Optical interferometric ranging sensor

Abstract

This invention provides an optical interferometric ranging sensor that improves measurement accuracy by suppressing backlight between optical couplers. One aspect of the optical interferometric ranging sensor according to this invention includes: a light source that projects light while continuously varying its wavelength; a plurality of interferometers that generate interference light based on measurement light reflected from the measurement object by guiding the supplied light to the measurement object and at least a portion of reference light along an optical path different from the measurement light; a multi-stage optical coupler, which is a series-connected multi-stage optical coupler that receives light from the light source from a preceding stage and branches the light into corresponding interferometers and subsequent stages of the plurality of interferometers; a suppression mechanism that suppresses the supply of light from the subsequent stage to the preceding stage of the multi-stage optical coupler; and a processing unit that calculates the distance to the measurement object based on the plurality of interference lights generated by the plurality of interferometers.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical interference distance measuring sensor. BACKGROUND

[0002] In recent years, optical distance measuring sensors that measure a distance to a measurement object in a non-contact manner are becoming widespread. For example, as an optical distance measuring sensor, an optical interference distance measuring sensor that generates interference light based on reference light and measurement light from light projected by a wavelength-swept light source, and measures a distance to a measurement object based on the interference light is known. For example, Patent Literature 1 discloses an optical interference tomographic apparatus that includes a beam controller, a branching mechanism that branches a plurality of light beams from the beam controller into object light and reference light, an irradiation mechanism that irradiates a plurality of object light beams to a measurement object, and an interference mechanism that causes object light scattered from the measurement object to interfere with the reference light and guides the interference light to a light receiver.

[0003] In particular, from the viewpoint of improving measurement accuracy and the like, a multi-stage optical interference distance measuring sensor that has a plurality of interferometers that generate interference light is known. For example, Patent Literature 1 discloses an optical interference tomographic apparatus that includes a beam controller, a branching mechanism that branches a plurality of light beams from the beam controller into object light and reference light, an irradiation mechanism that irradiates a plurality of object light beams to a measurement object, and an interference mechanism that causes object light scattered from the measurement object to interfere with the reference light and guides the interference light to a light receiver.

[0004] In addition, Non-Patent Literature 1 discloses an optical interference distance measuring sensor that branches light without using a circulator or the like, which is a high-cost component. That is, Non-Patent Literature 1 discloses an optical interference distance measuring sensor that includes a wavelength-swept light source, a plurality of optical couplers, a plurality of interferometers corresponding to the respective optical couplers, and a light receiver. The plurality of optical couplers included in the optical interference distance measuring sensor are connected in series, and are configured to supply a portion of light from the wavelength-swept light source to a rear-stage coupler in order from a front-stage optical coupler, and to branch another portion of the light and supply it to the interferometers corresponding to the respective optical couplers.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: International Publication No. 2019 / 131298

[0008] Non-Patent Literature 1: Jesse Zheng, “Optical Frequency-Modulated Continuos-Wave (FMCW) Interferometry”, Springer, January 4, 2005, p. 154 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] However, in a configuration in which light is branched to each interferometer in a plurality of optical couplers connected in series, return light from a rear-stage to a front-stage can occur, and thus the measurement accuracy can sometimes be reduced.

[0011] Here, the object of the present invention is to provide an optical interferometric ranging sensor that improves measurement accuracy by suppressing the return light between optical couplers.

[0012] Solutions for solving technical problems

[0013] One aspect of the present invention relates to an optical interferometric ranging sensor comprising: a light source that projects light while continuously varying its wavelength; a plurality of interferometers that generate interference light based on measurement light reflected from the measurement object by guiding the supplied light to the measurement object and at least a portion of reference light along an optical path different from the measurement light; a multi-stage optical coupler that is a series-connected multi-stage optical coupler that receives light from the light source from a preceding stage and branches the light into corresponding interferometers and subsequent stages of the plurality of interferometers; a suppression mechanism that suppresses the supply of light from the subsequent stage of the multi-stage optical coupler to the preceding stage; and a processing unit that calculates the distance to the measurement object based on the plurality of interference lights generated by the plurality of interferometers.

[0014] According to this method, in a multi-stage optical coupler, the supply of light from the later stage to the earlier stage is suppressed, thus suppressing the return light between optical couplers, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0015] In the above-described manner, the suppression mechanism may include an optical coupler, which is at least one of a multi-stage optical coupler, and is configured to make the amount of light branched to the subsequent stage greater than the amount of light branched to the corresponding interferometer.

[0016] According to this method, the supply of light from the later stage to the earlier stage is suppressed in the multi-stage optical coupler. Therefore, the light returning from the later stage optical coupler to the earlier stage optical coupler is suppressed, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0017] In the above method, it can also be set such that, when the ratio of the light quantity branched to the corresponding interferometer for the i-th stage optical coupler in a multi-stage optical coupler to the light quantity branched to the subsequent stage is Ri, it becomes R. i+1 ≥R i .

[0018] According to this method, the inconsistency in the amount of light received by each interferometer is reduced, thus improving the measurement accuracy of the optical interferometric ranging sensor.

[0019] In the above-described manner, the interferometer may generate interference beams based on the first reflected beam in the measurement beam that illuminates the object to be measured and is reflected by the object to be measured, and the second reflected beam in the reference beam that is reflected by the reference surface.

[0020] According to this method, interference beams are generated based on a first reflected beam from the measurement beam that illuminates and is reflected by the object being measured, and a second reflected beam from the reference beam that is reflected by a reference surface. For each beam branching off corresponding to multiple spots, the optical path length difference between the measurement beam and the reference beam is set to be different. Therefore, each peak can be appropriately measured, and the distance to the object being measured can be calculated with high precision based on the distance value corresponding to the detected peak.

[0021] Alternatively, as described above, the optical path length from the i-th optical coupler to the reference plane of its corresponding interferometer can be set to L. CR,i Let L be the optical path length from the i-th stage optical coupler to the (i+1)-th stage optical coupler. CC,i In the case of |L CR,i -(L CR,i+1 +L CC,i | Becomes above the first threshold.

[0022] According to this method, the interference between multiple interferometric beams generated by multiple interferometers can be suppressed, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0023] In the above method, the first threshold may also be set based on the frequency band of the light-receiving unit that converts multiple interference lights into electrical signals and supplies them to the processing unit.

[0024] According to this method, the interference between multiple interfering beams can be effectively suppressed based on the frequency band of the light-receiving part, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0025] In the above-described manner, the suppression mechanism may also include a partition, which is connected between two optical couplers in a multi-stage optical coupler and configured to guide light from the preceding optical coupler to the following optical coupler, but not from the following optical coupler to the preceding optical coupler.

[0026] According to this method, the return light from the subsequent optical coupler to the preceding optical coupler can be suppressed, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0027] Alternatively, as described above, the optical path length from the i-th optical coupler to the reference plane of its corresponding interferometer can be set to L. CR,i Let L be the optical path length from the i-th stage optical coupler to the partition on the subsequent stage connected to it. CI,i In the case of |L CR,i -L CI,i |Becomes above the second threshold.

[0028] According to this method, the interference between the reflected light from the partition and the interference light generated by the interferometer can be suppressed, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0029] In the above method, the second threshold may also be set based on the frequency band of the light-receiving part of the processing unit, which converts multiple interference lights into electrical signals and supplies them to the processing unit.

[0030] According to this method, the interference between the reflected light from the isolation section and the interference light generated by the interferometer can be effectively suppressed based on the frequency band of the light receiving section, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0031] Invention Effects

[0032] According to the present invention, an optical interferometric ranging sensor is provided that improves measurement accuracy by suppressing the return light between optical couplers. Attached Figure Description

[0033] Figure 1 This is a schematic diagram showing the outline of the displacement sensor 10 involved in this disclosure.

[0034] Figure 2 This is a flowchart illustrating the process of measuring the object T using the displacement sensor 10 disclosed herein.

[0035] Figure 3 This is a functional block diagram showing the general outline of a sensor system 1 using the displacement sensor 10 disclosed herein.

[0036] Figure 4 This is a flowchart illustrating the process of measuring the object T by using the sensor system 1 of the displacement sensor 10 disclosed herein.

[0037] Figure 5A This is a diagram used to illustrate the principle of measuring the object T by means of the displacement sensor 10 involved in this disclosure.

