Optical Interferometric Distance Sensor

Abstract

To improve the accuracy of inclination correction to an object being measured, in a light interference ranging sensor that performs distance measurement after preliminarily excluding interference light that is weak to a certain extent.SOLUTION: A processing unit that is included in a light interference ranging sensor pertaining to an aspect of the present invention comprises: a conversion unit that converts a first electric signal into a first distance value that indicates the distance from an interferometer to an objected being measured; an inclination value calculation unit that calculates an inclination value on the basis of the first distance value; a first distance value correction unit that corrects the first distance value on the basis of the inclination value; and a second distance value calculation unit that calculates a second distance value that indicates the distance from the light interference ranging sensor to the object being measured, on the basis of the first distance value having been corrected by the first distance value correction unit. When the number of times the first electric signal is detected is less than a second threshold, the first distance value correction unit corrects the first distance value on the basis of an inclination value that precedes in sequence the inclination value correlated to the first distance value in a storage unit.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to 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] For example, Patent Document 1 discloses an optical coherence tomography imaging device that includes a light beam controller, a branching means for branching multiple light beams from the light beam controller into object light and reference light, an irradiation means for irradiating a measurement object with the multiple object light beams, and an interference means for causing interference between the object light and the reference light scattered from the measurement object and guiding them to a light receiver. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 131298 Summary of the Invention [Problem to be solved by the invention]

[0005] In an optical interferometer distance measuring sensor, when multiple interferometers that generate interference light are provided, it may be necessary to correct the tilt between the measurement object and the multiple interferometers. On the other hand, from the viewpoint of improving accuracy, it may be necessary to exclude interference light that is weak to a certain extent in advance and calculate the distance to the measurement object based only on the interference light that has not been excluded. In such cases, the accuracy of the tilt correction may be reduced.

[0006] Therefore, the present invention aims to provide an optical interferometric ranging sensor that performs distance measurement after previously excluding a certain degree of weak interferometric light from multiple interferometric lights, and that improves the accuracy of tilt correction for the object to be measured. [Means for solving the problem]

[0007] An optical interferometric distance measuring sensor according to one aspect of the present invention is an optical interferometric distance measuring sensor comprising: a light source that projects light while continuously changing its wavelength; a plurality of interferometers that generate interference light based on measurement light that is supplied with the light projected from the light source and is irradiated onto and reflected from a measurement object; and reference light that follows an optical path that is at least partially different from that of the measurement light; a light receiving unit that receives the interference light generated by each of the plurality of interferometers and converts it into a plurality of electrical signals corresponding to each of the plurality of interferometers; and a processing unit that calculates and outputs the distance from the optical interferometric distance measuring sensor to the measurement object based on a first electrical signal among the plurality of electrical signals that has an intensity equal to or greater than a first threshold, and the processing unit converts the first electrical signal from the interferometer among the plurality of interferometers that corresponds to the first electrical signal to the measurement object. a conversion unit that converts the number of times the first electrical signal is detected into a first distance value that indicates the distance at a point in time at which the optical interferometer is located; a tilt value calculation unit that calculates a tilt value that indicates the tilt of the multiple interferometers relative to the object to be measured based on the first distance value; a first distance value correction unit that corrects the first distance value based on the tilt value by referring to a memory unit that sequentially stores the number of times the first electrical signal is detected, the first distance value, and the tilt value in association with each other; and a second distance value calculation unit that calculates a second distance value that indicates the distance from the optical interferometer to the object to be measured based on the first distance value corrected by the first distance value correction unit, wherein if the number of times the first electrical signal is detected among the multiple electrical signals is less than a second threshold, the first distance value correction unit corrects the first distance value based on the tilt value that precedes the tilt value associated with the first distance value in the memory unit.

[0008] According to this aspect, when the number of times that a first electrical signal having an intensity equal to or greater than the first threshold is detected among the plurality of electrical signals is less than the second threshold, the first distance value converted from the first electrical signal is corrected based on the gradient value that precedes the gradient value associated with the first distance value in the storage unit, thereby improving the accuracy of the gradient correction for the measurement object.

[0009] In the above aspect, the first threshold value may be a value obtained by multiplying the maximum intensity of the intensities of the plurality of electrical signals by a predetermined ratio.

[0010] According to this aspect, the effect of improving the accuracy of tilt correction for the measurement object is enhanced.

