Optical interference distance measuring sensor

Abstract

An optical interference distance measuring sensor is provided with a plurality of light receiving channels corresponding to one light projecting channel, and can improve resistance to interference. A light interference distance measuring sensor according to one embodiment of the present invention is provided with: a light source that projects light while changing the wavelength; an interferometer that generates interference light based on the measurement light and the reference light; a light receiving unit that receives the interference light from the interferometer and converts the interference light into an electric signal; and a processing unit that calculates the distance from the sensor head to the measurement object, the interferometer comprising: a light projection channel configured so as to propagate light supplied from the light source toward the sensor head and to irradiate the measurement object from the sensor head; and a plurality of light-receiving channels configured to receive the measurement light and propagate the measurement light toward the light-receiving unit, the light-projecting channel and / or the plurality of light-receiving channels further propagating the reference light.

Description

Technical Field

[0001] The invention relates to an optical interference distance measuring sensor. Background Art

[0002] In recent years, optical distance measuring sensors that measure the distance to a measurement object in a non-contact manner have become popular. For example, as an optical distance measuring sensor, the following optical interference distance measuring sensor is known: based on the light projected from a wavelength scanning light source, interference light based on reference light and measurement light is generated, and the distance to the measurement object is measured based on the interference light.

[0003] For example, Non-Patent Document 1 discloses a technique in which, in a Mach-Zehnder type optical interferometer ranging sensor, a plurality of light receiving channels are used to receive measurement light projected from a single light projecting channel in order to counteract speckle.

[0004] Prior art literature Non-patent literature Non-patent literature 1: Thomas Klein et al., “Joint aperture detection for speckle reduction and increased collection efficiency in ophthalmic MHz OCT” Summary of the invention

[0005] Technical problem to be solved by the invention However, as described in Non-Patent Document 1, in a Mach-Zehnder type optical interference distance measuring sensor, when disturbances such as vibration and temperature are applied, polarization and the like in reference light and measurement light may change, which may cause measurement errors.

[0006] Therefore, an object of the present invention is to provide an optical interference ranging sensor, which is provided with a plurality of light receiving channels corresponding to one light projecting channel and can improve resistance to interference.

[0007] Solutions for solving technical problems An optical interference ranging sensor involved in one embodiment of the present invention comprises: a light source that projects light while changing its wavelength; an interferometer that is supplied with the light projected from the light source and generates interference light based on measuring light and reference light, the measuring light is irradiated to a measuring object through a sensor head and reflected, and the reference light follows an optical path that is at least partially different from that of the measuring light; a light receiving unit that receives the interference light from the interferometer and converts it into an electrical signal; and a processing unit that calculates the distance from the sensor head to the measuring object based on the electrical signal, the interferometer including: a light projecting channel that is configured to propagate light supplied from the light source toward the sensor head and irradiate the light from the sensor head toward the measuring object; and a plurality of light receiving channels that are configured to receive the measuring light reflected by the measuring object and propagate it toward the light receiving unit, the light projecting channel and at least any one of the plurality of light receiving channels also propagating the reference light. According to this method, multiple light receiving channels are set for one light projection channel, so that speckle countermeasures can be taken. Furthermore, the reference light is propagated in the light projection channel and at least one of the multiple light receiving channels. Therefore, interference such as vibration and temperature change has the same impact on the measurement light and the reference light, and the impact of the interference can be reduced.

[0008] In the above-mentioned method, a reference light generating unit may be further provided, which generates reference light by reflecting a part of the light propagating in the light projection channel. According to this method, since the reference light propagates in the light projection channel, the influence of disturbances such as vibration and temperature change on the measurement light and the reference light is the same, and the influence of the disturbances can be reduced.

[0009] In the above method, the reference light generating unit may also be configured to transmit the reference light in the light projection channel toward the light receiving unit. According to this method, the reference light is transmitted in the light projection channel toward the light receiving unit, so that the influence of disturbances such as vibration and temperature change on the measurement light and the reference light is the same, and the influence of the disturbances can be reduced.

[0010] In the above method, the reference light generating unit may also be a partial reflector disposed in the optical path of the light in the light projection channel. According to this method, the partial reflector can transmit a part of the light propagating in the light projection channel as the measurement light, and reflect another part of the light propagating in the light projection channel as the reference light, so that the reference light can be generated with a simple structure.

[0011] In the above-mentioned method, the reference light generating unit may also be configured to propagate the reference light toward the light receiving unit in at least one of the plurality of light receiving channels. According to this method, since the reference light propagates in the light receiving channel, the influence of disturbances such as vibration and temperature change on the measurement light and the reference light is the same, and the influence of the disturbance can be reduced.

[0012] In the above method, the reference light generating unit may also be a reflective surface, which is arranged in the optical path of the light in the light projection channel and reflects the light propagating in the light projection channel toward any light receiving channel. According to this method, the reflective surface can reflect a part of the light propagating in the light projection channel toward any light receiving channel as reference light, and can generate reference light with a simple structure.

[0013] In the above-mentioned aspect, at least one of the plurality of light receiving channels may be further configured to propagate light supplied from the light source toward the sensor head, and the optical interference ranging sensor may further include a reference light generating unit, which generates reference light by reflecting a portion of light propagating in at least one of the light receiving channels. According to this aspect, since a portion of light is reflected in at least one of the light receiving channels and the reference light propagates toward the light receiving unit, the influence of disturbances such as vibrations and temperature changes on the measurement light and the reference light is the same, and the influence of the disturbances can be reduced.

[0014] In the above embodiment, the reference light generating unit may be a partial reflector disposed in the optical path of light in at least one of the light receiving channels. According to this embodiment, the partial reflector can reflect a portion of light propagating in at least one of the light receiving channels as reference light, and can generate reference light with a simple structure.

[0015] In the above-mentioned method, at least one of the light receiving channels may also include a light shielding unit, which shields at least a portion of the light supplied from the light source and propagating toward the sensor head. According to this method, the light shielding unit can shield the light propagating in at least one of the light receiving channels and transmitting through a portion of the reflector, thereby improving the accuracy of the optical interference ranging sensor.

[0016] In the above method, the light-emitting channel and at least one of the plurality of light-receiving channels may also be formed by an optical fiber for transmitting the measuring light and the reference light. According to this method, an optical interference ranging sensor having a plurality of light-receiving channels corresponding to one light-emitting channel, i.e., an optical interference ranging sensor capable of improving resistance to interference, can be formed through a simple structure.

[0017] In the above-mentioned method, the light-projecting channel and at least one of the plurality of light-receiving channels may also be configured to include: a first optical fiber for propagating the measurement light, and a second optical fiber for propagating the reference light. According to this method, an optical interference ranging sensor having a plurality of light-receiving channels corresponding to one light-projecting channel, i.e., an optical interference ranging sensor capable of improving resistance to interference, can be configured with a simple structure.

[0018] According to the present invention, it is possible to provide an optical interference distance measuring sensor which includes a plurality of light receiving channels corresponding to one light projecting channel and can improve resistance to disturbance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is a schematic external view showing an outline of the displacement sensor 10 according to the present disclosure.

[0020] Figure 2 1 is a flowchart showing a procedure of measuring the measurement object T using the displacement sensor 10 according to the present disclosure.

[0021] Figure 3 1 is a functional block diagram showing an overview of a sensor system 1 using the displacement sensor 10 according to the present disclosure.

[0022] Figure 4 1 is a flowchart showing a procedure of measuring the measurement object T by the sensor system 1 using the displacement sensor 10 according to the present disclosure.

[0023] Figure 5A This is a diagram for explaining the principle of measuring the measurement object T by the displacement sensor 10 according to the present disclosure.

[0024] Figure 5B This is a diagram for explaining another principle of measuring the measurement object T by the displacement sensor 10 according to the present disclosure.

