Optical interference distance measuring sensor

Abstract

To provide a light interference distance measuring sensor that can eliminate noise that affects measurement of an object to be measured and measure distance with high accuracy.SOLUTION: A light interference distance measuring sensor 100 comprises a wavelength sweep light source 110, an optical coupler 120, an interferometer 130, a light receiving unit 140, and a processing unit 150, and further comprises a reflection point that reflects, of rays of light projected from the wavelength sweep light source 110 and input to a first port A of the optical coupler 120, light branched to a fourth port D of the optical coupler 120. At this time, when the optical path length from a third port C of the optical coupler 120 to a reference surface is L1, the optical path length from the fourth port D of the optical coupler 120 to the reflection point is L2, the optical path length from the reference surface to a leading end of a sensor head 131 that irradiates an object to be measured with measurement light is LH, and a measuring range of the object to be measured T is R, L1-L2>(LH+R)*2 or L1-L2<LH*2 is satisfied.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to an optical interference distance measurement sensor.

Background Art

[0002] In recent years, optical distance measurement sensors that non - contact measure the distance to a measurement object have become widespread. For example, as an optical distance measurement sensor, an optical interference distance measurement sensor is known that generates interference light based on reference light and measurement light from light projected from a wavelength - swept light source, and measures the distance to a measurement object based on the interference light.

[0003] In such an optical interference distance measurement sensor, since noise generated in the waveform of the interference signal may cause a decrease in measurement accuracy, it is required to reduce the noise.

[0004] The optical interference unit described in Patent Document 1 below has a reference - light device, and arranges each device so that the transmission optical path length of the reference light transmitted through the reference - light device from the reference - light device to the multiplexing optical element is longer than the reflection optical path length of the reference light reflected by the detachment part of the reference - light device from the reference - light device to the multiplexing optical element.

[0005] Thereby, in the optical interference unit described in Patent Document 1, the noise generated in the entire waveform of the interference signal is reduced.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the optical interference unit disclosed in Patent Document 1, although the optical path length is adjusted by the arrangement of each device to reduce the noise generated in the entire waveform of the interference signal, the cause of the generation of the noise has not been investigated, and there is a problem that the noise affecting the measurement of the measurement object cannot be appropriately eliminated.

[0008] Therefore, an object of the present invention is to provide an optical interference distance measurement sensor that eliminates noise affecting the measurement of a measurement object and enables highly accurate distance measurement.

Means for Solving the Problems

[0009] The optical interference distance measurement sensor according to one aspect of the present invention has at least four ports, an optical coupler that branches and combines light, a light source that is connected to the first port of the optical coupler and projects light while continuously changing the wavelength, an interferometer that generates interference light based on the first reflected light reflected by the measurement object by irradiating the measurement object with the light branched to the third port of the optical coupler among the light projected from the light source and input to the first port of the optical coupler and the second reflected light reflected by the reference surface as reference light, a reflection point that reflects the light branched to the fourth port of the optical coupler among the light projected from the light source and input to the first port of the optical coupler, a light receiving unit that receives the light output from the second port of the optical coupler by combining the interference light from the third port and the reflected light at the reflection point from the fourth port and converts it into an electrical signal, and a processing unit that calculates the distance to the measurement object based on the electrical signal converted by the light receiving unit. When the optical path length L1 from the third port of the optical coupler to the reference surface, the optical path length L2 from the fourth port of the optical coupler to the reflection point, the optical path length LH from the reference surface to the tip of the sensor head that irradiates the measurement object with the measurement light, and the measurement range R of the measurement object are considered, L1 - L2 > (LH + R) * 2 or L1 - L2 < LH * 2 is satisfied.

[0010] According to this aspect, since the optical coupler, the interferometer including the sensor head, and the optical fiber connecting them are configured and arranged so as to satisfy L1 - L2 > (LH + R) * 2 or L1 - L2 < LH * 2, in the signal waveform received by the light receiving unit and used by the processing unit to calculate the distance to the measurement object, noise that affects the measurement of the measurement object can be excluded outside the measurement range of the measurement object. As a result, distance measurement can be performed with high precision.

[0011] In the above aspect, the reference surface may be the end face of the optical fiber connecting the third port of the optical coupler and the sensor head.

[0012] According to this aspect, the light output from the third port of the optical coupler is transmitted through the optical fiber, and a part of the light is reflected at the end face of the optical fiber as reference light. Using the reflected light as the second reflected light, interference light can be generated together with the first reflected light reflected by the measurement object.

[0013] In the above aspect, among the light projected from the light source and input to the first port of the optical coupler, the power of the light branched to the third port of the optical coupler may be smaller than the power of the light branched to the fourth port.

[0014] According to this aspect, since the power of the light branched to the second port among the return light from the interferometer input to the third port of the optical coupler is large, the amount of light received by the light receiving unit is large, and the processing unit can more appropriately calculate the distance to the measurement object.

[0015] In the above aspect, an optical amplifier for amplifying the light projected from the light source may be further provided between the light source and the first port of the optical coupler.

[0016] According to this aspect, since the optical amplifier can amplify the light projected from the light source, the power of the measurement light irradiated on the object to be measured can be adjusted. That is, the optical amplifier can cause the light receiving unit to receive the light necessary for measuring the distance to the object to be measured while ensuring safety by adjusting the power of the light received by the light receiving unit while maintaining eye safety, for example.

[0017] In the above aspect, the reflection point may be a terminator.

[0018] According to this aspect, the light branched to the fourth port of the optical coupler can be attenuated by the terminator, and the reflected light to the optical coupler can be reduced. As a result, the noise affecting the measurement of the object to be measured can be reduced, and the distance can be measured with higher accuracy.

[0019] In the above aspect, the reflection point may be an isolator.

[0020] According to this aspect, the light branched to the fourth port of the optical coupler can be transmitted to another system by the isolator, and the return light to the optical coupler can be suppressed. As a result, the noise affecting the measurement of the object to be measured can be reduced, and the distance can be measured with higher accuracy.

[0021] In the above aspect, it has at least four ports, an isolator is connected to the first port, a second optical coupler that branches and combines light, and among the light guided from the isolator and input to the first port of the second optical coupler, the light branched to the third port of the second optical coupler is irradiated onto the measurement object as measurement light, and a second interferometer that generates second interference light based on the third reflected light reflected by the measurement object and the fourth reflected light reflected by the reference surface as reference light, a second reflection point that reflects the light branched to the fourth port of the second optical coupler among the light guided from the isolator and input to the first port of the second optical coupler, the second interference light from the third port of the second optical coupler and the reflected light at the second reflection point from the fourth port of the second optical coupler are combined, and a second light receiving unit that receives the light output to the second port of the second optical coupler and converts it into an electrical signal, and a second processing unit that calculates the distance to the measurement object based on the electrical signal converted by the second light receiving unit may be provided.

[0022] According to this aspect, the light branched to the fourth port of the optical coupler is input to the first port of the second optical coupler via the isolator, and the measurement object can be distance-measured by the second optical coupler, the second interferometer, the second light receiving unit, and the second processing unit. That is, since it functions as an optical interference distance measurement sensor having a multi-head with a multi-stage configuration, distance measurement can be performed with higher accuracy based on the distances to the measurement object calculated by the processing unit and the second processing unit respectively.

Effects of the Invention

[0023] According to the present invention, it is possible to provide an optical interference distance measurement sensor that eliminates noise affecting the measurement of a measurement object and enables high-precision distance measurement.