[0011] In the above aspect, the first distance value correcting unit may correct the first distance value when the tilt value satisfies a predetermined condition.

[0012] According to this aspect, it is possible to improve the accuracy of tilt correction depending on the degree of tilt.

[0013] In the above aspect, the predetermined condition may include at least one of the gradient values ​​being equal to or greater than a third threshold value.

[0014] According to this aspect, it is possible to improve the accuracy of tilt correction depending on the degree of tilt.

[0015] In the above aspect, when the number of times a first electrical signal is detected among the multiple electrical signals is less than a second threshold, the first distance value correction unit may correct the first distance value based on a gradient value associated in the memory unit with an order in which the number of times the first electrical signal is detected is greater than or equal to a fourth threshold.

[0016] According to this aspect, it is possible to improve the accuracy of tilt correction for the measurement object.

[0017] In the above aspect, the processing unit may further output a gradient value.

[0018] According to this aspect, convenience for the user is improved.

[0019] In the above aspect, the gradient value calculation unit may calculate, as the gradient value, a value obtained by dividing the difference between the first distance values ​​corresponding to each of two interferometers among the plurality of interferometers by a number obtained by adding 1 to the number of interferometers disposed between the two interferometers.

[0020] According to this aspect, it is possible to improve the accuracy of tilt correction for the measurement object.

[0021] In the above aspect, the multiple interferometers include at least three interferometers arranged so that the heads of each interferometer form an approximate triangle in a plane, and the tilt value calculation unit may select two interferometers from the interferometers corresponding to the electrical signal having an intensity equal to or greater than a first threshold, such that the difference between the direction of the vector formed by the starting points of two of the three interferometers and the axial direction of the tilt of the measurement object is closest to a right angle, and calculate the tilt value based at least on the first distance values ​​corresponding to the two selected interferometers.

[0022] According to this aspect, the degree of freedom in the configuration of the optical interferometric distance measuring sensor increases, which allows for improved accuracy in tilt correction for the measurement object. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an optical interferometric distance measuring sensor that improves measurement accuracy by suppressing return light between optical couplers. [Brief explanation of the drawings]

[0024] [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 executed by a processing unit 59 in the controller 30 for calculating individual distance values ​​to the measurement object T of each of the interferometers a, b, and c and comparing them with a predetermined threshold value. [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 10A] 10 is a diagram for explaining the inclination between the sensor head 20 and the measurement object T. FIG. [Figure 10B] 10 is a diagram for explaining the inclination between the sensor head 20 and the measurement object T. FIG. [Figure 11] 3 is a diagram for explaining a table stored in the displacement sensor 10. FIG. [Figure 12]10 is a flowchart showing a method for calculating a final distance value from the displacement sensor 10 to the measurement object T, which is executed by a processing unit 59 in the controller 30. [Figure 13] FIG. 10 is a diagram for explaining a first modified example of the interferometer. [Figure 14] FIG. 10 is a diagram illustrating a second modified example of the interferometer. DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] [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).

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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).

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] [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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] As specific examples, the measurement mode, operation mode, measurement period, material of the measurement object T, etc. are set.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 optical coupler 54 may be configured to branch the light to the main interferometer and the sub interferometer at a ratio of 90:10 to 99:1.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The amplifier circuits 57a to 57c amplify the electrical signals output from the light receiving elements 56a to 56c, respectively.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The optical coupler 54d and the optical coupler 54e may both branch light at a ratio of 50:50.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] Then, based on the interference light obtained from each, the distance to the measurement object T and the like are measured (multi-channel).

[0101] [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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] The plurality of amplifier circuits 72a to 72c convert the current signals into voltage signals (IV conversion) and amplify them.

[0110] 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.

[0111] The processing unit 75 corresponds to the processing unit 59 shown in Figure 5A, and converts the digital signals from the AD conversion units 74a to 74c into frequencies using FFT, calculates distance values ​​to the measurement object corresponding to each collimator lens 22a to 22c (sometimes referred to as "individual distance values"), and then analyzes these to calculate the distance value from the displacement sensor 10 to the measurement object T (sometimes referred to as "final distance value").

[0112] 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.

[0113] 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.

[0114] 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 7, 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 7.