[0038] Figure 5B This is a diagram used to illustrate other principles of measuring the object T by the displacement sensor 10 involved in this disclosure.

[0039] Figure 6A This is a perspective view showing the schematic structure of the sensor head 20.

[0040] Figure 6B This is a perspective view showing the schematic structure of the collimating lens holder disposed inside the sensor head 20.

[0041] Figure 6C This is a cross-sectional view showing the internal structure of the sensor head 20.

[0042] Figure 7 This is a block diagram used to illustrate the signal processing of the controller 30.

[0043] Figure 8 This is a flowchart illustrating the method by which the processing unit 59 in the controller 30 calculates the distance to the object being measured, T.

[0044] Figure 9A It is a graph that shows how a waveform signal (voltage vs. time) is converted from frequency to spectrum (voltage vs. frequency).

[0045] Figure 9B It is a diagram showing how the spectrum (voltage vs. frequency) is converted from distance to spectrum (voltage vs. distance).

[0046] Figure 9C This is a graph showing how values ​​(distance value, SNR) corresponding to peak values ​​are calculated based on the spectrum (voltage vs. distance).

[0047] Figure 10 This is a schematic diagram showing the structural outline of the optical interferometric ranging sensor 100 according to the first embodiment of the present invention.

[0048] Figure 11 This is a schematic diagram showing the structural outline of the optical interferometric ranging sensor 200 according to the second embodiment of the present invention.

[0049] Figure 12 This is a diagram showing the changes in the interferometer used to produce interference light by using measuring light and reference light.

[0050] Explanation of reference numerals in the attached figures

[0051] 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; 22, 22a-22c;Colliding lens; 23...Objective lens holder; 24, 24a-24c...Colliding lens unit; 30...Controller; 31...Display unit; 32...Setting unit; 33...External interface (I / F) unit; 34...Fiber optic connection unit; 35...External storage unit; 36...Measurement processing unit; 40...Fiber optic cable; 51...Wavelength scanning light source; 52...Optical amplifier; 53, 53a-53b...Isolator; 54, 54a-54e...Optical coupler; 55...Attenuator; 56a-56c...Light receiving element; 57...Synthetic circuit; 58...AD converter; 59...Processing unit; 60...Balance detector; 61...Correction signal generator Components; 71a~71e...light receiving element; 72a~72c...amplifier circuit; 73...wave combiner circuit; 74...AD converter; 75...processing unit; 76...differential amplifier circuit; 77...correction signal generation unit; 100, 200...optical interferometric ranging sensor; 110...wavelength scanning light source; 120a~120c...optical coupler; 122...attenuator; 130a~130c...interferometer; 131a~13 1c...Sensor head; 132a~132c...Objective lens; 140a~140c...Light receiving part; 141a~141c...Light receiving element; 142a~142c...AD conversion part; 150...Processing part; 221a, 221b...Isolators; a1~a4, b1~b4, c1~c4...Ports of optical coupler; T...Measured object; Lm1~Lm3...Measurement optical path; Lr1~Lr3...Reference optical path. Detailed Implementation

[0052] Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings. Furthermore, the embodiments described below are merely illustrative examples of specific ways to implement the present invention and are not intended to limit the scope of the invention. Additionally, for ease of understanding, the same structural elements in the various drawings will be labeled with the same reference numerals as much as possible, and sometimes repeated descriptions will be omitted.

[0053] [Overview of Displacement Sensors]

[0054] First, a summary of the displacement sensor involved in this disclosure will be given.

[0055] Figure 1 This is a schematic diagram showing the outline of the displacement sensor 10 involved in this disclosure.Figure 1 As shown, the displacement sensor 10 includes a sensor head 20 and a controller 30, and measures the displacement (distance to the object T) of the object being measured.

[0056] The sensor head 20 is connected to the controller 30 via an optical fiber 40, and an objective lens 21 is mounted on the sensor head 20. In addition, the controller 30 includes a display unit 31, a setting unit 32, an external interface (I / F) unit 33, an optical fiber connection unit 34, an external storage unit 35, and a measurement processing unit 36 ​​inside.

[0057] The sensor head 20 illuminates the object being measured, T, with light output from the controller 30 and receives reflected light from the object being measured, 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 interferes with the reflected light from the object being measured, T.

[0058] Furthermore, an objective lens 21 is mounted on the sensor head 20, but this objective lens 21 is a detachable structure. The objective lens 21 can also be replaced with an objective lens with an appropriate focal length depending on the distance between the sensor head 20 and the object being measured T, or a variable focus objective lens can be used.

[0059] Alternatively, when setting the sensor head 20, the sensor head 20 and / or the object being measured can be set in such a way that the object being measured T is illuminated with guiding light (visible light) and the object being measured T is properly positioned within the measurement area of ​​the displacement sensor 10.

[0060] The optical fiber 40 is connected to and extends from the optical fiber connector 34 disposed on the controller 30, connecting the controller 30 to the sensor head 20. Thus, the optical fiber 40 is configured to guide light projected from the controller 30 to the sensor head 20 and to guide reflected light from the sensor head 20 back to the controller 30. Furthermore, the optical fiber 40 can be detached from and mounted on both the sensor head 20 and the controller 30, allowing for the application of various optical fibers in terms of length, thickness, and characteristics.

[0061] The display unit 31 is, for example, composed of a liquid crystal display or an organic EL display. The display unit 31 displays the set value of the displacement sensor 10, the amount of light received from the return light from the sensor head 20, and the measurement results such as the displacement of the object T being measured (the distance to the object T being measured) measured by the displacement sensor 10.

[0062] The setting unit 32 allows users to make settings for the object T being measured, for example, by operating mechanical buttons or a touch panel. All or some of these settings can be preset or set from an external connection device (not shown) connected to the external I / F unit 33. Furthermore, the external connection device can be connected via a network in a wired or wireless manner.

[0063] Here, the external I / F unit 33 may be configured with Ethernet (registered trademark), RS232C, or analog output, for example. Alternatively, the external I / F unit 33 may connect to other connection devices and perform the required settings from those external connection devices, or output the measurement results measured by the displacement sensor 10 to the external connection devices.

[0064] Alternatively, the controller 30 may acquire data stored in the external storage unit 35, thereby performing the settings required for measuring the object T. The external storage unit 35 may be an auxiliary storage device such as a USB (Universal Serial Bus) memory, which pre-stores settings required for measuring the object T.

[0065] The measurement processing unit 36 ​​of the controller 30 includes, for example, a wavelength scanning light source that projects 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. In the measurement processing unit 36, based on the returned light from the sensor head 20, various processes are performed using a control unit and a storage unit to calculate the displacement (distance to the measured object T) of the object being measured. Details of these processes will be described later.

[0066] Figure 2 This is a flowchart illustrating the process by which the displacement sensor 10 involved in this disclosure measures the object T. For example... Figure 2 As shown, the process includes steps S11 to S14.

[0067] In step S11, the sensor head 20 is set. For example, a guide light is shone from the sensor head 20 onto the object T to be measured, and the object T is used as a reference to set the sensor head 20 in an appropriate position.

[0068] Specifically, the display unit 31 of the controller 30 can display the amount of light received from the sensor head 20, and the user can check this amount of light while adjusting the orientation of the sensor head 20 and the distance (height position) between it and the object being measured T. If the light from the sensor head 20 can be shone substantially perpendicularly (at an angle closer to perpendicular) to the object being measured T, the amount of light reflected from the object being measured T increases, and the amount of light received from the sensor head 20 also increases.

[0069] Alternatively, an objective lens 21 with an appropriate focal length can be used depending on the distance between the sensor head 20 and the object being measured, T.

[0070] Furthermore, if the measurement object T cannot be properly set (for example, the required amount of light is not obtained, or the focal length of the objective lens 21 is inappropriate), the error or setting incomplete information can be displayed on the display unit 31 or output to an external connection device to notify the user.

[0071] In step S12, various measurement conditions are set when measuring the object T. For example, the inherent correction data (correction linearity function, etc.) of the sensor head 20 are set by the setting unit 32 of the user operation controller 30.

[0072] In addition, various parameters can be set. For example, sampling time, measurement range, and thresholds for determining whether the measurement results are normal or abnormal can be set. Furthermore, the measurement period can be set based on the characteristics of the object T, such as its reflectivity and material, and the measurement mode corresponding to the material of the object T can be set.