[0025] Figure 5C This is a diagram for explaining another principle of measuring the measurement object T by the displacement sensor 10 according to the present disclosure.

[0026] Figure 5D This is a diagram for explaining another principle of measuring the measurement object T by the displacement sensor 10 according to the present disclosure.

[0027] Fig. 6A It is a perspective view showing a schematic structure of the sensor head 20 .

[0028] Figure 6B 2 is a schematic diagram showing the internal structure of the sensor head 20 .

[0029] Figure 7 It is a block diagram for explaining signal processing in the controller 30 .

[0030] Figure 8 1 is a flowchart showing a method of calculating the distance to the measurement object T executed by the processing unit 59 in the controller 30 .

[0031] Fig.9A 2 is a diagram showing how a waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency).

[0032] Fig. 9B2 is a diagram showing how a frequency spectrum (voltage vs. frequency) is converted into a frequency spectrum (voltage vs. distance) by distance.

[0033] Fig. 9C 3 is a diagram showing a case where a peak is detected based on a frequency spectrum (voltage vs. distance) and a distance value corresponding thereto is calculated.

[0034] Fig. 10A This is a diagram showing a specific example of the structure of the optical fiber cable involved in the present disclosure.

[0035] Fig. 10B It is shown from Fig. 10A FIG. 4 is a diagram showing an example of a schematic diagram of an end portion of an optical fiber cable 44 as viewed along an arrow 44D.

[0036] Fig.11A This is a diagram showing another specific example of the structure of the optical fiber cable involved in the present disclosure.

[0037] Fig. 11B It is shown from Fig.11A FIG. 4 is a diagram showing an example of a schematic diagram of an end portion of an optical fiber cable 45 as viewed along an arrow 45D shown. DETAILED DESCRIPTION

[0038] Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings. In addition, each embodiment described below is only a specific example for implementing the present invention, and does not limit the present invention. In addition, in order to facilitate the understanding of the description, the same reference numerals are marked as much as possible for the same components in each drawing, and repeated descriptions are sometimes omitted.

[0039] [Overview of Displacement Sensor] First, the outline of the displacement sensor according to the present disclosure will be described. Figure 1 FIG. 1 is a schematic diagram showing the appearance of the displacement sensor 10 according to the present disclosure. Figure 1 As shown, 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).

[0040] The sensor head 20 and the controller 30 are connected via an optical fiber cable 40, and an objective lens 21 is mounted on 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 cable connection unit 34, and an external storage unit 35, and further has a measurement processing unit 36 ​​inside.

[0041] The sensor head 20 irradiates the light output from the controller 30 to the measurement object T, and receives the reflected light from the measurement object T. The sensor head 20 has a reference surface inside, and the reference surface is used to reflect the light output from the controller 30 and received via the optical fiber cable 40 and interfere with the reflected light from the measurement object T.

[0042] The sensor head 20 is provided with a detachable objective lens 21. 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 measurement object T, or a variable-focus objective lens can be used.

[0043] Furthermore, when installing the sensor head 20 , the sensor head 20 and / or the object T may be installed so that the object T is appropriately located within the measurement area of ​​the displacement sensor 10 by irradiating the object T with guide light (visible light).

[0044] The optical fiber cable 40 is connected to the optical fiber cable connection part 34 arranged in the controller 30 and extends to connect the controller 30 and the sensor head 20. The optical fiber cable 40 may also include at least one optical fiber 41P for guiding the reference light and at least one optical fiber 42P for guiding the measurement light. Thus, 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. In addition, the optical fiber cable 40 can be detached from the sensor head 20 and the controller 30, and various optical fiber cables can be applied in terms of length, thickness, characteristics, etc. In addition, the optical fiber cable 40 can be configured as a single core with one core formed in one cladding, or it can be configured as a multi-core with multiple cores formed in one cladding. In the case of a multi-core, since the distance of the multiple optical paths is close, it is possible to suppress the change of the measurement optical path and the reference optical path caused by the bending and temperature changes applied to the optical fiber cable 40.

[0045] The display unit 31 is composed of, for example, a liquid crystal display or an organic EL display, etc. The display unit 31 displays the set value of the displacement sensor 10, the amount of light received by the return light 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).

[0046] The setting unit 32 performs settings required for measuring the measurement object T, for example, by the user operating a mechanical button, a touch panel, etc. All or part of these required 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.

[0047] Here, the external I / F unit 33 is composed of, for example, Ethernet (registered trademark), RS232C, analog output, etc. The external I / F unit 33 may be connected to other connected devices to perform required settings from the external connected devices, or output measurement results measured by the displacement sensor 10 to the external connected devices.

[0048] Furthermore, the controller 30 may also perform settings required for measuring the measurement object T by taking in data stored in the external storage unit 35. The external storage unit 35 is an auxiliary storage device such as a USB (Universal Serial Bus) memory, and stores settings required for measuring the measurement object T in advance.

[0049] The measurement processing unit 36 ​​in the controller 30 includes, for example, a wavelength scanning light source that projects light while continuously changing the wavelength, a light receiving element that receives the 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 based on the return light from the sensor head 20 using a control unit and a storage unit, and the displacement of the measurement object T (the distance to the measurement object T) is finally calculated. The details of these processes will be described later.

[0050] Figure 2 FIG. 1 is a flowchart showing the steps of measuring the measurement object T by the displacement sensor 10 according to the present disclosure. Figure 2 As shown, this step includes steps S11 to S14.

[0051] In step S11, the sensor head 20 is set. For example, the sensor head 20 irradiates the measurement target T with guide light, and the sensor head 20 is set at an appropriate position with reference to this guide light.

[0052] Specifically, the amount of light received by the return light from the sensor head 20 may be displayed on the display unit 31 in the controller 30, and the user may check the amount of light received while adjusting the orientation of the sensor head 20 and the distance (height position) from the measurement target T. Basically, if the light from the sensor head 20 can be irradiated perpendicularly (at an angle closer to perpendicular) to the measurement target T, the amount of light reflected from the measurement target T increases, and the amount of light received by the return light from the sensor head 20 also increases.

[0053] Furthermore, the objective lens 21 may be replaced with one having an appropriate focal length according to the distance between the sensor head 20 and the measurement target object T.

[0054] Furthermore, when 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 setting can be displayed on the display unit 31 or output to an externally connected device to notify the user.

[0055] In step S12 , various measurement conditions are set when measuring the measurement object T. For example, the user operates the setting unit 32 in the controller 30 to set calibration data (such as a linear calibration function) inherent to the sensor head 20 .

[0056] In addition, various parameters may be set. For example, the sampling time, the measurement range, and the threshold value for determining whether the measurement result is normal or abnormal may be set. Furthermore, the measurement cycle 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 may be set according to the material of the measurement object T.

[0057] The measurement conditions and various parameters are set by operating the setting unit 32 in the controller 30 , but may be set from an externally connected device or by loading data from the external storage unit 35 .

[0058] 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 .

[0059] Specifically, in the measurement processing unit 36 ​​of the controller 30, light is projected from the wavelength scanning light source, and the return light from the sensor head 20 is received by the light receiving element. The signal processing circuit performs frequency analysis, distance conversion, peak detection, etc., and calculates the displacement of the measurement object T (the distance to the measurement object T). The specific measurement processing will be described in detail later.

[0060] In step S14 , the measurement result measured in step S13 is outputted. For example, the displacement of the measurement object T (the distance to the measurement object T) measured in step S13 is displayed on the display unit 31 in the controller 30 or outputted to an externally connected device.

[0061] In addition, based on the threshold value set in step S12, whether the displacement of the measurement object T (the distance to the measurement object T) measured in step S13 is within the normal range or abnormal can also be displayed or output as a measurement result. Furthermore, the measurement conditions, various parameters, and measurement mode set in step S12 can also be displayed or output together.

