WO2024048103A1 - Optical interferometric ranging sensor - Google Patents

Abstract

Provided is an optical interferometric ranging sensor that makes it possible to properly measure the distance to a measurement target, while alleviating the influence of light reflected by an optical element disposed in a sensor head. An optical interferometric ranging sensor 100 is provided with: a light source 110 that projects light while changing the wavelength of the light; an interferometer 120 to which the light projected from the light source 110 is supplied and that generates interference light based on measurement light and reference light, the measurement light being radiated onto a measurement target T by a sensor head 102 and being reflected by the measurement target T, and the reference light following an optical path at least partially different from that of the measurement light; a light reception unit 130 that receives the interference light and converts the interference light into an electrical signal; and a processing unit 140 that calculates the distance to the measurement target T on the basis of the electrical signal. The sensor head 102 includes an optical element 170 disposed so as to be tilted by a prescribed angle with respect to a direction perpendicular to the optical axis L of light radiated from an optical fiber 150 to the inside of the sensor head 102.

Description

Optical interference ranging sensor

The present invention relates to an optical interference ranging sensor.

In recent years, optical distance measurement sensors that measure the distance to an object without contact have become popular. For example, as an optical distance measurement sensor, an optical interference sensor generates interference light based on a reference light and measurement light from light emitted from a wavelength swept light source, and measures the distance to a measurement target based on the interference light. Distance sensors are known.

Since such optical interferometric distance measuring sensors measure the distance to the measurement target based on interference light, for example, noise or unnecessary peaks may be present in the light received by a photodetector that receives the interference light. It is required that they not be mixed.

For example, Patent Document 1 relates to an optical interference measurement device that generates an interference signal by combining a reference light and a measurement light reflected by an object to be measured, and measures the object to be measured based on the interference signal. The technology has been disclosed. This optical interference measurement device adjusts the optical path length of the reference light transmitted through the reference light device and the reference light reflected by the reference light device, thereby reducing the noise generated in the entire waveform of the interference signal. has been reduced.

JP 2018-205203 Publication

However, in the optical measurement device disclosed in Patent Document 1, the noise generated in the entire waveform of the interference signal is reduced by adjusting the optical path length, but the noise generated in the entire waveform of the interference signal is reduced. No measures have been taken regarding light. In particular, optical interferometric distance measurement sensors are placed inside the sensor head to measure the distance to the measurement target based on an interference signal generated by the reflected light from the measurement target and a reference light that follows another optical path. The reflected light from the optical element may interfere with the reference light that follows other optical paths, causing unnecessary peaks in the entire waveform, which may cause problems such as not being able to properly measure the distance to the measurement target. .

Therefore, an object of the present invention is to provide an optical interference distance measuring sensor that can reduce the influence of reflected light from an optical element arranged in a sensor head and appropriately measure the distance to a measurement target.

An optical interferometric ranging sensor according to one aspect of the present invention includes a light source that projects light while changing the wavelength, and the light projected from the light source is supplied to the object to be measured and reflected by the sensor head. an interferometer that generates interference light based on a measurement light that follows a measurement light and a reference light that follows an optical path that is at least partially different from that of the measurement light; a light receiver that receives the interference light from the interferometer and converts it into an electrical signal; a processing section that calculates the distance from the sensor head to the measurement target based on the electrical signal converted by the section, and the sensor head includes a processing section that calculates the distance from the sensor head to the measurement target based on the electrical signal converted by the section, It includes an optical element connected to a fiber and arranged at a predetermined angle with respect to a direction perpendicular to the optical axis of light emitted from the optical fiber into the sensor head.

According to this aspect, the optical element in the sensor head is arranged at an angle of a predetermined angle with respect to the vertical direction of the optical axis of light emitted from the optical fiber into the sensor head. It is possible to reduce the influence of reflected light and appropriately measure the distance to the measurement target.

In the above aspect, the optical element tilted at a predetermined angle is at least one of a collimating lens, an objective lens, an optical filter, a polarizing element, a wavelength plate, a beam splitter, a diffraction grating, a prism, and a diffractive optical element. There may be.

According to this aspect, the optical element tilted at a predetermined angle is at least one of a collimating lens, an objective lens, an optical filter, a polarizing element, a wavelength plate, a beam splitter, a diffraction grating, a prism, and a diffractive optical element. As described above, the influence of light reflected by the optical elements can be appropriately reduced depending on the shape and characteristics of these optical elements.

In the above aspect, the sensor head includes, in order from the side connected to the optical fiber, a collimating lens and an objective lens tilted at a predetermined angle, and the light emitted from the optical fiber into the sensor head is transmitted through the objective lens. The reflected light may pass through a collimating lens so that the center of the spot of the reflected light is outside the core diameter of the optical fiber.

According to this aspect, the sensor head includes a collimating lens and an objective lens tilted at a predetermined angle, and since the center of the spot of reflected light on the objective lens is outside the core diameter of the optical fiber, the reflected light The distance to the object to be measured can be appropriately measured with high accuracy while reducing the influence of light.

In the above embodiment, using the focal length f of the collimating lens, the numerical aperture NA of the optical fiber, the core radius r of the optical fiber, and the wavelength λ of the light, the predetermined angle θ is calculated as f} may be satisfied.

According to this aspect, even if the center of the spot of the reflected light on the objective lens shifts to the outside of the core diameter of the optical fiber and a part of the reflected light is incident on the core diameter of the optical fiber, the light Since the intensity is small, the distance to the measurement target can be appropriately measured with higher accuracy while reducing the influence of the reflected light.

In the above aspect, when the predetermined angle becomes smaller than a threshold value, a notification to that effect may be sent.

According to this aspect, when the predetermined angle becomes smaller than the threshold value, a notification to that effect is given, so it is possible to appropriately adjust the arrangement of the optical elements in the sensor head.

An optical interferometric ranging sensor according to one aspect of the present invention includes a light source that projects light while changing the wavelength, and the light projected from the light source is supplied to the object to be measured and reflected by the sensor head. an interferometer that generates interference light based on a measurement light that follows a measurement light and a reference light that follows an optical path that is at least partially different from that of the measurement light; a light receiver that receives the interference light from the interferometer and converts it into an electrical signal; a processing section that calculates the distance from the sensor head to the measurement target based on the electrical signal converted by the section, and the sensor head includes a processing section that calculates the distance from the sensor head to the measurement target based on the electrical signal converted by the section, An optical device connected to a fiber and tilted at a predetermined angle so that the light emitted from the optical fiber into the sensor head is reflected and the center of the spot of the reflected light is outside the core diameter of the optical fiber. Contains elements.