[0115] First Embodiment

[0116] FIG. 8 is a flowchart showing a method executed by the processing unit 59 of the controller 30 to calculate individual distance values ​​to the measurement target T for each of the interferometers a, b, and c and compare the calculated distance values ​​with a predetermined threshold. Here, the interferometers a, b, and c correspond to the collimating lenses 22a, 22b, and 22c, respectively. In the following description, it is assumed that the collimating lenses 22a to 22c are positioned at the same position in the optical axis direction. However, in the displacement sensor 10 according to this embodiment, the positions of the collimating lenses 22a to 22c in the optical axis direction do not have to be the same. As shown in FIG. 8, the method includes steps S31 to S34. The method may be executed at each sampling time of the main interferometer.

[0117] In step S31, processing unit 59 frequency-converts the waveform signals (voltage vs. time) corresponding to each of interferometers a to c into spectra (voltage vs. frequency) using the following FFT: Fig. 9A is a diagram showing how the waveform signals (voltage vs. time) are frequency-converted into spectra (voltage vs. frequency).

number

[0118] In step S32, the processing unit 59 performs distance conversion on the spectra (voltage vs. frequency) corresponding to each of the interferometers a to c to convert them into spectra (voltage vs. distance). Fig. 9B is a diagram showing how the spectra (voltage vs. frequency) corresponding to each of the interferometers a to c are converted into spectra (voltage vs. distance).

[0119] In step S33, processing unit 59 calculates individual distance values ​​corresponding to the peaks based on the spectra (voltage vs. distance) corresponding to each of interferometers a to c. Fig. 9C is a diagram showing how peaks are detected based on the spectra (voltage vs. distance) corresponding to each of interferometers a to c and how the individual distance values ​​corresponding to the peaks are calculated. As shown in Fig. 9C, peaks are detected in three channels based on the spectra (voltage vs. distance) corresponding to each of interferometers a to c, and individual distance values ​​(D1, D2, and D3 in the example shown in the figure) corresponding to the peaks are calculated.

[0120] In step S34, the processing unit 59 compares the peak voltage values ​​(SN values) corresponding to each of the interferometers a to c (voltages V1, V2, and V3 in the example of FIG. 9C ) detected in step S33 with a predetermined threshold (an example of a first threshold), and then determines the number of peaks equal to or greater than the threshold. Here, the predetermined threshold may be a predetermined constant. Alternatively, the predetermined threshold may be a value calculated based on the SN values ​​corresponding to each of the interferometers a to c. Specifically, for example, the predetermined threshold may be a value obtained by multiplying the maximum value of the SN values ​​corresponding to each of the interferometers a to c by a predetermined ratio. The ratio may be set arbitrarily, and may be, for example, 0.8, 0.5, 0.3, etc. For example, if the SN value SNa corresponding to the interferometer a is 100, the SN value SNb corresponding to the interferometer b is 80, and the SN value SNc corresponding to the interferometer c is 40, the maximum SN value is SNa, which is 100. When the predetermined ratio is 0.5, the value obtained by multiplying 100, which is the maximum SN value, SNa by 0.5, is 50, so this 50 becomes the threshold value mentioned above. Since SNa(100) and SNb(80) are equal to or greater than the threshold value (50), and SNc(40) is less than the threshold value (50), the number of peaks equal to or greater than the threshold value is determined to be 2.

[0121] In step S35, the processing unit 59 calculates a tilt value. Here, the tilt value may be a correction coefficient for each individual distance value to reduce the influence of the tilt between the sensor head 20 and the measurement object T.

[0122] The tilt between the sensor head 20 and the measurement object T will be described with reference to FIGS. 10A and 10B. The left side of FIG. 10A shows the optical fiber array 24 and collimating lenses 22a to 22c of the displacement sensor 10, and the measurement object T, when the measurement object T is not tilted relative to the sensor head 20 (when the interferometers a to c are arranged parallel to the measurement object T). For convenience, other components of the displacement sensor 10, such as the objective lens 21, are omitted from the illustration. The right side of FIG. 10A also shows a schematic graph showing the relationship between the SN value (signal strength) and the individual distance values ​​corresponding to the interferometers a to c. In the figure, the SN value corresponding to the interferometer a is indicated by the symbol a, the SN value corresponding to the interferometer b by the symbol b, and the SN value corresponding to the interferometer c by the symbol c. The peak of the SN value corresponding to the interferometer a is indicated by SNa, the peak of the SN value corresponding to the interferometer b by the symbol SNb, and the peak of the SN value corresponding to the interferometer c by the symbol SNc.

