WO2024070430A1

WO2024070430A1 - Controller and optical interferometric ranging sensor

Info

Publication number: WO2024070430A1
Application number: PCT/JP2023/031329
Authority: WO
Inventors: 和哉木村; 裕介長崎
Original assignee: オムロン株式会社
Priority date: 2022-09-28
Filing date: 2023-08-29
Publication date: 2024-04-04
Also published as: JP2024048669A

Abstract

The present invention reduces deviation in sampling timing. A controller (110) is connected, via an optical fiber cable (130), to each of a first sensor head (121) and a second sensor head (122) that irradiate an object to be measured with light. The controller (110) is provided with: a light source (140); a first main interferometer (151) that generates a first main interference signal; a second main interferometer (152) that generates a second main interference signal; and a sub-interferometer (160) that generates a sub-interference signal. The controller (110) is further provided with: a first correction signal generation unit (171) that generates a first correction signal; a delay amount generation unit that generates a delay amount based on an optical path length difference between an optical path length of a first optical fiber (131) and an optical path length of a second optical fiber (132); and a second correction signal generation unit (172) that generates, on the basis of the sub-interference signal and the delay amount, a second correction signal for correcting a sampling period of the second main interference signal.

Description

Controller and optical interference distance measuring sensor

The present invention relates to a controller and an optical interferometric distance sensor.

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

　Conventionally, this type of optical frequency domain reflectometry device has a sweep light source, an auxiliary interferometer that gives a predetermined delay time difference to a portion of the output light of the sweep light source to cause interference and output as an auxiliary interference signal, a measurement interferometer that inputs a portion of the output light of the sweep light source to the optical fiber under test and causes the reflected light from the optical fiber under test and a portion of the output light of the sweep light source to interfere with each other and output as a measurement interference signal, a linearization section that uses the auxiliary interference signal to correct the nonlinearity of the wavelength sweep of the sweep light source for the measurement interference signal, and a Fourier transform section that performs a Fourier transform on the output signal of the linearization section to output a frequency domain signal, in which the linearization section has multiple linearization sections each having a different delay time, and the Fourier transform section has a weighted addition/Fourier transform section that adds the output signals of the multiple linearization sections with different weights and outputs the Fourier transformed result (see Patent Document 1). This optical frequency domain reflectometry device corrects the nonlinearity of the wavelength sweep over a wide range of the optical fiber under test.

JP 2017-181115 A

On the other hand, in an optical interferometric distance measuring sensor equipped with a controller and multiple sensor heads, it is necessary to accommodate measurement targets at different distances by changing the length of the optical fiber connecting the controller and the sensor heads among the multiple sensor heads.

However, if the lengths of the optical fibers in the main interferometer are different, a mismatch occurs in the sampling timing between the main interferometer signal and the sub-interferometer signal, and the signal generated by the interference between the two signals can result in a decrease in signal strength (signal level).

The present invention was made in consideration of these circumstances, and one of its objectives is to provide a controller and optical interferometric distance sensor that can reduce deviations in sampling timing.

A controller according to one aspect of the present disclosure is a controller connected via an optical fiber cable to each of a first sensor head and a second sensor head that irradiate light onto a measurement object, and includes a light source that projects light while changing the wavelength, a first main interferometer that receives the light projected from the light source and generates a first main interference signal based on a first measurement light that is irradiated onto the measurement object by the first sensor head and reflected, and a first reference light that follows at least a part of an optical path different from that of the first measurement light, a second main interferometer that receives the light projected from the light source and generates a second main interference signal based on a second measurement light that is irradiated onto the measurement object by the second sensor head and reflected, and a second reference light that follows at least a part of an optical path different from that of the second measurement light, and a sub-interferometer that receives the light projected from the light source and generates a sub-interference signal based on two lights that follow different optical paths, The fiber cable includes a first optical fiber connected to the first main interferometer and transmitting light from the first main interferometer to the first sensor head and transmitting light from the first sensor head to the first main interferometer, and a second optical fiber connected to the second main interferometer and transmitting light from the second main interferometer to the second sensor head and transmitting light from the second sensor head to the second main interferometer, the second optical fiber having an optical path length different from that of the first optical fiber, and the controller further includes a first correction signal generating unit that generates a first correction signal for correcting the sampling period of the first main interference signal based on the sub-interference signal, a delay amount generating unit that generates a delay amount based on the optical path length difference between the optical path length of the first optical fiber and the optical path length of the second optical fiber, and a second correction signal generating unit that generates a second correction signal for correcting the sampling period of the second main interference signal based on the sub-interference signal and the delay amount.

According to this aspect, a delay amount is generated based on the optical path length difference between the optical path length of the first optical fiber and the optical path length of the second optical fiber, and a second correction signal that corrects the sampling period of the second main interference signal is generated based on the sub-interference signal and the delay amount. This makes it possible to generate a delay in the second main interference signal that corresponds to the optical path length difference between the optical path length of the first optical fiber and the optical path length of the second optical fiber. Therefore, it is possible to reduce the timing deviation when sampling the second main interference signal and suppress a decrease in the signal strength of the sampled digital signal.

In the above aspect, the delay amount generating unit may include a third optical fiber that propagates the secondary interference signal and has an optical path length based on the optical path length difference.

According to this aspect, a third optical fiber is included that propagates the secondary interference signal and has an optical path length based on the optical path length difference between the optical path length of the first optical fiber and the optical path length of the second optical fiber. This makes it easy to set the amount of delay by changing the optical path length of the third optical fiber.

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

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

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

According to this aspect, the second correction signal generating unit generates a pulse signal, which is the second correction signal, based on a signal in which a delay corresponding to the amount of delay is generated in the time axis direction in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal. This makes it easy to match (synchronize) the timing of sampling the second main interference signal.

In the above embodiment, the device may further include an AD converter that samples the second main interferometer signal, which is obtained by converting the second main interference signal into an electrical signal, based on the second correction signal and converts the signal into a digital signal.

According to this aspect, the second main interferometer signal, which is obtained by converting the second main interference signal into an electrical signal, is further provided with an AD conversion unit that samples the second main interferometer signal based on the second correction signal and converts it into a digital signal. This makes it easy to realize a configuration in which the second main interferometer signal is converted into a digital signal with a corrected sampling period.

In the above embodiment, the delay amount may be set so that the absolute value of the difference between the delay time of the light due to the optical path length difference is smaller than the minimum sampling period of the AD conversion unit.

According to this aspect, the delay amount is set so that the absolute value of the difference between the delay time of the light due to the optical path length difference is smaller than the minimum sampling period in the AD conversion unit. This makes it possible to suppress the decrease in the signal strength of the sampled digital signal to a predetermined percentage or less, for example, 10% or less.

In the above aspect, the system may further include a processing unit that measures the distance to the measurement object based on at least one of the first main interference signal and the second main interference signal and the sub-interference signal.

According to this aspect, a processing unit is further provided that measures the distance to the measurement object based on at least one of the first main interference signal and the second main interference signal and the sub-interference signal. This makes it possible to easily realize a configuration that measures the distance to the measurement object.

