WO2024070358A1

WO2024070358A1 - Optical fiber cable, controller connected thereto, and optical interference ranging sensor using same

Info

Publication number: WO2024070358A1
Application number: PCT/JP2023/030496
Authority: WO
Inventors: 雅之早川
Original assignee: オムロン株式会社
Priority date: 2022-09-28
Filing date: 2023-08-24
Publication date: 2024-04-04
Also published as: JP2024048644A

Abstract

The present invention makes it possible to easily adjust the length of an optical fiber cable in accordance with the measurement environment. An optical fiber cable according to one embodiment of the present invention is used in an optical interference ranging sensor having a light source unit for supplying light while sweeping the wavelength at a fixed periodicity, a light splitting means for splitting the light into measurement light and reference light, an optical multiplexing means for multiplexing the reference light and reflected light from a measurement target, an interference light detection means for detecting interference light multiplexed by the optical multiplexing means, and a distance calculation means for calculating the distance to the measurement target by subjecting the interference light to a frequency analysis, the optical fiber cable having: a first optical fiber for guiding at least a portion of the light supplied from the light source unit and the measurement light that has been split off by the splitting means; and a second optical fiber for guiding at least a portion of the light supplied from the light source unit and the reference light that has been split by the splitting means.

Description

Optical fiber cable, controller connected thereto, and optical interference distance measuring sensor using the same

The present invention relates to an optical fiber cable, a controller connected to the cable, and an optical interferometric distance sensor using the cable and the controller.

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.

For example, Patent Document 1 discloses an optical coherence tomography imaging device that includes a light beam controller, a splitting means for splitting a plurality of light beams from the light beam controller into object light and reference light, an irradiating means for irradiating a measurement object with the plurality of object light beams, and an interference means for causing interference between the object light scattered from the measurement object and the reference light and guiding them to a light receiver.

International Publication No. 2019/131298

In devices that use the interference light between measurement light and reference light as described above, for example, a configuration may be adopted in which the measurement light is guided through a fiber optic cable connecting the controller and the sensor head. However, when the fiber optic cable is replaced, the optical path length difference between the measurement light and the reference light may deviate from the initial setting, making it difficult to adjust the length of the fiber optic cable according to the measurement environment.

The present invention aims to provide an optical fiber cable whose length can be easily adjusted according to the measurement environment, a controller connected to the cable, and an optical interferometric distance measuring sensor using the cable and the controller.

The optical fiber cable according to one aspect of the present invention is an optical fiber cable used in an optical interference distance measuring sensor having a light source unit that supplies light while sweeping the wavelength at a constant cycle, a light splitting means that splits the light supplied from the light source unit into measurement light and reference light, a combining means that combines the reference light and reflected light from the measurement object when the measurement light split by the light splitting means is irradiated onto the measurement object, an interference light detection means that detects interference light between the reflected light and the reference light combined by the combining means, and a distance calculation means that calculates the distance to the measurement object by performing frequency analysis on the interference light detected by the interference light detection means, and has a first optical fiber that guides at least a portion of the light supplied from the light source unit and the measurement light split by the splitting means, and a second optical fiber that guides at least a portion of the light supplied from the light source unit and the reference light split by the splitting means.

According to this aspect, the optical fiber cable has a first optical fiber that guides at least a portion of the light supplied from the light source unit and the measurement light split by the splitting means, and a second optical fiber that guides at least a portion of the light supplied from the light source unit and the reference light split by the splitting means. Therefore, both the measurement light and the reference light are guided within the optical fiber cable, or the light before being split into the measurement light and the reference light is guided, so that the setting of the optical path length difference between the measurement light and the reference light does not change even when the optical fiber cable is replaced. Therefore, it is possible to easily adjust the length of the optical fiber cable according to the measurement environment.

In the above embodiment, the first optical fiber may include an optical path for the measurement light, and the second optical fiber may include an optical path for the reference light.

According to this aspect, both the measurement light and the reference light are guided within the optical fiber cable, so the setting of the optical path length difference between the measurement light and the reference light does not change even when the optical fiber cable is replaced, and therefore the length of the optical fiber cable can be easily adjusted according to the measurement environment.

In the above embodiment, the second optical fiber may be the first optical fiber.

This simplifies the configuration of the optical fiber cable.

The above embodiment may further include a light splitting means.