[0073] Furthermore, these measurement conditions and various parameter settings can be set via the setting unit 32 of the operation controller 30, but they can also be set via an external connection device or by acquiring data from the external storage unit 35.

[0074] In step S13, the sensor head 20 set in step S11 measures the object T according to the measurement conditions and various parameters set in step S12.

[0075] Specifically, in the measurement processing unit 36 ​​of the controller 30, light is projected from the wavelength scanning light source, and the reflected light from the sensor head 20 is received by the light receiving element. The signal processing circuit performs frequency analysis, distance conversion, and peak detection, and calculates the displacement of the object being measured (the distance to the object being measured T). Details of the specific measurement processing will be described later.

[0076] In step S14, the measurement results measured in step S13 are output. For example, the displacement of the measured object T (the distance to the measured object T) measured in step S13 is displayed on the display unit 31 of the controller 30, or output to an external connection device.

[0077] Alternatively, the displacement of the object T measured in step S13 (the distance to object T) can be displayed or output as a measurement result, based on the threshold set in step S12, indicating whether it falls within the normal range or is abnormal. Furthermore, the measurement conditions, various parameters, and measurement modes set in step S12 can also be displayed or output.

[0078] [Overview of a system including displacement sensors]

[0079] Figure 3 This is a functional block diagram showing the general outline of a sensor system 1 using the displacement sensor 10 according to the present invention. For example... Figure 3 As shown, the sensor system 1 includes a displacement sensor 10, a control device 11, a control signal input sensor 12, and an external connection device 13. Furthermore, the control device 11 and the external connection device 13 are connected, for example, via communication cables or external connection lines (e.g., including external input lines, external output lines, and power lines), and the control device 11 and the control signal input sensor 12 are connected via signal lines.

[0080] If used Figure 1 as well as Figure 2 As explained, the displacement sensor 10 measures the displacement (distance to the object T) of the object being measured. Furthermore, the displacement sensor 10 can output the measurement results to the control device 11 and the external connection device 13.

[0081] The control device 11 is, for example, a PLC (Programmable Logic Controller), and provides various indications to the displacement sensor 10 when the displacement sensor 10 measures the object T being measured.

[0082] For example, based on the input signal from the control signal input sensor 12 connected to the control device 11, the control device 11 may output a measurement timing signal to the displacement sensor 10, or output a zero reset command signal (a signal used to set the current measurement value to 0) to the displacement sensor 10.

[0083] The control signal input sensor 12 outputs a timing on / off signal indicating the time of the measured object T from the displacement sensor 10 to the control device 11. For example, the control signal input sensor 12 is placed near the production line where the measured object T moves, and upon detecting that the measured object T has moved to a predetermined position, it outputs an on / off signal to the control device 11.

[0084] The external connection device 13 is, for example, a PC (Personal Computer), which allows the user to make various settings for the displacement sensor 10.

[0085] As a specific example, the measurement mode, action mode, measurement cycle, and the material of the object T to be measured are set.

[0086] As for the setting of the measurement mode, you can choose either the "internal synchronous measurement mode" in which the measurement starts periodically inside the control device 11 or the "external synchronous measurement mode" in which the measurement starts based on the input signal from outside the control device 11.

[0087] As for setting the operation mode, you can select the "operation mode" of the actual object T being measured or set the "adjustment mode" for the measurement conditions of the object T being measured.

[0088] The measurement period is the period during which the object T is measured, and it can be set according to the reflectivity of the object T. However, if the reflectivity of the object T is low, the object T can be measured appropriately by making the measurement period longer.

[0089] For the object T being measured, select the "rough surface mode" which is suitable for cases where diffuse reflection is more of a component of reflected light, the "mirror mode" which is suitable for cases where specular reflection is more of a component of reflected light, or the "standard mode" in between.

[0090] By making appropriate settings based on the reflectivity and material of the object being measured, T can be measured with higher precision.

[0091] Figure 4 This is a flowchart illustrating the process of measuring the object T by using the sensor system 1 of the displacement sensor 10 disclosed herein. Figure 4 As shown, the process is the same as the external synchronous measurement mode described above, and includes steps S21 to S24.

[0092] In step S21, sensor system 1 detects the object to be measured, namely the object T. Specifically, the control signal input is used by sensor 12 to detect that the object T has moved to a predetermined position on the production line.

[0093] In step S22, the sensor system 1 provides measurement indication by measuring the 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 indicate the timing of measuring the object T detected in step S21, and the control device 11 provides measurement indication by outputting a measurement timing signal to the displacement sensor 10 based on the on / off signal and measuring the object T.

[0094] In step S23, the object to be measured, T, is measured by the displacement sensor 10. Specifically, the displacement sensor 10 measures the object T based on the measurement instruction received in step S22.

[0095] In step S24, the sensor system 1 outputs the measurement results obtained in step S23. Specifically, the displacement sensor 10 displays the measurement results on the display unit 31, or outputs them to the control device 11 or external connection device 13 via the external I / F unit 33.

[0096] It should be noted that the term used here is... Figure 4 The following describes the process in the case of an external synchronous measurement mode where the object T is measured by detecting it using sensor 12 via a control signal input, but is not limited thereto. For example, in the case of an internal synchronous measurement mode, instead of steps S21 and S22, the displacement sensor 10 is indicated by generating a measurement timing signal based on a preset period to measure the object T.

[0097] Next, the principle of measuring the object T by means of the displacement sensor 10 involved in this disclosure will be explained. Figure 5A This diagram illustrates the principle of measuring the object T using the displacement sensor 10 disclosed herein. (See diagram for example.) Figure 5A As shown, the displacement sensor 10 includes a sensor head 20 and a controller 30. The sensor head 20 includes an objective lens 21 and multiple collimating lenses 22a-22c. The controller 30 includes a wavelength scanning light source 51, an optical amplifier 52, multiple isolators 53 and 53a-53b, multiple optical couplers 54 and 54a-54e, an attenuator 55, multiple light-receiving elements (e.g., photodetectors (PD)) 56a-56c, a multiplexing circuit 57, an analog-to-digital (AD) conversion unit (e.g., an analog-to-digital converter) 58, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generation unit 61.

[0098] The wavelength scanning light source 51 projects laser light that has scanned the wavelength. As a wavelength scanning light source 51, for example, if a current-modulated VCSEL (Vertical Cavity Surface Emitting Laser) is used, mode hopping is not easy to occur due to the short resonator length, and wavelength changes are easy to achieve, which can be implemented at low cost.

[0099] Optical amplifier 52 amplifies the light projected from wavelength scanning light source 51. Optical amplifier 52 may be an EDFA (erbium-doped fiber amplifier), or a dedicated 1550nm optical amplifier.

[0100] Isolator 53 is an optical element that allows incident light to pass through in one direction. In order to prevent the influence of noise generated by the return light, it can also be configured immediately after the wavelength scanning light source 51.

[0101] In this way, the light projected from the wavelength scanning light source 51 is amplified by the optical amplifier 52, and then branched into a main interferometer and a secondary interferometer by the optical coupler 54 via the isolator 53. For example, in the optical coupler 54, the main interferometer and the secondary interferometer can also branch the light in a ratio of 90:10 to 99:1.

[0102] The light from the main interferometer is further split into the direction of the sensor head 20 and the direction of the second-stage optical coupler 54b by the first-stage optical coupler 54a.

[0103] Light branching from the first-stage optical coupler 54a into the sensor head 20 passes through the collimating lens 22a and the objective lens 21 from the front end of the optical fiber in the sensor head 20 and illuminates the object T being measured. Furthermore, the front end (end face) of this optical fiber serves as a reference surface. The light reflected from this reference surface interferes with the light reflected from the object T, generating interference light that returns to the first-stage optical coupler 54a. Subsequently, it is received by the light-receiving element 56a and converted into an electrical signal.