An optical interferometric distance measuring sensor according to one embodiment of the present disclosure is an optical interferometric distance measuring sensor including a controller and an optical fiber cable connected to the controller, the controller including a light source that projects light while changing the wavelength, a first main interferometer that receives the light projected from the light source and generates a first main interference signal based on a first measurement light that is irradiated on a measurement object by a first sensor head and reflected, and a first reference light that follows at least a part of an optical path different from that of the first measurement light, a second main interferometer that receives the light projected from the light source and generates a second main interference signal based on a second measurement light that is irradiated on a measurement object by a second sensor head and reflected, and a second reference light that follows at least a part of an optical path different from that of the second measurement light, and a sub-interferometer that receives the light projected from the light source and generates a sub-interference signal based on two lights that follow different optical paths, and the optical fiber cable is connected to the controller. The cable includes a first optical fiber connected to the first main interferometer and propagating light from the first main interferometer to the first sensor head and propagating light from the first sensor head to the first main interferometer, and a second optical fiber connected to the second main interferometer and propagating light from the second main interferometer to the second sensor head and propagating light from the second sensor head to the second main interferometer, the second optical fiber having an optical path length different from that of the first optical fiber, and the controller further includes a first correction signal generating unit that generates a first correction signal for correcting the sampling period of the first main interference signal based on the sub-interference signal, a delay amount generating unit that generates a delay amount based on the optical path length difference between the optical path length of the first optical fiber and the optical path length of the second optical fiber, and a second correction signal generating unit that generates a second correction signal for correcting the sampling period of the second main interference signal based on the sub-interference signal and the delay amount.

The present invention can reduce the deviation in sampling timing.

1 is a schematic external view showing an overview of a displacement sensor 10 according to the present disclosure. 5 is a flowchart showing a procedure for measuring a measurement object T by the displacement sensor 10 according to the present disclosure. 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 for measuring a measurement object T by a sensor system 1 in which a displacement sensor 10 according to the present disclosure is used. 1 is a diagram for explaining the principle by which a measurement object T is measured by a displacement sensor 10 according to the present disclosure. 11A and 11B are diagrams for explaining another principle by which the measurement object T is measured by the displacement sensor 10 according to the present disclosure. FIG. 2 is a perspective view showing a schematic configuration of a sensor head 20. 2 is a schematic diagram showing the internal structure of a sensor head 20. FIG. FIG. 2 is a block diagram for explaining signal processing in a controller 30. 10 is a flowchart showing a method for calculating a distance to a measurement object T, which is executed by a processing unit 59 in the controller 30. 1 is a diagram showing how a waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency). FIG. 13 is a diagram showing how a spectrum (voltage vs. frequency) is distance-transformed into a spectrum (voltage vs. distance). FIG. 13 is a diagram showing how a peak is detected based on a spectrum (voltage vs. distance) and a corresponding distance value is calculated. 1 is a schematic diagram showing an outline of the configuration of an optical interferometric distance measuring sensor 100 according to an embodiment of the present invention. FIG. 13 is a schematic diagram showing an outline of the configuration of another optical interferometric distance measuring sensor 101 according to an embodiment of the present invention. FIG. 11 is a diagram for explaining the sampling timing of the first main interferometer signal and the second main interferometer signal. 11 is a diagram for explaining the relationship between the signal intensity of the second main interferometer signal converted into a digital signal and the time difference Δt. FIG. FIG. 13 is a schematic diagram showing an example of a specific configuration of a secondary interferometer 160 and its subsequent stages when three sensor heads are provided. FIG. 13 is a schematic diagram showing another example of the specific configuration of the secondary interferometer 160 and the subsequent stages when three sensor heads are provided. 13A and 13B are diagrams showing variations of an interferometer that generates interference light using measurement light and reference light.

Below, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Note that each embodiment described below is merely a specific example for implementing the present invention, and is not intended to limit the interpretation of the present invention. Furthermore, in order to facilitate understanding of the description, the same reference numerals are used as far as possible for the same components in each drawing, and duplicate descriptions may be omitted.

[Displacement sensor overview]
First, an overview of the displacement sensor according to the present disclosure will be described.
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 a measurement object T (the distance to the measurement object 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 unit 31, a setting unit 32, an external interface (I/F) unit 33, an optical fiber connection unit 34, and an external memory unit 35, and further includes a measurement processing unit 36 inside.

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

In addition, the objective lens 21 is attached to the sensor head 20, but the objective lens 21 is configured to be removable. The objective lens 21 can be replaced with an objective lens having an appropriate focal length depending on the distance between the sensor head 20 and the measurement target T, or a variable-focus objective lens may be used.

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

The optical fiber 40 is connected to and extends from the optical fiber connection section 34 disposed in the controller 30, connecting the controller 30 and the sensor head 20. As a result, the optical fiber 40 is configured to guide the light projected from the controller 30 to the sensor head 20, and further guide the return light from the sensor head 20 to the controller 30. The optical fiber 40 is detachable from the sensor head 20 and the controller 30, and various optical fibers can be used in terms of length, thickness, characteristics, etc.

The display unit 31 is configured, for example, with 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 returned light received from the sensor head 20, and the measurement results such as the displacement of the measurement object T measured by the displacement sensor 10 (the distance to the measurement object T).

The setting unit 32 performs the settings necessary for measuring the measurement target T, for example, by the 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 unit 33. In addition, the external connection device may be connected via a network in a wired or wireless manner.

Here, the external I/F unit 33 is composed of, for example, Ethernet (registered trademark), RS232C, and analog output. The external I/F unit 33 may be connected to another connected device to allow necessary settings to be made from the external connected device, or may output the measurement results, etc., measured by the displacement sensor 10 to the external connected device.

In addition, the controller 30 may import data stored in the external memory unit 35 to perform settings required for measuring the measurement object T. The external memory unit 35 is, for example, an auxiliary storage device such as a USB (Universal Serial Bus) memory, and stores in advance settings required for measuring the measurement object T.

The measurement processing unit 36 in the controller 30 includes, for example, a wavelength swept light source that emits light while continuously changing the wavelength, a light receiving element that receives the return 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, various processes are performed using a control unit, a memory unit, etc. based on the return light from the sensor head 20 so that the displacement of the measurement object T (the distance to the measurement object T) is ultimately calculated. Details of these processes will be described later.

FIG. 2 is a flowchart showing the procedure for measuring the measurement object T 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, guide light is irradiated from the sensor head 20 onto the measurement target T, and the sensor head 20 is installed in an appropriate position based on the guide light.

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

In addition, the objective lens 21 may be replaced with one having an appropriate focal length depending on the distance between the sensor head 20 and the measurement object T.

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

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

Various parameters may also be set. For example, the sampling time, the measurement range, and a threshold for determining whether the measurement result is normal or abnormal may be 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 a measurement mode may be set according to the material of the measurement object T.

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

In step S13, the sensor head 20 installed in step S11 measures the measurement object 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 projected from the wavelength swept light source, the light returning from the sensor head 20 is received by a light receiving element, and the signal processing circuit performs frequency analysis, distance conversion, peak detection, etc., to calculate the displacement of the measurement object T (the distance to the measurement object T). Specific details of the measurement process will be described later.

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

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

[Overview of a system including a displacement sensor]
Fig. 3 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. As shown in Fig. 3, the sensor system 1 includes the displacement sensor 10, a control device 11, a control signal input sensor 12, and an external connection device 13. Note that the displacement sensor 10 is connected to the control device 11 and the external connection device 13 by, for example, a communication cable or an external connection cord (including, for example, an external input line, an external output line, a power line, etc.), and the control device 11 and the control signal input sensor 12 are connected by a signal line.