This aspect improves the design freedom of the optical fiber cable.

The above embodiment may further include a reference surface that reflects the reference light.

This aspect improves the design freedom of the optical fiber cable.

A controller according to one aspect of the present invention includes a light source unit that supplies light while sweeping the wavelength at a constant cycle, a light splitting means that splits the light supplied from the light source unit into measurement light and reference light, a combining means that combines the reference light and reflected light from the measurement object when the measurement light split by the light splitting means is irradiated onto the measurement object, an interference light detection means that detects interference light between the reflected light and the reference light combined by the combining means, and a distance calculation means that calculates the distance to the measurement object by performing frequency analysis on the interference light detected by the interference light detection means, and includes a first connection part that is connected to a first optical fiber that guides at least a portion of the light supplied from the light source unit and the measurement light split by the splitting means, and a second connection part that is connected to a second optical fiber that guides at least a portion of the light supplied from the light source unit and the reference light split by the splitting means.

The optical interferometric distance measuring sensor according to one aspect of the present invention is an optical interferometric distance measuring sensor having an optical fiber cable and a controller, the controller having a light source unit that supplies light while sweeping the wavelength at a constant cycle, an optical splitting means that splits the light supplied from the light source unit into measurement light and reference light, a combining means that combines the reference light and reflected light from the measurement object when the measurement light split by the optical splitting means is irradiated onto the measurement object, an interference light detection means that detects interference light between the reflected light and the reference light combined by the combining means, and a distance calculation means that calculates the distance to the measurement object by performing frequency analysis on the interference light detected by the interference light detection means, and the optical fiber cable has a first optical fiber that guides at least a part of the light supplied from the light source unit and the measurement light split by the splitting means, and a second optical fiber that guides at least a part of the light supplied from the light source unit and the reference light split by the splitting means.

In the above embodiment, the optical fiber cable may further include a reference surface that reflects the reference light.

This aspect improves the design freedom of the optical fiber cable.

The present invention provides an optical fiber cable capable of connecting an appropriate second optical fiber to a secondary interferometer in correspondence with a first optical fiber connected to a primary interferometer, a controller connected thereto, and an optical interferometric distance sensor using the same.

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. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. FIG. 1 is a schematic diagram showing an example of the configuration of an optical fiber cable. 11A and 11B are diagrams for explaining modified examples of optical fiber cables. 11A and 11B are diagrams for explaining modified examples of optical fiber cables.

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 cable 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 cable 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 cable 40 is connected to and extends from the optical fiber cable connection section 34 disposed in the controller 30, and connects the controller 30 and the sensor head 20. The optical fiber cable 40 may include at least one optical fiber 41P that guides the reference light and at least one optical fiber 42P that guides the measurement light. As a result, the optical fiber cable 40 is configured to guide the light projected from the controller 30 to the sensor head 20 via the optical fiber 42P, and further guide the return light from the sensor head 20 to the controller 30 via the optical fiber 42P. The optical fiber cable 40 is detachable from the sensor head 20 and the controller 30, and various optical fiber cables can be applied in terms of length, thickness, characteristics, etc. The optical fiber cable 40 may be configured as a single core in which one core is formed in one clad, or as a multi-core in which multiple cores are formed in one clad. In the case of a multi-core, the distance between the multiple optical paths is short, so that it is possible to suppress the fluctuation of the measurement optical path and the reference optical path due to bending applied to the optical fiber cable 40 or temperature fluctuation.

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, an optical fiber cable 40, 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 optical fiber cable 40 includes optical fibers 41Pa to 41Pc and optical fibers 42Pa to 42Pc.

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 is branched by the optical coupler 62a toward the first-stage optical fiber 41Pa and optical fiber 42Pa of the optical fiber cable 40. The light branched toward the optical fiber 41Pa becomes reference light, and the light branched toward the optical fiber 42Pa becomes measurement light. That is, the reference light incident on the optical fiber 41Pa from the end 41Ia is guided inside the optical fiber 41Pa, reflected by the reference surface 41Ra, guided inside the optical fiber 41Pa toward the end 41Ia, and supplied from the end 41Ia to the optical coupler 62a. On the other hand, the measurement light incident on the optical fiber 42Pa from the end 42Ia is guided inside the optical fiber 42Pa and enters the optical fiber in the sensor head 20 from the end 42Oa, and in the sensor head 20, passes through the collimator lens 22a and the objective lens 21 to be irradiated to the measurement object T. The measurement light reflected by the measurement object T enters the end 42Oa of the optical fiber 42Pa via the sensor head 20, is guided through the optical fiber 42Pa, and is supplied from the end 42Ia to the optical coupler 62a. The reference light supplied from the end 41Ia of the optical fiber cable 40 and the measurement light supplied from the end 42Ia of the optical fiber cable 40 interfere with each other in the optical coupler 62a, generating interference light, at least a portion of which is supplied to the light receiving element 56a. The interference light received by the light receiving element 56a is converted into an electrical signal.