According to this aspect, the optical element in the sensor head is tilted at a predetermined angle so that the center of the spot of the reflected light on the optical element is outside the core diameter of the optical fiber, so that the reflected light The distance to the object to be measured can be appropriately measured with high accuracy while reducing the influence of

According to the present invention, it is possible to provide an optical interference ranging sensor that can reduce the influence of reflected light from an optical element disposed within a sensor head and appropriately measure the distance to a measurement target.

1 is a schematic external view showing an outline of a displacement sensor 10 according to the present disclosure. It is a flowchart which shows the procedure by which the measurement target object T is measured by the displacement sensor 10 based on this indication. 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. 1 is a flowchart showing a procedure in which a measurement target T is measured by a sensor system 1 in which a displacement sensor 10 according to the present disclosure is used. FIG. 3 is a diagram for explaining the principle by which a measurement target T is measured by the displacement sensor 10 according to the present disclosure. FIG. 7 is a diagram for explaining another principle in which the measurement target T is measured by the displacement sensor 10 according to the present disclosure. 2 is a perspective view showing a schematic configuration of a sensor head 20. FIG. 2 is a schematic diagram showing the internal structure of a sensor head 20. FIG. 3 is a block diagram for explaining signal processing in a controller 30. FIG. 5 is a flowchart illustrating a method of calculating the distance to a measurement target T, which is executed by a processing unit 59 in the controller 30. FIG. FIG. 2 is a diagram showing how a waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency). FIG. 2 is a diagram showing how a spectrum (voltage vs. frequency) is distance-converted into a spectrum (voltage vs. distance). FIG. 6 is a diagram showing how a peak is detected based on a spectrum (voltage vs. distance) and a distance value corresponding to the peak is calculated. 1 is a schematic diagram showing an outline of the configuration of an optical interference ranging sensor 100 according to an embodiment of the present invention. 5 is a diagram illustrating the state of the reflected light on the objective lens 170 and the reflected light on the measurement target T when the measurement target T is far from the sensor head 102. FIG. 5 is a diagram illustrating the state of the reflected light on the objective lens 170 and the reflected light on the measurement target T when the measurement target T is close to the sensor head 102. FIG. 3 is a diagram schematically showing a state in which an objective lens 170 is tilted at a predetermined angle θ with respect to a direction perpendicular to an optical axis L of light emitted from an optical fiber 150 into a sensor head 102. FIG. FIG. 3 is a diagram showing a specific example of a sensor head composed of one lens. FIG. 6 is a diagram showing variations of an interferometer that generates interference light using measurement light and reference light.

Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings. Note that each embodiment described below is merely a specific example for implementing the present invention, and is not intended to be interpreted in a limited manner. Furthermore, in order to facilitate understanding of the explanation, the same components in each drawing may be given the same reference numerals as much as possible, and redundant explanation may be omitted.

[Overview of displacement sensor]
First, an overview of the displacement sensor according to the present disclosure will be explained.
FIG. 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 the measurement target T (distance to the measurement target T).

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 section 31, a setting section 32, an external interface (I/F) section 33, an optical fiber connection section 34, and an external storage section 35, and further includes a measurement processing section inside. It has a section 36.

The sensor head 20 irradiates the measurement object T with the light output from the controller 30 and receives the reflected light from the measurement object T. The sensor head 20 has a reference surface therein for reflecting the light outputted from the controller 30 and received via the optical fiber 40 and making it interfere with the reflected light from the measurement object T described above.

Note that an objective lens 21 is attached to the sensor head 20, but the objective lens 21 is configured to be 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 applied.

Furthermore, when installing the sensor head 20, the sensor head irradiates the measurement target T with guide light (visible light) so that the measurement target T is appropriately positioned within the measurement area of the displacement sensor 10. 20 and/or the measurement target T may be installed.

The optical fiber 40 is connected to and extends to the optical fiber connection section 34 disposed in the controller 30, and connects the controller 30 and the sensor head 20. Thereby, the optical fiber 40 is configured to guide light projected from the controller 30 to the sensor head 20 and further guide return light from the sensor head 20 to the controller 30. Note that the optical fiber 40 can be attached to and detached from the sensor head 20 and the controller 30, and various optical fibers can be used in terms of length, thickness, characteristics, etc.

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

In the setting unit 32, settings necessary for measuring the measurement target T are performed, 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 external connection device (not shown) connected to the external I/F section 33. Further, the externally connected device may be connected by wire or wirelessly via a network.

Here, the external I/F section 33 is configured with, for example, Ethernet (registered trademark), RS232C, and analog output. The external I/F section 33 is connected to other connected devices and performs necessary settings from the external connected devices, and outputs measurement results etc. measured by the displacement sensor 10 to the external connected devices. Good too.

Further, settings necessary for measuring the measurement target T may be performed by the controller 30 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 target T in advance.

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 return light from the sensor head 20 and converts it into an electrical signal, and an electrical signal. It includes a signal processing circuit etc. that processes. The measurement processing unit 36 controls a control unit, a storage unit, etc. so that the displacement of the measurement target T (distance to the measurement target T) is finally calculated based on the return light from the sensor head 20. It is used for various treatments. Details of these processes will be described later.

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

In step S11, the sensor head 20 is installed. For example, a guide light is irradiated from the sensor head 20 onto the measurement target T, and the sensor head 20 is installed at an appropriate position using this as a reference.

Specifically, the amount of return light received from the sensor head 20 is displayed on the display unit 31 of the controller 30, and the user checks the direction of the sensor head 20 and the relationship with the measurement target T while checking the amount of received light. The distance (height position) etc. may be adjusted. Basically, if the light from the sensor head 20 can be irradiated perpendicularly to the measurement target T (at an angle closer to perpendicular), the amount of reflected light from the measurement target T will be large, and the light from the sensor head 20 will The amount of returned light received also increases.

Furthermore, depending on the distance between the sensor head 20 and the measurement target T, the objective lens 21 may be replaced with an appropriate focal length.

Furthermore, if appropriate settings cannot be made when measuring the measurement target T (for example, the amount of received light necessary for measurement cannot be obtained, or the focal length of the objective lens 21 is inappropriate), an error or setting The user may be notified of incompleteness, etc. by displaying it on the display unit 31 or outputting it to an externally connected device.

In step S12, various measurement conditions are set when measuring the measurement target T. For example, the user sets unique calibration data (a function for correcting linearity, etc.) possessed by the sensor head 20 by operating the setting section 32 in the controller 30.

Additionally, various parameters may be set. For example, a sampling time, a measurement range, a threshold value for determining whether a measurement result is normal or abnormal, etc. are set. Furthermore, the measurement period may be set according to the characteristics of the measurement object T such as the reflectance and material of the measurement object T, and the measurement mode etc. may be set according to the material of the measurement object T. .