[0104] Light branched from the first-stage optical coupler 54a into the second-stage optical coupler 54b is directed towards the second-stage optical coupler 54b via the isolator 53a. The second-stage optical coupler 54b further branches the light towards the sensor head 20 and the third-stage optical coupler 54c. The light branched from the optical coupler 54b into the sensor head 20 is the same as in the first stage. In the sensor head 20, the light from the front end of the optical fiber passes through the collimating lens 22b and the objective lens 21 and illuminates the object being measured, T. Furthermore, the front end (end face) of the optical fiber serves as a reference surface. The light reflected from this reference surface interferes with the light reflected from the object being measured, T, generating interference light that returns to the second-stage optical coupler 54b. Through the optical coupler 54b, the light is branched towards the isolator 53a and the light-receiving element 56b, respectively. The light branched from the optical coupler 54b towards the light-receiving element 56b is received by the light-receiving element 56b and converted into an electrical signal. On the other hand, isolator 53a is an example of a suppression mechanism and a blocking part. It allows light to pass through from the front-stage optical coupler 54a to the rear-stage optical coupler 54b and blocks the light from the rear-stage optical coupler 54b to the front-stage optical coupler 54a. Therefore, the light branching from the optical coupler 54b to the isolator 53a is blocked.

[0105] Light branched from the second-stage optical coupler 54b into the third-stage optical coupler 54c is directed towards the third-stage optical coupler 54c via the isolator 53b. The third-stage optical coupler 54c further branches the light in the direction of the sensor head 20 and the attenuator 55. The light branched from the optical coupler 54c into the sensor head 20 is the same as that of the first and second stages. In the sensor head 20, the light passes from the front end of the optical fiber through the collimating lens 22c and the objective lens 21 and illuminates the object being measured, T. Furthermore, the light reflected from the front end (end face) of the optical fiber interferes with the light reflected from the object being measured, T, producing interference light that returns to the third-stage optical coupler 54c, branching from the optical coupler 54c in the respective directions of the isolator 53b and the light-receiving element 56c. The isolator 53b is an example of a suppression mechanism that suppresses the supply of light from the subsequent-stage optical coupler 54c to the preceding-stage optical coupler 54b. 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.

[0106] The light that is branched into the direction of the attenuator 55 by the third-stage optical coupler 54c is not used in the measurement of the object T and is therefore attenuated in a way that it is not reflected back.

[0107] Thus, the main interferometer has three optical paths (three channels), which become an interferometer that uses twice the distance (reciprocating) from the front end (end face) of the optical fiber of each sensor head 20 to the object T to be measured as the optical path length difference, and generates three interference beams corresponding to each optical path length difference.

[0108] The light-receiving elements 56a to 56c receive interference light from the main interferometer as described above, and generate an electrical signal corresponding to the amount of light received.

[0109] The multiplexing circuit 57 performs multiplexing on the electrical signals output from the light-receiving elements 56a to 56c.

[0110] The AD conversion unit 58 receives an electrical signal from the multiplexing circuit 57 and converts the electrical signal from an analog signal to a digital signal (AD conversion). Here, the AD conversion unit 58 performs AD conversion based on the correction signal from the correction signal generation unit 61 of the sub-interferometer.

[0111] In the sub-interferometer, in order to correct the nonlinearity of the wavelength during the scanning of the wavelength scanning light source 51, the sub-interferometer is used to acquire the interference signal and generate a correction signal called the K clock.

[0112] Specifically, the light branched into a sub-interferometer by optical coupler 54 is further branched by optical coupler 54d. Here, the optical paths of each branched light are configured, for example, to have a path length difference by using optical fibers of different lengths between optical coupler 54d and optical coupler 54e, and the interference light corresponding to this path length difference is output from optical coupler 54e. Moreover, the balanced detector 60 receives the interference light from optical coupler 54e, removes noise by taking the difference between the signal and the signal out of phase, and amplifies the optical signal to convert it into an electrical signal.

[0113] In addition, both optical couplers 54d and 54e can be used to branch the light in a 50:50 ratio.

[0114] The correction signal generation unit 61, based on the electrical signal from the balance detector 60, grasps the nonlinearity of the wavelength of the wavelength scanning light source 51 during scanning, generates a K clock corresponding to the nonlinearity, and outputs it to the AD conversion unit 58.

[0115] Due to the nonlinearity of the wavelength during scanning by the wavelength scanning light source 51, the intervals of the analog signal waves input to the AD converter 58 in the main interferometer are not equal. In the AD converter 58, the sampling time is corrected for AD conversion (sampling) based on the aforementioned K clock to make the intervals of the waves equal.

[0116] Furthermore, as described above, the K clock is a correction signal used to sample the analog signal of the main interferometer; therefore, it 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 can be made greater than the optical path length difference between the front end (end face) of the optical fiber in the main interferometer and the object being measured, or the frequency can be multiplied (e.g., by 8 times) by the correction signal generation unit 61 to achieve a higher frequency.

[0117] Processing unit 59 acquires the digital signal after nonlinearity correction by AD conversion unit 58 and AD conversion, and calculates the displacement of the measured object T (the distance to the measured object T) based on the digital signal. Specifically, in processing unit 59, high-speed Fourier transform (FFT) is used to perform frequency conversion on the digital signal, and the distance is calculated by analyzing it. The detailed processing of processing unit 59 will be described later.

[0118] Furthermore, high-speed processing is required in the processing unit 59, so it is often implemented using integrated circuits such as field-programmable gate arrays (FPGAs).

[0119] Alternatively, the multiplexer circuit 57 is positioned before the AD converter 58, but it can also be positioned after the AD converter 58. The outputs from multiple PDs 56a to 56c are converted to AD values ​​separately, and then combined by the multiplexer circuit 57.

[0120] Furthermore, here, a three-stage optical path is set in the main interferometer. Measurement light is irradiated from each optical path relative to the object T through the sensor head 20. Based on the interference light (return light) obtained from each path, the distance to the object T is measured (multi-channel). The number of channels in the main interferometer is not limited to three; it can also be one, two, or more than four.

[0121] Figure 5B This is a diagram used to illustrate other principles of measuring the object T by means of the displacement sensor 10 involved in this disclosure. For example... Figure 5B As shown, the displacement sensor 10 includes a sensor head 20 and a controller 30. The sensor head 20 includes an objective lens 21 and multiple collimating lenses 22a-22c. The controller 30 includes a wavelength scanning light source 51, an optical amplifier 52, multiple isolators 53 and 53a-53b, multiple optical couplers 54 and 54a-54j, an attenuator 55, multiple light-receiving elements (e.g., photodetectors (PD)) 56a-56c, a multiplexing circuit 57, an analog-to-digital (AD) conversion unit (e.g., an analog-to-digital converter) 58, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generation unit 61. Figure 5B The displacement sensor 10 shown is mainly similar to the one with optical couplers 54f to 54j. Figure 5A The displacement sensor 10 shown has a different structure. Regarding the principle based on this different structure, and... Figure 5A Compare and explain in detail.

[0122] The light projected from the wavelength scanning light source 51 is amplified by the optical amplifier 52, and then split into the main interferometer side and the sub-interferometer side via the isolator 53 and the optical coupler 54. However, the light split into the main interferometer side is further split into the measurement light and the reference light via the optical coupler 54f.

[0123] like Figure 5A As explained, the measuring light passes through the first-stage optical coupler 54a, then through the collimating lens 22a and the objective lens 21, and illuminates the object T being measured, and is reflected by the object T. Here, Figure 5A In this process, the front end (end face) of the optical fiber is used as a reference surface. The light reflected from this reference surface interferes with the light reflected from the object being measured, T, generating interference light. Figure 5B In this context, no reference surface is provided for light reflection. That is, Figure 5B In, such as Figure 5A Therefore, no light is generated that is reflected from the reference surface, and the measurement light reflected from the object being measured, T, returns to the first-stage optical coupler 54a.

[0124] Similarly, light from the direction where the first-stage optical coupler 54a branches into the second-stage optical coupler 54b passes through the second-stage optical coupler 54b, through the collimating lens 22b and the objective lens 21, and illuminates the object T being measured. Light is then reflected by the object T and returns to the second-stage optical coupler 54b. Light from the direction where the second-stage optical coupler 54b branches into the third-stage optical coupler 54c passes through the third-stage optical coupler 54c, through the collimating lens 22c and the objective lens 21, and illuminates the object T being measured. Light is then reflected by the object T and returns to the third-stage optical coupler 54c.

[0125] On the other hand, the reference light branched by optical coupler 54f is further branched by optical coupler 54g into optical couplers 54h, 54i and 54j.