The light branched by the first-stage optical coupler 54a toward the second-stage optical coupler 54b passes through the isolator 53a and travels to the second-stage optical coupler 54b, which then branches it further toward the sensor head 20 and the third-stage optical coupler 54c. The light branched from the optical coupler 54b toward the sensor head 20 is branched by the optical coupler 62b toward the second-stage optical fiber 41Pb and optical fiber 42Pb of the optical fiber cable 40, as in the first stage. The light branched toward the optical fiber 41Pb becomes the reference light, and the light branched toward the optical fiber 42Pb becomes the measurement light. That is, the reference light incident on the optical fiber 41Pb from the end 41Ib is guided through the optical fiber 41Pb, reflected by the reference surface 41Rb, guided through the optical fiber 41Pb toward the end 41Ib, and supplied from the end 41Ib to the optical coupler 62b. On the other hand, the measurement light incident on the optical fiber 42Pb from the end 42Ib is guided through the optical fiber 42Pb and enters the optical fiber in the sensor head 20 from the end 42Ob, and passes through the collimator lens 22b and the objective lens 21 in the sensor head 20 to be irradiated onto the measurement object T. Then, the measurement light reflected by the measurement object T enters the end 42Ob of the optical fiber 42Pb via the sensor head 20, is guided through the optical fiber 42Pb, and is supplied from the end 42Ib to the optical coupler 62b. Then, the reference light supplied from the end 41Ib of the optical fiber cable 40 and the measurement light supplied from the end 42Ib of the optical fiber cable 40 interfere with each other in the optical coupler 62b, generating interference light, and at least a part of the interference light is supplied to the light receiving element 56b. The interference light received by the light receiving element 56b is converted into an electrical signal.

The light branched by the second-stage optical coupler 54b toward the third-stage optical coupler 54c travels through the isolator 53b to the third-stage optical coupler 54c, which further branches it toward the sensor head 20 and the attenuator 55. The light branched from the optical coupler 54c toward the sensor head 20 is branched by the optical coupler 62c toward the optical fiber 41Pc and optical fiber 42Pc of the third stage of the optical fiber cable 40, as in the first and second stages. The light branched toward the optical fiber 41Pc becomes the reference light, and the light branched toward the optical fiber 42Pc becomes the measurement light. That is, the reference light incident on the optical fiber 41Pc from the end 41Ic is guided through the optical fiber 41Pc, reflected by the reference surface 41Rc, guided through the optical fiber 41Pc toward the end 41Ic, and supplied from the end 41Ic to the optical coupler 62c. On the other hand, the measurement light incident on the optical fiber 42Pc from the end 42Ic is guided through the optical fiber 42Pc and enters the optical fiber in the sensor head 20 from the end 42Oc, and passes through the collimator lens 22c and the objective lens 21 in the sensor head 20 to be irradiated onto the measurement object T. Then, the measurement light reflected by the measurement object T enters the end 42Oc of the optical fiber 42Pc via the sensor head 20, is guided through the optical fiber 42Pc, and is supplied from the end 42Ic to the optical coupler 62c. Then, the reference light supplied from the end 41Ic of the optical fiber cable 40 and the measurement light supplied from the end 42Ic of the optical fiber cable 40 interfere with each other in the optical coupler 62c, generating interference light, and at least a part of the interference light is supplied to the light receiving element 56c. The interference light received by the light receiving element 56c is converted into an electrical signal.

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 generating unit 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 of measuring the measurement object T by the displacement sensor 10 according to the present disclosure. As shown in FIG. 5B, the displacement sensor 10 includes a sensor head 20, an optical fiber cable 40, and a controller 30. The sensor head 20 includes an objective lens 21 and a plurality of collimating lenses 22a to 22c, and the controller 30 includes a wavelength swept light source 51, an optical amplifier 52, a plurality of

isolators

53 and 53a to 53b, a plurality of

optical couplers

54 and 54a to 54j, an attenuator 55, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generating unit 61. The optical fiber cable 40 includes optical fibers 42Pa-42Pc and optical fibers 43Pa-43Pc.