Note that these measurement conditions and various parameters are set by operating the setting section 32 in the controller 30, but they may also be set from an externally connected device, or by importing data from the external storage section 35. May be set.

In step S13, the sensor head 20 installed in step S11 measures the measurement target T according to the measurement conditions and various parameters set in step S12.

Specifically, in the measurement processing unit 36 of the controller 30, light is emitted from the wavelength swept light source, the return light from the sensor head 20 is received by the light receiving element, and the signal processing circuit performs frequency analysis, distance conversion, and peak detection. etc., and the displacement of the measurement target T (distance to the measurement target T) is calculated. Details of the specific measurement process will be described later.

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

The measurement results also include whether the displacement of the measurement target T measured in step S13 (distance to the measurement target T) is within the normal range or abnormal based on the threshold set in step S12. It may be displayed or output. Furthermore, the measurement conditions, various parameters, measurement mode, etc. set in step S12 may also be displayed or output.

[Summary of system including displacement sensor]
FIG. 3 is a functional block diagram showing an overview of the sensor system 1 in which the displacement sensor 10 according to the present disclosure is used. As shown in FIG. 3, 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. 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.

As explained using FIGS. 1 and 2, the displacement sensor 10 measures the displacement of the measurement target T (distance to the measurement target T). The displacement sensor 10 may output the measurement results and the like to the control device 11 and the externally connected device 13.

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.

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 output a zero reset command signal (current A signal for setting the measured value to 0) etc. may be output to the displacement sensor 10.

The control signal input sensor 12 outputs an on/off signal that instructs the timing at which the displacement sensor 10 measures the measurement target T to the control device 11. For example, the control signal input sensor 12 is installed near a production line where the object to be measured T moves, and upon detecting that the object to be measured T has moved to a predetermined position, controls the control device 11 to turn on/off. Just output the signal.

The externally connected device 13 is, for example, a PC (Personal Computer), and can be operated by a user to perform various settings for the displacement sensor 10.

As a specific example, the measurement mode, operation mode, measurement period, material of the measurement target T, etc. are set.

As the measurement mode setting, an "internal synchronous measurement mode" in which measurement is started periodically inside 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, etc. is selected. .

As the setting of the operation mode, an "operating mode" for actually measuring the measurement object T, an "adjustment mode" for setting measurement conditions for measuring the measurement object T, etc. are selected.

The measurement period is the period of measuring the measurement target T, and may be set according to the reflectance of the measurement target T. However, even if the reflectance of the measurement target T is low, the measurement cycle can be set according to the reflectance of the measurement target T. If the measurement period is set appropriately by increasing the period of time, the object T to be measured can be appropriately measured.

Regarding the measurement target T, "rough surface mode" is suitable when there is a relatively large amount of diffuse reflection as a component of reflected light, "specular mode" is suitable when there is a relatively large amount of specular reflection as a component of reflected light, or An intermediate "standard mode" or the like is selected.

In this way, by making appropriate settings according to the reflectance and material of the measurement target T, the measurement target T can be measured with higher precision.

FIG. 4 is a flowchart showing a procedure in which the measurement target T is measured by the sensor system 1 in which the displacement sensor 10 according to the present disclosure is used. As shown in FIG. 4, this procedure is for the externally synchronous measurement mode described above, and includes steps S21 to S24.

In step S21, the sensor system 1 detects the measurement object T that is the 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.

In step S22, the sensor system 1 instructs the displacement sensor 10 to measure the measurement target T detected in step S21. Specifically, the control signal input sensor 12 outputs an on/off signal to the control device 11 to instruct the timing to measure the measurement target T detected in step S21, and the control device 11 Based on the on/off signal, a measurement timing signal is output to the displacement sensor 10 to instruct the displacement sensor 10 to measure the measurement target T.

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

In step S24, the sensor system 1 outputs the measurement results measured 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.

In addition, here, using FIG. 4, the procedure for the case of the external synchronous measurement mode in which the measurement target T is measured by the measurement target T being detected by the control signal input sensor 12 has been explained. It is not limited to. For example, in the case of the internal synchronous 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 target T. do.

Next, the principle by which the measurement target T is measured by the displacement sensor 10 according to the present disclosure will be explained.
FIG. 5A is a diagram for explaining the principle by which the measurement target T is measured by the 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, and a plurality of optical couplers. 54 and 54a to 54e, an attenuator 55, a plurality of light receiving elements (for example, a photodetector (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, and a plurality of analog-to-digital (AD) converters (for example, (analog-digital converters) 58a to 58c, a processing section (for example, a processor) 59, a balance detector 60, and a correction signal generation section 61.

The wavelength swept light source 51 emits laser light whose wavelength has been swept. As the wavelength swept light source 51, for example, if a method of modulating a VCSEL (Vertical Cavity Surface Emitting Laser) with current is applied, mode hops are less likely to occur due to the short resonator length, and the wavelength can be easily changed. , can be realized at low cost.

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

The isolator 53 is an optical element that transmits incident light in one direction, and may be placed immediately after the wavelength swept light source 51 in order to prevent the influence of noise generated by returned light.

In this way, the light projected from the wavelength swept light source 51 is amplified by the optical amplifier 52, passed through the isolator 53, and branched by the optical coupler 54 into a main interferometer and a sub interferometer. For example, in the optical coupler 54, 90% or more of the light may be split into the main interferometer and the sub interferometer.

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.

The light branched in the direction of the sensor head 20 by the first-stage optical coupler 54a passes through the collimating lens 22a and the objective lens 21 from the tip of the optical fiber in the sensor head 20, and is irradiated onto the measurement target T. Then, the tip (end surface) of the optical fiber becomes a reference surface, and the light reflected from the reference surface and the light reflected from the measurement target T interfere to generate interference light, which is then connected to the first stage optical coupler. After that, the light is received by the light receiving element 56a and converted into an electric signal.

The light branched in the direction of the second-stage optical coupler 54b by the first-stage optical coupler 54a heads toward the second-stage optical coupler 54b via the isolator 53a, and is further split by the second-stage optical coupler 54b. It branches into the direction of the sensor head 20 and the direction of the third stage optical coupler 54c. The light branched from the optical coupler 54b in the direction of the sensor head 20 passes from the tip of the optical fiber to the collimating lens 22b and the objective lens 21 in the sensor head 20, and irradiates it onto the measurement target T, as in the first stage. be done. Then, the tip (end surface) of the optical fiber becomes a reference surface, and the light reflected from the reference surface and the light reflected from the measurement target T interfere to generate interference light, which is then connected to the second stage optical coupler. 54b, the light is branched to the isolator 53a and the light receiving element 56b by the optical coupler 54b. 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 optical coupler 54a at the front stage to the optical coupler 54b at the rear stage, and blocks the light from the optical coupler 54b at the rear stage to the optical coupler 54a at the front stage, so the direction from the optical coupler 54b to the isolator 53a is The branched light is blocked.