[0062] [Overview of System Including Displacement Sensor] Figure 31 is a functional block diagram showing an overview of a sensor system 1 using the displacement sensor 10 according to the present disclosure. Figure 3 As shown, the sensor system 1 includes a displacement sensor 10, a control device 11, a control signal input sensor 12, and an external connection device 13. In addition, the displacement sensor 10 is connected to the control device 11 and the external connection device 13, for example, through a communication cable or an external connection line (for example, including an external input line, an external output line, and a power line, etc.), and the control device 11 is connected to the control signal input sensor 12 through a signal line.

[0063] The displacement sensor 10 is used as Figure 1 as well as Figure 2 As described above, the displacement of the measurement object T (the distance to the measurement object T) is measured. Furthermore, the displacement sensor 10 may output the measurement result and the like to the control device 11 and the external connection device 13 .

[0064] 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 object T to be measured.

[0065] 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 measured value to 0) to the displacement sensor 10 .

[0066] The control signal input sensor 12 outputs an on / off signal indicating the timing of the displacement sensor 10 measuring the measurement object T to the control device 11. For example, the control signal input sensor 12 is set near a production line where the measurement object T moves, detects that the measurement object T moves to a predetermined position, and outputs an on / off signal to the control device 11.

[0067] The external connection device 13 is, for example, a PC (Personal Computer), and various settings can be made on the displacement sensor 10 through user operations.

[0068] As a specific example, a measurement mode, an operation mode, a measurement cycle, and a material of the measurement object T are set.

[0069] As the setting of the measurement mode, an “internal synchronous measurement mode” in which measurement is periodically started inside the control device 11 , an “external synchronous measurement mode” in which measurement is started based on an input signal from outside the control device 11 , or the like is selected.

[0070] As the setting of the operation mode, an “operation mode” for actually measuring the measurement object T, an “adjustment mode” for setting measurement conditions for measuring the measurement object T, or the like is selected.

[0071] The measurement cycle is a cycle for measuring the object T, and can be set according to the reflectivity of the object T. Even when the reflectivity of the object T is low, the object T can be properly measured if the measurement cycle is extended to appropriately set the measurement cycle.

[0072] For the measurement object T, the "rough surface mode" suitable for the case where diffuse reflection is a large component of reflected light, the "mirror mode" suitable for the case where specular reflection is a large component of reflected light, or the "standard mode" between them is selected.

[0073] In this way, by making appropriate settings according to the reflectivity and material of the measurement object T, the measurement object T can be measured with higher accuracy.

[0074] Figure 4 1 is a flowchart showing a procedure for measuring the measurement object T by the sensor system 1 using the displacement sensor 10 according to the present disclosure. Figure 4 As shown, this step is a step in the case of the above-mentioned external synchronization measurement mode, and includes steps S21 to S24.

[0075] In step S21, the sensor system 1 detects the measurement object T to be measured. Specifically, the control signal input sensor 12 detects that the measurement object T moves to a predetermined position on the production line.

[0076] In step S22, the sensor system 1 performs a measurement instruction to measure the measurement object T detected in step S21 through the displacement sensor 10. 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 perform a measurement instruction so that the measurement object T is measured.

[0077] In step S23, the displacement sensor 10 measures the measurement object T. Specifically, the displacement sensor 10 measures the measurement object T based on the measurement instruction received in step S22.

[0078] In step S24 , the sensor system 1 outputs the measurement result measured in step S23 . Specifically, the displacement sensor 10 displays the measurement result on the display unit 31 , or outputs it to the control device 11 or the external connection device 13 via the external I / F unit 33 .

[0079] In addition, here, use Figure 4 , the steps in the case of the external synchronous measurement mode in which the object T is measured by detecting the object T by the control signal input sensor 12 are described, but the present invention is not limited to this. For example, in the case of the internal synchronous measurement mode, instead of steps S21 and S22, a measurement timing signal is generated based on a preset cycle, thereby instructing the displacement sensor 10 to measure the object T.

[0080] Next, the structure of the displacement sensor 10 according to the present disclosure will be described.

[0081] Figure 5A 1 is a diagram for explaining an example of the structure of the displacement sensor 10 involved in the present disclosure. Figure 5A As shown, 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 scanning light source 51, an optical amplifier 52, an isolator 53, a plurality of optical couplers 54, 54a to 54e, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generation unit 61. The optical fiber cable 40 includes optical fibers 41Pa to 41Pc and optical fibers 42Pa to 42Pc.

[0082] The sensor head 20, the optical fiber cable 40, and a plurality of optical couplers 62a, 62b, and 62c constitute a main interferometer 10A. Here, the main interferometer 10A is supplied with light projected from the wavelength scanning light source 51, and generates interference light based on the measurement light and the reference light. The measurement light is irradiated to the measurement object T through the sensor head 20 and is reflected, and the reference light follows an optical path that is at least partially different from that of the measurement light. The plurality of light receiving elements 56a to 56c are each an example of a light receiving unit, and receive the interference light from the main interferometer 10A and convert it into an electrical signal. The controller is an example of a processing unit, and calculates the distance from the sensor head 20 to the measurement object T based on the electrical signal generated by the light receiving unit.

[0083] The displacement sensor 10 is configured to include a first channel, a second channel, and a third channel. That is, the optical path including the optical fiber 42Pa in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22a constitute the first channel. In addition, the optical path including the optical fiber 42Pb in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22b constitute the second channel. In addition, the optical path including the optical fiber 42Pc in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22c constitute the third channel.

[0084] exist Figure 5A In an example of the structure of the displacement sensor 10 shown in the figure, the first channel is configured as a light receiving channel, the second channel is configured as a light projecting channel and a light receiving channel, and the third channel is configured as a light receiving channel. Here, the light projecting channel may be a channel configured to transmit light supplied from a light source to a sensor head and irradiate the light from the sensor head to a measurement object. In addition, the light receiving channel may be a channel configured to receive measurement light reflected by a measurement object and transmit it to a light receiving part. In the displacement sensor 10 involved in this embodiment, for example, the light projecting channel and at least one of the plurality of light receiving channels also transmit reference light.

[0085] The wavelength scanning light source 51 projects a laser beam having a scanned wavelength. For example, if a method of modulating a VCSEL (Vertical Cavity Surface Emitting Laser) by current is applied as the wavelength scanning light source 51, it is not easy to cause mode hopping due to the short resonator length, and the wavelength can be easily changed, which can be realized at low cost.

[0086] The optical amplifier 52 amplifies the light projected from the wavelength scanning light source 51. The optical amplifier 52 may be, for example, an EDFA (erbium-doped fiber amplifier), or may be, for example, an optical amplifier dedicated to 1550 nm.

[0087] The isolator 53 is an optical element that transmits incident light in one direction, and may be disposed immediately after the wavelength scanning light source 51 in order to prevent the influence of noise generated by return light.

[0088] In this way, the light projected from the wavelength scanning light source 51 is amplified by the optical amplifier 52, and is branched to the main interferometer 10A and the sub-interferometer 10B by the optical coupler 54 via the isolator 53. For example, in the optical coupler 54, the ratio of the light branched to the main interferometer 10A and the sub-interferometer 10B may be 90% or more to the main interferometer 10A side.

[0089] The light branched to the main interferometer 10A propagates toward the optical coupler 62 b via the circulator 54 b , and further propagates from the optical coupler 62 b toward the end 42Ib of the optical fiber 42Pb of the second channel of the optical fiber cable 40 .

[0090] The light incident on the optical fiber 42Pb from the end 42Ib is guided in the optical fiber 42Pb and propagates to the end 42Ob.