As described with reference to Figures 1 and 2, the displacement sensor 10 measures the displacement of the measurement object T (the distance to the measurement object T). The displacement sensor 10 may then output the measurement results, etc. to the control device 11 and the externally connected device 13.

The control device 11 is, for example, a PLC (Programmable Logic Controller), and provides various instructions to the displacement sensor 10 when the displacement sensor 10 measures the measurement object 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 may output a zero reset command signal (a signal for setting the current measurement value to 0) or the like to the displacement sensor 10.

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

The external connection device 13 is, for example, a PC (Personal Computer), and the user can operate it to configure various settings for the displacement sensor 10.

Specific examples include the measurement mode, operation mode, measurement period, and the material of the measurement object T.

As a measurement mode setting, an "internal synchronous measurement mode" in which measurement is started periodically within the control device 11, or an "external synchronous measurement mode" in which measurement is started in response to an input signal from outside the control device 11, etc. can be selected.

As the operation mode setting, an "operation mode" for actually measuring the measurement object T, or an "adjustment mode" for setting the measurement conditions for measuring the measurement object T, etc. can be selected.

The measurement period is the period for measuring the measurement object T, and may be set according to the reflectance of the measurement object T. Even if the reflectance of the measurement object T is low, the measurement object T can be properly measured by lengthening the measurement period and setting it appropriately.

For the measurement object T, the "rough surface mode" is selected when the reflected light component is relatively high in diffuse reflection, the "mirror surface mode" is selected when the reflected light component is relatively high in specular reflection, or the "standard mode" is selected as an intermediate mode between the two.

In this way, by making appropriate settings according to the reflectance and material of the measurement object T, it is possible to measure the measurement object T with higher accuracy.

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

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

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

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

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

Note that, while FIG. 4 has been used to explain the procedure for the external synchronous measurement mode in which the measurement object T is measured by the control signal input sensor 12 detecting the measurement object T, the procedure is not limited to this. For example, in 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 object T.

Next, the principle of measurement of the measurement target T by the displacement sensor 10 according to the present disclosure will be described.
5A is a diagram for explaining the principle of measuring the measurement target T 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 collimator lenses 22a to 22c, and the controller 30 includes a wavelength swept light source 51, an optical amplifier 52, a plurality of isolators 53 and 53a to 53b, a plurality of

optical couplers

54 and 54a to 54e, an attenuator 55, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generating unit 61.

The wavelength swept light source 51 emits a laser beam with a swept wavelength. For example, if a VCSEL (Vertical Cavity Surface Emitting Laser) is used as the wavelength swept light source 51 by modulating the laser current, mode hopping is unlikely to occur due to the short resonator length, the wavelength can be easily changed, and it can be realized at low cost.

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

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 to prevent the effects of noise caused by returned light.

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

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

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

The light branched by the first-stage optical coupler 54a in the direction of the second-stage optical coupler 54b travels through the isolator 53a to the second-stage optical coupler 54b, which then branches it further into the direction of the sensor head 20 and the direction of the third-stage optical coupler 54c. As in the first stage, the light branched from the optical coupler 54b in the direction of the sensor head 20 passes through the collimator lens 22b and the objective lens 21 from the tip of the optical fiber in the sensor head 20 and is irradiated onto the measurement object T. The tip (end face) of the optical fiber then becomes the reference surface, and the light reflected by the reference surface and the light reflected by the measurement object T interfere with each other to generate interference light, which returns to the second-stage optical coupler 54b and is branched by the optical coupler 54b in the directions of the isolator 53a and the light receiving element 56b. The light branched from the optical coupler 54b in the direction of 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 in the front stage to the optical coupler 54b in the rear stage and blocks light from the optical coupler 54b in the rear stage to the optical coupler 54a in the front stage, so the light branched from the optical coupler 54b in the direction of the isolator 53a is blocked.

The light branched by the second-stage optical coupler 54b in the direction of the third-stage optical coupler 54c travels through the isolator 53b to the third-stage optical coupler 54c, where it is further branched by the third-stage optical coupler 54c in the direction of the sensor head 20 and the direction of the attenuator 55. As in the first and second stages, the light branched from the optical coupler 54c in the direction of the sensor head 20 passes from the tip of the optical fiber through the collimator lens 22c and the objective lens 21 in the sensor head 20 and is irradiated onto the measurement object T. The tip (end face) of the optical fiber then becomes the reference surface, and the light reflected by the reference surface interferes with the light reflected by the measurement object T to generate interference light, which returns to the third-stage optical coupler 54c and is branched by the optical coupler 54c in the directions of the isolator 53b and the light receiving element 56c. The light branched from the optical coupler 54c in the direction of 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 in the front stage to the optical coupler 54c in the rear stage and blocks light from the optical coupler 54c in the rear stage to the optical coupler 54b in the front stage, so the light branched from the optical coupler 54c in the direction of the isolator 53b is blocked.

In addition, since the light branched off by the third-stage optical coupler 54c in a direction other than the sensor head 20 is not used to measure the measurement object T, it is advisable to attenuate it by an attenuator 55 such as a terminator so that it is not reflected back.

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

The light receiving elements 56a to 56c receive the interference light from the main interferometer as described above and generate an electrical signal according to the amount of light received.

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

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

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

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

In addition, optical coupler 54d and optical coupler 54e each need to split light in a 50:50 ratio.

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

Due to the nonlinearity of the wavelength when the wavelength swept light source 51 is swept, the intervals between the waves of the analog signals input to the AD converters 58a to 58c in the main interferometer are not equal. In the AD converters 58a to 58c, the sampling time is corrected based on the K clock described above and AD conversion (sampling) is performed so that the intervals between the waves become equal.

As described above, the K clock is a correction signal used to sample the analog signal of the main interferometer, and therefore needs to be generated at a higher frequency than the analog signal of the main interferometer. Specifically, the optical path length difference between optical couplers 54d and 54e in the sub interferometer may be made longer than the optical path length difference between the tip (end face) of the optical fiber in the main interferometer and the measurement object T, or the frequency may be multiplied (e.g., 8 times) by the correction signal generator 61 to make it higher frequency.

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

In addition, because high-speed processing is required for the processing unit 59, it is often realized by an integrated circuit such as an FPGA (field-programmable gate array).

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

5B is a diagram for explaining another principle by which the measurement object 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 collimator lenses 22a to 22c, and the controller 30 includes a wavelength swept light source 51, an optical amplifier 52, a plurality of isolators 53 and 53a to 53b, a plurality of

optical couplers

54 and 54a to 54j, an attenuator 55, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generation unit 61. The displacement sensor 10 shown in FIG. 5B differs from the configuration of the displacement sensor 10 shown in FIG. 5A mainly in that it includes optical couplers 54f to 54j, and the principle of this different configuration will be described in detail in comparison with FIG. 5A.

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

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

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

On the other hand, the reference light split by optical coupler 54f is further split by optical coupler 54g to

optical couplers

54h, 54i, and 54j.

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

Similarly, in optical coupler 54i, interference light is generated according to the difference in optical path length between the optical path of the measurement light (the optical path from optical coupler 54f, through

optical couplers

54a and 54b, collimating lens 22b, objective lens 21, reflected by the measurement object T, and reaching optical coupler 54i) and the optical path of the reference light (the optical path from optical coupler 54f to optical coupler 54i via optical coupler 54g), and the interference light is received by light-receiving element 56b and converted into an electrical signal.