Brief Description of the Drawings

[0024]

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[0025] Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings. It should be noted that each of the embodiments described below is merely a specific example for carrying out the present invention, and does not limit the present invention. Also, for ease of understanding of the description, the same reference numerals are attached to the same components in each drawing as much as possible, and duplicate descriptions may be omitted.

[0026] [Overview of Displacement Sensor] First, an overview of the displacement sensor according to the present disclosure will be described. FIG. 1 is an external schematic diagram showing an overview of a displacement sensor 10 according to the present disclosure. As shown in FIG. 1, the displacement sensor 10 includes a sensor head 20 and a controller 30, and measures the displacement of the measurement object T (the distance to the measurement object T).

[0027] The sensor head 20 and the controller 30 are connected by an optical fiber 40, and an objective lens 21 is attached to the sensor head 20. The controller 30 includes a display unit 31, a setting unit 32, an external interface (I / F) unit 33, an optical fiber connection unit 34, and an external storage unit 35, and further has a measurement processing unit 36 inside.

[0028] The sensor head 20 irradiates the object to be measured T with the light output from the controller 30 and receives the reflected light from the object to be measured T. The sensor head 20 has inside it a reference surface for reflecting the light output from the controller 30 and received via the optical fiber 40 and causing interference with the reflected light from the object to be measured T described above.

[0029] Note that an objective lens 21 is attached to the sensor head 20, and the objective lens 21 is configured to be detachable. The objective lens 21 can be replaced with an objective lens having an appropriate focal length according to the distance between the sensor head 20 and the object to be measured T, or an objective lens with a variable focal length may be applied.

[0030] Furthermore, when installing the sensor head 20, the object to be measured T may be irradiated with guide light (visible light) so that the object to be measured T is appropriately positioned within the measurement area of the displacement sensor 10, and the sensor head 20 and / or the object to be measured T may be installed.

[0031] The optical fiber 40 is connected to the optical fiber connection part 34 arranged in the controller 30 and extends to connect the controller 30 and the sensor head 20. Thereby, 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. Note that the optical fiber 40 is detachable from the sensor head 20 and the controller 30, and various optical fibers can be applied in terms of length, thickness, characteristics, etc.

[0032] The display unit 31 is composed of, for example, a liquid crystal display or an organic EL display. Measurement results such as the set value of the displacement sensor 10, the light reception amount of the return light from the sensor head 20, and the displacement of the object to be measured T (distance to the object to be measured T) measured by the displacement sensor 10 are displayed on the display unit 31.

[0033] The setting unit 32 performs settings necessary for measuring the measurement object T when the user operates, for example, a mechanical button or a touch panel. 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. The external connection device may be connected by wire or wirelessly via a network.

[0034] 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 other connection devices to perform necessary settings from the external connection device, or may output measurement results measured by the displacement sensor 10 to the external connection device.

[0035] Further, the controller 30 may perform settings necessary for measuring the measurement object T by taking in data stored in the external storage unit 35. The external storage unit 35 is, for example, an auxiliary storage device such as a USB (Universal Serial Bus) memory, and stores in advance settings necessary for measuring the measurement object T.

[0036] The measurement processing unit 36 in the controller 30 includes, for example, a wavelength sweep light source that projects 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 storage unit, etc. so that finally the displacement (distance to the measurement object T) of the measurement object T is calculated based on the return light from the sensor head 20. Details of these processes will be described later.

[0037] 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.

[0038] In step S11, the sensor head 20 is installed. For example, the sensor head 20 irradiates the measurement object T with guide light, and based on this, the sensor head 20 is installed at an appropriate position.

[0039] Specifically, the display unit 31 in the controller 30 displays the amount of received light of the return light from the sensor head 20, 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 received light amount. Basically, if the light from the sensor head 20 can be irradiated onto the measurement object T perpendicularly (at an angle closer to perpendicular), the amount of reflected light from the measurement object T will be large, and the amount of received light of the return light from the sensor head 20 will also be large.

[0040] Also, according to the distance between the sensor head 20 and the measurement object T, the objective lens 21 with an appropriate focal length may be replaced.

[0041] Furthermore, when appropriate settings cannot be made when measuring the measurement object T (for example, the required amount of received light for measurement cannot be obtained, or the focal length of the objective lens 21 is inappropriate, etc.), an error or incomplete setting, etc. may be displayed on the display unit 31 or output to an external connection device to notify the user.

[0042] In step S12, various measurement conditions are set when measuring the measurement object T. For example, the user sets the specific calibration data (such as a function for correcting linearity) that the sensor head 20 has by operating the setting unit 32 in the controller 30.

[0043] Also, various parameters may be set. For example, the sampling time, measurement range, and threshold for determining whether the measurement result is normal or abnormal are set. Furthermore, the measurement period may be set according to the characteristics of the measurement object T such as the reflectivity and material of the measurement object T, and the measurement mode according to the material of the measurement object T may be set.

[0044] Note that the settings of these measurement conditions and various parameters are set by operating the setting unit 32 in the controller 30, but may also be set from an external connection device or by importing data from the external storage unit 35.

[0045] 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.

[0046] Specifically, in the measurement processing unit 36 of the controller 30, light is projected from a wavelength-sweeping light source, the return light from the sensor head 20 is received by a light-receiving element, and frequency analysis, distance conversion, peak detection, etc. are performed by a signal processing circuit to calculate the displacement (distance to the measurement object T) of the measurement object T. Details of the specific measurement processing will be described later.

[0047] In step S14, the measurement result measured in step S13 is output. For example, the displacement (distance to the measurement object T) of the measurement object T measured in step S13 is displayed on the display unit 31 in the controller 30 or output to an external connection device.

[0048] Also, whether the displacement (distance to the measurement object T) of the measurement object T measured in step S13 is within the normal range or abnormal based on the threshold value set in step S12 may also be displayed or output as a measurement result. Furthermore, the measurement conditions, various parameters, measurement modes, etc. set in step S12 may also be displayed or output together.

[0049] [Overview of the System including a Displacement Sensor] FIG. 3 is a functional block diagram showing an overview of the sensor system 1 in which the displacement sensor 10 according to the present invention is used. As shown in FIG. 3, the sensor system 1 includes a displacement sensor 10, a control device 11, a sensor 12 for inputting a control signal, and an external connection device 13. 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 supply line, etc.), and the control device 11 and the sensor 12 for inputting a control signal are connected by a signal line.

[0050] As described with reference to FIGS. 1 and 2, the displacement sensor 10 measures the displacement of the measurement object T (the distance to the measurement object T). Then, the displacement sensor 10 may output the measurement result and the like to the control device 11 and the external connection device 13.

[0051] The control device 11 is, for example, a PLC (Programmable Logic Controller), and gives various instructions to the displacement sensor 10 when the displacement sensor 10 measures the measurement object T.

[0052] For example, the control device 11 may output a measurement timing signal to the displacement sensor 10 based on an input signal from the sensor 12 for inputting a control signal connected to the control device 11, or may output a zero reset command signal (a signal for setting the current measurement value to 0) or the like to the displacement sensor 10.

[0053] The sensor 12 for inputting a control signal outputs an on / off signal for instructing the timing at which the displacement sensor 10 measures the measurement object T to the control device 11. For example, the sensor 12 for inputting a control signal is installed near the production line where the measurement object T moves, and may detect that the measurement object T has moved to a predetermined position and output an on / off signal to the control device 11.