[0126] In optical coupler 54h, the measurement light reflected by the object being measured T and output from optical coupler 54a interferes with the reference light output from optical coupler 54g, generating interference light, which is received by light-receiving element 56a and converted into an electrical signal. In other words, the measurement light is branched into a measurement light and a reference light by optical coupler 54f, generating interference light corresponding to the optical path length difference between the measurement light (the optical path from optical coupler 54f through optical coupler 54a, collimating lens 22a, and objective lens 21, reflected by the object being measured T, and reaching optical coupler 54h) and the reference light (the optical path from optical coupler 54f through optical coupler 54g, reaching optical coupler 54h). This interference light is received by light-receiving element 56a and converted into an electrical signal.

[0127] Similarly, in the optical coupler 54i, interference light is generated corresponding to the optical path length difference between the measurement light (the optical path from optical coupler 54f through optical couplers 54a, 54b, collimating lens 22b, objective lens 21, reflected by the object T to reach optical coupler 54i) and the reference light (the optical path from optical coupler 54f through optical coupler 54g to reach optical coupler 54i). This interference light is received by the light receiving element 56b and converted into an electrical signal.

[0128] In the optical coupler 54j, interference light is generated corresponding to the optical path length difference between the optical path of the measurement light (the optical path from optical coupler 54f through optical couplers 54a, 54b, 54c, collimating lens 22c, objective lens 21, reflected by the object T to reach optical coupler 54j) and the optical path of the reference light (the optical path from optical coupler 54f through optical coupler 54g to reach optical coupler 54j). This interference light is received by the light receiving element 56c and converted into an electrical signal.

[0129] Thus, the main interferometer has three optical paths (three channels) to generate three interference beams corresponding to the optical path length differences between the measurement beams reflected by the object T and input to optical couplers 54h, 54i, and 54j, and the illumination beams input to optical couplers 54h, 54i, and 54j via optical couplers 54f and 54g, respectively.

[0130] Alternatively, the difference in optical path length between the measuring light and the reference light can be set to be different in each of the three channels. For example, the optical path length between optical coupler 54g and each of the optical couplers 54h, 54i and 54j can be different.

[0131] Furthermore, based on the interference light obtained from each of them, the distance to the object T being measured is measured (multi-channel).

[0132] [Sensor head construction]

[0133] Here, the construction of the sensor head used for displacement sensor 10 will be described.

[0134] Figure 6A This is a perspective view showing the schematic structure of the sensor head 20. Figure 6B This is a perspective view showing the schematic structure of the collimating lens holder arranged inside the sensor head 20. Figure 6C It is a cross-sectional view showing the internal structure of the sensor head.

[0135] like Figure 6AAs shown, the sensor head 20 stores the objective lens 21 and the collimating lens in the objective lens holder 23. For example, for the size of the objective lens holder 23, the length of one side surrounding the objective lens 21 is about 10 mm, and the length in the optical axis direction is about 22 mm.

[0136] like Figure 6B As shown, the collimating lens unit 24 is configured such that the collimating lens 22 is fixed to the collimating lens holder using an adhesive material. Furthermore, it is configured to insert an optical fiber, allowing the spot diameter to be adjusted according to the insertion depth. For example, the collimating lens 22 has a diameter of approximately 2 mm.

[0137] like Figure 6C As shown, the three collimating lenses 22a to 22c are held by collimating lens holders to form collimating lens units 24a to 24c, and the three optical fibers are inserted into the collimating lens units 24a to 24c in a manner corresponding to the three collimating lenses 22a to 22c. Alternatively, the three optical fibers may each be held by a collimating lens holder.

[0138] Furthermore, the aforementioned optical fiber and collimating lens units 24a to 24c, together with the objective lens 21, are held by the objective lens holder 23 to form the sensor head 20.

[0139] It should be noted that here, such as Figure 6C As shown, the three collimating lens units are staggered to create different optical path length differences at positions along the optical axis of the sensor head 20.

[0140] In addition, the objective lens holder 23 and collimating lens units 24a to 24c constituting the sensor head 20 can also be made of a high-strength metal that can be machined with high precision (e.g., A2017).

[0141] Figure 7 This is a block diagram used to illustrate the signal processing in controller 30. For example... Figure 7 As shown, the controller 30 includes multiple light-receiving elements 71a to 71e, multiple amplification circuits 72a to 72c, a multiplexing circuit 73, an AD conversion unit 74, a processing unit 75, a differential amplifier circuit 76, and a correction signal generation unit 77.

[0142] In controller 30, such as Figure 5A As shown, the light projected from the wavelength scanning light source 51 is branched into the main interferometer and the sub-interferometer by the optical coupler 54, and the distance to the object T to be measured is calculated by processing the main interference signal and the sub-interferometer obtained from them respectively.

[0143] Multiple light-receiving elements 71a to 71c are equivalent to Figure 5AThe light-receiving elements 56a to 56c shown receive the main interference signal from the main interferometer and output it as a current signal to the amplifier circuits 72a to 72c.

[0144] Multiple amplifier circuits 72a to 72c convert the current signal (IV conversion) into a voltage signal and amplify it.

[0145] The multiplexing circuit 73 combines the voltage signals output from the amplifier circuits 72a to 72c and outputs them as a single voltage signal to the AD converter 74.

[0146] AD converter 74 is equivalent to Figure 5A The AD conversion unit 58 shown converts the voltage signal (AD conversion) into a digital signal based on the K clock from the correction signal generation unit 77 described later.

[0147] Processing unit 75 is equivalent to Figure 5A The processing unit 59 shown uses FFT to convert the digital signals from the AD conversion unit 74 into frequencies, and analyzes them to calculate the distance value up to the object being measured, T.

[0148] Multiple light-receiving elements 71d to 71e and differential amplifier circuit 76 are equivalent to Figure 5A The balanced detector 60 shown receives interference light from the sub-interferometer, and outputs a phase-reversed interference signal. Noise is removed by taking the difference between the two signals, and the interference signal is amplified and converted into a voltage signal.

[0149] The correction signal generation unit 77 is equivalent to Figure 5A The correction signal generation unit 61 shown binarizes the voltage signal using a comparator, generates a K clock, and outputs it to the AD conversion unit 74. The K clock needs to be generated at a higher frequency than the analog signal of the main interferometer; therefore, the frequency can also be multiplied (e.g., by 8 times) by the correction signal generation unit 77 to achieve a higher frequency.

[0150] In addition, for Figure 7 In the controller 30 shown, the multiplexing circuit 73 is located in the pre-stage of the AD converter 74, but it can also be located in the post-stage of the AD converter 74. The outputs of the multiple light-receiving elements 71a to 71c and the multiple amplifier circuits 72a to 72c are respectively converted by AD, and then combined by the multiplexing circuit 73.

[0151] Figure 8 This is a flowchart illustrating the method for calculating the distance to the object T being measured, executed by the processing unit 59 of the controller 30. (Example) Figure 8 As shown, the method includes steps S31 to S35.

[0152] In step S31, the processing unit 59 uses the following FFT to convert the frequency of the waveform signal (voltage vs time) into a spectrum (voltage vs frequency). Figure 9A It is a diagram showing the conversion of the frequency of a waveform signal (voltage vs. time) into a spectrum (voltage vs. frequency).

[0153] Formula 1

[0154]

[0155] N: Number of data points

[0156] In step S32, the processing unit 59 converts the spectrum (voltage vs. frequency) distance into a spectrum (voltage vs. distance). Figure 9B This is a diagram showing the conversion of spectral (voltage vs. frequency) distance to spectral (voltage vs. distance).

[0157] In step S33, the processing unit 59 calculates the value (distance value, SNR) corresponding to the peak value based on the spectrum (voltage vs. distance). Figure 9C It is a graph that shows the values ​​(distance value, SNR) corresponding to the peak value calculated based on the spectrum (voltage vs. distance).

[0158] (1) Calculate the peak voltage. Specifically, for Figure 9C The voltage shown is a combination of the distance from which the differential value of the voltage changes from positive to negative, and the voltage value (D). x V x The groups are arranged in descending order of voltage value.

[0159] (D1, V1), (D2, V2), (D3, V3), ..., (D n V n )

[0160] (2) Exclude combinations with more than one head. For example, such as... Figure 5A As shown, for the displacement sensor 10, a three-stage optical path is set in the main interferometer. Measurement light is irradiated onto the object T through each optical path via the sensor head 20, and the interference light (return light) received from each path is received (number of heads = 3). If there are more than four peak values, the peak values ​​exceeding three are based on noise sources and can be excluded from the calculation. With a number of heads = 3, these become (D1, V1), (D2, V2), and (D3, V3).