The light branched by the second-stage optical coupler 54b toward the third-stage optical coupler 54c goes to the third-stage optical coupler 54c via the isolator 53b, and is further split by the third-stage optical coupler 54c. It is branched into the direction of the sensor head 20 and the direction of the attenuator 55. The light branched from the optical coupler 54c in the direction of the sensor head 20 passes from the tip of the optical fiber to the collimating lens 22c and the objective lens 21 in the sensor head 20, as in the first and second stages, and reaches the measurement target. Object T is irradiated. Then, the tip (end surface) of the optical fiber becomes a reference surface, and the light reflected from the reference surface and the light reflected from the measurement target T interfere to generate interference light, which is then connected to the third stage optical coupler. 54c, the light is branched to the isolator 53b and the light receiving element 56c by the optical coupler 54c. 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 optical coupler 54b at the front stage to the optical coupler 54c at the rear stage, and blocks the light from the optical coupler 54c at the rear stage to the optical coupler 54b at the front stage, so the direction from the optical coupler 54c to the isolator 53b is The branched light is blocked.

Note that the light branched in a direction other than the sensor head 20 by the third-stage optical coupler 54c is not used for measuring the measurement target T, so an attenuator such as a terminator is used to prevent it from being reflected back. 55.

In this way, the main interferometer has three stages of optical paths (three channels), each with an optical path length that is twice the distance (round trip) from the tip (end face) of the optical fiber of the sensor head 20 to the measurement target T. This interferometer generates three interference lights each corresponding to the difference in optical path length.

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

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

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

The sub-interferometer acquires an interference signal and generates a correction signal called a K clock in order to correct the non-linearity of the wavelength during sweeping by the wavelength-swept light source 51.

Specifically, the light branched to the sub-interferometer by the optical coupler 54 is further branched by the optical coupler 54d. Here, the optical path of each branched light is configured to have an optical path length difference between the optical coupler 54d and the optical coupler 54e by using optical fibers of different lengths, for example. Corresponding interference light is output from the optical coupler 54e. The balance detector 60 receives the interference light from the optical coupler 54e, and removes noise by taking the difference between the interference light and the signal of the opposite phase, and amplifies the optical signal and converts it into an electrical signal.

Note that both the optical coupler 54d and the optical coupler 54e may split light at a ratio of 50:50.

The correction signal generation unit 61 grasps the wavelength nonlinearity during sweeping 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 generates a K clock according to the nonlinearity, Output to 58c.

Due to the nonlinearity of the wavelength during sweeping by the wavelength swept light source 51, the intervals between the analog signal waves input to the AD converters 58a to 58c in the main interferometer are not equal. The AD converters 58a to 58c perform AD conversion (sampling) by correcting the sampling time based on the above-mentioned K clock so that the intervals between waves are equal.

Note that, as described above, the K clock is a correction signal used to sample the analog signal of the main interferometer, so it needs to be generated at a higher frequency than the analog signal of the main interferometer. Specifically, the optical path length difference provided between the optical coupler 54d and the optical coupler 54e in the sub-interferometer is equal to the difference in optical path length provided between the tip (end surface) of the optical fiber and the measurement target T in the main interferometer. The optical path length difference may be made longer than the difference in optical path length, or the frequency may be multiplied by the correction signal generating section 61 (for example, by a factor of 8) to make the frequency higher.

The processing unit 59 acquires digital signals whose nonlinearities are corrected and AD converted by the AD conversion units 58a to 58c, respectively, and calculates the displacement of the measurement target T (distance to the measurement target T) based on the digital signals. ) is calculated. Specifically, the processing unit 59 converts the frequency of the digital signal using fast Fourier transform (FFT), and calculates the distance by analyzing them. Detailed processing in the processing unit 59 will be described later.

Note that the processing unit 59 is often implemented with an integrated circuit such as an FPGA (field-programmable gate array) because high-speed processing is required.

In addition, here, three stages of optical paths are provided in the main interferometer, and measurement light is irradiated onto the measurement target T from each optical path by the sensor head 20, and based on the interference light (return light) obtained from each. Then, the distance to the measurement target T is measured (multi-channel). The number of channels in the main interferometer is not limited to three stages, but may be one or two stages, or four or more stages.

FIG. 5B is a diagram for explaining another principle in 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, and a plurality of optical couplers. 54 and 54a to 54j, an attenuator 55, a plurality of light receiving elements (for example, a photodetector (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, and a plurality of analog-to-digital (AD) converters (for example, (analog-digital converters) 58a to 58c, a processing section (for example, a processor) 59, a balance detector 60, and a correction signal generation section 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. I will explain in detail by comparing.

The light projected from the wavelength swept light source 51 is amplified by an optical amplifier 52, passed through an isolator 53, and branched by an optical coupler 54 into a main interferometer side and a sub-interferometer side. The branched light is further branched into measurement light and reference light by an optical coupler 54f.

As explained in FIG. 5A, the measurement light passes through the collimator lens 22a and the objective lens 21 by the first-stage optical coupler 54a, is irradiated onto the measurement target T, and is reflected by the measurement target T. Here, in FIG. 5A, the tip (end surface) of the optical fiber is used as a reference surface, and the light reflected from the reference surface and the light reflected from the measurement target T interfere, and interference light is generated. 5B does not have a reference surface on which light is reflected. That is, in FIG. 5B, since no light is reflected on the reference surface as in FIG. 5A, the measurement light reflected on the measurement target T returns to the first-stage optical coupler 54a.

Similarly, the light branched from the first-stage optical coupler 54a toward the second-stage optical coupler 54b passes through the collimating lens 22b and the objective lens 21 by the second-stage optical coupler 54b to the measurement target. The light is irradiated onto T, is reflected by the measurement target T, and returns to the second-stage optical coupler 54b. The light branched from the second stage optical coupler 54b in the direction of the third stage optical coupler 54c passes through the collimating lens 22c and the objective lens 21 and is irradiated onto the measurement target T by the third stage optical coupler 54c. The light is reflected by the measurement target T and returns to the third stage optical coupler 54c.