[0054] The external connection device 13 is, for example, a PC (Personal Computer), and various settings can be made to the displacement sensor 10 by the user's operation.

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

[0056] As the setting of the measurement mode, an "internal synchronous measurement mode" that periodically starts measurement inside the control device 11, an "external synchronous measurement mode" that starts measurement according to an input signal from outside the control device 11, etc. are selected.

[0057] As the setting of the operation mode, an "operation mode" that actually measures the measurement object T, an "adjustment mode" that sets the measurement conditions for measuring the measurement object T, etc. are selected.

[0058] The measurement period is the period for measuring the measurement object T, and it may be set according to the reflectance of the measurement object T. However, even if the reflectance of the measurement object T is low, if the measurement period is lengthened and the measurement period is appropriately set, the measurement object T can be appropriately measured.

[0059] Regarding the measurement object T, a "rough surface mode" suitable for the case where there is relatively much diffuse reflection as a component of the reflected light, a "specular mode" suitable for the case where there is relatively much specular reflection as a component of the reflected light, or an "intermediate standard mode" between these is selected.

[0060] In this way, by making appropriate settings according to the reflectance and material of the measurement object T, the measurement object T can be measured with higher accuracy.

[0061] FIG. 4 is a flowchart showing the procedure for measuring the measurement object T by the sensor system 1 in which the displacement sensor 10 according to the present disclosure is used. As shown in FIG. 4, the procedure is the procedure in the case of the external synchronous measurement mode described above and includes steps S21 to S24.

[0062] In step S21, the sensor system 1 detects the measurement object T to be measured. Specifically, the sensor 12 for inputting a control signal detects that the measurement object T has moved to a predetermined position on the production line.

[0063] In step S22, the sensor system 1 gives a measurement instruction to measure the measurement object T detected in step S21 by the displacement sensor 10. Specifically, the sensor 12 for inputting a control signal outputs an on / off signal to the control device 11 to indicate the timing of measuring the measurement object T detected in step S21. Based on the on / off signal, the control device 11 outputs a measurement timing signal to the displacement sensor 10 to give a measurement instruction to measure the measurement object T.

[0064] In step S23, the measurement object T is measured by the displacement sensor 10. Specifically, the displacement sensor 10 measures the measurement object T based on the measurement instruction received in step S22.

[0065] In step S24, the sensor system 1 outputs the measurement result measured in step S23. Specifically, the displacement sensor 10 displays the result of the measurement process on the display unit 31, or outputs it to the control device 11 or an external connection device 13 etc. via the external I / F unit 33.

[0066] Here, the procedure in the case of the external synchronous measurement mode in which the measurement object T is measured by detecting the measurement object T by the sensor 12 for inputting a control signal using FIG. 4 has been described, but it is not limited thereto. For example, in the case of the internal synchronous measurement mode, instead of steps S21 and S22, a measurement timing signal is generated based on a preset period to instruct the displacement sensor 10 to measure the measurement object T.

[0067] Next, the principle of measuring the measurement object T by the displacement sensor 10 according to the present disclosure will be described. FIG. 5 is a diagram for explaining the principle by which the displacement sensor 10 according to the present disclosure measures the measurement object T. As shown in FIG. 5, the displacement sensor 10 includes a sensor head 20 and a controller 30. The sensor head 20 includes an objective lens 21 and a plurality of collimating lenses 22a to 22c, and the controller 30 includes a wavelength-sweeping 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 (for example, photodetectors (PD)) 56a to 56c, a multiplexing circuit 57, an analog-digital (AD) conversion unit (for example, an analog-digital converter) 58, a processing unit (for example, a processor) 59, a balance detector 60, and a correction signal generation unit 61.

[0068] The wavelength-sweeping light source 51 projects a laser beam with a swept wavelength. As the wavelength-sweeping light source 51, for example, if a method of modulating a VCSEL (Vertical Cavity Surface Emitting Laser) with a current is applied, since the resonator length is short, mode hopping is less likely to occur, the wavelength can be easily changed, and it can be realized at low cost.

[0069] The optical amplifier 52 amplifies the light projected from the wavelength-sweeping light source 51. As the optical amplifier 52, for example, an EDFA (erbium-doped fiber amplifier) may be applied, and it may be an optical amplifier dedicated to 1550 nm, for example.

[0070] The isolator 53 is an optical element that transmits the incident light in one direction, and may be disposed immediately after the wavelength-sweeping light source 51 in order to prevent the influence of noise generated by the return light.

[0071] Thus, the light projected from the wavelength-sweeping light source 51 is amplified by the optical amplifier 52 and branched by the optical coupler 54 into a main interferometer and a sub-interferometer via the isolator 53. For example, in the optical coupler 54, the light may be branched between the main interferometer and the sub-interferometer at a ratio of 90:10 to 99:1.

[0072] The light branched into the main interference measurement is further branched by the first-stage optical coupler 54a into the direction of the measurement object T and the direction of the second-stage optical coupler 54b.

[0073] The light branched in the direction of the measurement object T by the first-stage optical coupler 54a is irradiated onto the measurement object T through the collimating lens 22a and the objective lens 21 from the tip of the optical fiber in the sensor head 20. Then, the tip (end face) of the optical fiber serves as a reference surface, and the light reflected by the reference surface interferes with the light reflected by the measurement object T to generate interference light, which returns to the first-stage optical coupler 54a, and then is received by the light receiving element 56a and converted into an electrical signal.

[0074] The light branched in the direction of the second-stage optical coupler 54b by the first-stage optical coupler 54a travels toward the second-stage optical coupler 54b via the isolator 53a, and is further branched by the second-stage optical coupler 54b in the direction of the sensor head 20. The light branched in the direction of the sensor head 20 is irradiated onto the measurement object T through the collimating lens 22b and the objective lens 21 from the tip of the optical fiber in the sensor head 20 in the same manner as in the first stage. Then, the tip (end face) of the optical fiber serves as a reference surface, and the light reflected by the reference surface interferes with the light reflected by the measurement object T 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, respectively. The light branched 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, since the isolator 53a transmits light from the previous-stage optical coupler 54a to the subsequent-stage optical coupler 54b and blocks the light from the subsequent-stage optical coupler 54b to the previous-stage optical coupler 54a, the light branched in the direction of the isolator 53a is blocked.

[0075] The light branched by the second-stage optical coupler 54b in the direction of the third-stage optical coupler 54c travels toward the third-stage optical coupler 54c via the isolator 53b, and is further branched by the third-stage optical coupler 54c in the direction of the sensor head 20. The light branched in the direction of the sensor head 20, similar to the first and second stages, passes through the collimating lens 22c and the objective lens 21 from the tip of the optical fiber in the sensor head 20 and irradiates the measurement object T. Then, the tip (end face) of the optical fiber serves 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, 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, respectively. The light branched 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 previous-stage optical coupler 54b to the subsequent-stage optical coupler 54c and blocks the light from the subsequent-stage optical coupler 54c to the previous-stage optical coupler 54b. Therefore, the light branched in the direction of the isolator 53b is blocked.

[0076] Note that the light branched by the third-stage optical coupler 54c in a direction other than the sensor head 20 is not used for measuring the measurement object T. Therefore, it may be attenuated by an attenuator 55 such as a terminator so that it does not reflect and return.

[0077] In this way, the main interferometer has three optical paths (three channels), and is an interferometer with the optical path length difference being twice the distance (round trip) from the tip (end face) of the optical fiber of the sensor head 20 to the measurement object T for each path, and generates three interference lights corresponding to the optical path length differences respectively.