In the optical coupler 54j, interference light is generated according to the difference in optical path length between the optical path of the measurement light (the optical path from optical coupler 54f through

optical couplers

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

In this way, the main interferometer has three optical paths (three channels) and generates three interference lights according to the optical path length difference between the measurement light reflected by the measurement object T and input to

optical couplers

54h, 54i, and 54j, and the reference light input to

optical couplers

54h, 54i, and 54j via

optical couplers

54f and 54g, respectively.

In addition, the optical path length difference between the measurement light and the reference light may be set to be different for each of the three channels, for example, the optical path lengths of optical coupler 54g and each of

optical couplers

54h, 54i, and 54j may be set to be different.

Then, based on the interference light obtained from each, the distance to the measurement object T, etc. is measured (multi-channel).

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

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

As shown in FIG. 6B, the lens holder 23 stores one objective lens 21 and three collimating lenses 22a to 22c. Light from the optical fiber is guided to the three collimating lenses 22a to 22c via the optical fiber array 24, and the light that passes through the three collimating lenses 22a to 22c is irradiated onto the measurement object T via the objective lens 21.

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

The lens holder 23 that constitutes the sensor head 20 may also be made of a metal (e.g., A2017) that is strong and can be machined 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-71e, a plurality of amplifier circuits 72a-72c, a plurality of AD conversion units 74a-74c, a processing unit 75, a differential amplifier circuit 76, and a correction signal generation unit 77.

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

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

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

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

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 distance value to the measurement target T.

The multiple light receiving elements 71d-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, one of which outputs an interference signal with an inverted phase, and the interference signal is amplified and converted into a voltage signal while noise is removed by taking the difference between the two signals.

The correction signal generating unit 77 corresponds to the correction signal generating unit 61 shown in FIG. 5A, and binarizes the voltage signal using a comparator, generates a K clock, and outputs it to the AD conversion units 74a to 74c. Since the K clock needs to be generated at a higher frequency than the analog signal of the main interferometer, the correction signal generating unit 77 may multiply the frequency (e.g., 8 times) to increase the frequency.

FIG. 8 is a flowchart showing a method for 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 performs frequency conversion of the waveform signal (voltage vs. time) into a spectrum (voltage vs. frequency) using the following FFT: Fig. 9A is a diagram showing how the waveform signal (voltage vs. time) is frequency converted into a spectrum (voltage vs. frequency).

In step S32, the processing unit 59 performs distance conversion from the spectrum (voltage vs. frequency) to a spectrum (voltage vs. distance). FIG. 9B is a diagram showing how the spectrum (voltage vs. frequency) is distance converted to 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 peaks are detected based on the spectrum (voltage vs. distance) and the corresponding distance values are calculated. As shown in FIG. 9C, peaks are detected in each of the three channels based on the spectrum (voltage vs. distance), and distance values corresponding to each peak are calculated.

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

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

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

<One embodiment>
[Configuration of optical interferometric distance measuring sensor]
Fig. 10 is a schematic diagram showing an outline of the configuration of an optical interferometric distance measuring sensor 100 according to an embodiment of the present invention. As shown in Fig. 10, the optical interferometric distance measuring sensor 100 includes a controller 110, and an optical fiber cable 130 that connects the controller 110 to a first sensor head 121 and a second sensor head 122. The optical interferometric distance measuring sensor 100 may further include the first sensor head 121 and the second sensor head 122.

The controller 110 includes a wavelength swept light source 140, an optical branching unit 111, a main interferometer 150, a sub interferometer 160, first photodiodes (PD) 112, 113,

amplifier circuits

114, 115, second photodiodes (PD) 116, 117, a first correction signal generating unit 171, a second correction signal generating unit 172,

AD conversion units

181, 182, and a processing unit 118.

The optical fiber cable 130 is an optical fiber group consisting of a plurality of optical fibers. The optical fiber cable 130 is configured to be detachable, that is, to be attached and detached, to each of the controller 110, the first sensor head 121, and the second sensor head 122. The optical fiber cable 130 is configured to include, for example, a first optical fiber 131 and a second optical fiber 132. The first optical fiber 131 has an optical path length proportional to the length L1, and the second optical fiber 132 has an optical path length proportional to the length L2. The length L1 of the first optical fiber 131 is set based on the distance to the measurement object T1, and the length L2 of the second optical fiber 132 is set based on the distance to the measurement object T2. The measurement object T2 is assumed to be an object that exists at a different distance from the measurement object T1, that is, at a far distance in the example shown in FIG. 1. Therefore, the optical path length of the second optical fiber 132 is different from the optical path length of the first optical fiber 131 and is longer than the optical path length of the first optical fiber 131.

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

The main interferometer 150 has multiple optical paths (multiple channels), and in the example shown in FIG. 10, it includes a first main interferometer 151 and a second main interferometer.

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

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

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

In this way, the first main interferometer 151 is supplied with light projected from the swept light source 140, and generates a first main interference signal based on the first measurement light that is irradiated onto the measurement object T and reflected by the first sensor head 121, and the first reference light that follows at least a part of an optical path different from that of the first measurement light. Note that, because the first main interferometer 151 is supplied with light projected from the swept light source and generates a first main interference signal, the first main interferometer 151 including the first sensor head 121 can also be called the first main interferometer.

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

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

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

In this way, the second main interferometer 152 is supplied with light projected from the swept light source 140, and generates a second main interference signal based on the second measurement light that is irradiated onto the measurement object T and reflected by the second sensor head 122, and the second reference light that follows at least a part of an optical path different from that of the second measurement light. Note that, because the second main interferometer 152 is supplied with light projected from the swept light source and generates a second main interference signal, the second main interferometer 152 including the second sensor head 122 can also be called the second main interferometer.

The first photodiode 112 receives the first main interference signal generated by the first main interferometer 151 and converts it into an electrical signal. The electrical signal converted by the first photodiode 112 is, for example, a current signal. The first photodiode 113 receives the second main interference signal generated by the second main interferometer 152 and converts it into an electrical signal. The electrical signal converted by the first photodiode 113 is similarly, for example, a current signal.

The amplifier circuit 114 amplifies the electrical signal input from the first photodiode 112 with a predetermined gain (also called "gain"). When a current signal is input from the first photodiode 112, the amplifier circuit 114 converts the current signal into a voltage signal (also called "I-V conversion") and amplifies it. The amplified electrical signal is output to the AD conversion unit 181. The amplifier circuit 115 amplifies the electrical signal input from the first photodiode 113 with a predetermined gain. When a current signal is input from the first photodiode 113, the amplifier circuit 115 converts the current signal into a voltage signal and amplifies it. The amplified electrical signal is output to the AD conversion unit 182.

The sub-interferometer 160 receives light emitted from the wavelength swept light source 140, which is split by the optical splitter 111 and supplied to generate a sub-interference signal based on the two lights that follow optical paths of different optical path lengths. Specifically, the first optical coupler 161 splits the light into two lights that follow optical paths of different optical path lengths, and the two lights are then combined and interfered with by the second optical coupler 162 to generate a sub-interference signal based on the difference in optical path length. The sub-interference signal propagates through the optical fiber 163 and is guided to the second photodiode 116, and also propagates through the optical fiber 164 and is guided to the second photodiode 117.

