit sets the variable delay amount based on at least one of a maximum value of peak intensity in a signal based on a plurality of digital signals of the main interference signal and a maximum value of peak intensity in a signal based on a plurality of digital signals of the reflected signal. The controller of claim 2 .

4. the variable delay amount setting unit sets the variable delay amount based on at least one of a predetermined peak value width in a signal based on a digital signal of the main interference signal and a predetermined peak value width in a signal based on a digital signal of the reflected signal. The controller of claim 1 .

5. the variable delay amount setting unit sets the variable delay amount based on at least one of a minimum value of a peak predetermined value width in a signal based on a plurality of digital signals of the main interference signal and a minimum value of a peak predetermined value width in a signal based on a plurality of digital signals of the reflected signal. The controller of claim 4 .

6. the variable delay amount setting unit sets the variable delay amount so that at least one of the number of measurement points included in a predetermined peak value width in a signal based on a digital signal of the main interference signal and the number of measurement points included in a predetermined peak value width in a signal based on a digital signal of the reflected signal is less than a predetermined number. The controller of claim 1 .

7. the reflected signal is generated when a part of the light projected from the light source and supplied to the main interferometer is reflected by a member having a reflecting surface formed in the main interferometer. The controller of claim 1 .

8. the variable delay amount generation unit includes a variable delay line that generates a delay in a time axis direction according to the variable delay amount in a sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal and outputs the delay to the correction signal generation unit. The controller of claim 1 .

9. the correction signal generation unit generates a pulse signal as the correction signal based on a signal obtained by converting the sub-interference signal into an electrical signal and delaying the sub-interferometer signal in a time axis direction according to the variable delay amount. The controller of claim 1 .

10. further comprising an AD converter that samples a main interferometer signal obtained by converting the main interference signal into an electrical signal based on the correction signal and converts the signal into a digital signal; The controller of claim 1 .

11. An optical interferometric ranging sensor including a controller and an optical fiber cable connected to the controller, The controller a light source that projects light while changing the wavelength; a main interferometer connected to a sensor head via an optical fiber included in the optical fiber cable, the main interferometer receiving light projected from the light source and generating a main interference signal based on measurement light that is irradiated onto a measurement object and reflected by the sensor head, and reference light that follows an optical path at least partially different from that of the measurement light; a sub-interferometer that receives light projected from the light source and generates a sub-interference signal based on two lights that follow different optical paths; a variable delay amount generating unit that generates a variable delay amount; a correction signal generator that generates a correction signal for correcting a sampling period of the main interference signal based on the secondary interference signal and the variable delay amount; a processing unit that measures the distance to the measurement object based on the main interference signal and the correction signal; a variable delay amount setting unit that sets the variable delay amount based on at least one of a peak in a signal based on a digital signal of the main interference signal sampled based on the correction signal and a peak in a digital signal of a reflected signal generated by the main interferometer and based on the digital signal sampled based on the correction signal. Optical interferometric ranging sensor.

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