[0091] The end 42Ob is configured as a partial reflector (an example of a reference light generating unit) that transmits a portion of the light propagating to the end 42Ob and reflects the other portion. That is, the partial reflector is configured to propagate the reference light to the light receiving element (an example of a light receiving unit) in the second channel as the light projection channel. In this way, a reference light common to the first channel to the third channel can be generated. In addition, since the reference light propagates in the light projection channel, the influence of interference such as vibration and temperature change is reduced. The partial reflector can be formed by coating the front end face of the optical fiber with a partial reflective film with a reflectivity of about 1%, or it can be formed by PC (Physical Contact) polishing in a manner that produces Fresnel reflection (reflectivity of about 4%) between the optical fiber and the air.

[0092] Part of the light propagating to the end 42Ob is incident on the sensor head 20 as measurement light through the end 42Ob, and in the sensor head 20, passes through the collimating lens 22b and the objective lens 21 to irradiate the measurement object T, and is reflected by the measurement object T. Then, the measurement light reflected by the measurement object T is received by the first channel, the second channel, and the third channel of the displacement sensor 10, respectively. That is, part of the measurement light reflected by the measurement object T is incident on the end 42Oa of the optical fiber 42Pa via the objective lens 21 and the collimating lens 22a, another part is incident on the end 42Ob of the optical fiber 42Pb via the objective lens 21 and the collimating lens 22b, and another part is incident on the end 42Oc of the optical fiber 42Pc via the objective lens 21 and the collimating lens 22c.

[0093] Another part of the light propagating to the end 42Ob is reflected by the end 42Ob as reference light. Moreover, the reference light reflected by the end 42Ob and the measurement light reflected by the measured object T and incident on the end 42Ob of the second channel interfere in the end 42Ob to generate interference light of the second channel. The interference light is guided toward the end 42Ib in the optical fiber 42Pb and supplied from the end 42Ib to the optical coupler 62b. The interference light received by the light receiving element 56b is converted into an electrical signal.

[0094] The measurement light, which is irradiated to the measurement object T via the end 42Ob of the optical fiber 42Pb and then reflected by the measurement object T and incident on the end 42Oa of the optical fiber 42Pa of the first channel, is guided in the optical fiber 42Pa and supplied from the end 42Ia to the optical coupler 62a. On the other hand, the reference light reflected by the end 42Ob of the optical fiber 42Pb propagates in the optical fiber 42Pb and is supplied to the optical coupler 62b. The optical coupler 62b supplies part of the reference light to the optical coupler 62a and the optical coupler 62c. The reference light supplied from the optical coupler 62b and the measurement light supplied from the end 42Ia of the optical fiber 42Pa interfere in the optical coupler 62a to generate interference light of the first channel, and at least a part of the interference light is supplied to the light receiving element 56a. The interference light received by the light receiving element 56a is converted into an electrical signal.

[0095] The measurement light which is irradiated to the measurement object T via the end 42Ob of the optical fiber 42Pb and then reflected by the measurement object T and incident on the end 42Oc of the optical fiber 42Pc of the third channel is guided in the optical fiber 42Pc and supplied from the end 42Ic to the optical coupler 62c. On the other hand, the reference light reflected by the end 42Oc of the optical fiber 42Pc propagates in the optical fiber 42Pc and is supplied to the optical coupler 62c. The optical coupler 62b supplies part of the reference light to the optical coupler 62a and the optical coupler 62c. The reference light supplied from the optical coupler 62b and the measurement light supplied from the end 42Ic of the optical fiber 42Pc interfere in the optical coupler 62c to generate interference light of the third channel, 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.

[0096] As described above, the light receiving elements 56 a to 56 c receive interference light from each of the first channel, the second channel, and the third channel of the main interferometer 10A, and generate electrical signals corresponding to the amounts of the received light.

[0097] The amplifier circuits 57a to 57c amplify the electrical signals output from the light receiving elements 56a to 56c, respectively.

[0098] The AD converters 58a to 58c receive the electrical signals amplified by the amplifier circuits 57a to 57c, respectively, and convert (AD-convert) the electrical signals from analog signals to digital signals. Here, the AD converters 58a to 58c perform AD conversion based on the correction signal from the correction signal generator 61 in the sub-interferometer 10B.

[0099] In the sub-interferometer 10B, in order to correct the nonlinearity of the wavelength when the wavelength-sweeping light source 51 is swept, the sub-interferometer 10B acquires an interference signal and generates a correction signal called a K clock.

[0100] Specifically, the light branched by the optical coupler 54 to the sub-interferometer 10B 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 by using optical fibers of different lengths between the optical coupler 54d and the optical coupler 54e, for example, and interference light corresponding to the optical path length difference is output from the optical coupler 54e. Then, the balanced detector 60 receives the interference light from the optical coupler 54e, removes the difference of the signal with the opposite phase, removes the noise, and amplifies the optical signal and converts it into an electrical signal.

[0101] In addition, the optical coupler 54d and the optical coupler 54e may each branch light at a ratio of 50:50.

[0102] The correction signal generator 61 detects the nonlinearity of the wavelength when the wavelength scanning light source 51 scans based on the electrical signal from the balanced detector 60, generates a K clock corresponding to the nonlinearity, and outputs it to the AD converters 58a to 58c.

[0103] The wavelength scanning light source 51 has nonlinear wavelength when scanning, so the intervals of the analog signals input to the AD converters 58a to 58c in the main interferometer 10A are not equal. In the AD converters 58a to 58c, the sampling time is corrected based on the K clock so that the intervals of the waves are equal and AD conversion (sampling) is performed.

[0104] In addition, as described above, the K clock is a correction signal for sampling the analog signal of the main interferometer 10A, and therefore needs to be generated at a higher frequency than the analog signal of the main interferometer 10A. Specifically, the optical path length difference between the optical coupler 54d and the optical coupler 54e in the sub-interferometer 10B may be made longer than the optical path length difference between the front end (end face) of the optical fiber in the main interferometer 10A and the measurement target T, or the correction signal generating unit 61 may multiply the frequency (e.g., 8 times) to increase the frequency.

[0105] The processing unit 59 obtains the digital signals that have been corrected for nonlinearity and AD-converted 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 performs frequency conversion on the digital signals using fast Fourier transform (FFT), and calculates the distance by analyzing them. The detailed processing in the processing unit 59 will be described later.

[0106] In addition, in the processing unit 59 , since high-speed processing is required, it is often implemented by an integrated circuit such as an FPGA (field-programmable gate array).

[0107] Here, three optical paths of channels are provided in the main interferometer 10A, and the sensor head 20 irradiates the measurement object T from each optical path with measurement light, and based on the interference light (return light) obtained from each, the distance to the measurement object T is measured (multi-channel). The number of channels in the main interferometer 10A is not limited to three, and may be two, or may be four or more.

[0108] Figure 5B FIG. 1 is a diagram for explaining another example of the structure of the displacement sensor 10 according to the present disclosure. Figure 5B The structure of the displacement sensor 10 shown in FIG. Figure 5A The difference in the structure of the displacement sensor 10 shown in FIG. Figure 5A The description of the same parts of the displacement sensor 10 as shown will be appropriately omitted.

[0109] The displacement sensor 10 is configured to include a first channel, a second channel, and a third channel. That is, the optical path including the optical fiber 42Pa in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22a constitute the first channel. In addition, the optical path including the optical fiber 42Pb in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22b constitute the second channel. In addition, the optical path including the optical fiber 42Pc in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22c constitute the third channel.