[0123] The left side of FIG. 10B shows the optical fiber array 24 and collimating lenses 22a-22c oscillated by the displacement sensor 10, and the measurement object T, when the measurement object T is inclined with respect to the sensor head 20 (when the interferometers a-c are not arranged parallel to the measurement object T). For convenience, other components of the displacement sensor 10, such as the objective lens 21, are omitted from the illustration. The right side of FIG. 10B also shows a schematic graph of the SN value (signal strength) and the individual distance values ​​corresponding to the interferometers a-c. In the figure, the SN value corresponding to the interferometer a is indicated by the symbol a, the SN value corresponding to the interferometer b by the symbol b, and the SN value corresponding to the interferometer c by the symbol c. The peak of the SN value corresponding to the interferometer a is indicated by SNa, the peak of the SN value corresponding to the interferometer b by the symbol SNb, and the peak of the SN value corresponding to the interferometer c by the symbol SNc.

[0124] As shown on the right side of FIG. 10A, the individual distance values Ea, Eb, and Ec corresponding to the interferometers a to c indicate substantially the same value. This corresponds to the fact that the measurement object T is not inclined with respect to the sensor head 20 as shown on the left side of the same figure. When the positions of the collimating lenses 22a to 22c in the optical axis direction are not the same, the individual distance values Ea, Eb, and Ec are not necessarily the same. On the other hand, as shown on the right side of FIG. 10B, for the individual distance value Ea corresponding to the interferometer a, the individual distance value Eb corresponding to the interferometer b, and the individual distance value Ec corresponding to the interferometer c, the relationship Ea < Eb < Ec is satisfied. This corresponds to the fact that the measurement object T is inclined with respect to the sensor head 20 as shown on the right side of the same figure. When the positions of the collimating lenses 22a to 22c in the optical axis direction are not the same, the individual distance values Ea, Eb, and Ec do not necessarily satisfy the relationship Ea < Eb < Ec.

[0125] Next, the gradient value calculated by the processing unit 59 will be described. The gradient value may be calculated based at least on the difference between the individual distance values ​​corresponding to two interferometers among the multiple interferometers included in the sensor head 20. For example, in the example shown in FIG. 10B , the gradient value may be calculated as Ga = Eb - Ea based on the individual distance value Ea corresponding to interferometer a and the individual distance value Eb corresponding to interferometer b. The gradient value may also be calculated as Gb = Ec - Eb based on the individual distance value Eb corresponding to interferometer b and the individual distance value Ec corresponding to interferometer c. The gradient value may also be calculated as a value obtained by dividing the difference between the individual distance values ​​corresponding to two interferometers among the multiple interferometers included in the sensor head 20 by an index indicating the degree of separation between the two interferometers. The index indicating the degree of separation between the two interferometers may be, for example, the number of interferometers disposed between the two interferometers or a number obtained by adding one to the number. 10B, the two interferometers are interferometer a and interferometer c, and one interferometer b is disposed between interferometer a and interferometer c. Therefore, the tilt value may be calculated by dividing the difference between the individual distance value Ea corresponding to interferometer a and the individual distance value Ec corresponding to interferometer c by 2, which is the number of interferometers disposed between interferometer a and interferometer c (1 for interferometer b) plus 1, i.e., Gc = (Ec - Ea) / 2. Alternatively, an index indicating the degree of separation between the two interferometers may be, for example, the distance between the two interferometers. The distance may be, for example, the distance in a direction perpendicular to the optical axis, and more specifically, the distance between the collimating lenses in a direction perpendicular to the optical axis. In particular, when the index indicating the degree of separation between the two interferometers is expressed as the distance between the two interferometers, the tilt value, i.e., the value obtained by dividing the difference between the individual distance values ​​corresponding to each of the two interferometers by the index, corresponds to the angle of tilt between the sensor head 20 and the object to be measured T.