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.

The measurement light passes through the first-stage optical coupler 54a, the optical fiber 42Pa of the optical fiber cable 40, the collimator lens 22a of the sensor head 20, and the objective lens 21 in sequence, and is irradiated onto the measurement object T, and is reflected by the measurement object T. The measurement light reflected by the measurement object T is incident on the end 42Oa of the optical fiber 42Pa via the sensor head 20, is guided through the optical fiber 42Pa, and is supplied from the end 42Ia to the optical coupler 54h via the optical coupler 54a.

Similarly, the light branched from the first-stage optical coupler 54a toward the second-stage optical coupler 54b passes through the optical fiber 42Pb of the optical fiber cable 40, the collimating lens 22b of the sensor head 20, and the objective lens 21 in sequence via the second-stage optical coupler 54b, is irradiated onto the measurement object T, is reflected by the measurement object T, returns to the second-stage optical coupler 54b, and is supplied to the optical coupler 54i via the optical coupler 54b. The light branched from the second-stage optical coupler 54b toward the third-stage optical coupler 54c passes through the optical fiber 42Pc of the optical fiber cable 40, the collimating lens 22c of the sensor head 20, and the objective lens 21 in sequence via the third-stage optical coupler 54c, is irradiated onto the measurement object T, is reflected by the measurement object T, returns to the third-stage optical coupler 54c, and is supplied to the optical coupler 54j via the optical coupler 54c.

Meanwhile, the reference light branched by optical coupler 54f is further branched by optical coupler 54g in the direction of each of ends 43Ia to 43Ic of optical fiber cable 40. The reference light incident on each of ends 43Ia to 43Ic of optical fiber cable 40 is guided through optical fibers 43Pa to 43Pc of optical fiber cable 40. Ends 43Oa to 43Oc are provided on the opposite side of optical fibers 43Pa to 43Pc from ends 43Ia to 43Ic. The reference light guided through optical fibers 43Pa to 43Pc is supplied from ends 43Oa to 43Oc to

optical couplers

54h, 54i, and 54j, respectively.

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 and guided through the optical fiber 43Pa in the optical fiber cable 40, 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 optical fiber 42Pa, the collimating lens 22a, the objective lens 21, reflected by the measurement object T, and reaches 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 and guided through the optical fiber 43Pa to reach the optical coupler 54h), and the interference light is received by the light receiving element 56a and converted into an electrical signal.

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

optical couplers

54a and 54b, optical fiber 42Pb, collimating lens 22b, objective lens 21, reflected by the measurement target T, and reaching optical coupler 54i) and the optical path of the reference light (the optical path from optical coupler 54f through optical coupler 54g, guided through optical fiber 43Pb, and reaching optical coupler 54i), and the interference light is received by the 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, optical fiber 42Pc, collimating lens 22c, objective lens 21, reflected by the measurement target 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, guided through optical fiber 43Pc, and reaching optical coupler 54j). The interference light is received by the light receiving element 56c and converted into an electrical signal. 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 passed through

optical couplers

54f and 54g and optical fiber cable 40 and input to

optical couplers

54h, 54i, and 54j, respectively.

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 an objective lens 21 and a collimator lens stored in a lens holder 23. For example, the size of the lens holder 23 is such that the length of one side surrounding the objective lens 21 is about 20 mm, and the length in the optical axis direction is about 40 mm. An optical fiber cable 40 is connected to the sensor head 20.

As shown in FIG. 6B, the lens holder 23 stores one objective lens 21 and three collimator lenses 22a to 22c. The light from the optical fibers that guide the measurement light contained in the optical fiber cable 40 is configured to be guided to the collimator lenses 22a to 22c, respectively, and the light that passes through the three collimator lenses 22a to 22c is irradiated onto the measurement object T via the objective lens 21. Note that although the example shown in FIG. 6B shows three collimator lenses, the number of collimator lenses may be a number according to the number of optical fibers that guide the measurement light contained in the optical fiber cable 40.