Optical fiber 163 has an optical path length proportional to length L1r, and optical fiber 164 has an optical path length proportional to length L2r. Optical fiber 164 in this embodiment corresponds to an example of a "delay amount generating unit" in the present invention. Optical fiber 164 in this embodiment also corresponds to an example of a "third optical fiber" in the present invention.

In other words, the optical fiber 164 is configured to generate a delay amount based on the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132.

Specifically, the optical fiber 164 propagates the sub-interference signal and has an optical path length based on the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132. Therefore, the sub-interference signal guided to the second photodetector 117 via the optical fiber 164 is a sub-interferometer signal delayed by the optical fiber 164 (hereinafter also referred to as a "delayed sub-interference signal"). In this way, the optical fiber 164 propagates the sub-interference signal and has an optical path length based on the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132, and therefore the amount of delay can be easily set by changing the optical path length of the optical fiber 164.

The second photodiode 116 receives the sub-interference signal propagated through the optical fiber 163 of the sub-interferometer 160 and converts it into an electrical signal (hereinafter also referred to as the "sub-interferometer signal"). The electrical signal converted by the second photodiode 116 is, for example, a current signal. The second photodiode 117 receives the sub-interference signal propagated through the optical fiber 164 of the sub-interferometer 160 and converts it into an electrical signal (hereinafter also referred to as the "delayed sub-interferometer signal"). The electrical signal converted by the second photodiode 116 is, for example, a current signal.

The electrical signals output from the

second photodiodes

116 and 117 may be amplified at a predetermined gain by an amplifier circuit (not shown). In this case, the amplifier circuit outputs the amplified electrical signals to the first correction signal generating unit 171 and the second correction signal generating unit 172.

The first correction signal generating unit 171 is configured to generate a first correction signal (also referred to as the "first K clock signal" or simply the "first K clock") based on the secondary interference signal. The first correction signal is a signal that corrects the sampling period of the first main interference signal generated by the first main interferometer 151. The secondary interference signal is nonlinear like the first main interference signal due to the nonlinearity of the wavelength during sweeping, so the first correction signal generating unit 171 can grasp the nonlinearity of the wavelength during sweeping based on the secondary interference signal, thereby generating a first correction signal, i.e., a first K clock signal, for appropriately sampling and AD converting the analog signal of the first main interference signal.

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

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

In this way, by generating a delay amount based on the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132, and generating a second correction signal that corrects the sampling period of the second main interference signal based on the sub-interference signal and the delay amount, it is possible to generate a delay in the second main interference signal according to the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132. Therefore, it is possible to reduce the timing deviation when sampling the second main interference signal and suppress a decrease in the signal strength of the sampled digital signal.

More specifically, the second correction signal generating unit 172 is configured to generate the second correction signal based on the delayed sub-interferometer signal. That is, the second correction signal is generated based on a signal in which a delay is generated in the time axis direction in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal. The delay is a time according to the delay amount described above.

In order for the second correction signal generating unit 172 to generate an appropriate second correction signal, the second correction signal generating unit 172 needs to properly grasp the nonlinearity of the second main interference signal received by the first photodiode 113. For this purpose, it is preferable to match the characteristics (nonlinearity) of the second main interference signal and the delayed sub-interference signal, in other words, to align the first main interference signal and the sub-interference signal in time.

The second correction signal generating unit 172 may generate a pulse signal, which is the second correction signal, based on a signal in which a delay corresponding to the above-mentioned delay amount is generated in the time axis direction in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal. This makes it possible to easily match (synchronize) the timing of sampling of the second main interference signal.

Similar to the second correction signal generating unit 172, the first correction signal generated by the first correction signal generating unit 171 may be a pulse signal.

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

The AD conversion unit 182 is configured to sample the second main interferometer signal, which is obtained by converting the second main interference signal into an electrical signal, based on the first correction signal and convert it into a digital signal. The second main interference signal input to the AD conversion unit 182 is an analog signal in which the waves are not spaced at equal intervals. The AD conversion unit 182 samples and AD converts the analog signal of the second main interference signal at a sampling period (sampling interval) corrected based on the above-mentioned second correction signal, i.e., the second K clock signal, so that the waves in the second main interference signal are spaced at equal intervals.

In this way, the AD converter 182 converts the second main interference signal into an electrical signal, and the second main interferometer signal is sampled based on the second correction signal and converted into a digital signal, thereby easily realizing a configuration in which the second main interferometer signal is converted into a digital signal with a corrected sampling period.

The processing unit 118 is configured to calculate the distance to the measurement object T based on at least one of the first main interference signal generated by the first main interferometer 151 and the second main interference signal generated by the second main interferometer 152, and the sub-interference signal generated by the sub-interferometer 160.

More specifically, the processing unit 118 is configured to calculate the distance to the measurement object T based on the first main interference signal received by the first photodiode 112 and amplified by the amplifier circuit 114, the second main interference signal received by the first photodiode 113 and amplified by the amplifier circuit 115, and the sub-interference signal received by the

second photodiodes

116 and 117.

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

In addition, in the AD conversion unit 182, the nonlinear analog signal based on the second main interference signal is converted into a digital signal at a sampling period corrected by a second correction signal based on the sub-interference signal and the delay amount, and the processing unit 118 converts the digital signal into a frequency using FFT or the like, analyzes them, and calculates the distance value to the measurement target T.

In this way, the processing unit 118 calculates the distance to the measurement object T based on at least one of the first main interference signal generated by the first main interferometer 151 and the second main interference signal generated by the second main interferometer 152, and the sub-interference signal generated by the sub-interferometer 160, thereby easily realizing a configuration for measuring the distance to the measurement object T.

FIG. 11 is a schematic diagram showing the general configuration of another optical interferometric distance measuring sensor 101 according to one embodiment of the present invention. Note that in FIG. 11, the same or similar components as those in the optical interferometric distance measuring sensor 100 shown in FIG. 10 are denoted by the same or similar reference numerals, and their description will be omitted as appropriate. Furthermore, similar effects and functions due to the same configuration as the optical interferometric distance measuring sensor 100 shown in FIG. 10 will not be mentioned in sequence.

As shown in FIG. 11, the optical interferometric distance measuring sensor 101 includes a controller 110, a first sensor head 121, and a second sensor head 122, and further includes an optical fiber cable 130 that connects the controller 110 to the first sensor head 121 and the second sensor head 122. The controller 110 of the optical interferometric distance measuring sensor 101 shown in FIG. 11 differs from the controller 110 of the optical interferometric distance measuring sensor 100 shown in FIG. 10 in that it does not include an optical fiber 164, but includes a delay line 191.

The sub-interferometer 160 of the controller 110 receives light projected from the wavelength swept light source 140, which is split by the optical splitter 111 and supplied to generate a sub-interference signal based on two lights that follow optical paths of different optical path lengths. Specifically, the first optical coupler 161 splits the light into two lights that follow optical paths of different optical path lengths, and the second optical coupler 162 then combines and causes interference to generate a sub-interference signal based on the optical path length difference. The sub-interference signal propagates through the optical fiber 163 and is guided to the second photodiode 116. Meanwhile, the remaining port of the second optical coupler 162 is connected to an optical fiber with a coreless fiber termination, or to an attenuator.