[0161] (3) Sort by distance. For example, if arranged in ascending order of distance, it becomes (D3, V3), (D1, V1), (D2, V2).

[0162] (4) Obtain the voltage between peak values. Specifically, obtain the midpoint distance between D3 and D1, i.e., D... 31 voltage V 31 To obtain the midpoint distance between D1 and D2, i.e., D... 12 voltage V 12 Furthermore, its average voltage Vn = (V 31 +V 12 ) / 2.

[0163] (5) Calculate their respective SNRs. Specifically, it becomes SN1 = V1 / V n SN2 = V2 / V n SN3 = V3 / V n .

[0164] Thus, based on the spectrum (voltage vs. distance), the values ​​corresponding to the peak values ​​(distance value, SNR) are calculated as (D1, SN1), (D2, SN2), and (D3, SN3).

[0165] return Figure 8 In step S34, the processing unit 59 corrects the distance value in the values ​​(distance value, SNR) corresponding to the peak value calculated in step S33. Specifically, as follows... Figure 6C As shown, the three collimating lens units 24a to 24c (collimating lenses 22a to 22c and each optical fiber) are staggered in position along the optical axis of the sensor head 20. Therefore, the distance values ​​D1, D2, and D3 corresponding to the peak values ​​are corrected according to the staggered amount (e.g., h1, h2, h3, etc.).

[0166] Therefore, the values ​​corresponding to the peak (corrected distance value, SNR) are (D1+h1, SN1), (D2+h2, SN2), and (D3+h3, SN3).

[0167] In step S35, the processing unit 59 averages the distance values ​​(corrected distance value, SNR) corresponding to the peak value calculated in step S34. Specifically, the processing unit 59 preferably averages the corrected distance values ​​(corrected distance value, SNR) corresponding to the peak value where the SNR is above a threshold, and outputs the averaged calculation result as the distance to the object T being measured.

[0168] Next, this disclosure will be described in detail, focusing on its more characteristic structure, function, and properties, as well as specific embodiments. Furthermore, the optical interferometric ranging sensor shown below is equivalent to using… Figure 1 The displacement sensor 10 illustrated in Figure 9, the optical interferometric ranging sensor, includes all or part of its basic structure, function, and properties as described above, and is used in conjunction with... Figure 1The displacement sensor 10 illustrated in Figure 9 shares the same structure, function, and properties.

[0169] <First Embodiment>

[0170] Figure 10 This is a schematic diagram showing the structural outline of the optical interferometric ranging sensor 100 according to the first embodiment of the present invention. Figure 10 As shown, the optical interferometric ranging sensor 100 includes a wavelength scanning light source 110, optical couplers 120a-120c, an attenuator 122, interferometers 130a-130c, light-receiving units 140a-140c, and a processing unit 150. Furthermore, when it is not necessary to distinguish between the optical couplers 120a-120c, they are sometimes referred to simply as optical coupler 120; when it is not necessary to distinguish between the interferometers 130a-130c, they are sometimes referred to simply as interferometer 130; and when it is not necessary to distinguish between the light-receiving units 140a-140c, they are sometimes referred to simply as light-receiving units 140. Figure 10 The optical interferometric ranging sensor 100 shown is configured as a multi-stage optical interferometric ranging sensor. As an example, it is configured as a three-stage optical interferometric ranging sensor with three interferometers, but the number of interferometers (i.e., the number of stages) can also be two or more.

[0171] The wavelength scanning light source 110 is directly connected to the first port a1 of the optical coupler 120 or indirectly connected to the first port a1 of the optical coupler 120 via other components (optical amplifier 52, isolator 53, optical coupler 54, etc.) to project light while continuously changing the wavelength.

[0172] Optical couplers 120a to 120c have a three-stage structure connected in series. That is, optical coupler 120a constitutes the first stage corresponding to interferometer 130a, optical coupler 120b constitutes the second stage corresponding to interferometer 130b, and optical coupler 120c constitutes the third stage corresponding to interferometer 130c.

[0173] Each optical coupler 120 has 2×2 (4) ports, and light input to one port at one end is output to the other two ports at a predetermined branch ratio. Specifically, the first-stage optical coupler 120a has a first port a1, a second port a2, a third port a3, and a fourth port a4. Light input to either the first port a1 or the second port a2 is output to the third port a3 and the fourth port a4 at a predetermined branch ratio. Additionally, light input to either the third port a3 or the fourth port a4 is output to the first port a1 and the second port a2 at a predetermined branch ratio.

[0174] Additionally, the second-stage optical coupler 120b has a first port b1, a second port b2, a third port b3, and a fourth port b4. Light input to either the first port b1 or the second port b2 is output to the third port b3 and the fourth port b4 with a predetermined branch ratio. Similarly, light input to either the third port b3 or the fourth port b4 is output to the first port b1 and the second port b2 with a predetermined branch ratio.

[0175] Additionally, the third-stage optical coupler 120c has a first port c1, a second port c2, a third port c3, and a fourth port c4. Light input to either the first port c1 or the second port c2 is output to the third port c3 and the fourth port c4 with a predetermined branching ratio. Similarly, light input to either the third port c3 or the fourth port c4 is output to the first port c1 and the second port c2 with a predetermined branching ratio.

[0176] The first port a1 of the first-stage optical coupler 120a is connected to the wavelength scanning light source 110, and light with continuously changing wavelength is directly or indirectly input from the wavelength scanning light source 110.

[0177] The first-stage optical coupler 120a branches the light input from the wavelength scanning light source 110 to port a1 at a predetermined branch ratio and outputs it to ports a3 and a4. The light output from port a3 of the first-stage optical coupler 120a is input to the first-stage interferometer 130a. The light output from port a4 of the first-stage optical coupler 120a is input to port b1 of the second-stage optical coupler 120b.

[0178] The second-stage optical coupler 120b branches the light input from the first-stage optical coupler 120a to port 1b1 at a predetermined branch ratio and outputs it to ports 3b3 and 4b4. The light output from port 3b3 of the second-stage optical coupler 120b is input to the second-stage interferometer 130b. The light output from port 4b4 of the second-stage optical coupler 120b is input to port 1c1 of the third-stage optical coupler 120c.

[0179] The third-stage optical coupler 120c branches the light input from the second-stage optical coupler 120b to port 1 (c1) at a predetermined branch ratio and outputs it to ports 3 (c3) and 4 (c4). The light output from port 3 (c3) of the third-stage optical coupler 120c is input to the third-stage interferometer 130c. The light output from port 4 (c4) of the third-stage optical coupler 120c is input to the attenuator 122.

[0180] Interferometers 130a to 130c each have sensor heads 131a to 131c. Sensor heads 131a to 131c each have objective lenses 132a to 132c. Alternatively, sensor heads 131a to 131c may each have a collimating lens disposed between the front end of the optical fiber and the objective lenses 132a to 132c.

[0181] Light input from port a3 of the first-stage optical coupler 120a to the first-stage interferometer 130a is input to the sensor head 131a via an optical fiber. A portion of the light input to the sensor head 131a is used as measurement light and is irradiated onto the object T being measured via the objective lens 132a, and reflected by the object T. Furthermore, the measurement light reflected from the object T is focused by the objective lens 132a of the sensor head 131a and input to the sensor head 131a. Another portion of the light input to the sensor head 131a is used as reference light and is reflected by a reference surface located at the front end of the optical fiber. The measurement light and the reference light interfere at the reference surface of the sensor head 131a, thereby generating a first interference light corresponding to the difference in optical path length between the measurement light and the reference light. This first interference light is output from the interferometer 130a and input to port a3 of the optical coupler 120a.

[0182] Light input from port b3 of the second-stage optical coupler 120b to the second-stage interferometer 130b is input to the sensor head 131b via an optical fiber. A portion of the light input to the sensor head 131b is used as measurement light and is irradiated onto the object T being measured via the objective lens 132b, and reflected by the object T. The measurement light reflected from the object T is then focused by the objective lens 132b of the sensor head 131b and input to the sensor head 131b. Another portion of the light input to the sensor head 131b is used as reference light and is reflected by a reference surface located at the tip of the optical fiber. The measurement light and the reference light interfere at the reference surface of the sensor head 131b, thereby generating a second interference light corresponding to the difference in optical path length between the measurement light and the reference light. This second interference light is output from the interferometer 130b and input to port b3 of the optical coupler 120b.