[0110] exist Figure 5B In the example of the structure of the displacement sensor 10 shown in FIG. 1 , the first channel is configured as a light receiving channel, the second channel is configured as a light projecting channel, and the third channel is configured as a light receiving channel. Figure 5B The displacement sensor 10 shown does not include the circulator 54b, the light receiving element 56b, the amplifier circuit 57b, and the AD converter 58b. Figure 5B In the displacement sensor 10 shown, the optical couplers 62a and 62c may be configured as circulators.

[0111] The light branched to the main interferometer 10A propagates toward the optical coupler 62b, and then propagates from the optical coupler 62b to the end 42Ib of the optical fiber 42Pb of the second channel of the optical fiber cable 40 and the optical couplers 62a and 62c. The light propagated to the optical coupler 62a propagates to the end 42Ia of the optical fiber 42Pa of the first channel. The light propagated to the optical coupler 62c propagates to the end 42Ic of the optical fiber 42Pc of the third channel.

[0112] The light incident on the optical fiber 42Pb from the end 42Ib is guided in the optical fiber 42Pb and propagates to the end 42Ob.

[0113] The light propagating to the end 42Ob is incident on the sensor head 20 as the measurement light through the end 42Ob, and in the sensor head 20, passes through the collimating lens 22b and the objective lens 21 to irradiate the measurement object T, and is reflected by the measurement object T. Then, the measurement light reflected by the measurement object T is received by the first channel and the third channel of the displacement sensor 10, respectively. That is, a part of the measurement light reflected by the measurement object T is incident on the end 42Oa of the optical fiber 42Pa via the objective lens 21 and the collimating lens 22a, and the other part is incident on the end 42Oc of the optical fiber 42Pc via the objective lens 21 and the collimating lens 22c. In addition, the light shielding plate 24a provided on the collimating lens 22a is configured as a one-way transmission element, and the measurement light reflected by the measurement object T passes through the objective lens 21, bypasses the light shielding plate 24a, and is received by the end 42Oa of the optical fiber 42Pa. Similarly, the light shielding plate 24c provided on the collimating lens 22c is configured as a one-way transmission element, and the measurement light reflected by the measurement target T passes through the objective lens 21, bypasses the light shielding plate 24c, and is received by the end 42Oc of the optical fiber 42Pc.

[0114] The light propagated to the end 42Ia of the optical fiber 42Pa of the first channel via the optical coupler 62b, 62a enters the optical fiber 42Pa from the end 42Ia, is guided in the optical fiber 42Pa, and propagates to the end 42Oa. The end 42Oa is configured as a partial reflector (an example of a reference light generating unit) that transmits a part of the light propagated to the end 42Oa and reflects another part. That is, the partial reflector is configured to propagate the reference light toward the light receiving element (an example of a light receiving unit) in the first channel as the light receiving channel. As a result, the reference light propagates in the light receiving channel, thereby reducing the influence of disturbances such as vibration and temperature changes.

[0115] A shading plate 24a configured as a one-way transmission element is provided on the collimating lens 22a, and the light transmitted through the end 42Oa is shielded by the shading plate 24a. The shading plate 24a may be configured as an absorption type ND (Neutral Density) filter, for example. Thus, the first channel can be configured as a light receiving channel that does not output a light beam of the measuring light, thereby reducing the light spot of the measuring light. In addition, an isolator may be used instead of the shading plate 24a. Another part of the light propagating to the end 42Oa is reflected by the end 42Oa as reference light.

[0116] The reference light reflected by the end 42Oa and the measurement light reflected by the measurement object T and incident on the end 42Oa of the first channel interfere with each other in the end 42Oa, thereby generating interference light of the first channel. The interference light is guided toward the end 42Ia in the optical fiber 42Pa, and is supplied from the end 42Ia to the optical coupler 62a. The interference light received by the light receiving element 56a is converted into an electrical signal.

[0117] The light propagated to the end 42Ic of the optical fiber 42Pc of the third channel via the optical coupler 62b, 62c enters the optical fiber 42Pc from the end 42Ic, is guided in the optical fiber 42Pc, and propagates to the end 42Oc. The end 42Oc is configured as a partial reflector (an example of a reference light generating unit) that transmits a part of the light propagated to the end 42Oc and reflects another part. That is, the partial reflector is configured to propagate the reference light toward the light receiving element (an example of a light receiving unit) in the third channel as the light receiving channel. As a result, the reference light propagates in the light receiving channel, thereby reducing the influence of interference such as vibration and temperature change.

[0118] The collimating lens 22c is provided with a shading plate 24c configured as a one-way passing element, and the light transmitted through the end 42Oc is shielded by the shading plate 24c. The shading plate 24c may be configured as an absorption type ND (Neutral Density) filter, for example. Thus, the third channel can be configured as a light receiving channel that does not output a light beam of the measuring light, thereby reducing the light spot of the measuring light. In addition, an isolator may be used instead of the shading plate 24c. Another part of the light propagating to the end 42Oc is reflected by the end 42Oc as reference light.

[0119] The reference light reflected by the end 42Oc and the measurement light reflected by the measured object T and incident on the end 42Oc of the third channel interfere with each other in the end 42Oc, generating interference light of the third channel. The interference light is guided toward the end 42Ic in the optical fiber 42Pc and supplied from the end 42Ic to the optical coupler 62c. The interference light received by the light receiving element 56c is converted into an electrical signal.

[0120] Figure 5C FIG. 1 is a diagram for explaining another example of the structure of the displacement sensor 10 according to the present disclosure. Figure 5C The structure of the displacement sensor 10 shown in FIG. Figure 5B The difference in the structure of the displacement sensor 10 shown in FIG. Figure 5B The description of the same parts of the displacement sensor 10 as shown will be appropriately omitted.

[0121] The displacement sensor 10 is configured to include a first channel, a second channel, and a third channel. That is, the optical path including the optical fiber 42Pa in the optical fiber cable 40 and the sensor head 20 constitutes the first channel. In addition, the optical path including the optical fiber 42Pb in the optical fiber cable 40 and the sensor head 20 constitutes the second channel. In addition, the optical path including the optical fiber 42Pc in the optical fiber cable 40 and the sensor head 20 constitutes the third channel.

[0122] exist Figure 5CIn the example of the structure of the displacement sensor 10 shown in FIG. 1 , the first channel is configured as a light receiving channel, the second channel is configured as a light projecting channel, and the third channel is configured as a light receiving channel. Figure 5C The displacement sensor 10 shown does not include the collimating lenses 22a, 22b, 22c, the light receiving element 56b, the amplifier circuit 57b, and the AD converter 58b. Figure 5C The displacement sensor 10 shown has a reference light generating element 25. Here, the reference light generating element 25 is an example of a reference light generating unit configured to receive reference light by at least any one of a plurality of light receiving channels. The reference light generating element 25 may also be formed by a transparent component. The raw material of the component is not particularly limited, and may be, for example, resin, glass, etc. A reflecting surface 26 that reflects a portion of the light propagated from the end 42Ob of the optical fiber 42Pb of the second channel is provided on the reference light generating element 25. The reflecting surface 26 may be formed, for example, by evaporating aluminum, or by applying a coating that becomes a diffuser.

[0123] The light branched to the main interferometer 10A propagates toward the optical coupler 62 b , and further propagates from the optical coupler 62 b to the end 42I b of the optical fiber 42Pb of the second channel of the optical fiber cable 40 .

[0124] The light incident on the optical fiber 42Pb from the end 42Ib is guided in the optical fiber 42Pb and propagates to the end 42Ob.

[0125] Part of the light propagating to the end 42Ob is incident on the sensor head 20 as measurement light through the end 42Ob, and in the sensor head 20, it passes through the reference light generating element 25 and the objective lens 21 to be irradiated to the measurement target T, and is reflected by the measurement target T. Then, the measurement light reflected by the measurement target T is respectively received by the first channel, the second channel, and the third channel of the displacement sensor 10. That is, part of the measurement light reflected by the measurement target T is incident on the end 42Oa of the optical fiber 42Pa via the objective lens 21 and the collimating lens 22a, and the other part is incident on the end 42Oc of the optical fiber 42Pc via the objective lens 21 and the collimating lens 22c.