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

In the optical coupler 54h, the measurement light output from the optical coupler 54a and reflected by the measurement target T interferes with the reference light output from the optical coupler 54g to generate interference light, which is received by the light receiving element 56a. and converted into electrical signals. In other words, the optical coupler 54f branches the measurement light into the measurement light and the reference light, and the optical path of the measurement light (from the optical coupler 54f, passes through the optical coupler 54a, the collimating lens 22a, and the objective lens 21, and is reflected by the measurement target T). , the optical path reaching the optical coupler 54h) and the optical path of the reference light (the optical path reaching the optical coupler 54h from the optical coupler 54f via the optical coupler 54g). , the interference light is received by the light receiving element 56a and converted into an electrical signal.

Similarly, in the optical coupler 54i, the optical path of the measurement light (the optical path from the optical coupler 54f, through the optical couplers 54a and 54b, the collimating lens 22b, and the objective lens 21, reflected by the measurement target T, and reaching the optical coupler 54i) Interference light is generated according to the optical path length difference between the reference light and the optical path of the reference light (the optical path from the optical coupler 54f to the optical coupler 54i via the optical coupler 54g), and the interference light is received by the light receiving element 56b. and converted into electrical signals.

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

In this way, the main interferometer has three stages of optical paths (three channels), and the measurement light that is reflected by the measurement target T and input into the optical couplers 54h, 54i, and 54j, and the optical couplers 54f and 54g. Three interference lights are generated according to the difference in optical path length from the reference lights that are input to the optical couplers 54h, 54i, and 54j via the respective optical couplers 54h, 54i, and 54j.

Note that, for example, the optical path lengths of the optical coupler 54g and each of the optical couplers 54h, 54i, and 54j may be set to be different so that the difference in optical path length between the measurement light and the reference light is different for each of the three channels. .

Then, based on the interference light obtained from each, the distance to the measurement target T, etc. is measured (multichannel).

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

As shown in FIG. 6A, the sensor head 20 has an objective lens 21 and a collimating lens housed in a 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 approximately 20 mm, and the length in the optical axis direction is approximately 40 mm.

As shown in FIG. 6B, the lens holder 23 stores one objective lens 21 and three collimating lenses 22a to 22c. The light from the optical fiber is configured to be guided to 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 guided to the objective lens 21. The object T to be measured is irradiated through the beam.

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

Furthermore, the lens holder 23 that constitutes the sensor head 20 may be made of a metal (for example, A2017) that has high strength and can be processed with high precision.

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 converters 74a to 74c, a processing unit 75, and a differential amplifier circuit 76. and a correction signal generation section 77.

In the controller 30, as shown in FIG. 5A, the light projected from the wavelength swept light source 51 is split into a main interferometer and a sub-interferometer by an optical coupler 54, and a main interference signal and a sub-interference signal obtained from each are obtained. The distance value to the measurement target T is calculated by processing the signal.

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

The plurality of amplifier circuits 72a to 72c convert the current signal into a voltage signal (IV conversion) and amplify it.

The plurality of AD converters 74a to 74c correspond to the AD converters 58a to 58c shown in FIG. 5A, and convert voltage signals into digital signals based on K clocks from a correction signal generator 77, which will be described later. AD conversion).

The processing unit 75 corresponds to the processing unit 59 shown in FIG. 5A, and converts the digital signals from the AD conversion units 74a to 74c into frequencies using FFT, analyzes them, and calculates the frequency up to the measurement target T. Calculate distance value.

The plurality of light receiving elements 71d to 71e and the differential amplifier circuit 76 correspond to the balanced detector 60 shown in FIG. 5A, and each receives the interference light from the sub-interferometer, and one outputs an interference signal with an inverted phase. Then, by taking the difference between the two signals, noise is removed, and the interference signal is amplified and converted into a voltage signal.

The correction signal generation section 77 corresponds to the correction signal generation section 61 shown in FIG. 5A, binarizes the voltage signal with a comparator, generates a K clock, and outputs it to the AD conversion sections 74a to 74c. Since the K clock needs to be generated at a higher frequency than the analog signal of the main interferometer, the frequency may be multiplied (for example, by 8 times) in the correction signal generation section 77 to make the K clock higher frequency.

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

In step S31, the processing unit 59 frequency-converts the waveform signal (voltage vs. time) into a spectrum (voltage vs. frequency) using the FFT described below. FIG. 9A is a diagram showing how a waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency).

In step S32, the processing unit 59 performs distance conversion from the spectrum (voltage vs. frequency) to the spectrum (voltage vs. distance). FIG. 9B is a diagram showing how a spectrum (voltage vs. frequency) is distance-converted into a spectrum (voltage vs. distance).

In step S33, the processing unit 59 calculates a distance value corresponding to the peak based on the spectrum (voltage vs. distance). FIG. 9C is a diagram showing how a peak is detected based on the spectrum (voltage vs. distance) and the corresponding distance value is calculated. As shown in FIG. 9C, here, peaks are detected in each of the three channels based on the spectrum (voltage vs. distance), and distance values corresponding to the respective peaks are calculated.

In step S34, the processing unit 59 averages the distance values calculated in step S33. Specifically, since peaks have been detected based on the spectrum (voltage vs. distance) in each of the three channels in step S33 and the corresponding distance values have been calculated, the processing unit 59 averages them and calculates the corresponding The averaged calculation result is output as the distance to the measurement target T.

Note that in step S34, when the processing unit 59 averages the distance values calculated in step S33, it is preferable that the processing unit 59 averages the distance values whose SNR is equal to or greater than a threshold value. For example, if a peak is detected in one of the three channels based on its spectrum (voltage vs. distance), but the SNR is less than the threshold, the distance value calculated based on the spectrum will be , judged to be unreliable and not adopted.

Next, the present disclosure will be described in detail as a specific embodiment, focusing on more characteristic configurations, functions, and properties. The optical interference ranging sensor shown below corresponds to the displacement sensor 10 described using FIGS. 1 to 9, and all or all of the basic configuration, functions, and properties included in the optical interference ranging sensor Some parts are common to the configuration, functions, and properties included in the displacement sensor 10 described using FIGS. 1 to 9.

<One embodiment>
[Configuration of optical interference ranging sensor]
FIG. 10 is a schematic diagram showing an outline of the configuration of an optical interference ranging sensor 100 according to an embodiment of the present invention. As shown in FIG. 10, the optical interference ranging sensor 100 includes a controller 101 and a sensor head 102. The controller 101 includes a wavelength swept light source 110, an interferometer 120, a light receiving section 130, and a processing section 140. The sensor head 102 is connected to the controller 101 via an optical fiber 150 and includes a collimating lens 160 and an objective lens 170. Note that since the light projected from the wavelength swept light source 110 is supplied to generate interference light for calculating the distance to the measurement target T, the interferometer 120 including the sensor head 102 is used as an interferometer. You can also say

The wavelength swept light source 110 projects light while continuously changing the wavelength. That is, the wavelength of the light projected from the wavelength swept light source 110 is continuously changing.