The second photodiode 116 receives the second interference signal propagated through the optical fiber 163 of the sub-interferometer 160 and converts it into a sub-interferometer signal, which is an electrical signal. The electrical signal converted by the second photodiode 116 is, for example, a current signal. The electrical signal output from the second photodiode 116 may be amplified at a predetermined gain by an amplifier circuit (not shown). In this case, the amplifier circuit outputs the amplified electrical signal to the first correction signal generator 171 and the delay line 191.

The delay line 191 is configured to generate a delay in the time axis direction according to the delay amount in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and output the signal to the second correction signal generating unit 172. The delay amount of the delay line 191 is set based on the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132, similar to the delay amount of the optical fiber 164. The delay line 191 of this embodiment corresponds to an example of a "delay amount generating unit" in the present invention. The delay line 191 outputs a delayed signal, i.e., a "delayed sub-interferometer signal", to the second correction signal generating unit 172.

The delay line 191 includes electronic components that delay the propagation of an electrical signal, such as a delay line. Note that the structure, type, number, etc. of the electronic components of the delay line 191 are not important as long as they cause a delay in the secondary interference signal.

In this way, the delay line 191 generates a delay in the time axis direction according to the amount of delay in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and outputs the signal to the second correction signal generation unit 172. By outputting the sub-interferometer signal with an electrical delay, the second correction signal generation unit 172 can easily generate the second correction signal, which is an electrical signal.

[Sampling Timing of First Main Interferometer Signal and Second Main Interferometer Signal]
Fig. 12 is a diagram for explaining the timing of sampling the first main interferometer signal and the second main interferometer signal. In Fig. 12, the upper part shows a signal when the first main interferometer signal based on the first interference signal of the first main interferometer 151 is sampled, and the lower part shows a signal when the second main interferometer signal based on the second interference signal of the second main interferometer 152 is sampled. In the following example, unless otherwise specified, the optical interferometer sensor 100 shown in Fig. 10 is used for explanation, and the explanation of the case where the optical interferometer sensor 101 shown in Fig. 11 is used is omitted.

As shown in the upper part of FIG. 12, at time t1, sampling of the first main interferometer signal begins with a first correction signal generated based on a sub-interferometer signal obtained by converting the sub-interferometer signal into an electrical signal. The first main interferometer signal is then sampled at a period corrected by the first correction signal and converted into a digital signal.

On the other hand, as shown in the lower part of Figure 12, the second main interferometer signal is not generated at time t1, but is generated at time t2 (t2>t1). This time difference (hereinafter also referred to as "delay time t12") is the optical delay time caused by the difference in optical path length between the first optical fiber 131 and the second optical fiber 132.

In order to correspond to the delay time t12 in the second main interferometer signal, the optical fiber 164 of the optical interferometer distance measuring sensor 100 shown in Fig. 10 generates a delay amount tdelay. The delay amount tdelay is expressed by the following formula (1) using the length L1r of the optical fiber 163, the length L2r of the optical fiber 164, and the speed of light c.
tdelay=|L2r-L1r|/c ... (1)

Therefore, at time t2, sampling of the second main interferometer signal begins using the second correction signal generated based on this delay amount tdelay and the sub-interferometer signal obtained by converting the sub-interferometer signal into an electrical signal. The second main interferometer signal is then sampled at a period corrected by the second correction signal and converted into a digital signal.

The delay amount tdelay generated by the optical fiber 164 is preferably set so that the absolute value of the difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132 and the optical delay time t12 due to the optical path length difference is smaller than the minimum sampling period Tsmin in the AD conversion unit 182.

In other words, the delay amount tdelay is set so that the time difference Δt between the optical delay time t12 and the delay amount tdelay satisfies the following formula (2).
Δt = |t12-tdelay| < Tsmin ... (2)

[Relationship between signal strength and time difference of second main interferometer signal converted into digital signal]
Fig. 13 is a diagram for explaining the relationship between the signal intensity of the second main interferometer signal converted into a digital signal and the time difference Δt. In Fig. 12, the signal intensity of the second main interferometer signal converted into a digital signal is normalized with the signal intensity when the time difference Δt is zero as a reference value "1". The example shown in Fig. 12 will be explained using the optical interferometric distance measuring sensor 100 shown in Fig. 10, and an explanation of the case where the optical interferometric distance measuring sensor 101 shown in Fig. 11 is used will be omitted.

10, if the distance from the first sensor head 121 to the measurement object T1 is 1 [m], the length L1 of the first optical fiber 131 is 2 [m], the distance from the second sensor head 122 to the measurement object T2 is 1 [m], the length L2 of the second optical fiber 132 is 10 [m], the refractive index of the first optical fiber 131 and the second optical fiber 132 is 1.5, and the speed of light c is 3×10 ⁸ [m/s], the delay time t12 is calculated to be 8×10 ⁻⁸ [s]. Here, if the optical interferometric distance measuring sensor 100 includes

AD converters

181 and 182 having a maximum sampling time of 100 [MHz], the minimum sampling period Tsmin of the

AD converters

181 and 182 is 1×10 ⁻⁸ [s]. These values are substituted into the above-mentioned equation (2), and the delay amount tdelay is set to 7×10 ⁻⁸ [s] or more and 9×10 ⁻⁸ [s] or less.

13, when the delay amount tdelay is set to 7×10 ⁻⁸ [s] or more and 9×10 ⁻⁸ [s] or less, the signal intensity of the second main interferometer signal converted into a digital signal can be suppressed to a decrease of 10% or less. For example, when the length L1r of the optical fiber 163 of the secondary interferometer 160 is 1 [m], the length L2r of the optical fiber 164 of the secondary interferometer 160 is set to 14 [m].

In this way, the delay amount tdelay is set so that the absolute value of the difference between the optical delay time t12 due to the optical path length difference between the optical path length of the first optical fiber 131 and the optical path length of the second optical fiber 132 is smaller than the minimum sampling period Tsmin in the AD conversion unit 182, thereby making it possible to suppress the decrease in signal strength of the sampled digital signal to a predetermined percentage or less, for example, 10% or less.

In this embodiment, the optical interferometer sensors 100, 101 each have two sensor heads and an optical fiber cable including two optical fibers connecting each sensor head to the controller 110, but this is not limited to the above. The optical interferometer sensor may have three or more sensor heads and an optical fiber cable including the same number of optical fibers. For the sake of simplicity, the following description will be given of the configuration of the controller 110, particularly the configuration of the sub-interferometer 160 and the subsequent stage (downstream) when the optical interferometer sensor has three sensor heads and an optical fiber cable including two optical fibers.

[Specific configuration of the secondary interferometer and the subsequent stages when three sensor heads are provided]
Figure 14 is a schematic diagram showing an example of the specific configuration of the secondary interferometer 160 and its subsequent stages when it is equipped with three sensor heads, and Figure 15 is a schematic diagram showing another example of the specific configuration of the secondary interferometer 160 and its subsequent stages when it is equipped with three sensor heads.

14, the sub-interferometer 160 receives light emitted from the wavelength swept light source 140, which is split by the optical splitter 111 and supplied to generate a sub-interference signal based on two lights that follow optical paths of different optical path lengths. Specifically, the first optical coupler 161 splits the light into two lights that follow optical paths of different optical path lengths, and then the second optical coupler 162 combines and interferes with the light to generate a sub-interference signal based on the optical path length difference. The sub-interference signal propagates through the optical fiber 163 and is guided to the second photodiode 116, and also propagates through the optical fiber 164 and is guided to the second photodiode 117. Furthermore, the sub-interference signal generates a delay amount, similar to the optical fiber 164. It propagates through the optical fiber 165 and is guided to the second photodiode 119. The optical fiber 165 and the second photodiode 119 receive the sub-interference signal propagated through the optical fiber 165 of the sub-interferometer 160 and convert it into an electrical signal (hereinafter also referred to as the "delayed sub-interferometer signal").