[0078] The light receiving elements 56a to 56c receive the interference light from the main interferometer as described above and generate an electrical signal corresponding to the received light amount.

[0079] The multiplexing circuit 57 multiplexes the electrical signals output from the light receiving elements 56a to 56c.

[0080] The AD conversion unit 58 receives the electrical signal from the multiplexing circuit 57 and converts the electrical signal from an analog signal to a digital signal (AD conversion). Here, the AD conversion unit 58 performs AD conversion based on the correction signal from the correction signal generation unit 61 in the secondary interferometer.

[0081] In the secondary interferometer, in order to correct the non-linearity of the wavelength during the sweep of the wavelength-sweeping light source 51, an interference signal is acquired in the secondary interferometer, and a correction signal called a K clock is generated.

[0082] Specifically, the light branched into the secondary interferometer by the optical coupler 54 is further branched by the optical coupler 54d. Here, the optical paths of the branched lights are configured to have an optical path length difference using optical fibers of different lengths, for example, between the optical coupler 54d and the optical coupler 54e, and interference light corresponding to the optical path length difference is output from the optical coupler 54e. Then, the balance detector 60 receives the interference light from the optical coupler 54e, amplifies the optical signal and converts it into an electrical signal while removing noise by taking the difference from the signal of its opposite phase.

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

[0084] The correction signal generation unit 61 grasps the non-linearity of the wavelength during the sweep of the wavelength-sweeping light source 51 based on the electrical signal from the balance detector 60, generates a K clock corresponding to the non-linearity, and outputs it to the AD conversion unit 58.

[0085] Due to the non-linearity of the wavelength during the sweep of the wavelength-sweeping light source 51, the interval between the waves of the analog signal input to the AD conversion unit 58 in the main interferometer is not equidistant. In the AD conversion unit 58, the sampling time is corrected based on the above-described K clock so that the interval between the waves becomes equidistant, and AD conversion (sampling) is performed.

[0086] Note that, as described above, since the K clock is a correction signal used to sample the analog signal of the main interferometer, it needs to be generated at a higher frequency than the analog signal of the main interferometer. Specifically, the optical path length difference provided between the optical couplers 54d and 54e in the secondary interferometer may be made longer than the optical path length difference provided between the tip (end face) of the optical fiber in the main interferometer and the measurement object T, or the frequency may be multiplied (for example, 8 times, etc.) by the correction signal generation unit 61 to increase the frequency.

[0087] The processing unit 59 acquires the digital signal that has been AD-converted while the non-linearity is corrected by the AD conversion unit 58, and calculates the displacement (distance to the measurement object T) of the measurement object T based on the digital signal. Specifically, in the processing unit 59, the digital signal is frequency-converted using a fast Fourier transform (FFT), and the distance is calculated by analyzing them. The detailed processing in the processing unit 59 will be described later.

[0088] Note that, since high-speed processing is required for the processing unit 59, it is often realized by an integrated circuit such as a field-programmable gate array (FPGA).

[0089] Also, here, the multiplexing circuit 57 is arranged in the front stage of the AD conversion unit 58, but it may be arranged in the rear stage of the AD conversion unit 58. The outputs from the plurality of light receiving elements 56a to 56c may be AD-converted respectively, and then multiplexed by the multiplexing circuit 57.

[0090] Also, here, in the main interferometer, three stages of optical paths are provided, and the measurement light is irradiated to the measurement object T from each optical path by the sensor head 20, and the distance to the measurement object T etc. are measured based on the interference light (return light) obtained from each (multi-channel). The channels in the main interferometer are not limited to three stages, and may be one stage or two stages, or four stages or more.

[0091] [Structure of Sensor Head] 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, FIG. 6B is a perspective view showing a schematic configuration of the collimating lens holder disposed inside the sensor head 20, and FIG. 6C is a cross-sectional view showing the internal structure of the sensor head.

[0092] As shown in FIG. 6A, the sensor head 20 stores an objective lens 21 and a collimating lens in an objective lens holder 23. For example, the size of the objective lens holder 23 is such that the length of one side surrounding the objective lens 21 is about 10 mm, and the length in the optical axis direction is about 22 mm.

[0093] As shown in FIG. 6B, the collimating lens unit 24 is configured by fixing a collimating lens 22 to a collimating lens holder using an adhesive. And it is configured such that an optical fiber can be inserted and the spot diameter can be adjusted according to the insertion amount. For example, the size of the collimating lens 22 is about 2 mm in diameter.

[0094] As shown in FIG. 6C, three collimating lenses 22a to 22c are respectively held by collimating lens holders to form collimating lens units 24a to 24c, and three optical fibers are inserted into the collimating lens units 24a to 24c so as to correspond to the three collimating lenses 22a to 22c respectively. Note that each of the three optical fibers may be held by a collimating lens holder.

[0095] And these optical fibers and collimating lens units 24a to 24c, together with the objective lens 21, are held by the objective lens holder 23 to form the sensor head 20.

[0096] Here, as shown in FIG. 6C, the three collimating lens units are respectively displaced and arranged in order to form different optical path length differences at the positions in the optical axis direction of the sensor head 20.

[0097] In addition, the objective lens holder 23 and the collimating lens units 24a to 24c that constitute the sensor head 20 may be made of a metal (for example, A2017) that can be processed with high strength and high precision.

[0098] FIG. 7 is a block diagram for explaining signal processing in the controller 30. As shown in FIG. 7, the controller 30 includes a plurality of light receiving elements 71a to 71e, a plurality of amplifier circuits 72a to 72c, a multiplexing circuit 73, an AD conversion unit 74, a processing unit 75, a differential amplifier circuit 76, and a correction signal generation unit 77.

[0099] In the controller 30, as shown in FIG. 5, the light projected from the wavelength-sweeping light source 51 is branched by the optical coupler 54 into a main interferometer and a sub-interferometer, and the distance value to the measurement object T is calculated by processing the main interference signal and the sub-interference signal obtained respectively.

[0100] The plurality of light receiving elements 71a to 71c correspond to the light receiving elements 56a to 56c shown in FIG. 5, receive the main interference signals from the main interferometer respectively, and output them to the amplifier circuits 72a to 72c as current signals respectively.

[0101] The plurality of amplifier circuits 72a to 72c convert (I-V conversion) the current signal into a voltage signal and amplify it.

[0102] The multiplexing circuit 73 multiplexes the voltage signals output from the amplifier circuits 72a to 72c and outputs them to the AD conversion unit 74 as one voltage signal.

[0103] The AD conversion unit 74 corresponds to the AD conversion unit 58 shown in FIG. 5, and converts (AD conversion) the voltage signal into a digital signal based on the K clock from the correction signal generation unit 77 described later.

[0104] The processing unit 75 corresponds to the processing unit 59 shown in FIG. 5, converts the digital signal from the AD conversion unit 74 into a frequency using FFT, analyzes them, and calculates the distance value to the measurement object T.

[0105] The plurality of light receiving elements 71d to 71e and the differential amplifier circuit 76 correspond to the balance detector 60 shown in FIG. 5, receive the interference light in the sub-interferometer respectively, output an interference signal with a phase inversion on one side, and while removing noise by taking the difference between the two signals, amplify the interference signal and convert it into a voltage signal.