[0183] Light input from port c3 of the third-stage optical coupler 120c to the third-stage interferometer 130c is input to the sensor head 131c via an optical fiber. A portion of the light input to the sensor head 131c is used as measurement light and is irradiated onto the object T being measured via the objective lens 132c, and reflected by the object T. Furthermore, the measurement light reflected from the object T is focused by the objective lens 132c of the sensor head 131c and input to the sensor head 131c. Additionally, another portion of the light input to the sensor head 131c is used as reference light and is reflected by a reference surface located at the front end of the optical fiber. The measurement light and the reference light interfere at the reference surface of the sensor head 131c, thereby generating a third interference beam corresponding to the difference in optical path length between the measurement light and the reference light. This third interference beam is output from the interferometer 130c and input to port c3 of the optical coupler 120c.

[0184] Attenuator 122 attenuates the light input from port 4 (c4) of optical coupler 120c, reducing the reflected light to optical coupler 120c. By reducing this reflected light, the influence of phase noise can be reduced, and the optical interferometric ranging sensor 100 can measure the distance to the object T with higher accuracy.

[0185] The optical element used as the front connection to the optical fiber connected to the optical coupler 120c is not limited to attenuator 122, and can be other optical elements. For example, it can also be connected with an isolator, or the fiber tip can be processed to use coreless fiber, etc. In these cases, for example, it is preferable to reduce the reflected light to the optical coupler 120c by applying fusion splicing and APC polishing, etc., to reduce the effects of the aforementioned phase noise.

[0186] The light-receiving units 140a to 140c each have light-receiving elements 141a to 141c and AD conversion units 142a to 141c. The light-receiving elements 141a to 141c are, for example, photodetectors that receive light output from ports a2 to c2 of the optocouplers 120a to 120c and convert it into an electrical signal. The AD conversion units 142a to 142c convert this electrical signal from an analog signal to a digital signal.

[0187] The light-receiving parts 140a to 140c correspond to the optical couplers 120a to 120c, respectively, and receive the light output from the second ports a2 to c2 of the optical couplers 120a to 120c.

[0188] As described above, the first interference light generated by the first-stage interferometer 130a is output from the interferometer 130a and input to the third port a3 of the optical coupler 120a. Furthermore, the first-stage optical coupler 120a branches the first interference light input to the third port a3 at a predetermined branch ratio and outputs it to the first port a1 and the second port a2. The light receiving unit 140a receives the light output from the second port a2 of the optical coupler 120a, generates a digital signal based on this, and supplies it to the processing unit 150.

[0189] As described above, the second interference light generated by the second-stage interferometer 130b is output from the interferometer 130b and input to the third port b3 of the optical coupler 120b. Furthermore, the second-stage optical coupler 120b branches the second interference light input to the third port b3 at a predetermined branch ratio and outputs it to the first port b1 and the second port b2. The light receiving unit 140b receives the light output from the second port b2 of the optical coupler 120b and generates a digital signal based on this signal, which is then supplied to the processing unit 150.

[0190] As described above, the third interference light generated by the third-stage interferometer 130c is output from the interferometer 130c and input to the third port c3 of the optical coupler 120c. Furthermore, the third-stage optical coupler 120c branches the third interference light input to the third port c3 at a predetermined branch ratio and outputs it to the first port c1 and the second port c2. The light receiving unit 140c receives the light output from the second port c2 of the optical coupler 120c and generates a digital signal based on this signal, which is then supplied to the processing unit 150.

[0191] The processing unit 150 calculates the distance to the object being measured T based on the digital signals converted by the light receiving units 140a to 140c. For example, the processing unit 150 is a processor implemented by an integrated circuit such as an FPGA, and it uses FFT to perform frequency conversion on the input digital signals, and calculates the distance to the object being measured T based on this.

[0192] The optical interferometric ranging sensor 100 according to the first embodiment includes a suppression mechanism in a multi-stage optical coupler 120 that suppresses the supply of light from a later stage to a later stage. Specifically, the optical interferometric ranging sensor 100 according to the first embodiment includes an optical coupler 120 as a suppression mechanism, wherein the optical coupler 120 is configured to make the amount of light branching to a later stage greater than the amount of light branching to the corresponding interferometer 130. For example, the first-stage optical coupler 120a can also be an example of a suppression mechanism, and the ratio of "the amount of light branching to the corresponding interferometer 130c: the amount of light branching to the later stage (second-stage optical coupler 120b)" can be "10:90". Alternatively, for example, the second-stage optical coupler 120b can be an example of a suppression mechanism, and the ratio of "the amount of light branching to the corresponding interferometer 130b: the amount of light branching to the later stage (third-stage optical coupler 120c)" can be "15:85". Alternatively, for example, the third-stage optical coupler 120c can be a suppression mechanism, and the ratio of the light quantity branching off to the corresponding interferometer 130c to the light quantity branching off to the subsequent stage (attenuator 122) can be "20:80". Thus, by suppressing the supply of light from the subsequent stage to the preceding stage in a multi-stage optical coupler, the light returning from the subsequent stage coupler to the preceding stage optical coupler is suppressed, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0193] The optical interferometric ranging sensor 100 according to the first embodiment can also be configured such that the proportion of light branching to the corresponding interferometer 130 is relatively higher the further away the optical coupler 120 is from the wavelength scanning light source 110. That is, it can also be configured such that when the number of stages of the optical coupler 120 of the optical interferometric ranging sensor 100 is set to i (i is any natural number from 1 to n when the number of stages of the optical coupler 120 of the optical interferometric ranging sensor 100 is set to n), and when the ratio of the light branching to the corresponding interferometer 130 for the i-th stage optical coupler 120 to the light branching to the subsequent stage, i.e., the branching ratio, is set to Ri, it becomes R. i+1 ≥R i For example, in the case above, R1 is "10 / 90", R2 is "15 / 85", and R3 is "20 / 80". Therefore, the following conditions must be met: R3 ≥ R2 ≥ R1, R... i+1 ≥R i (Where i = 1, 2, 3). This reduces the inconsistency in the amount of light received by each interferometer, thus improving the measurement accuracy of the optical interferometric ranging sensor.

[0194] The optical interferometric ranging sensor 100 according to the first embodiment can also be configured such that the optical path length from the i-th stage optical coupler 120 to the reference plane of the corresponding interferometer 130 is set to L. CR,iLet the optical path length from the i-th stage optical coupler 120 to the (i+1)-th stage optical coupler 120 be L. CC,i In the case of |L CR,i -(L CR,i+1 +L CC,i || becomes a predetermined threshold (the first threshold) or higher ("||" is the symbol for absolute value). Furthermore, L, as the optical path length... CR,i and L CC,i These values ​​are all obtained by multiplying the spatial length of the optical path by the refractive index. Therefore, interference between multiple interferometric beams generated by multiple interferometers can be suppressed, improving the measurement accuracy of the optical interferometric ranging sensor.

[0195] In particular, for |L CR,i -(L CR,i+1 +L CC,i The aforementioned threshold (first threshold) can also be determined based on the frequency band of the light-receiving section 140. Therefore, based on the frequency band of the light-receiving section, interference between multiple interfering beams can be effectively suppressed, improving the measurement accuracy of the optical interferometric ranging sensor.

[0196] <Second Implementation>

[0197] Figure 11 This is a schematic diagram showing the structural outline of the optical interferometric ranging sensor 200 according to the second embodiment of the present invention. In addition to the structure of the optical interferometric ranging sensor 100 according to the first embodiment described above, the optical interferometric ranging sensor 200 according to the second embodiment also includes isolators 221a and 221b.

[0198] Isolators 221a and 221b are examples of suppression mechanisms in multi-stage optical couplers that suppress light supply from subsequent stages to preceding stages. Specifically, they are examples of isolation sections configured to guide light from the preceding stage optical coupler to the following stage optical coupler, but not from the following stage optical coupler to the preceding stage optical coupler. Isolators 221a and 221b are configured, as detailed below, to guide light from the preceding stage optical coupler 120 to the following stage optical coupler, but not from the following stage optical coupler to the preceding stage optical coupler. This suppresses the return light from the following stage optical coupler to the preceding stage optical coupler, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0199] Isolator 221a is optically connected between port 4 a4 of the first-stage optical coupler 120a and port 1 b1 of the second-stage optical coupler 120b. Isolator 221a is configured to guide light from the first-stage optical coupler 120a to the second-stage optical coupler 120b, but not to guide light from the second-stage optical coupler 120b to the first-stage optical coupler 120a. Therefore, isolator 221a blocks the light from port 1 b1 that is output from the second interference light input from port 3 b3 to the optical coupler 120b and directed towards the first-stage optical coupler 120a, as described above.