In this way, these optical fiber cables 40 and collimator lenses 22a to 22c, together with the objective lens 21, are held by the lens holder 23 to form the 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 that 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.

<Embodiment>
[Configuration of optical fiber cable]
The optical fiber cables shown in FIGS. 10 to 12 are applicable to the displacement sensor 10 shown in FIG. 5A, for example.

FIG. 10 is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 110 has three optical fibers 110Fs for measurement light, three optical fibers 110Fr for reference light, and a connector section 110C connected to the optical fibers 110Fs and 110Fr. Three optical waveguides 111p and three optical waveguides 112p are formed inside the connector section 110C. The

optical waveguides

111p and 112p are configured to be able to guide light as a core with a higher refractive index than the surrounding cladding.

The optical waveguide 111p is optically connected to the optical fiber 110Fr, and guides the reference light propagating through the optical fiber 110Fr toward the end 111r. The end 111r is coated with a metal such as aluminum, and serves as a reference surface. Therefore, the reference light that is guided through the optical waveguide 111p and reaches the end 111r is reflected by the end 111r, and is guided through the optical waveguide 111p toward the optical fiber 110Fr.

The optical waveguide 112p is optically connected to the optical fiber 110Fs, and guides the measurement light propagating through the optical fiber 110Fs toward the end 112o. The measurement light that reaches the end 112o is supplied to the sensor head 20, guided inside the optical waveguide and optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical waveguide 112p via 112o, and then propagates through the optical fiber 120Fs.

The method of producing the connector portion 110C and the

optical waveguides

111p and 112p is not particularly limited, but may be produced, for example, by a flame deposition method using glass. Alternatively, the

optical waveguides

111p and 112p may be formed as optical fibers, and the optical fibers may be sandwiched between the glass that forms the base of the connector portion 110C.

FIG. 11A is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 120 has three optical fibers 120Fs for measurement light, three optical fibers 120Fr for reference light, a connector section 120C connected to the optical fibers 120Fs and 120Fr, and a mirror 123. Three optical waveguides 121p and three optical waveguides 122p are formed inside the connector section 120C. The

optical waveguides

121p and 122p are configured to be able to guide light as a core with a higher refractive index than the surrounding cladding.

The optical waveguide 121p is optically connected to the optical fiber 120Fr, and guides the reference light propagating through the optical fiber 120Fr toward the end 121o. The reference light that reaches the end 121o is emitted from the end 121o and reflected by the mirror 123 provided in front of the end 121o. The reference light reflected by the mirror 123 is incident on the end 121o and guided through the optical waveguide 121p toward the optical fiber 120Fr.

Here, FIG. 11B is a schematic diagram showing an example of the configuration of an optical fiber cable. As shown in FIG. 11B, the reference light emitted from the end 121o of the connector portion 120C may be reflected sequentially by the retroreflector 125 and the mirror 124, and then reflected again by the retroreflector 125 before entering the end 121o and being guided through the optical waveguide 121p toward the optical fiber 120Fr.

Returning to FIG. 11A, the optical waveguide 122p is optically connected to the optical fiber 120Fs, and guides the measurement light propagating through the optical fiber 120Fs toward the end 122o. The measurement light that reaches the end 122o is supplied to the sensor head 20, guided inside the optical waveguide and optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical waveguide 122p via 122o, and then propagates through the optical fiber 120Fs.

The method of making the connector portion 120C and the

optical waveguides

121p and 122p is not particularly limited, but may be made by flame deposition deposition using glass, for example. Alternatively, the

optical waveguides

121p and 122p may be formed as optical fibers, and the optical fibers may be sandwiched between the glass that forms the base of the connector portion 120C.

FIG. 12 is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 130 has three optical fibers 130Fs for measurement light and three optical fibers 130Fr for reference light. The three optical fibers 130Fs for measurement light and the three optical fibers 130Fr for reference light are fixed to each other with a resin (not shown) or the like. The optical fibers 130Fs and the optical fibers 130Fr are each attached to a housing with the tip of the optical fiber fixed to a ferrule.

The end 131r of the optical fiber 130Fr is coated with a metal such as aluminum and serves as a reference surface. Therefore, the reference light that is guided through the optical fiber 130Fr and reaches the end 131r is reflected by the end 131r and is guided in the opposite direction through the optical fiber 130Fr.