[0106] The correction signal generation unit 77 corresponds to the correction signal generation unit 61 shown in FIG. 5, binarizes the voltage signal with a comparator, generates a K clock, and outputs it to the AD conversion unit 74. Since the K clock needs to be generated at a higher frequency than the analog signal of the main interferometer, the frequency may be multiplied (for example, 8 times, etc.) in the correction signal generation unit 77 to increase the frequency.

[0107] Note that in the controller 30 shown in FIG. 7, the multiplexer circuit 73 is arranged in front of the AD conversion unit 74, but it may also be arranged behind the AD conversion unit 74. The outputs of the plurality of light receiving elements 71a to 71c and the plurality of amplifier circuits 72a to 72c may be respectively AD-converted and then multiplexed by the multiplexer circuit 73.

[0108] FIG. 8 is a flowchart showing a method for calculating the distance to the measurement object T, which is executed by the processing unit 59 in the controller 30. As shown in FIG. 8, the method includes steps S31 to S35.

[0109] In step S31, the processing unit 59 frequency-converts the waveform signal (voltage vs. time) into a spectrum (voltage vs. frequency) using the following FFT. FIG. 9A is a diagram showing the state where the waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency).

Equation

[0110] In step S32, the processing unit 59 performs distance conversion on the spectrum (voltage vs. frequency) to the spectrum (voltage vs. distance). FIG. 9B is a diagram showing the state in which the spectrum (voltage vs. frequency) is distance-converted to the spectrum (voltage vs. distance).

[0111] In step S33, the processing unit 59 calculates values (distance value, SNR) corresponding to the peaks based on the spectrum (voltage vs. distance). FIG. 9C is a diagram showing the state in which values (distance value, SNR) corresponding to the peaks are calculated based on the spectrum (voltage vs. distance).

[0112] (1) Calculate the peak value of the voltage. Specifically, for the voltage shown in FIG. 9C, create a set (D x , V x ) of the distance value and voltage value at the distance where the differential value of the voltage changes from positive to negative, and arrange them in descending order of the voltage value in those sets. (D 1 , V 1 ), (D 2 , V 2 ), (D 3 , V 3 ), ···, (D n , V n )

[0113] (2) Exclude combinations exceeding the number of multi-heads. For example, as shown in FIG. 5, in the displacement sensor 10, three optical paths are provided in the main interferometer, and the measurement light is irradiated from each optical path to the measurement object T by the sensor head 20, and the interference light (return light) obtained from each is received (number of multi-heads = 3). If there are four or more peaks, the peaks exceeding three are due to noise and can be excluded from the calculation targets. When the number of multi-heads = 3, it becomes (D 1 , V 1 ), (D 2 , V 2 ), (D 3 , V 3 ).

[0114] (3) Sort in ascending order of distance. For example, when sorted in ascending order of distance, (D3 , V 3 ), (D 1 , V 1 ), (D 2 , V 2 ) is obtained.

[0115] (4) Obtain the voltage between peaks. Specifically, D 3 and D 1 , the voltage V 31 at the midpoint D 31 between them is obtained, and the voltage V 1 and D 2 , the voltage V 12 at the midpoint D 12 between them is obtained. Then, the average voltage Vn = (V 31 + V 12 ) / 2 is calculated.

[0116] (5) Calculate the SNR for each. Specifically, SN 1 = V 1 / V n , SN 2 = V 2 / V n , SN 3 = V 3 / V n is obtained.

[0117] In this way, based on the spectrum (voltage vs distance), the values corresponding to the peaks (distance value, SNR) = (D 1 , SN 1 ), (D 2 , SN 2 ), (D 3 , SN 3 ) are calculated.

[0118] Returning to FIG. 8, in step S34, the processing unit 59 corrects the distance value among the values (distance value, SNR) corresponding to the peaks calculated in step S33. Specifically, as shown in FIG. 6C, since the three collimating lens units 24a to 24c (collimating lenses 22a to 22c and each optical fiber) are respectively displaced in the optical axis direction position of the sensor head 20, the displacement amount (for example, h 1 , h 2 , h3 According to (such as), distance values D corresponding to the peaks respectively 1 , D 2 , D 3 are corrected.

[0119] Thus, the values corresponding to the peaks (corrected distance value, SNR) = (D 1 +h 1 , SN 1 ), (D 2 +h 2 , SN 2 ), (D 3 +h 3 , SN 3 ) are obtained.

[0120] In step S35, the processing unit 59 averages the distance values among the values (corrected distance value, SNR) corresponding to the peaks calculated in step S34. Specifically, the processing unit 59 preferably averages the corrected distance values among the values (corrected distance value, SNR) corresponding to the peaks where the SNR is equal to or greater than the threshold value, and outputs the averaged calculation result as the distance to the measurement object T.

[0121] Next, regarding the present disclosure, more characteristic configurations, functions, and properties will be described in detail as specific embodiments. Note that the optical interference distance measurement sensor described below corresponds to the displacement sensor 10 described with reference to FIGS. 1 to 9, and all or part of the basic configurations, functions, and properties included in the optical interference distance measurement sensor are common to the configurations, functions, and properties included in the displacement sensor 10 described with reference to FIGS. 1 to 9.

[0122] <First Embodiment> [Configuration of Optical Interference Distance Measurement Sensor] FIG. 10 is a schematic diagram showing a schematic configuration of an optical interference distance measurement sensor 100 according to the first embodiment of the present invention. As shown in FIG. 10, the optical interference distance measurement sensor 100 includes a wavelength-sweeping light source 110, an optical coupler 120, an interferometer 130, a light receiving unit 140, and a processing unit 150. The optical coupler 120 has first to fourth ports A to D. The interferometer 130 has a sensor head 131, and an objective lens 132 is attached to or included in the sensor head 131. In the sensor head 131, a collimating lens may be disposed between the tip of the optical fiber and the objective lens 132. The light receiving unit 140 includes a light receiving element 141 and an AD conversion unit 142.

[0123] The wavelength-sweeping light source 110 is connected to the first port A of the optical coupler 120 and projects light while continuously changing the wavelength.

[0124] The optical coupler 120 branches and outputs the light projected from the wavelength-sweeping light source 110 and input to the first port A to the third port C and the fourth port D.

[0125] The light output from the third port C of the optical coupler 120 is input to the sensor head 131 via an optical fiber, irradiated as measurement light onto the measurement object T through the objective lens 132, and reflected by the measurement object T. The reflected light (first reflected light) reflected by the measurement object T is condensed by the objective lens 132 of the sensor head 131 and returns from the sensor head 131 to the third port C of the optical coupler 120.

[0126] Also, the light output from the third port C of the optical coupler 120 is input to the sensor head 131 via an optical fiber, and a part of it is reflected by a reference surface as reference light. Here, the tip of the optical fiber serves as the reference surface, and the reflected light (second reflected light) reflected by the reference surface returns from the sensor head 131 to the third port C of the optical coupler 120.

[0127] At this time, the light output from the third port C of the optical coupler 120 enters the sensor head 131 via an optical fiber. The measurement light is irradiated onto the measurement object T and returns from the sensor head 131 to the third port C of the optical coupler 120 as the first reflected light. The reference light returns from the sensor head 131 to the third port C of the optical coupler 120 as the second reflected light reflected by the reference surface. Therefore, interference light is generated according to the optical path length difference between the measurement light and the reference light. That is, the interferometer 130 generates interference light based on the first reflected light and the second reflected light, and outputs it as the light returning to the third port C of the optical coupler 120. Note that the optical path lengths of the measurement light and the reference light may both be values obtained by multiplying the spatial length of the optical path by the refractive index.