[0126] Another part of the light propagating in the optical fiber 42Pb to the end 42Ob is reflected by the reflection surface 26 of the reference light generating element 25 as reference light, and then enters the optical fiber 42Pa from the end 42Oa of the optical fiber 42Pa, and also enters the optical fiber 42Pc from the end 42Oc of the optical fiber 42Pc.

[0127] The reference light reflected by the reflection surface 26 of the reference light generating element 25 and incident from the end 42Oa of the optical fiber 42Pa and the measurement light reflected by the measurement object T and incident on the end 42Oa of the first channel interfere with each other in the end 42Oa, thereby generating interference light of the first channel. The interference light is guided toward the end 42Ia in the optical fiber 42Pa, and is supplied from the end 42Ia to the optical coupler 62a. The interference light received by the light receiving element 56a is converted into an electrical signal.

[0128] The reference light reflected by the reflection surface 26 of the reference light generating element 25 and incident from the end 42Oc of the optical fiber 42Pc and the measurement light reflected by the measurement object T and incident on the end 42Oc of the third channel interfere in the end 42Oc to generate interference light of the third channel. The interference light is guided toward the end 42Ic in the optical fiber 42Pc and supplied from the end 42Ic to the optical coupler 62c. The interference light received by the light receiving element 56c is converted into an electrical signal.

[0129] Figure 5D 1 is a diagram for explaining another example of the structure of the displacement sensor 10 according to the present disclosure. Figure 5D As shown, 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 scanning light source 51, an optical amplifier 52, an isolator 53, a plurality of optical couplers 54, 54b, 54h, 54i, 54j, a plurality of light receiving elements (e.g., photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) conversion units (e.g., analog-to-digital converters) 58a to 58c, a processing unit (e.g., a processor) 59, a balance detector 60, and a correction signal generation unit 61. The optical fiber cable 40 includes optical fibers 42Pa to 42Pc and optical fibers 43Pa to 43Pc.

[0130] For example, the displacement sensor 10 is configured to include a first channel, a second channel, and a third channel. Here, some of the channels may also be configured to include a plurality of adjacent optical paths (optical fibers). Figure 5D As an example, the first channel and the third channel are configured to include a plurality of adjacent optical paths (optical fibers). That is, the optical path including the optical fibers 42Pa and 43Pa in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22a constitute the first channel. In addition, the optical path including the optical fibers 42Pc and 43Pc in the optical fiber cable 40 and the sensor head 20, and the collimating lens 22c constitute the third channel.

[0131] In other words, the first channel includes an optical fiber 42Pa (an example of the first optical fiber) for propagating the measurement light and an optical fiber 43Pa (an example of the second optical fiber) for propagating the reference light. The third channel includes an optical fiber 42Pc (an example of the first optical fiber) for propagating the measurement light and an optical fiber 43Pc (an example of the second optical fiber) for propagating the reference light.

[0132] exist Figure 5D In the example of the structure of the displacement sensor 10 shown, the first channel is configured as a light receiving channel, the second channel is configured as a light projecting channel and a light receiving channel, and the third channel is configured as a light receiving channel.

[0133] The light projected from the wavelength scanning light source 51 is amplified by the optical amplifier 52 and branched to the main interferometer 10A side and the sub-interferometer 10B side by the optical coupler 54 via the isolator 53. However, the light branched to the main interferometer 10A side is further branched into measurement light and reference light by the optical coupler 54f.

[0134] The measurement light 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, and is irradiated onto the measurement object T, and is reflected by the measurement object T. Then, the measurement light reflected by the measurement object T is received by the first channel and the third channel of the displacement sensor 10, respectively. That is, a part of the measurement light reflected by the measurement object T is incident on the end 42Oa of the optical fiber 42Pa via the objective lens 21 and the collimating lens 22a, and the other part is incident on the end 42Oc of the optical fiber 42Pc via the objective lens 21 and the collimating lens 22c.

[0135] The measuring light that is irradiated to the object T via the end 42Ob of the optical fiber 42Pb, is reflected by the object T, and enters the end 42Oa of the optical fiber 42Pa. The measuring light is guided in the optical fiber 42Pa and supplied from the end 42Ia to the optical coupler 54h. The measuring light that is irradiated to the object T via the end 42Ob of the optical fiber 42Pb, is reflected by the object T, and enters the end 42Oc of the optical fiber 42Pc. The measuring light is guided in the optical fiber 42Pc and supplied from the end 42Ic to the optical coupler 54j.

[0136] On the other hand, the reference light branched by the optical coupler 54f is further branched by the optical coupler 54g in the directions of the ends 43Ia and 43Ic of the optical fiber cable 40. The reference light incident on the ends 43Ia and 43Ic of the optical fiber cable 40 is guided in the optical fibers 43Pa and 43Pc of the optical fiber cable 40, respectively. Ends 43Oa and 43Oc are provided on the opposite sides of the optical fibers 43Pa and 43Pc to the ends 43Ia and 43Ic. The reference light guided in the optical fibers 43Pa and 43Pc is supplied from the ends 43Oa and 43Oc to the optical couplers 54h and 54j.

[0137] In the optical coupler 54h, the measuring light and the reference light interfere with each other to generate interference light, which is received by the light receiving element 56a and converted into an electrical signal. The measuring light is irradiated onto the measuring object T via the end 42Ob of the optical fiber 42Pb, is reflected by the measuring object T, and is incident on the end 42Oa of the optical fiber 42Pa and output from the end 42Ia. The reference light is output from the optical coupler 54g and is guided into the optical fiber 43Pa in the optical fiber cable 40. In other words, the optical coupler 54f branches into measuring light and reference light, and interference light corresponding to the optical path length difference between the measuring light (the optical path from the optical coupler 54f via the optical coupler 54b, the optical fiber 42Pb, the collimating lens 22b, and the objective lens 21, which is reflected by the measuring object T, and reaches the optical coupler 54h via the objective lens 21, the collimating lens 22a, and the optical fiber 42Pa) and the reference light (the optical path from the optical coupler 54f via the optical coupler 54g, which is guided in the optical fiber 43Pa, and reaches the optical coupler 54h) is generated. The interference light is received by the light receiving element 56a and converted into an electrical signal.

[0138] In the optical coupler 54j, the measuring light and the reference light interfere with each other to generate interference light, which is received by the light receiving element 56c and converted into an electrical signal. The measuring light is irradiated onto the measuring object T via the end 42Ob of the optical fiber 42Pb, is reflected by the measuring object T, and is incident on the end 42Oc of the optical fiber 42Pc and is output from the end 42Ib. The reference light is output from the optical coupler 54g and is guided into the optical fiber 43Pc in the optical fiber cable 40. In other words, the optical coupler 54f branches into measuring light and reference light, and interference light corresponding to the optical path length difference between the measuring light (the optical path from the optical coupler 54f via the optical coupler 54b, the optical fiber 42Pb, the collimating lens 22b, and the objective lens 21, which is reflected by the measuring object T, and reaches the optical coupler 54j via the objective lens 21, the collimating lens 22c, and the optical fiber 42Pc) and the reference light (the optical path from the optical coupler 54f via the optical coupler 54g, which is guided in the optical fiber 43Pc, and reaches the optical coupler 54j) is generated. The interference light is received by the light receiving element 56c and converted into an electrical signal.

[0139] In addition, the light receiving elements 56a to 56c may be balanced photodetectors, for example.