[0126] Returning to FIG. 8 , in step S36, the processing unit 59 registers various values ​​related to the individual distance values ​​calculated in step S33 in a table, such as that shown in FIG. 11 , stored in a predetermined storage unit in association with the sampling time. The table may include, for example, the individual distance values ​​calculated in step S33, as shown in FIG. 11 . While the table is denoted as d1, d2, etc. for convenience, these may include individual distance values ​​corresponding to multiple interferometers. The table may also include, for example, the number of peaks equal to or greater than a predetermined threshold calculated in step S34, as shown in FIG. 11 . The table may also include, for example, the tilt value calculated in step S35, as shown in FIG.

[0127] 12 is a flowchart showing a method for calculating a final distance value from the displacement sensor 10 to the measurement object T, which is executed by the processing unit 59 in the controller 30. As shown in Fig. 12, the method includes steps S41 to S45. The method may be executed, for example, at each sampling time in the main interferometer.

[0128] In step S41, the processing unit 59 acquires a gradient value associated with the sampling time by referring to the table shown in FIG. 11, and then compares the gradient value with a predetermined threshold to determine whether the gradient value is equal to or greater than the threshold. When there are multiple gradient values, the processing unit 59 may compare all of the gradient values ​​with the threshold, or may compare only some of the gradient values ​​with the threshold. For example, in the example shown in FIG. 10B, the processing unit 59 may compare the gradient value Ga (the difference between the individual distance value Eb and the individual distance value Ea) with the threshold C. Additionally or alternatively, the processing unit 59 may compare the gradient value Gb (the difference between the individual distance value Ec and the individual distance value Eb) with the threshold C.

[0129] In step S41, if it is determined that the tilt value is not equal to or greater than the threshold value (S41; No), the process proceeds to step S45. On the other hand, if it is determined that the tilt value is equal to or greater than the threshold value (S41; Yes), the process proceeds to step S42.

[0130] In step S42, the processing unit 59 determines whether or not there is at least one missing peak in the number of peaks associated with the time. That is, the processing unit 59 refers to the table shown in FIG. 11 to obtain the number of peaks equal to or greater than a predetermined threshold associated with the time, and determines whether or not there is at least one missing peak in the number of peaks. For example, in the example shown in FIG. 10B, the number of complete peaks without missing peaks is three. Therefore, if the number of peaks associated with the time in the table shown in FIG. 11 is two or less, the processing unit 59 determines that there is at least one missing peak in the number of peaks. In step S42, if it is determined that there is at least one missing peak in the number of peaks associated with the time (S42; Yes), the processing proceeds to step S43. On the other hand, if it is determined that there is not at least one missing peak in the number of peaks associated with the time (S42; No), the processing proceeds to step S44.

[0131] In step S43, the processing unit 59 corrects the individual distance values ​​using the gradient value associated with the most recent time without any missing peaks. Here, the most recent time without any missing peaks may be the time before the current time that has no missing peaks and is closest to the current time. Correcting the individual distance values ​​refers to performing a calculation on the individual distance values ​​based on the gradient value, but may also include, for example, adding the gradient value to the individual distance values. For example, in the example shown in FIG. 10B , the corrected individual distance value of interferometer a is da, the corrected individual distance value of interferometer b is db, and the corrected individual distance value of interferometer c is ca. In this case, the corrections may be made, for example, as da = Ea + G, db = Eb, dc = Ec - G, etc. Note that these correction formulas are merely examples, and corrections may be made using other calculation formulas.

[0132] In step S44, the processing unit 59 corrects the individual distance values ​​using the tilt value associated with the current time. The method for correcting the individual distance values ​​may be the same as in step S43.

[0133] In step S45, the processing unit 59 calculates a final distance value from the displacement sensor 10 to the measurement target T. For example, the final distance value may be calculated based on the individual distance values ​​corrected in step S43 or S44. In particular, the final distance value may be an average value of the individual distance values ​​or an average value of the individual distance values ​​equal to or greater than a predetermined threshold. Alternatively, the final distance value may be the individual distance value having the strongest signal strength. As described in step S24 above, the processing unit 59 displays the final distance value as a result of the measurement process on the display unit 31 or outputs it to the control device 11, the externally connected device 13, or the like via the external I / F unit 33. Furthermore, the processing unit 59 may display the tilt value calculated in step S35 above on the display unit 31 or output it to the control device 11, the externally connected device 13, or the like via the external I / F unit 33.

[0134] 11, in step S42, it is determined whether or not there is at least one missing peak. However, the number of missing peaks determined in this step is not limited to at least one, and may be at least two, at least three, etc.