[0128] On the other hand, the light output from the fourth port D of the optical coupler 120 is reflected by a reflection point existing at the tip of the optical fiber connected to the fourth port D and returns to the fourth port D again as reflected light.

[0129] Then, the interference light input to the third port C and the reflected light input to the fourth port D are combined by the optical coupler 120 and output from the second port B of the optical coupler 120.

[0130] The light receiving unit 140 receives the light output from the second port B of the optical coupler 120. In the light receiving unit 140, the light receiving element 141 is, for example, a photodetector that receives the light output from the second port B of the optical coupler 120 and converts it into an electrical signal. Then, the AD conversion unit 142 converts the electrical signal from an analog signal to a digital signal.

[0131] The processing unit 150 calculates the distance to the measurement object T based on the digital signal converted by the light receiving unit 140. For example, the processing unit 150 is a processor implemented by an integrated circuit such as an FPGA, which frequency-converts the input digital signal using FFT, and calculates the distance to the measurement object T based on this.

[0132] Here, the light received by the light receiving unit 140 includes, in addition to the interference light generated from the first and second reflected lights of the measurement light and the reference light in the interferometer 130, for example, unnecessary signals with an increased level due to phase noise generated by, for example, the time error of the interference light and the influence of the reflected light from the fourth port D of the optical coupler 120.

[0133] In the present embodiment, due to the configuration and arrangement of the optical coupler 120, the interferometer 130, and the optical fibers connecting them in the optical interference distance measurement sensor 100, when the processing unit 150 calculates the distance to the measurement object T, the influence of the phase noise is eliminated so that the distance to the measurement object T can be calculated with high accuracy.

[0134] FIG. 11 is a diagram showing the configuration and arrangement of the optical coupler 120, the interferometer 130, and the optical fibers connecting them in the optical interference distance measurement sensor 100. As shown in FIG. 11, when the optical path length L1 from the third port C of the optical coupler 120 to the reference surface, the optical path length L2 from the fourth port D of the optical coupler 120 to the reflection point, the optical path length LH from the reference surface to the tip of the sensor head 131 that irradiates the measurement light to the measurement object T, and the measurement range R of the measurement object T are considered, the optical coupler 120, the interferometer 130, and the optical fibers connecting them are configured and arranged so as to satisfy the following (Conditional Expression 1). Note that L1, L2, and LH, which are optical path lengths, may all be values obtained by multiplying the spatial length of the optical path by the refractive index. L1 - L2 > (LH + R) * 2, or L1 - L2 < LH * 2 ··· (Conditional Expression 1)

[0135] Here, the measurement range R specifically indicates the range from the tip of the housing of the sensor head 131 to the range where the measurement object T can be measured. Further, for example, when the fourth port D is configured inside the optical coupler 120, L2 = 0 may be set.

[0136] FIG. 12 is a diagram showing the relationship between the signal waveform received by the light receiving unit 140 and processed by the processing unit 150, and the measurement range R of the measurement object T calculated by the processing unit 150. Among the above-described (conditional expression 1), when the optical coupler 120, the interferometer 130, and the optical fibers connecting them are configured and arranged so as to satisfy L1 - L2 > (LH + R) * 2, the signal waveform received by the light receiving unit 140 and processed by the processing unit 150 can exclude the peaks of unnecessary signals due to the influence of phase noise from the measurement range R of the measurement object T.

[0137] Specifically, as shown in FIG. 12(A), since the peaks of unnecessary signals due to the influence of phase noise exceed the measurement range R, when the processing unit 150 calculates the distance to the measurement object T, the measurement peak within the measurement range R can be measured with high accuracy.

[0138] Also, among the above-described (conditional expression 1), when the optical coupler 120, the interferometer 130, and the optical fibers connecting them are configured and arranged so as to satisfy L1 - L2 < LH * 2, the signal waveform received by the light receiving unit 140 and processed by the processing unit 150 can exclude the peaks of unnecessary signals due to the influence of phase noise from the measurement range R of the measurement object T.

[0139] Specifically, as shown in FIG. 12(B), since the peaks of unnecessary signals due to the influence of phase noise are less than the measurement range R (inside the tip of the housing of the sensor head 131), when the processing unit 150 calculates the distance to the measurement object T, the measurement peak within the measurement range R can be measured with high accuracy.

[0140] As described above, according to the optical interference distance measurement sensor 100 according to the first embodiment of the present invention, under predetermined conditions (satisfying Conditional Expression 1), the optical coupler 120, the interferometer 130, and the optical fibers connecting them in the optical interference distance measurement sensor 100 are configured and arranged, and in the signal waveform received by the light receiving unit 140 and processed by the processing unit 150, unnecessary signal peaks due to the influence of phase noise can be excluded from the measurement range R of the measurement object T. As a result, the measurement peak in the measurement range R of the measurement object T can be measured with high accuracy.

[0141] Further, in the optical interference distance measurement sensor 100, since it is possible to accurately measure the distance to the measurement object T using the optical coupler 120, there is no need to use an expensive circulator. As a result, cost reduction can be achieved.

[0142] Here, the optical coupler 120 has the first port A to the fourth port D as an element that branches and combines light, and is a so-called 2×2 optical coupler, but is not limited thereto. For example, a 3×3 optical coupler may be used.

[0143] Specifically, when a 3×3 optical coupler is used, the light projected from the wavelength sweep light source 110 and input to the first port A is branched into three ports including the third port C and the fourth port D of the 3×3 optical coupler, and another port (for example, additional port E). The additional port E of the 3×3 optical coupler has a reflection point at the end of the additional port E in the same manner as the fourth port D, and the optical path length L3 from the additional port E of the 3×3 optical coupler to the reflection point is defined.

[0144] In this case, the 3×3 optical coupler, the interferometer 130, and the optical fibers connecting them may be configured and arranged so as to satisfy the above-described (Conditional Expression 1) and the following (Conditional Expression 2). L1 - L3 > (LH + R) * 2, or L1 - L3 < LH * 2 ··· (Conditional Expression 2)

[0145] Thus, even when the number of ports increases by applying a 3×3 optical coupler to the optical coupler 120, the optical coupler, the interferometer 130, and the optical fibers connecting them are configured and arranged so as to satisfy a predetermined condition (conditional expression 1 and conditional expression 2). In the signal waveform received by the light receiving unit 140 and processed by the processing unit 150, unnecessary signal peaks due to the influence of phase noise can be excluded from the measurement range R of the measurement object T.

[0146] In addition, the light projected from the wavelength-sweeping light source 110 is branched into the third port C and the fourth port D of the optical coupler 120. However, the power of the light branched into the third port C is smaller than the power of the light branched into the fourth port D. For example, an optical coupler branched at a ratio of the third port C: the fourth port D = 10:90 may be applied.

[0147] As a result, when the return light from the interferometer 130 input to the third port C of the optical coupler 120 is transmitted to the light receiving unit 140 via the optical coupler 120, the power of the light branched into the second port B of the optical coupler 120 connected to the light receiving unit 140 increases (in this case, about 90% of the return light). As a result, the amount of received light of the light received by the light receiving unit 140 increases. The processing unit 150 can calculate the distance to the measurement object T with higher accuracy.