[0200] Isolator 221b is optically connected between port 4 b4 of the second-stage optical coupler 120b and port 1 c1 of the third-stage optical coupler 120c. Isolator 221b is configured to guide light from the second-stage optical coupler 120b to the third-stage optical coupler 120c, but not from the third-stage optical coupler 120c to the second-stage optical coupler 120b. Therefore, isolator 221b blocks the light from port 1 c1 that is output from the third port c1 and directed towards the second-stage optical coupler 120b in the third interference light input from port 3 c3 to the optical coupler 120c as described above.

[0201] Reflected light can be generated from isolators 221a and 221b towards the forward-stage optical coupler 120. This reflected light can further interfere with the interference light received by the forward-stage optical coupler 120 from the corresponding interferometer 130. Therefore, the optical interferometric ranging sensor 200 according to the second embodiment can also be configured, for example, as follows, to suppress interference between the reflected light from isolators 221a and 221b towards the forward-stage optical coupler 120 and the interference light generated by the interferometer 130. That is, it can also be configured such that the optical path length from the i-th stage optical coupler to the reference plane of its corresponding interferometer is L. CR,i Let L be the optical path length from the i-th stage optical coupler to the isolator connected to it on the subsequent stage. CI,i In the case of |L CR,i -L CI,i |Becoming above a predetermined threshold (the second threshold). Alternatively, it could be L, which is the optical path length. CR,i and L CI,i These values ​​are all obtained by multiplying the length of the optical path by the refractive index. This allows for the suppression of interference between reflected light from the isolator (isolation section) and interference light generated by the interferometer, thus improving the measurement accuracy of the optical interferometric ranging sensor.

[0202] In particular, for |L CR,i -L CI,iThe aforementioned threshold (second threshold) can also be determined based on the frequency band of the light-receiving section 140. Therefore, interference between reflected light from the isolator (isolation section) and interference light generated by the interferometer can be effectively suppressed based on the frequency band of the light-receiving section, thereby improving the measurement accuracy of the optical interferometric ranging sensor.

[0203] [Examples of interferometers]

[0204] In the above-described embodiment, the optical interferometric ranging sensor 100 uses a Fizeau interferometer that generates reference light by using the front end of an optical fiber as a reference surface in each of the interferometers 130a to 130c, but the interferometer is not limited to this.

[0205] Figure 12 It is a diagram showing the changes in the interferometer that produces interference light using measuring light and reference light. Figure 12 In (a), in the optical paths A to C branched out by the branch 121, the front end (end face) of each optical fiber is used as a reference surface, and the positions of the front ends of each optical fiber are staggered in the optical axis direction to achieve different differences in optical path length. This reference surface can also be configured to reflect light due to the difference in refractive index between the optical fiber and air (Fresnel reflection), which is the structure of the interferometer 120 of the optical interferometric ranging sensor 100 described in this embodiment. Alternatively, a reflective film can be coated on the front end of the optical fiber, or a non-reflective coating can be applied to the front end of the optical fiber, and a reflective surface such as a lens can be additionally provided.

[0206] Figure 12 In (b), in the optical paths A to C branched out by the branch 121, measurement optical paths Lm1 to Lm3 that guide the measurement light to the object T being measured and reference optical paths Lr1 to Lr3 that guide the reference light are formed. Reference surfaces (Michelson interferometers) are respectively arranged in front of the reference optical paths Lr1 to Lr3. The reference surfaces can be coated with a reflective film at the front end of the optical fiber, or they can be coated with a non-reflective film and have a reflective surface such as a lens surface separately arranged. In this structure, the optical path lengths of each measurement optical path Lm1 to Lm3 are the same, and a difference in optical path length is set in each reference optical path Lr1 to Lr3, thereby creating different differences in optical path lengths in each optical path A to C. Because the optical path lengths of each measurement optical path Lm1 to Lm3 are the same, the optical design of the sensor head can be simplified.

[0207] Figure 12In (c), among the optical paths A to C branched off by the branch 121, measurement optical paths Lm1 to Lm3 are formed to guide the measurement light to the object T being measured, and reference optical paths Lr1 to Lr3 are formed to guide the reference light. A balance detector (Mach-Zehnder interferometer) is arranged in the reference optical paths Lr1 to Lr3. In this structure, the optical path lengths of each measurement optical path Lm1 to Lm3 are made the same, and a difference in optical path length is set in each reference optical path Lr1 to Lr3, thereby making the difference in optical path length different in each optical path A to C. Because the optical path lengths of each measurement optical path Lm1 to Lm3 can be made the same, the optical design of the sensor head can be simplified.

[0208] Thus, the interferometer is not limited to the Fizeau-type interferometer described in this embodiment. For example, it can also be a Michelson interferometer, a Mach-Zehnder interferometer, or any interferometer, as long as interference light can be generated by setting the difference in optical path length between the measuring light and the reference light. Combinations of these or other structures can also be used.

Claims

1. An optical interferometric distance measuring sensor, characterized in that Possessing: a light source that projects light while continuously changing the wavelength; a plurality of interferometers that generate interference light based on measurement light that is reflected from a measurement object by guiding light supplied to the measurement object and reference light that is at least a part of the measurement light that travels along a different optical path; a multi-stage optical coupler that is a multi-stage optical coupler connected in series, and that accepts light from the light source from an earlier stage, branches the light to a corresponding interferometer among the plurality of interferometers, and supplies the light to a later stage; a suppression mechanism that suppresses supply of light from the later stage to the earlier stage of the multi-stage optical coupler; and a processing section that calculates a distance to the measurement object based on frequencies of a plurality of interference lights generated by the plurality of interferometers, the suppression mechanism includes an optical coupler that is at least any one of the optical couplers in the multi-stage optical coupler, and that is configured to make the amount of light branched to the later stage larger than the amount of light branched to the corresponding interferometer.

2. The optical interference distance measuring sensor according to claim 1, wherein The optical interference distance measuring sensor is configured so that, when a ratio of an amount of light branched to the corresponding interferometer with respect to an amount of light branched to the subsequent stage for the i-th stage optical coupler among the multi-stage optical couplers is set to Ri, Ri becomes R i+1 ≥R i . the interferometers generate each interference light based on first reflected light that is the measurement light irradiated on the measurement object and reflected by the measurement object, and second reflected light that is the reference light reflected by a reference surface.

3. The optical interference distance measuring sensor according to claim 2, wherein the first threshold value is set based on a frequency band of a light receiving section of the processing section to which the plurality of interference lights are converted into electric signals are supplied. The optical interference distance measuring sensor is configured such that a length of an optical path from the i-th optical coupler to a reference surface of the interferometer corresponding to the i-th optical coupler is set as L CR,i A length of an optical path from the i-th optical coupler to the i+1-th optical coupler is set as L CC,i In this case, |L CR,i - (L CR,i+1 + L CC,i ) | becomes equal to or greater than the first threshold value, 4. The optical interference distance measuring sensor according to claim 2 or 3, wherein the suppression mechanism includes a partition section that is connected between two optical couplers among the multi-stage optical couplers, and that is configured to guide light from the optical coupler of the earlier stage to the optical coupler of the later stage, but not to guide light from the optical coupler of the later stage to the optical coupler of the earlier stage.

5. The optical interference distance measuring sensor according to claim 4, wherein the second threshold value is set based on a frequency band of a light receiving section of the processing section to which the plurality of interference lights are converted into electric signals are supplied. The optical interference distance measuring sensor is configured to set the optical path length from the i-th optical coupler to the reference surface of the interferometer corresponding to the i-th optical coupler as L CR,i The optical path length from the i-th optical coupler to the partition portion on the side of the subsequent stage connected to the i-th optical coupler is set as L CI,i In the case where |L CR,i -L CI,i becomes equal to or greater than the second threshold value, ​

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