The interferometer 120 is supplied with light projected from the wavelength swept light source 110, and the measurement light that is irradiated onto the measurement target T by the sensor head 102 and reflected, and the reference light that follows an optical path that is at least partially different from the measurement light. Interference light is generated based on the light. For example, the interferometer 120 is configured with an optical coupler, a circulator, etc., supplies the light projected from the wavelength swept light source 110 to the sensor head 102 via the optical fiber 150, and also supplies the light reflected from the sensor head 102. is guided to the light receiving section 130.

Specifically, light projected from the wavelength swept light source 110 is supplied to the interferometer 120, and guided to the sensor head 102 via the optical fiber 150 by an optical branching section such as an optical coupler. In the sensor head 102, the light emitted from the optical fiber 150 is irradiated onto the measurement target T as measurement light via the collimator lens 160 and the objective lens 170. The measurement light reflected by the measurement target T enters the optical fiber 150 via the objective lens 170 and the collimating lens 160.

Further, a part of the light supplied from the interferometer 120 to the sensor head 102 via the optical fiber 150 is reflected as reference light by a reference surface provided at the tip of the optical fiber 150. Then, the above-mentioned measurement light and the reference light interfere, thereby generating interference light according to the optical path length difference between the measurement light and the reference light.

Further, although the objective lens 170 may reduce the reflection of light emitted from the optical fiber 150 by, for example, taking measures such as coating the surface with an anti-reflection film (AR coat), The emitted light is reflected on the surface of the objective lens 170, and the reflected light returns to the optical fiber 150 side via the collimating lens 160. In the sensor head 102 of the optical interference ranging sensor 100, by tilting and arranging the objective lens 170, the reflected light from the objective lens 170 that returns to the optical fiber 150 side and enters the optical fiber 150 is reduced. It is being reduced. Details of the reflected light will be described later.

The light receiving unit 130 receives interference light from the interferometer 120 and converts it into an electrical signal. Specifically, the light receiving unit 130 includes a light receiving circuit and an AD converter, and the light receiving circuit includes a light receiving element, which is a photodetector, for example, receives light from the interferometer 120, and generates electricity according to the amount of light received. Convert to signal. The AD converter converts the electrical signal from an analog signal to a digital signal.

The processing unit 140 calculates the distance from the sensor head 102 to the measurement target T based on the electrical signal converted by the light receiving unit 130. For example, the processing unit 140 is a processor realized by an integrated circuit such as an FPGA, and converts the frequency of each input digital signal using FFT, and calculates the distance to the measurement target T based on the frequency conversion. .

Note that the distance from the sensor head 102 to the measurement target T is typically the distance from the tip of the sensor head 102 to the measurement target T, and the processing unit 140 calculates the distance. It is not limited to. For example, the processing unit 140 determines the distance from the sensor head 102 to the measurement target T, the distance from the tip of the optical fiber connected to the sensor head 102 to the measurement target T, and the distance from the objective lens 170 disposed on the sensor head 102. The distance from to the measurement target T, or the distance from a reference position preset inside the sensor head 102 to the measurement target T, etc. may be calculated.

Here, the waveform signal processed by the processing unit 140 based on the reflected light from the objective lens 170 and the reflected light from the measurement target T will be described.

FIG. 11A is a diagram showing the reflected light on the objective lens 170 and the reflected light on the measurement target T when the measurement target T is far from the sensor head 102, and FIG. 11B is a diagram showing how the measurement target T is far from the sensor head 102. 5 is a diagram illustrating the state of reflected light on an objective lens 170 and reflected light on a measurement target T when the object is close to the sensor head 102. FIG.

As shown in FIG. 11A, when the measurement target T is far from the sensor head 102, in the waveform signal processed by the processing unit 140, there is a peak due to the reflected light from the objective lens 170 and a peak due to the measurement target T. The peak associated with the reflected light is far away.

In FIG. 11A, the light supplied to the sensor head 102 is emitted from the optical fiber 150, and is irradiated onto the measurement target T from the sensor head 102 as measurement light via the collimating lens 160 and the objective lens 170. The light reflected by the measurement target T returns to the sensor head 102 and enters the optical fiber 150 again via the objective lens 170 and the collimating lens 160. On the other hand, a part of the light supplied to the sensor head 102 is reflected as reference light by the reference surface, which serves as the tip (end surface) of the optical fiber 150.

The measurement light reflected by the measurement target T and the reference light reflected by the reference surface interfere to generate interference light. Based on the interference light, the processing unit 140 Calculate the distance to. The waveform signal in FIG. 11A is based on interference light received by the light receiving unit 130, and the processing unit 140 generates interference between the measurement light reflected by the measurement target T and the reference light reflected by the reference surface. The distance from the peak that appears to the measurement target T is calculated.

Further, the light supplied to the sensor head 102 is emitted from the optical fiber 150, and a portion of the light is reflected by the surface of the objective lens 170 via the collimating lens 160. The light reflected by the objective lens 170 returns to the optical fiber 150 side via the collimating lens 160. Here, since the objective lens 170 is tilted at a predetermined angle with respect to the vertical direction of the optical axis L of the light emitted from the optical fiber 150 into the sensor head 102, the light that is reflected back to the optical fiber 150 is Reduces light. That is, the center of the spot of light reflected by the objective lens 170 is set to be outside the core diameter of the optical fiber 150.

If the reflected light reflected by the objective lens 170 returns to the optical fiber 150, a peak will appear due to interference between the reflected light and the reference light reflected by the reference surface. By arranging the optical fiber 170 at an angle, the reflected light from the objective lens 170 returning to the optical fiber 150 is reduced. Thereby, in the waveform signal of FIG. 11A, a peak due to interference between the reflected light and the reference light reflected by the reference surface becomes less likely to appear.

In this way, in the waveform signal of FIG. 11A, by making it difficult for unnecessary peaks to appear other than the peaks that appear due to interference between the measurement light reflected by the measurement target T and the reference light reflected by the reference surface, the processing section 140 can appropriately calculate the distance to the measurement target T.

In particular, as shown in FIG. 11B, this effect is remarkable when the measurement target T is close to the sensor head 102. In FIG. 11B, similarly to FIG. 11A, a peak appears due to interference between the measurement light reflected from the measurement target T and the reference light reflected from the reference surface of the tip (end surface) of the optical fiber 150.

Here, when the measurement target T is close to the sensor head 102, the distance between the measurement target T and the objective lens 170 is short. Therefore, if the reflected light reflected by the objective lens 170 returns to the optical fiber 150, a peak will occur due to interference between the reflected light and the reference light reflected by the reference surface, and the peak will be It is close to the peak generated by interference between the measurement light reflected by the measurement target T and the reference light reflected by the reference surface of the tip (end face) of the optical fiber 150 (partially overlapped in FIG. 11B).