[0148] Note that the ratio of branching into the third port C and the fourth port D of the optical coupler 120 is not limited to 10:90, and any ratio may be used as long as the amount of received light of the light received by the light receiving unit 140 is equal to or more than a predetermined value and within a range that can be calculated with high accuracy by the processing unit 150.

[0149] An optical amplifier may be added to the optical interference distance measurement sensor 100. FIG. 13 is a schematic diagram showing a schematic configuration of an optical interference distance measurement sensor 101 in which an optical amplifier 160 is added to the optical interference distance measurement sensor 100 shown in FIG. 10. As shown in FIG. 13, an optical amplifier 160 is provided between the wavelength-sweeping light source 110 and the optical coupler 120.

[0150] Generally, an optical sensor including an optical interference distance measurement sensor irradiates light onto a measurement object to be measured and measures its distance and displacement. The light irradiated onto the measurement object is preferably a so-called eye-safe laser. On the other hand, if the amount of light received by the light receiving unit 140 is large, the processing unit 150 can calculate the distance to the object T with higher accuracy because the signal waveform used for calculating the distance to the object T becomes clearer.

[0151] The optical amplifier 160 may amplify (adjust) the light projected from the wavelength-sweeping light source 110 so that the light is received by the light receiving unit 140 with high efficiency while maintaining the eye-safe laser. Thereby, the eye-safe laser can be maintained safely, the SNR can be improved, and the distance to the measurement object T can be calculated with higher accuracy.

[0152] Also, for example, regarding the above-described optical coupler 120, when it is configured to be branched at a ratio of the third port C: the fourth port D = 10:90 and the power of the light irradiated onto the measurement object T is small, the optical amplifier 160 may amplify (adjust) the power of the light projected from the wavelength-sweeping light source 110 within the range of maintaining the eye-safe laser.

[0153] In FIG. 10, it was explained that there is a reflection point at the tip of the optical fiber connected to the fourth port D of the optical coupler 120 in the optical interference distance measurement sensor 100 according to the first embodiment of the present invention. The reflection point will be specifically described.

[0154] FIG. 14 is a schematic diagram showing a schematic configuration of an optical interference distance measurement sensor 102 in which a terminator 170 is connected to the tip of the optical fiber connected to the fourth port D of the optical coupler 120 in the optical interference distance measurement sensor 100 shown in FIG. 10. As shown in FIG. 14, a terminator 170 is connected to the tip of the optical fiber connected to the fourth port D.

[0155] The terminator 170 attenuates the light branched to the fourth port D of the optical coupler 120, reducing the reflected light to the optical coupler 120. By reducing the reflected light, the influence of the phase noise described above can be reduced, and the optical interference distance measurement sensor 102 can measure the distance to the measurement object T with higher accuracy.

[0156] Note that the optical fiber connected to the fourth port D and the terminator 170 are fusion-connected to further reduce the reflected light.

[0157] In addition, the optical element connected to the tip of the optical fiber connected to the fourth port D is not limited to the terminator 170. If another optical element is connected and a connection point or the like where the refractive index changes is formed, it can be a reflection point that reflects the light from the fourth port D.

[0158] For example, an isolator may be connected, or the tip of the optical fiber may be processed and a coreless fiber or the like may be applied. Also in these cases, it is preferable to reduce the reflected light to the optical coupler 120 by applying, for example, fusion connection and APC polishing, etc., and reduce the influence of the phase noise described above.

[0159] <Second Embodiment> Next, in the second embodiment of the present invention, an optical interference distance measurement sensor having a multi-head in which the optical interference distance measurement sensor 100 described in the first embodiment has a multi-stage configuration will be described. In this embodiment, the description of the configuration common to the first embodiment will be omitted, and mainly, the points different from the first embodiment will be described centering around them.

[0160] FIG. 15 is a schematic diagram showing a schematic configuration of an optical interference distance measurement sensor 200 according to the second embodiment of the present invention. As shown in FIG. 15, in addition to the optical interference distance measurement sensor 100 described in the first embodiment, an isolator 210 is connected to the fourth port D of the optical coupler 120, and further includes a second optical coupler 220, a second interferometer 230, a second light receiving unit 240, a second processing unit 250, and a terminator 270. The second optical coupler 220 has first to fourth ports A to D, the second interferometer 230 has a second sensor head 231, and a second objective lens 232 is attached to or included in the second sensor head 231. The second light receiving unit 240 includes a second light receiving element 241 and a second AD conversion unit 242.

[0161] The isolator 210 is connected to the fourth port D of the optical coupler 120, and guides the light branched to the fourth port D by the optical coupler 120 among the light continuously changing in wavelength by the wavelength sweeping light source 110 to the first port A of the second optical coupler 220.

[0162] The second optical coupler 220 branches and outputs the light guided from the isolator 210 to the first port A to the third port C and the fourth port D. Here, if the optical coupler 120 is configured to branch at a ratio of third port C: fourth port D = 10:90, the light guided from the isolator 210 to the first port A of the second optical coupler 220 has sufficient power.

[0163] The light output from the third port C of the second optical coupler 220 is input to the second sensor head 231 via an optical fiber, irradiated as measurement light to the measurement object T via the second objective lens 232, and reflected by the measurement object T. The reflected light (third reflected light) reflected by the measurement object T is condensed by the second objective lens 232 of the second sensor head 231 and returns from the second sensor head 231 to the third port C of the second optical coupler 220.

[0164] Also, the light output from the third port C of the second optical coupler 220 enters the second sensor head 231 via an optical fiber, and a part of it is reflected by the reference surface as reference light. Here, the tip of the optical fiber serves as the reference surface, and the reflected light (the fourth reflected light) reflected by the reference surface returns from the second sensor head 231 to the third port C of the second optical coupler 220.

[0165] In this way, similar to the interferometer 130 described in the first embodiment, the second interferometer 230 generates interference light (the second interference light) based on the third reflected light and the fourth reflected light, and outputs it as the light returning to the third port C of the second optical coupler 220.

[0166] On the other hand, the light output from the fourth port D of the second optical coupler 220 is reflected by the connection portion (the second reflection point) with the terminator 270 existing at the tip of the optical fiber connected to the fourth port D, and returns to the fourth port D again as reflected light.

[0167] Then, the interference light input to the third port C and the reflected light input to the fourth port D are combined by the second optical coupler 220 and output from the second port B of the second optical coupler 220.

[0168] Similar to the light receiving unit 140 described in the first embodiment, the second light receiving unit 240 receives the light output from the second port B of the second optical coupler 220 by the second light receiving element 241, converts it into an electrical signal, and then converts the electrical signal from an analog signal to a digital signal by the second AD conversion unit 242.

[0169] Similar to the processing unit 150 described in the first embodiment, the second processing unit 250 calculates the distance to the measurement object T based on the digital signal converted by the second light receiving unit 240. The calculation method is the same as that in the first embodiment, and detailed description is omitted.

[0170] Here, the configuration and arrangement of the second optical coupler 220, the second interferometer 230, and the optical fibers connecting them in the optical interference distance measurement sensor 200 according to the present embodiment are the same as those of the optical coupler 120, the interferometer 130, and the optical fibers connecting them in the optical interference distance measurement sensor 100 according to the first embodiment. Specifically, as described with reference to FIGS. 11 and 12, the second optical coupler 220, the second interferometer 230, and the optical fibers connecting them are configured and arranged so as to satisfy L1 - L2 > (LH + R) * 2 or L1 - L2 < LH * 2.