The measurement light that reaches the end 132o of the optical fiber 130Fs is supplied into the sensor head 20, guided through the optical waveguide, optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical fiber 130Fs via 132o, and then propagates through the optical fiber 130Fs.

The optical fiber cables shown in Figures 13A to 15 can be applied to the displacement sensor 10 shown in Figure 5B, for example.

FIG. 13A is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 210 has three optical fibers 210Fs for measurement light, three optical fibers 210Fr for reference light, and a connector section 210C connected to the optical fibers 210Fs and 210Fr. Three optical waveguides 211p and three optical waveguides 212p are formed inside the connector section 210C. The

optical waveguides

211p and 212p are configured to be able to guide light as a core with a higher refractive index than the surrounding cladding.

The optical waveguide 211p is optically connected to the optical fiber 210Fr, and guides the reference light propagating through the optical fiber 210Fr from one end of the optical fiber 210Fr, and guides the light to the other end of the optical fiber 210Fr via the folded portion 211m formed in a substantially U-shape. The shape of the folded portion 211m is not particularly limited, and may be arbitrarily configured based on the set value of the optical path length difference between the measurement light and the reference light.

The optical waveguide 212p is optically connected to the optical fiber 210Fs, and guides the measurement light propagating through the optical fiber 210Fs toward the end 212o. The measurement light that reaches the end 212o is supplied to the sensor head 20, guided inside the optical waveguide and optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical waveguide 212p via 212o, and then propagates through the optical fiber 210Fs.

The method of creating the connector portion 210C and the

optical waveguides

211p and 212p is not particularly limited, but may be created, for example, by a flame deposition method using glass. Alternatively, the

optical waveguides

211p and 212p may be formed as optical fibers, and the optical fibers may be sandwiched between the glass that forms the base of the connector portion 210C.

FIG. 13B is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 220 has three optical fibers 220Fs for measurement light, six optical fibers 220Fr for reference light, and a connector section 220C connected to the optical fibers 220Fs and 220Fr. Six optical waveguides 221p and three optical waveguides 222p are formed inside the connector section 220C. The optical waveguides 221p and 222p are configured to be able to guide light as a core with a higher refractive index than the surrounding cladding.

The optical waveguide 221p includes an optical waveguide 221p1 and an optical waveguide 221p2. The optical waveguide 221p1 is optically connected to the optical fiber 220Fr, guides the reference light propagating through the optical fiber 220Fr from one end of the optical fiber 220Fr, and emits it from the end 221s of the optical waveguide 221p1. The reference light emitted from the end 221s is reflected by the retroreflector 224, enters the end 221t, and is guided through the optical waveguide 221p2 toward the optical fiber 120Fr.

The optical waveguide 222p is optically connected to the optical fiber 220Fs, and guides the measurement light propagating through the optical fiber 220Fs toward the end 222o. The measurement light that reaches the end 222o is supplied to the sensor head 20, guided inside the optical waveguide and optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical waveguide 222p via 222o, and then propagates through the optical fiber 220Fs.

The method of creating the connector portion 220C and the optical waveguides 221p, 222p is not particularly limited, but may be created, for example, by a flame deposition method using glass. Alternatively, the optical waveguides 221p, 222p may be formed as optical fibers, and the optical fibers may be sandwiched between the glass that forms the base of the connector portion 220C.

FIG. 14 is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 230 has three optical fibers 230Fs for measurement light, three optical fibers 230Fr1 for reference light, and three optical fibers 230Fr2 for reference light. The three optical fibers 230Fs for measurement light, the three optical fibers 230Fr1 for reference light, and the three optical fibers 230Fr2 for reference light are fixed to each other by a fixing portion 234 formed of resin or the like.

The measurement light that reaches the end 232o of the optical fiber 230Fs is supplied into the sensor head 20, guided through the optical waveguide, optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical fiber 230Fs via 232o, and then propagates through the optical fiber 230Fs.

Optical fiber 230Fr1 guides the reference light propagating through optical fiber 230Fr1 and emits it from end 231s of optical fiber 230Fr1. The reference light emitted from end 231s is reflected by retroreflector 233, enters end 231t, and is guided through optical fiber 230Fr2.

FIG. 15 is a schematic diagram showing an example of the configuration of an optical fiber cable. The optical fiber cable 240 has three optical fibers 240Fs for measurement light and three optical fibers 240Fr for reference light. The three optical fibers 240Fs for measurement light and the three optical fibers 240Fr for reference light are fixed to each other by a fixing portion 243 formed of resin or the like.