[0135] [First Variant of Interferometer] The multiple interferometers included in the optical interferometer ranging sensor 100 may be configured so that their heads are not collinearly positioned within the same plane. In other words, the multiple interferometers included in the optical interferometer ranging sensor 100 may include three interferometers whose heads form a roughly triangular shape within the plane. For example, FIG. 13 shows three interferometers a, b, and c included in the optical interferometer ranging sensor 100. As shown in the figure, the heads of the interferometers a, b, and c are assumed to be positioned within the same XY plane. Furthermore, the measurement object has a surface parallel to the XY plane. In this case, it is assumed that the tilt axis direction of the measurement object is the X-axis direction, i.e., the measurement object is tilted by a predetermined angle around the X-axis. In this case, since the positions of interferometers b and c in the Y-axis direction are the same, the individual distance values ​​corresponding to interferometers b and c change by substantially the same value due to the tilt. On the other hand, since the position of interferometer a in the Y-axis direction is different from the positions of interferometers b and c in the Y-axis direction, the individual distance value corresponding to interferometer a changes by a value different from the individual distance values ​​corresponding to interferometers b and c due to the tilt.

[0136] Under these assumptions, the processing unit 59 may select two interferometers such that the difference between the direction of a vector formed by the starting points of any two interferometers and the direction of tilt of the measurement object is closest to a right angle, and calculate the tilt value based at least on the individual distance values ​​corresponding to the two selected interferometers. For example, in the example shown in FIG. 13 , a vector Vab connecting the starting points of interferometer a and interferometer b, a vector Vbc connecting the starting points of interferometer b and interferometer c, and a vector Vca connecting the starting points of interferometer c and interferometer a are shown. In this case, of vectors Vab, Vbc, and Vca, the vector Vab or Vca has a difference from the X-axis direction, which is the direction of tilt of the measurement object, that is closest to a right angle. Therefore, the processing unit 59 may select interferometers a and b corresponding to vector Vab, and calculate the tilt value based at least on the individual distance values ​​corresponding to the selected interferometers a and b. Alternatively, the processing unit 59 may select the interferometers c and a corresponding to the vector Vca, and calculate the tilt value based at least on the individual distance values ​​corresponding to the selected interferometers c and a.

[0137] [Second variant of the interferometer] In the above-described embodiment, the optical interferometer distance measuring sensor 100 uses a Fizeau interferometer in each of the interferometers 130a to 130c, which generates reference light by using the tip of an optical fiber as a reference surface, but the interferometer is not limited to this.

[0138] FIG. 14 shows variations of an interferometer that generates interference light using measurement light and reference light. In FIG. 14(a), in optical paths A to C branched by branching unit 121, interference light is generated based on the optical path length difference between reference light, which uses the tip (end face) of an optical fiber as a reference surface, and measurement light, which is irradiated from the sensor head and reflected by the measurement target T. This is the configuration of interferometers 130a to 130c of the optical interferometer distance measuring sensor 100 according to the present embodiment (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.

[0139] 14(b), optical paths A to C branched by branching unit 121 are formed with measurement optical paths Lm1 to Lm3 that guide measurement light to measurement object T and reference optical paths Lr1 to Lr3 that guide reference light, and a reference surface is disposed at the end of each of reference optical paths Lr1 to Lr3 (Michelson interferometer). The reference surface may be formed by coating the tip of an optical fiber with a reflective film, 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 in each of optical paths A to C by providing an optical path length difference between the optical path length of each of measurement optical paths Lm1 to Lm3 and the optical path length of each of reference optical paths Lr1 to Lr3.

[0140] 14(c), optical paths A to C branched by branching unit 121 are formed into measurement optical paths Lm1 to Lm3 that guide measurement light to measurement object T and reference optical paths Lr1 to Lr3 that guide reference light, and balance detectors are arranged in the reference optical paths Lr1 to Lr3 (Mach-Zehnder interferometers). In this configuration, interference light is generated in each of the optical paths A to C by providing an optical path length difference between the optical path length of each of the measurement optical paths Lm1 to Lm3 and the optical path length of each of the reference optical paths Lr1 to Lr3.

[0141] As described above, the interferometer is not limited to the Fizeau interferometer described in this embodiment, but may be, for example, a Michelson interferometer or a Mach-Zehnder interferometer. Any interferometer may be applied 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, or a combination of these or other configurations may be applied.