The third correction signal generating unit 173 is configured to generate a third correction signal (also referred to as a "third K clock signal" or simply a "third K clock") based on the secondary interference signal and the delay amount. The third correction signal is a signal that corrects the sampling period of the third main interference signal generated by a third main interferometer (not shown). The third correction signal generating unit 173 is able to grasp the nonlinearity of the wavelength during sweeping based on the secondary interference signal, and thereby generate a third correction signal, i.e., a third K clock signal, for appropriately sampling and AD converting the analog signal of the third main interference signal.

Also, as shown in FIG. 15, the sub-interferometer 160 receives light emitted from the wavelength swept light source 140, which is branched by the optical branching unit 111 and supplied to generate a sub-interference signal based on two lights that follow optical paths of different optical path lengths. Specifically, the first optical coupler 161 branches the light into two lights that follow optical paths of different optical path lengths, and then the second optical coupler 162 combines and causes interference to generate a sub-interference signal based on the optical path length difference. The sub-interference signal propagates through the optical fiber 163 and is guided to the second photodiode 116. Meanwhile, the remaining port of the second optical coupler 162 may be connected to an optical fiber with a coreless fiber termination, or to an attenuator.

The second photodiode 116 receives the second interference signal propagated through the optical fiber 163 of the sub-interferometer 160, converts it into a sub-interferometer signal, which is an electrical signal, and outputs it to the first correction signal generator 171 and the delay line 191.

The delay line 191 is configured to generate a delay in the time axis direction according to the amount of delay in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and output the signal to the second correction signal generating unit 172. The delay line 191 outputs the delayed signal, i.e., the delayed sub-interferometer signal, to the second correction signal generating unit 172 and the delay line 192. The delay line 192, like the delay line 191, is configured to generate a delay in the time axis direction according to the amount of delay in the sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal, and output the signal to the third correction signal generating unit 173. The delayed sub-interferometer signal is input to the delay line 192 from the delay line 191, and the sub-interferometer signal with a further delay is output to the third correction signal generating unit 173.

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

16 shows a variation of an interferometer that generates interference light using measurement light and reference light. In FIG. 16(a), in the optical path passing through the main interferometer 150, interference light is generated based on the optical path length difference between the reference light, whose reference surface is the tip (end face) of the optical fiber, and the measurement light that is irradiated from the sensor head and reflected by the measurement object T. This is the configuration of the main interferometer 150 of the optical interferometer distance measuring sensor 100, 101 according to the above-mentioned embodiment (Fizeau type interferometer), and the reference surface may be configured to reflect light due to the difference in refractive index between the optical fiber and air (Fresnel reflection). In addition, a reflective film may be coated on the tip of the optical fiber, or an anti-reflective coating may be applied to the tip of the optical fiber and a separate reflective surface such as a lens surface may be disposed on the tip of the optical fiber.

In FIG. 16(b), the optical path passing through the main interferometer 150 is formed with a measurement optical path Lm that guides measurement light to the measurement object T, and a reference optical path Lr that guides reference light, and a reference surface is disposed at the end of the reference optical path Lr (Michelson interferometer). The reference surface may be formed by coating the tip of an optical fiber with a reflective film, or the tip of the optical fiber may be coated with an anti-reflective coating and a mirror or the like disposed separately. 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.

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

In this way, the main interferometer is not limited to the Fizeau interferometer described in the embodiment, but may be, for example, a Michelson interferometer or a Mach-Zehnder interferometer. Any interferometer may be applied as long as it is possible to generate interference light by setting the optical path length difference between the measurement light and the reference light, or a combination of these or other configurations may be applied. Similarly, the secondary interferometer (not shown) may be a Fizeau interferometer, a Michelson interferometer, or a Mach-Zehnder interferometer. Any interferometer may be applied as long as it is possible to generate interference light by setting the optical path length difference between the measurement light and the reference light, or a combination of these or other configurations may be applied.

The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and equivalents are also included in the present invention. In other words, designs to which a person skilled in the art has made appropriate design changes are also included within the scope of the present invention as long as they include the characteristics of the present invention. For example, the elements of the embodiments and their arrangements, materials, conditions, shapes, sizes, etc. are not limited to those exemplified, and can be modified as appropriate. Furthermore, the embodiments are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible, and these are also included within the scope of the present invention as long as they include the characteristics of the present invention.

[Appendix 1]
A controller (110) connected via an optical fiber cable (130) to each of a first sensor head (121) and a second sensor head (122) which irradiate a measurement object with light,
A light source (140) that emits light while changing the wavelength;
a first main interferometer (151) that receives light projected from a light source (140), irradiates a first measurement light on a measurement object by a first sensor head (121) and reflects the first measurement light, and generates a first main interference signal based on a first reference light that follows an optical path at least partially different from that of the first measurement light;
a second main interferometer (152) that receives light projected from a light source (140), irradiates a measurement object with a second measurement light by a second sensor head (122) and reflects the measurement object, and generates a second main interference signal based on a second reference light that follows an optical path at least partially different from that of the second measurement light;
a sub-interferometer (160) that is supplied with light projected from a light source (140) and generates a sub-interference signal based on two lights that follow different optical paths;
a processing unit (118) for measuring a distance to a measurement object based on at least one of the first main interference signal and the second main interference signal and the secondary interference signal;
The optical fiber cable (130) includes a first optical fiber (131) connected to the first main interferometer (151) and transmitting light from the first main interferometer (151) to the first sensor head (121) and transmitting light from the first sensor head (121) to the first main interferometer (151), and a second optical fiber (132) connected to the second main interferometer (152) and transmitting light from the second main interferometer (152) to the second sensor head (122) and transmitting light from the second sensor head (122) to the second main interferometer (152);
The second optical fiber (132) has an optical path length different from the optical path length of the first optical fiber (131);
The controller (110)
a first correction signal generating unit (171) that generates a first correction signal for correcting a sampling period of the first main interference signal based on the secondary interference signal;
a delay amount generating unit that generates a delay amount based on an optical path length difference between an optical path length of the first optical fiber (131) and an optical path length of the second optical fiber (132);
and a second correction signal generating unit (172) that generates a second correction signal for correcting a sampling period of the second main interference signal based on the secondary interference signal and the delay amount.
Controller (110).
[Appendix 8]
An optical interferometric distance measuring sensor (100) including a controller (110) and a fiber optic cable (130) connected to the controller (110),
The controller (110)
A light source (140) that emits light while changing the wavelength;
a first main interferometer (151) that receives light projected from a light source (140), irradiates a first measurement light on a measurement object by a first sensor head (121) and reflects the first measurement light, and generates a first main interference signal based on a first reference light that follows an optical path at least partially different from that of the first measurement light;
a second main interferometer (152) that receives light projected from a light source (140), irradiates a measurement object with a second measurement light by a second sensor head (122) and reflects the measurement object, and generates a second main interference signal based on a second reference light that follows an optical path at least partially different from that of the second measurement light;
a sub-interferometer (160) that is supplied with light projected from a light source (140) and generates a sub-interference signal based on two lights that follow different optical paths;
The optical fiber cable (130) includes a first optical fiber (131) connected to the first main interferometer (151) and transmitting light from the first main interferometer (151) to the first sensor head (121) and transmitting light from the first sensor head (121) to the first main interferometer (151), and a second optical fiber (132) connected to the second main interferometer (152) and transmitting light from the second main interferometer (152) to the second sensor head (122) and transmitting light from the second sensor head (122) to the second main interferometer (152);
The second optical fiber (132) has an optical path length different from the optical path length of the first optical fiber (131);
The controller (110)
a first correction signal generating unit (171) that generates a first correction signal for correcting a sampling period of the first main interference signal based on the secondary interference signal;
a delay amount generating unit that generates a delay amount based on an optical path length difference between an optical path length of the first optical fiber (131) and an optical path length of the second optical fiber (132);
and a second correction signal generating unit (172) that generates a second correction signal for correcting a sampling period of the second main interference signal based on the secondary interference signal and the delay amount.
An optical interferometric ranging sensor (100).