Similar to FIG. 11A described above, by arranging the objective lens 170 at an angle, the reflected light at the objective lens 170 that returns to the optical fiber 150 is reduced, and even in the waveform signal of FIG. 11B, the reflected light and the reference light are A peak due to interference with the reference light reflected by the surface becomes less likely to appear.

In this way, in the waveform signal of FIG. 11B, by making it difficult for unnecessary peaks to appear other than the peaks that appear due to interference between the measurement light reflected by the measurement target T and the reference light reflected by the reference surface, the processing section 140 can appropriately calculate the distance to the measurement target T.

Next, the inclination of the objective lens 170 will be explained in detail.
FIG. 12 is a diagram schematically showing how the objective lens 170 is tilted by a predetermined angle θ with respect to the vertical direction of the optical axis L of light emitted from the optical fiber 150 into the sensor head 102. be. As shown in FIG. 12, it is assumed that the focal length f of the collimating lens 160, the numerical aperture NA of the optical fiber 150, the core radius r of the optical fiber 150, and the wavelength λ of light.

The spot radius _W0 , which is the radius at which the light intensity is (1/e) ² of the center intensity, can be expressed by the following (Equation 2).
W ₀ ≒0.82λ/NA ... (Math. 2)

Since the objective lens 170 is tilted by a predetermined angle θ with respect to the vertical direction of the optical axis L, the reflected light from the objective lens 170 returns to the optical fiber 150 side via the collimating lens 160. The center S of the spot of the reflected light is shifted by a distance d from the center of the core of the optical fiber 150. The distance d can be expressed using the following (Equation 3).
d=ftanθ...(Math. 3)

Then, the beam intensity at a position twice the spot radius W ₀ is 0.1% of the peak intensity (for example, in a Gaussian distribution, the intensity at a position twice the Gaussian radius is 0.0003 of the peak value), It is considered that the level is almost negligible. In other words, if the distance d satisfies the following (Equation 4), it is considered that among the light reflected by the objective lens 170, the light that returns to the core of the optical fiber 150 can be ignored.
d>r+2W ₀ ...(Math. 4)

That is, using the above (Equation 2) to (Equation 4), the predetermined angle θ at which the objective lens 170 is inclined with respect to the vertical direction of the optical axis L preferably satisfies the following (Equation 5).
θ>arctan {(r+1.64λ/NA)/f} ...(Math. 5)

As a result, the center S of the spot of the reflected light on the objective lens 170 is located outside the core diameter of the optical fiber 150, and the intensity of the reflected light incident on the core diameter of the optical fiber 150 is reduced to a negligible level. .

In other words, if the above (Equation 5) is not satisfied, the amount of light that returns to the core of the optical fiber 150 out of the light reflected by the objective lens 170 becomes so large that it cannot be ignored, and for example, the waveform shown in FIG. 11B If an unnecessary peak appears in the signal, there is a possibility that the distance to the measurement target T cannot be calculated appropriately. For example, if the angle of the objective lens 170 approaches the perpendicular direction of the optical axis L due to vibration, etc., we will notify you of this and adjust the arrangement of the objective lens 170 before the above (Equation 4) is no longer satisfied. good.

More specifically, when the predetermined angle θ at which the objective lens 170 is arranged at an angle with respect to the perpendicular direction of the optical axis L becomes smaller than a threshold value, it is preferable to notify that fact. Here, the threshold value is greater than or equal to arctan {(r+1.64λ/NA)/f} shown in the above (Equation 5).

As described above, according to the optical interferometric ranging sensor 100 according to one aspect of the present invention, the objective lens 170 in the sensor head 102 is aligned with the optical axis L of the light emitted from the optical fiber 150 into the sensor head 102. Since it is arranged to be inclined by a predetermined angle θ with respect to the vertical direction, the influence of reflected light from the objective lens 170 can be reduced, and the distance to the measurement target T can be appropriately measured.

In particular, as shown in FIG. 11B, when the measurement target T is close to the sensor head 102, unnecessary peaks are less likely to appear due to the influence of the reflected light from the objective lens 170, making measurement impossible with the optical interference distance measurement sensor 100. It is possible to prevent the existence of dead zones. That is, even if the measurement target T is close to the sensor head 102, the distance to the measurement target T can be appropriately measured.

In this embodiment, the collimating lens 160 and the objective lens 170 are arranged in the sensor head 102, but the invention is not limited to this. For example, a collimating lens may be further arranged, or conversely, A single lens may be used.

FIG. 13 is a diagram showing a specific example of a sensor head composed of one lens. As shown in FIG. 13(A), the sensor head 202 has a collimating lens 161 tilted at a predetermined angle. Further, as shown in FIG. 13(B), the sensor head 203 is provided with an objective lens 171 tilted by a predetermined angle.

In this way, by arranging the collimating lens 161 and the objective lens 171 at a predetermined angle, out of the light reflected by the collimating lens 161 and the objective lens 171, the light that returns to the core of the optical fiber 150 is reduced, and unnecessary peaks are can be made difficult to appear.

Note that in a sensor head composed of one lens, the collimating lens 161 and objective lens 171 are preferably arranged at a predetermined angle of 5 degrees or more.

Furthermore, here, the surface of the collimating lens 161 is exemplified as having a planar shape on the side where the light from the optical fiber 150 is incident, but in this embodiment, the surface of the collimating lens 161 has a convex shape. It's okay.

Further, in the present embodiment, the collimating lens and the objective lens are exemplified as optical elements arranged at a predetermined angle. However, the present invention is not limited to these, and examples include an optical filter, a polarizing element, It may be a wave plate, a beam splitter, a diffraction grating, a prism, a diffractive optical element, or other optical lens. Further, these optical elements are typically transmissive optical elements, and at least one or more may be arranged.

[Modified example of interferometer]
In the embodiment described above, the optical interferometric ranging sensor 100 uses a Fizeau interferometer that generates a reference light by using the tip of an optical fiber as a reference surface in the interferometer 120. It is not limited.

FIG. 14 is a diagram showing variations of an interferometer that generates interference light using measurement light and reference light. In FIG. 14(a), in the optical path branched by the optical branching section 121 in the interferometer, a reference light whose reference plane is the tip (end surface) of the optical fiber and a reference light irradiated from the sensor head and reflected by the measurement target T are shown. Interference light is generated based on the optical path length difference with the measurement light. This is the configuration of the interferometer of the optical interference ranging sensor 100 according to the embodiment described above (Fizeau type interferometer), and the reference surface is configured so that light is reflected due to the difference in refractive index between the optical fiber and the air. (Fresnel reflex). Further, the tip of the optical fiber may be coated with a reflective film, or the tip of the optical fiber may be coated with a non-reflective coating and a reflective surface such as a lens surface may be separately arranged.