The optical fiber 240Fr guides the reference light that has propagated through the optical fiber 240Fr from one end of the optical fiber 240Fr, and guides it to the other end of the optical fiber 240Fr via a folding section 241m formed in a substantially U-shape. The shape of the folding section 241m is not particularly limited, and may be arbitrarily configured based on the set value of the optical path length difference between the measurement light and the reference light.

The optical fiber 240Fs guides the measurement light propagating through the optical fiber 240Fs toward the end 242o. The measurement light that reaches the end 242o is supplied into the sensor head 20, guided inside the optical waveguide and optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided into the optical fiber 240Fs via 242o, and then propagates through the optical fiber 240Fs.

[Modification]
FIG. 16 is a diagram for explaining a modified example of the optical fiber cable.

The optical fiber cable 41 has optical fibers 44Pa-44Pc, 45Pa-45Pc, 46Pa-46Pc, 47Pa-47Pc, and optical couplers 63a-63c. Light emitted from the wavelength sweep light source 51 is supplied from each of the optical couplers 54a-54c to each of the optical fibers 44Pa-44Pc via the ends 44Ia-44Ic. The optical fibers 44Pa-44Pc guide the light to the optical couplers 63a-63c, which then split the light into reference light passing through the optical fibers 45Pa-45Pc and measurement light passing through the optical fibers 47Pa-47Pc.

The reference light guided through the optical fibers 45Pa to 45Pc is reflected by the reference surfaces 45Ra to 45Rc provided at the ends of the optical fibers 45Pa to 45Pc, and is guided through the optical fibers 45Pa to 45Pc and supplied again to the optical couplers 63a to 63c. The measurement light guided through the optical fibers 47Pa to 47Pc is supplied from the ends 47Oa to 47Oc of the optical fibers 47Pa to 47Pc into the sensor head 20, guided through the optical waveguide, optical fiber, etc., and irradiated onto the measurement object T. The measurement light reflected by the measurement object T is again incident on the sensor head 20, and the measurement light is guided through the ends 47Oa to 47Oc into the optical fibers 47Pa to 47Pc and supplied to the optical couplers 63a to 63c.

The reference light supplied from the optical fibers 45Pa-45Pc and the measurement light supplied from the optical fibers 47Pa-47Pc interfere with each other in the optical couplers 62a-62c to generate interference light, and at least a portion of the interference light is supplied to the light-receiving elements 56a-56c via the optical fibers 46Pa-46Pc. The interference light received by the light-receiving elements 56a-56c is converted into an electrical signal.

Figure 17 is a diagram to explain modified examples of optical fiber cables.

The optical fiber cable 42 has optical fibers 48Pa to 48Pc and 49Pa to 49Pc. The light emitted from the wavelength sweep light source 51 is supplied from the optical couplers 54a to 54c to the optical fibers 48Pa to 48Pc via the ends 48Ia to 48Ic. The optical fibers 48Pa to 48Pc guide the light to the ends 48Oa to 48Oc. The light supplied from the ends 48Oa to 48Oc to the sensor head 20 is supplied to the optical couplers 23a to 23c via the optical fibers 24Pa to 24Pc of the sensor head 20. The optical couplers 23a to 23c split the supplied light into reference light that passes through the optical fibers 25Pa to 25Pc and measurement light that passes through the optical fibers 27Pa to 27Pc.

The reference light guided through the optical fibers 25Pa-25Pc is reflected by the reference surfaces 25Ra-25Rc provided at the ends of the optical fibers 25Pa-25Pc, and is guided through the optical fibers 25Pa-25Pc and supplied again to the optical couplers 23a-23c. The measurement light guided through the optical fibers 27Pa-27Pc is irradiated onto the measurement object T via the collimator lenses 22a-22c and the objective lens 21. The measurement light reflected by the measurement object T is guided through the optical fibers 27Pa-27Pc and supplied to the optical couplers 23a-23c.

The reference light supplied from the optical fibers 25Pa-25Pc and the measurement light supplied from the optical fibers 27Pa-27Pc interfere with each other in the optical couplers 23a-23c to generate interference light, and at least a portion of the interference light is supplied to the light receiving elements 56a-56c via the optical fibers 26Pa-26Pc and the optical fibers 49Pa-49c of the optical fiber cable 42. The interference light received by the light receiving elements 56a-56c is converted into an electrical signal.