[0171] As described above, according to the optical interference distance measurement sensor 200 according to the second embodiment of the present invention, similar to the optical interference distance measurement sensor 100 according to the first embodiment of the present invention, in the signal waveform received by the second light receiving unit 240 and processed by the second processing unit 250, unnecessary signal peaks due to the influence of phase noise can be excluded from the measurement range R of the measurement object T. As a result, the measurement peak in the measurement range R of the measurement object T can be measured with high accuracy.

[0172] Furthermore, since the optical interference distance measurement sensor 200 functions as an optical interference distance measurement sensor having a two-stage multi-head, distance measurement can be performed with higher accuracy based on the distances to the measurement object T calculated by the processing unit 150 and the second processing unit 250, respectively.

[0173] Here, an optical interference distance measurement sensor having a two-stage multi-head is used, but the present invention is not limited to this, and for example, an optical interference distance measurement sensor having a multi-head with three or more stages may be used.

[0174] Also, here, mainly for the sake of easy understanding of the optical paths of the optical coupler 120 and the second optical coupler 220, the sensor head 131 and the second sensor head 231 are schematically described as being independent, but the present invention is not limited to this. For example, as shown in FIGS. 5 and 6A to 6C, a configuration in which a single sensor head has a plurality of optical fibers, optical paths, collimating lenses, etc. may be used.

[0175] Each of the optical interference distance measurement sensors described in the first and second embodiments is used in a displacement sensor, a distance meter, a lidar, etc. for measuring the distance to the measurement object T.

[0176] Each of the embodiments described above is for facilitating the understanding of the present invention and is not for limiting and interpreting the present invention. Each element included in the embodiments, as well as its arrangement, material, conditions, shape, size, etc. are not limited to those exemplified and can be changed as appropriate. Also, it is possible to partially replace or combine the configurations shown in different embodiments.

[0177] [Appendix] An optical coupler (120) having at least four ports for branching and combining light, A light source (110) connected to the first port of the optical coupler and projecting light while continuously changing the wavelength, An interferometer (130) that irradiates a measurement object with the light branched to the third port of the optical coupler among the light projected from the light source and input to the first port of the optical coupler as measurement light, and generates interference light based on the first reflected light reflected by the measurement object and the second reflected light reflected by the reference surface as reference light, A reflection point that reflects the light branched to the fourth port of the optical coupler among the light projected from the light source and input to the first port of the optical coupler, A light receiving unit (140) that combines the interference light from the third port and the reflected light at the reflection point from the fourth port, receives the light output to the second port of the optical coupler, and converts it into an electrical signal, A processing unit (150) that calculates the distance to the measurement object based on the electrical signal converted by the light receiving unit, When the optical path length L1 from the third port of the optical coupler to the reference surface, the optical path length L2 from the fourth port of the optical coupler to the reflection point, the optical path length LH from the reference surface to the tip of the sensor head that irradiates the measurement object with the measurement light, and the measurement range R of the measurement object, Satisfy L1 - L2 > (LH + R) * 2, or L1 - L2 < LH * 2, Optical interference distance measuring sensor (100).

Explanation of symbols

[0178] 1…Sensor system, 10…Displacement sensor, 11…Control device, 12…Sensor for control signal input, 13…External connection device, 20…Sensor head, 21…Objective lens, 22, 22a~22c…Collimating lens, 23…Objective lens holder, 24, 24a~24c…Collimating lens unit, 30…Controller, 31…Display unit, 32…Setting unit, 33…External interface (I / F) unit, 34…Optical fiber connection unit, 35…External memory unit, 36…Measurement processing unit, 40…Optical fiber, 51…Wavelength sweep light source, 52…Optical amplifier, 53, 53a~53b…Isolator, 54, 54a~54e…Optical coupler, 55…Attenuator, 56a~56c…Light receiving element, 57…Combining circuit, 58…AD conversion unit, 59…Processing unit, 60…Balance detector, 61…Correction signal generation unit, 71a~71e…Light receiving element, 72a~72c…Amplification circuit, 73…Combining circuit, 74…AD conversion unit, 75…Processing unit, 76…Differential amplification circuit, 77…Correction signal generation unit, 100~102, 200…Optical interference distance measuring sensor, 110…Wavelength sweep light source, 120, 220…Optical coupler, 130, 230…Interferometer, 131, 231…Sensor head, 132, 232…Objective lens, 140, 240…Light receiving unit, 141, 241…Light receiving element, 142, 242…AD conversion unit, 150, 250…Processing unit, 160…Optical amplifier, 170, 270…Terminator, 210…Isolator, A~E…Ports of optical coupler, L1~L3, LH…Optical path length, R…Measurement range, T…Measurement object

Claims

1. An optical coupler having at least four ports for branching and combining light, a light source connected to the first port of the optical coupler and projecting light while continuously changing the wavelength, an interferometer that irradiates a measurement object with the light branched to the third port of the optical coupler among the light projected from the light source and input to the first port of the optical coupler as measurement light, and generates interference light based on the first reflected light reflected by the measurement object and the second reflected light reflected by a reference surface as reference light, a reflection point that reflects the light branched to the fourth port of the optical coupler among the light projected from the light source and input to the first port of the optical coupler, a light receiving unit that combines the interference light from the third port and the reflected light at the reflection point from the fourth port, receives the light output to the second port of the optical coupler, and converts it into an electrical signal, a processing unit that calculates the distance to the measurement object based on the electrical signal converted by the light receiving unit, wherein when the optical path length L1 from the third port of the optical coupler to the reference surface, the optical path length L2 from the fourth port of the optical coupler to the reflection point, the optical path length LH from the reference surface to the tip of the sensor head that irradiates the measurement object with measurement light, and the measurement range R of the measurement object are considered, L1 - L2 > (LH + R) * 2 or L1 - L2 < LH * 2 is satisfied, an optical interference distance measurement sensor.

2. The reference surface is the end face of an optical fiber connecting the third port of the optical coupler and the sensor head. The optical interference distance measurement sensor according to Claim 1.

3. Among the light projected from the light source and input to the first port of the optical coupler, the power of the light branched to the third port of the optical coupler is smaller than the power of the light branched to the fourth port. The optical interference distance measurement sensor according to Claim 1 or 2.

4. Further comprising an optical amplifier between the light source and the first port of the optical coupler for amplifying the light projected from the light source. The optical interference distance measurement sensor according to any one of Claims 1 to 3.

5. The reflection point is a terminator. The optical interference distance measurement sensor according to any one of Claims 1 to 4.

6. The reflection point is an isolator. The optical interference distance measurement sensor according to any one of Claims 1 to 4.

7. A second optical coupler having at least four ports, with the isolator and the first port connected, for branching and combining light, Of the light guided from the isolator and input to the first port of the second optical coupler, the light branched to the third port of the second optical coupler is irradiated as measurement light onto a measurement object, and a second interferometer that generates second interference light based on the third reflected light reflected by the measurement object and the fourth reflected light reflected by a reference surface as reference light; A second reflection point that reflects the light branched to the fourth port of the second optical coupler among the light guided from the isolator and input to the first port of the second optical coupler; A second light receiving unit that receives the light output from the second port of the second optical coupler, in which the second interference light from the third port of the second optical coupler and the reflected light at the second reflection point from the fourth port of the second optical coupler are combined, and converts the received light into an electrical signal; A second processing unit that calculates the distance to the measurement object based on the electrical signal converted by the second light receiving unit. The optical interference distance measurement sensor according to claim 6.

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