In FIG. 14(b), in the optical paths branched by the optical branching unit 121 in the interferometer, a measurement optical path Lm that guides the measurement light to the measurement target T and a reference optical path Lr that guides the reference light are formed, and the reference optical path Lr A reference plane is placed beyond the (Michelson type interferometer). For the reference surface, the tip of the optical fiber may be coated with a reflective film, or the tip of the optical fiber may be coated with a non-reflective coating and a mirror or the like may be separately arranged. In this configuration, interference light is generated by providing an optical path length difference between the optical path length of the measurement optical path Lm and the optical path length of the reference optical path Lr.

In FIG. 14(c), in the optical paths branched by the optical branching section 121 in the interferometer, a measurement optical path Lm that guides the measurement light to the measurement target T and a reference optical path Lr that guides the reference light are formed, and the reference optical path Lr A balanced detector is arranged (Mach-Zehnder interferometer). In this configuration, interference light is generated by providing an optical path length difference between the measurement optical path Lm and the reference optical path Lr.

In this way, the interferometer is not limited to the Fizeau type interferometer described in the embodiment, but may also be a Michelson type interferometer or a Mach-Zehnder type interferometer, or a method that uses a measurement beam and a reference beam. Any type of interferometer may be used as long as interference light can be generated by setting the optical path length difference, and a combination of these or other configurations may be used.

In the embodiment of the present invention, the optical interferometric ranging sensor 100 has been described as a single channel, but it is not limited to this. For example, the light projected from the wavelength swept light source 110 is A multi-stage optical interference ranging sensor may be constructed by branching using a coupler or the like. The present invention can also be applied to a multi-stage optical interference ranging sensor.

The embodiments described above are intended to facilitate understanding of the present invention, and are not intended to be interpreted as limiting the present invention. Each element included in the embodiment, as well as its arrangement, material, conditions, shape, size, etc., are not limited to those illustrated, and can be changed as appropriate. Further, it is possible to partially replace or combine the structures shown in different embodiments.

[Appendix]
a light source (110) that emits light while changing the wavelength;
Light projected from the light source is supplied, and interference light is generated based on measurement light that is irradiated onto the measurement target by the sensor head and reflected, and reference light that follows an optical path that is at least partially different from the measurement light. an interferometer (120) to
a light receiving unit (130) that receives interference light from the interferometer and converts it into an electrical signal;
a processing unit (140) that calculates a distance from the sensor head to the measurement target based on the electrical signal converted by the light receiving unit;
The sensor head (102) includes:
connected to an optical fiber (150) for guiding light projected from the light source to the sensor head,
including an optical element arranged at a predetermined angle with respect to a direction perpendicular to an optical axis (L) of light emitted from the optical fiber into the sensor head;
Optical interference ranging sensor (100).

DESCRIPTION OF SYMBOLS 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-22c...Collimating lens, 23...Lens holder , 24... Optical fiber array, 30... Controller, 31... Display section, 32... Setting section, 33... External interface (I/F) section, 34... Optical fiber connection section, 35... External storage section, 36... Measurement processing section , 40... Optical fiber, 51... Wavelength swept light source, 52... Optical amplifier, 53, 53a-53b... Isolator, 54, 54a-54e... Optical coupler, 55... Attenuator, 56a-56c... Photodetector, 58... AD conversion Section, 59... Processing section, 60... Balance detector, 61... Correction signal generation section, 71a to 71e... Light receiving element, 72a to 72c... Amplifying circuit, 74a to 74c... AD conversion section, 75... Processing section, 76... Differential Amplification circuit, 77... Correction signal generation section, 100... Optical interference ranging sensor, 101... Controller, 102, 202, 203... Sensor head, 110... Wavelength swept light source, 120... Interferometer, 121... Optical branching unit, 130... Light receiving section, 140... Processing section, 150... Optical fiber, 160, 161... Collimating lens, 170, 171... Objective lens, T... Measurement object, L... Optical axis, Lm... Measurement optical path, Lr... Reference optical path

Claims (6)

A light source that emits light while changing the wavelength,
Light projected from the light source is supplied, and interference light is generated based on measurement light that is irradiated onto the measurement target by the sensor head and reflected, and reference light that follows an optical path that is at least partially different from the measurement light. an interferometer that
a light receiving unit that receives interference light from the interferometer and converts it into an electrical signal;
a processing unit that calculates a distance from the sensor head to the measurement target based on the electrical signal converted by the light receiving unit,
The sensor head is
connected to an optical fiber for guiding light projected from the light source to the sensor head,
an optical element arranged at a predetermined angle with respect to a direction perpendicular to an optical axis of light emitted from the optical fiber into the sensor head;
Optical interference ranging sensor. The optical element tilted at a predetermined angle is at least one of a collimating lens, an objective lens, an optical filter, a polarizing element, a wavelength plate, a beam splitter, a diffraction grating, a prism, and a diffractive optical element.
The optical interferometric ranging sensor according to claim 1. The sensor head includes, in order from the connection side with the optical fiber, a collimating lens and an objective lens tilted at the predetermined angle,
Light emitted from the optical fiber into the sensor head is reflected by the objective lens, and the reflected light passes through the collimating lens so that the center of the spot of the reflected light becomes outside the core diameter of the optical fiber. ,
The optical interferometric ranging sensor according to claim 1. Using the focal length f of the collimating lens, the numerical aperture NA of the optical fiber, the core radius r of the optical fiber, and the wavelength λ of the light, the predetermined angle θ is
θ>arctan {(r+1.64λ/NA)/f}
satisfy,
The optical interference ranging sensor according to claim 3. When the predetermined angle becomes smaller than a threshold, a notification to that effect is provided;
The optical interferometric ranging sensor according to claim 1. A light source that emits light while changing the wavelength,
Light projected from the light source is supplied, and interference light is generated based on measurement light that is irradiated onto the measurement target by the sensor head and reflected, and reference light that follows an optical path that is at least partially different from the measurement light. an interferometer that
a light receiving unit that receives interference light from the interferometer and converts it into an electrical signal;
a processing unit that calculates a distance from the sensor head to the measurement target based on the electrical signal converted by the light receiving unit,
The sensor head is
connected to an optical fiber for guiding light projected from the light source to the sensor head,
The sensor head includes an optical element that is tilted at a predetermined angle so that the light emitted from the optical fiber into the sensor head is reflected and the center of the spot of the reflected light is outside the core diameter of the optical fiber. ,
Optical interference ranging sensor.

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