[0142] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those illustrated and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other. [Explanation of symbols]

[0143] 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 to 22c...collimating lens, 23...lens holder, 24...optical fiber array, 30...controller, 31...display unit, 32...setting unit, 33...external interface (I / F) unit, 34...optical fiber connection unit, 35...external memory unit, 36...measurement processing unit, 40...optical fiber, 51...wavelength swept light source, 5 2...optical amplifier, 53, 53a to 53b...isolator, 54, 54a to 54e...optical coupler, 55...attenuator, 56a to 56c...light receiving element, 58...AD conversion unit, 59...processing unit, 60...balanced detector, 61...correction signal generation unit, 71a to 71e...light receiving element, 72a to 72c...amplification circuit, 74a to 74c...AD conversion unit, 75...processing unit, 76...differential amplification circuit, 77...correction signal generation unit, T...measurement object, Lm1 to Lm3...measurement optical path, Lr1 to Lr3...reference optical path

Claims

1. An optical interferometric ranging sensor, a light source that projects light while continuously changing the wavelength; a plurality of interferometers that receive light projected from the light source, irradiate a measurement object with light, and generate interference light based on reference light that follows an optical path at least partially different from that of the measurement light; and a light receiving unit that receives interference light generated by each of the plurality of interferometers and converts the interference light into a plurality of electrical signals corresponding to each of the plurality of interferometers; a processing unit that calculates and outputs a distance from the optical interferometric ranging sensor to the measurement object based on a first electrical signal having an intensity equal to or greater than a first threshold value among the plurality of electrical signals, The processing unit a conversion unit that converts the first electrical signal into a first distance value that indicates a distance from an interferometer corresponding to the first electrical signal among the plurality of interferometers to the measurement object; a tilt value calculation unit that calculates tilt values ​​indicating tilts of the plurality of interferometers with respect to the measurement object based on the first distance value; a first distance value correction unit that refers to a storage unit that sequentially stores the number of times the first electrical signal is detected, the first distance value, and the tilt value in association with each other, and corrects the first distance value based on the tilt value; a second distance value calculation unit that calculates a second distance value indicating a distance from the optical interferometric distance measuring sensor to the measurement object based on the first distance value corrected by the first distance value correction unit; Equipped with When the number of times that the first electrical signal among the plurality of electrical signals is detected is less than a second threshold, the first distance value correction unit corrects the first distance value based on the gradient value that precedes the gradient value associated with the first distance value in the storage unit. Optical interferometric ranging sensor.

2. The optical interferometric distance measuring sensor according to claim 1 , wherein the first threshold value is a value obtained by multiplying the maximum intensity of the intensities of the plurality of electrical signals by a predetermined ratio.

3. The optical interferometric distance measuring sensor according to claim 1 , wherein the first distance value correcting unit corrects the first distance value when the tilt value satisfies a predetermined condition.

4. The optical interferometric distance measuring sensor according to claim 3 , wherein the predetermined condition includes at least one of the tilt values ​​being equal to or greater than a third threshold value.

5. 5. An optical interferometric ranging sensor according to claim 1, wherein when the number of times the first electrical signal is detected among the plurality of electrical signals is less than a second threshold, the first distance value correction unit corrects the first distance value based on the inclination value associated in the memory unit with the order in which the number of times the first electrical signal is detected is greater than or equal to a fourth threshold.

6. The optical interferometric distance measuring sensor according to claim 1 , wherein the processing unit further outputs the tilt value.

7. 7. An optical interferometric ranging sensor according to claim 1, wherein the gradient value calculation unit calculates, as the gradient value, a value obtained by dividing the difference between the first distance values ​​corresponding to each of two interferometers among the plurality of interferometers by the number of interferometers arranged between the two interferometers plus one.

8. the plurality of interferometers includes at least three interferometers arranged such that heads of the interferometers form a substantial triangle in a plane; The gradient value calculation unit selecting two interferometers from the interferometers corresponding to the electrical signal having an intensity equal to or greater than the first threshold value such that a difference between a direction of a vector formed by the respective starting points of two interferometers and an axial direction of the tilt of the measurement object is closest to a right angle; calculating the tilt value based at least on the first distance values ​​corresponding to the two selected interferometers; The optical interferometric distance measuring sensor according to any one of claims 1 to 7.

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