The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those exemplified, and may be modified as appropriate. Furthermore, configurations shown in different embodiments may be partially substituted or combined.

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 to 22c...collimator lens, 23...lens holder, 30...controller, 31...display unit, 32...setting unit, 33...external interface (I/F) unit, 34...optical fiber connection unit, 35...external memory unit, 36...measurement processing unit, 40, 41, 42...optical fiber cable, 51...wavelength sweep light source, 52...optical amplifier, 53, 53a to 53b...isolator, 54, 54a to 54e...optical coupler, 55...attenuator, 56a to 56c...light receiving element, 58...AD conversion unit, 59...processing unit, 60...variable 1. A distance detector, 61...correction signal generating section, 62a to 62c...optical couplers, 63a to 63c...optical couplers, 71a to 71e...light receiving elements, 72a to 72c...amplifier circuits, 74a to 74c...AD conversion section, 75...processing section, 76...differential amplifier circuit, 77...correction signal generating section, 100 to 105...optical interference distance measuring sensor, 110...controller, 111...wavelength sweep light source, 112...main interferometer, 112a to 112c...optical couplers, 113, 113a to 113c...first photodetector (light receiving section), 114...second interferometer, 114a, 114b, 114d...optical couplers, 114c...circulator, 115...second photodetector (light receiving section), 116...processing section, T...measurement object

Claims

a light source unit that supplies light while sweeping the wavelength at a constant period;
a light splitting means for splitting the light supplied from the light source unit into a measurement light and a reference light;
a combining means for combining the reference light and a reflected light from a measurement object when the measurement light split by the light splitting means is irradiated onto the measurement object;
an interference light detection means for detecting interference light between the reflected light and the reference light combined by the combining means;
a distance calculation means for calculating a distance to the measurement object by performing frequency analysis on the interference light detected by the interference light detection means,
a first optical fiber that guides at least a part of the light supplied from the light source unit and the measurement light split by the splitting means;
a second optical fiber through which at least a part of the light supplied from the light source unit and the reference light split by the splitting means is guided;
1. A fiber optic cable comprising:
the first optical fiber includes an optical path of the measurement light,
The second optical fiber includes an optical path of the reference light.
2. The optical fiber cable according to claim 1.
The optical fiber cable of claim 1, wherein the second optical fiber is the first optical fiber.
The optical fiber cable of claim 1, further comprising the optical splitting means.
The optical fiber cable of claim 1, further comprising a reference surface that reflects the reference light.
a light source unit that supplies light while sweeping the wavelength at a constant period;
a light splitting means for splitting the light supplied from the light source unit into a measurement light and a reference light;
a combining means for combining the reference light and a reflected light from a measurement object when the measurement light split by the light splitting means is irradiated onto the measurement object;
an interference light detection means for detecting interference light between the reflected light and the reference light combined by the combining means;
a distance calculation means for calculating a distance to the measurement object by performing frequency analysis on the interference light detected by the interference light detection means,
a first connection portion connected to a first optical fiber that guides at least a part of the light supplied from the light source unit and the measurement light split by the splitting means;
a second connection portion connected to a second optical fiber through which at least a part of the light supplied from the light source unit and the reference light split by the splitting means is guided;
A controller having
An optical interferometric distance measuring sensor having a fiber optic cable and a controller,
The controller:
a light source unit that supplies light while sweeping the wavelength at a constant period;
a light splitting means for splitting the light supplied from the light source unit into a measurement light and a reference light;
a combining means for combining the reference light and a reflected light from a measurement object when the measurement light split by the light splitting means is irradiated onto the measurement object;
an interference light detection means for detecting interference light between the reflected light and the reference light combined by the combining means;
a distance calculation means for calculating a distance to the measurement object by performing frequency analysis on the interference light detected by the interference light detection means,
The optical fiber cable includes:
a first optical fiber that guides at least a part of the light supplied from the light source unit and the measurement light split by the splitting means;
a second optical fiber through which at least a part of the light supplied from the light source unit and the reference light split by the splitting means is guided;
Optical interferometric distance sensor.
The optical interferometric distance measuring sensor of claim 7, wherein the optical fiber cable further includes a reference surface that reflects the reference light.