[0140] In this way, the main interferometer 10A has a three-level optical path (three channels), and two interference lights corresponding to the difference in optical path length between the measurement light and the reference light are generated. The measurement light is irradiated to the measurement object T via the end 42Ob of the optical fiber 42Pb, and then reflected by the measurement object T and input into the optical couplers 54h and 54j. The reference light is input into the optical couplers 54h and 54j via the optical couplers 54f and 54g and the optical fiber cable 40.

[0141] Alternatively, the optical path length difference between the measurement light and the reference light may be set to be different in the two channels, for example, by setting the optical path length of the optical coupler 54g to be different from that of the optical couplers 54h and 54j.

[0142] Then, based on the interference light obtained from each, the distance to the measurement target object T and the like are measured (multi-channel).

[0143] [Sensor head structure] Here, the structure of the sensor head used for the displacement sensor 10 will be described. Fig. 6A is a perspective view showing a schematic structure of the sensor head 20. Figure 6B is a schematic diagram showing the internal structure of the sensor head.

[0144] like Fig. 6A As shown, the sensor head 20 accommodates the objective lens 21 and the collimating lens in the lens holder 23. For example, the size of the lens holder 23 is as follows: 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. The sensor head 20 is connected to the optical fiber cable 40.

[0145] like Figure 6B As shown in FIG. 1 , an objective lens 21 and three collimating lenses 22a to 22c are accommodated in the lens holder 23. Light from the optical fiber for guiding the measuring light included in the optical fiber cable 40 is guided to the collimating lenses 22a to 22c respectively, and then the light passing through the three collimating lenses 22a to 22c is irradiated to the measuring object T via the objective lens 21. Figure 6B In the example shown, three collimator lenses are shown, but the number of collimator lenses may be the same as the number of optical fibers included in the optical fiber cable 40 that guide the measuring light.

[0146] In this way, the optical fiber cables 40 and the collimator lenses 22 a to 22 c are held by the lens holder 23 together with the objective lens 21 , thereby constituting the sensor head 20 .

[0147] Furthermore, the lens holder 23 constituting the sensor head 20 may be made of a metal (for example, A2017) that can be processed with high strength and high precision.

[0148] Figure 7 30 is a block diagram for explaining signal processing in the controller 30. Figure 7 As shown, the controller 30 includes a plurality of light receiving elements 71 a to 71 e , a plurality of amplifier circuits 72 a to 72 c , a plurality of AD converters 74 a to 74 c , a processing unit 75 , a differential amplifier circuit 76 , and a correction signal generator 77 .

[0149] In the controller 30, as Figure 5A As shown, light projected from the wavelength scanning light source 51 is branched to the main interferometer 10A and the sub-interferometer 10B through the optical coupler 54, and the distance value to the measurement target T is calculated by processing the main interference signal and the sub-interference signal obtained from each.

[0150] The plurality of light receiving elements 71a to 71c correspond to Figure 5A The light receiving elements 56a to 56c shown receive the main interference signals from the main interferometer 10A, respectively, and output them as current signals to the amplifier circuits 72a to 72c, respectively.

[0151] The plurality of amplifier circuits 72 a to 72 c convert the current signal into a voltage signal (IV conversion) and amplify the voltage signal.

[0152] The plurality of AD conversion units 74a to 74c correspond to Figure 5A The AD converters 58 a to 58 c shown convert the voltage signal into a digital signal (AD conversion) based on the K clock from the correction signal generator 77 described later.

[0153] The processing unit 75 is equivalent to Figure 5A The processing unit 59 shown 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 object T.

[0154] The plurality of light receiving elements 71d to 71e and the differential amplifier circuit 76 correspond to Figure 5A The balanced detector 60 shown receives the interference light in the sub-interferometer 10B, outputs a phase-inverted interference signal, removes noise by removing the difference between the two signals, amplifies the interference signal and converts it into a voltage signal.

[0155] The correction signal generating unit 77 corresponds to Figure 5A The correction signal generating unit 61 shown in the figure binarizes the voltage signal through a comparator, generates a K clock and outputs it to the AD conversion units 74a to 74c. The K clock needs to be generated at a higher frequency than the analog signal of the main interferometer 10A, so it is necessary to multiply the frequency (for example, 8 times) by the correction signal generating unit 77 to make it high frequency.

[0156] Figure 8 4 is a flowchart showing a method of calculating the distance to the measurement object T executed by the processing unit 59 in the controller 30. Figure 8 As shown, the method includes steps S31 to S34.

[0157] In step S31 , the processing unit 59 converts the frequency of the waveform signal (voltage vs. time) into a frequency spectrum (voltage vs. frequency) using the following FFT. Fig.9A2 is a diagram showing how a waveform signal (voltage vs. time) is frequency-converted into a spectrum (voltage vs. frequency).

[0158]

Mathematical formula 1

[0159] N: number of data points In step S32 , the processing unit 59 converts the frequency spectrum (voltage vs. frequency) distance into frequency spectrum (voltage vs. distance). Fig. 9B 2 is a diagram showing how a frequency spectrum (voltage vs. frequency) is converted into a frequency spectrum (voltage vs. distance) by distance.

[0160] In step S33 , the processing unit 59 calculates a distance value corresponding to the peak value based on the frequency spectrum (voltage vs. distance). Fig. 9C is a diagram showing a case where a peak value is detected based on a spectrum (voltage vs. distance) and a distance value corresponding thereto is calculated. Fig. 9C As shown, here, in the three channels, peak values ​​are detected based on the spectrum (voltage vs. distance), and the distance values ​​corresponding to the peak values ​​are calculated.

[0161] In step S34, the processing unit 59 averages the distance values ​​calculated in step S33. Specifically, in step S33, the processing unit 59 detects peak values ​​based on the spectrum (voltage vs. distance) in each of the three channels and calculates the distance values ​​corresponding thereto, and then averages them and outputs the averaged calculation result as the distance to the measurement object T.

[0162] In addition, in step S34, when the processing unit 59 averages the distance values ​​calculated in step S33, it is preferred to average the distance values ​​for which the SNR is greater than the threshold value. For example, in any of the three channels, although a peak is detected based on its spectrum (voltage vs. distance), if the SNR is less than the threshold value, it is determined that the reliability of the distance value calculated based on the spectrum is low and is not adopted.

[0163] Next, the present disclosure will be described in detail as a specific embodiment, focusing on the more characteristic structure, function and properties. Figure 1 9, the displacement sensor 10, the optical interference ranging sensor includes all or part of the basic structure, function and properties and the use Figure 1 The structure, function and properties included in the displacement sensor 10 described in Figure 9 are the same.

[0164] <Implementation Method>

[0165] [Structure of optical fiber cable] Fig. 10AFIG. 1 is a diagram showing a specific example of the structure of the optical fiber cable involved in the present disclosure. Fig. 10A , a schematic diagram of an optical fiber cable 44 is shown as an example.

[0166] The optical fiber cable 44 is, for example, composed of three optical fibers 44Pa, 44Pb, and 44Pc each covered with a resin loose tube having a diameter of about 0.9 mm. Fig. 10A The three shown may also be two or more than four.

[0167] At least one of the optical fibers 44Pa, 44Pb, and 44Pc may also be configured as a light-projecting channel for projecting measurement light to the measurement object. In addition, at least any number of the optical fibers 44Pa, 44Pb, and 44Pc may also be configured as a light-receiving channel for receiving measurement light projected by the light-projecting channel and reflected by the measurement object.

[0168] Fiber optic cable (FC) connectors 44Ca, 44Cb, 44Cc for connection to other devices such as the controller 30 are provided at respective ends of the optical fibers 44Pa, 44Pb, and 44Pc.