1...sensor system, 10...displacement sensor, 11...control device, 12...sensor for inputting control signal, 13...external connection device, 20...sensor head, 21...objective lens, 22a...collimating lens, 22b...collimating lens, 22c...collimating lens, 23...lens holder, 24...optical fiber array, 30...controller, 31...display unit, 32...setting unit, 33...external I/F unit, 34...optical fiber connection unit, 35...external memory unit, 36...measurement processing unit, 40...optical fiber, 51...wavelength swept light source, 52...optical Amplifier, 53, 53a, 53b... isolator, 54, 54a, 54b, 54c, 53d, 54e, 54f, 54g, 54h, 54i, 54j... optical coupler, 55... attenuator, 56a, 56b, 56c... light receiving element, 57a, 57b, 57c... amplifier circuit, 58a, 58b, 58c... AD conversion unit, 59... processing unit, 60... balance detector, 61... correction signal generation unit, 71a, 71b, 71c, 71d, 71e... light receiving element,

72a

72b, 72c... amplifier circuit, 74a, 74b, 74c... AD conversion unit, 75 ...processing unit, 76...differential amplifier circuit, 77...correction signal generating unit, 100, 101...optical interference distance measuring sensor, 110...controller, 111...optical branching unit, 112, 113...first photodiode, 114, 115...amplification circuit, 116, 116, 119...second photodiode, 118...processing unit, 121...first sensor head, 122...second sensor head, 130...optical fiber cable, 131...first optical fiber, 132...second optical fiber, 140...wavelength swept light source, 150...main interferometer, 151...first main interferometer , 152...second main interferometer, 160...secondary interferometer, 161...first optical coupler, 162...second optical coupler, 163...optical fiber, 164...optical fiber, 165...optical fiber, 171...first correction signal generator, 172...second correction signal generator, 173...third correction signal generator, 181, 182...AD converter, 191, 192...delay line, Lm...measurement optical path, Lr...reference optical path, T, T1, T2...measurement object, t1...time, t2...time, t12...delay time, Tsmin...sampling period, vs...voltage, Δt...time difference.

Claims

a controller connected via an optical fiber cable to each of a first sensor head and a second sensor head which irradiate a measurement object with light,
A light source that projects light while changing the wavelength;
a first main interferometer that receives light projected from the light source, and generates a first main interference signal based on a first measurement light that is irradiated onto the measurement object by the first sensor head and reflected therefrom, and a first reference light that follows an optical path at least partially different from that of the first measurement light;
a second main interferometer configured to receive light projected from the light source, and generate a second main interference signal based on a second measurement light that is irradiated onto the measurement object by the second sensor head and reflected therefrom, and a second reference light that follows an optical path at least partially different from that of the second measurement light;
a sub-interferometer that receives light projected from the light source and generates a sub-interference signal based on two lights that follow different optical paths;
the optical fiber cable includes a first optical fiber connected to the first main interferometer and transmitting light from the first main interferometer to the first sensor head and transmitting light from the first sensor head to the first main interferometer, and a second optical fiber connected to the second main interferometer and transmitting light from the second main interferometer to the second sensor head and transmitting light from the second sensor head to the second main interferometer,
the second optical fiber has an optical path length different from an optical path length of the first optical fiber;
The controller:
a first correction signal generator that generates a first correction signal for correcting a sampling period of the first main interference signal based on the secondary interference signal;
a delay amount generating unit that generates a delay amount based on an optical path length difference between an optical path length of the first optical fiber and an optical path length of the second optical fiber;
and a second correction signal generating unit configured to generate a second correction signal for correcting a sampling period of the second main interference signal based on the sub interference signal and the delay amount.
controller.
The delay amount generating unit includes a third optical fiber that propagates the sub interference signal and has an optical path length based on the optical path length difference.
The controller of claim 1 .
The delay amount generating unit includes a delay line that generates a delay according to the delay amount in a time axis direction in a sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal and outputs the delay to the second correction signal generating unit.
The controller of claim 1 .
The second correction signal generating unit generates a pulse signal, which is the second correction signal, based on a signal in which a delay corresponding to the delay amount is generated in a time axis direction in a sub-interferometer signal obtained by converting the sub-interference signal into an electrical signal.
The controller of claim 1 .
an AD converter configured to convert the second main interference signal into an electrical signal, and to sample the electrical signal based on the second correction signal to convert the electrical signal into a digital signal;
The controller of claim 1 .
the delay amount is set so that an absolute value of a difference between the delay time of the light due to the optical path length difference is smaller than a minimum sampling period in the AD conversion unit.
The controller of claim 5 .
Further comprising a processing unit that measures a distance to the measurement object based on at least one of the first main interference signal and the second main interference signal and the sub-interference signal.
The controller of claim 1 .
An optical interferometric distance measuring sensor including a controller and a fiber optic cable connected to the controller,
The controller:
A light source that projects light while changing the wavelength;
a first main interferometer configured to generate a first main interference signal based on a first measurement light that is supplied with light projected from the light source and is irradiated onto a measurement object by a first sensor head and reflected therefrom, and a first reference light that follows an optical path at least partially different from that of the first measurement light;
a second main interferometer configured to receive light projected from the light source, and generate a second main interference signal based on a second measurement light that is irradiated onto the measurement object by a second sensor head and reflected by the second sensor head, and a second reference light that follows an optical path at least partially different from that of the second measurement light;
a sub-interferometer that receives light projected from the light source and generates a sub-interference signal based on two lights that follow different optical paths;
the optical fiber cable includes a first optical fiber connected to the first main interferometer and transmitting light from the first main interferometer to the first sensor head and transmitting light from the first sensor head to the first main interferometer, and a second optical fiber connected to the second main interferometer and transmitting light from the second main interferometer to the second sensor head and transmitting light from the second sensor head to the second main interferometer,
the second optical fiber has an optical path length different from an optical path length of the first optical fiber;
The controller:
a first correction signal generator that generates a first correction signal for correcting a sampling period of the first main interference signal based on the secondary interference signal;
a delay amount generating unit that generates a delay amount based on an optical path length difference between an optical path length of the first optical fiber and an optical path length of the second optical fiber;
and a second correction signal generating unit configured to generate a second correction signal for correcting a sampling period of the second main interference signal based on the sub interference signal and the delay amount.
Optical interferometric distance sensor.