[0169] The three optical fibers 44Pa, 44Pb, and 44Pc are collectively inserted into an optical cable 44FC made of polyvinyl chloride (PVC) with a diameter of about 30 mm, for example. The three optical fibers 44Pa, 44Pb, and 44Pc are housed in an aluminum housing 44TH disposed adjacent to the optical cable 44FC via a rubber sheath 44B. The aluminum housing 44TH is connected to other equipment such as the sensor head 20, for example.

[0170] Fig. 10B It is shown from Fig. 10A FIG. 4 is an example of a schematic diagram of the end of the optical fiber cable 44 as viewed from the arrow 44D shown. Fig. 10B As shown, at the end of the optical fiber cable 44, the ends 44Oa, 44Ob, and 44Oc of the three optical fibers 44Pa, 44Pb, and 44Pc are formed. The three optical fibers 44Pa, 44Pb, and 44Pc may be respectively clamped and fixed by two bases formed of glass or the like in an aluminum housing 44TH, for example. The ends 44Pa, 44Pb, and 44Pc correspond to Figure 5A Ends 42Oa, 42Ob, 42Oc are shown. Ends 44Pa, 44Pb, 44Pc may also be configured as partial reflectors for generating reference light.

[0171] Fig.11A FIG. 1 is a diagram showing another specific example of the structure of the optical fiber cable involved in the present disclosure. Fig.11A , a schematic diagram of an optical fiber cable 45 is shown as an example.

[0172] The optical fiber cable 45 is configured such that three optical paths 45Pa, 45Pb, and 45Pc as cores are formed inside the cladding of one optical fiber. The number of optical paths (cores) included in the optical fiber cable 45 is not limited to Fig.11A The three shown may also be two or more than four.

[0173] At least one of the optical paths 45Pa, 45Pb, and 45Pc may also be configured as a light-projecting channel for projecting measurement light to the measurement object. In addition, at least any number of the optical paths 45Pa, 45Pb, and 45Pc may also be configured as a light-receiving channel for receiving measurement light projected by the light-projecting channel and reflected by the measurement object.

[0174] An MPO (Multi-Fiber Push On) connector 45C is provided at one end of the optical fiber cable 45 for connecting to other devices such as the controller 30 , and a ferrule 45F is provided at the other end of the optical fiber cable 45 for connecting to other devices such as the sensor head 20 .

[0175] Fig. 11B It is shown from Fig.11A FIG. 4 is an example of a schematic diagram of the end of the optical fiber cable 45 as viewed from the arrow 45D shown. Fig. 11B As shown, at the end of the optical fiber cable 45, three optical paths 45Pa, 45Pb, and 45Pc are formed with respective ends 45Oa, 45Ob, and 45Oc. The ends 45Oa, 45Ob, and 45Oc correspond to, for example, Figure 5A Ends 42Oa, 42Ob, 42Oc are shown. Ends 45Oa, 45Ob, 45Oc may also be configured as partial reflectors for generating reference light.

[0176] The embodiments described above are intended to facilitate the understanding of the present invention, rather than to limit the present invention. The various elements and their configurations, materials, conditions, shapes, and sizes of the embodiments are not limited to the illustrated contents and can be appropriately changed. In addition, the structures shown in different embodiments can be partially replaced or combined with each other.

[0177] Description of Reference Numerals 1...Sensor system, 10...Displacement sensor, 10A...Main interferometer, 10B...Sub-interferometer, 11...Control device, 12...Control signal input sensor, 13...External connection device, 20...Sensor head, 21...Objective lens, 22a to 22c...Collimating lens, 23...Lens holder, 24a, 24c...Shading plate, 25...Reference light generating element, 26...Reflection surface, 30...Controller, 31...Display unit, 32...Setting unit, 33...External interface (I / F) unit, 34...External I / F unit, 35...Optical fiber cable connection unit, 35…external storage unit, 36…measurement processing unit, 40…optical fiber cable, 41P…optical fiber, 41Pa to 41Pc…optical fiber, 42Ia, 42Ib, 42Ic…end, 42Oa, 42Ob…end, 42Oa…end, 42Ob…end, 42Oc…end, 42P, 42Pa to 42Pc…optical fiber, 43Ia to 43Ic…end, 43Oa to 43Oc…end, 43Pa to 43Pc…optical fiber, 44…optical fiber cable, 44B…rubber sheath, 44Ca, 44Cb…connector, 44FC…optical cable, 44Oa, 44Ob…end, 44Pa, 44Pb…optical fiber, 44Pa, 44Pb…end, 44TH…aluminum housing, 45…optical fiber cable, 45C…MPO connector, 45F…ferrule, 45Oa, 45Ob…end, 45Pa, 45Pb…optical path, 51…wavelength scanning light source, 52…optical amplifier, 53…isolator, 54, 54b, 54h, 54i, 54j…optical coupler, 54, 54a~54e…optical coupler, 54f, 54g…optical coupler, 54 h, 54i, 54j…optical coupler, 56a~56c…light receiving element, 57a~57c…amplifying circuit, 58a~58c…AD conversion unit, 58a…AD conversion unit, 58b…AD conversion unit, 58c…AD conversion unit, 59…processing unit, 60…balanced detector, 61…correction signal generating unit, 62a~62c…optical coupler, 71a~71e…light receiving element, 74a~74c…AD conversion unit, 75…processing unit, 76…differential amplifier circuit, 77…correction signal generating unit, T…measurement object.

Claims

1. An optical interference ranging sensor, comprising: A light source that projects light while changing its wavelength; an interferometer supplied with the light projected from the light source and generating interference light based on measurement light and reference light, the measurement light being irradiated to the measurement object through the sensor head and reflected, and the reference light following an optical path at least partially different from that of the measurement light; A light receiving unit, receiving the interference light from the interferometer and converting it into an electrical signal; as well as a processing unit that calculates a distance from the sensor head to the measurement object based on the electrical signal; The interferometer comprises: a light projection channel configured to propagate light supplied from the light source toward the sensor head and irradiate the measurement object from the sensor head; as well as a plurality of light receiving channels configured to receive the measurement light reflected by the measurement object and transmit the measurement light toward the light receiving unit; The light projection channel and at least any one of the plurality of light receiving channels also propagate the reference light.

2. The optical interferometric ranging sensor according to claim 1, wherein: The optical interference distance measuring sensor further includes a reference light generating unit configured to generate the reference light by reflecting a part of the light propagating in the light projection channel.

3. The optical interferometric ranging sensor according to claim 2, wherein: The reference light generating unit is configured to propagate the reference light in the light projecting channel toward the light receiving unit.

4. The optical interferometric ranging sensor according to claim 3, wherein: The reference light generator is a partial reflector provided in the optical path of the light in the light projection channel.

5. The optical interferometric ranging sensor according to claim 2, wherein: The reference light generating unit is configured to propagate the reference light toward the light receiving unit through at least one of the plurality of light receiving channels.

6. The optical interferometric ranging sensor according to claim 5, wherein: The reference light generating unit is a reflecting surface, which is provided in the optical path of the light in the light projection channel and reflects the light propagating in the light projection channel toward any one of the light receiving channels.

7. The optical interferometric ranging sensor according to claim 1, wherein: At least one of the plurality of light receiving channels is further configured to transmit light supplied from the light source toward the sensor head. The optical interference distance measuring sensor further includes a reference light generating unit configured to generate the reference light by reflecting a part of the light propagating in at least one of the light receiving channels.

8. The optical interferometric ranging sensor according to claim 7, wherein: The reference light generating unit is a partial reflecting mirror provided in the optical path of the light in at least any one of the light receiving channels.

9. The optical interferometric ranging sensor according to claim 7, wherein: The at least one light receiving channel includes a light shielding portion that shields at least a portion of the light supplied from the light source and propagating toward the sensor head.

10. The optical interferometric ranging sensor according to claim 1, wherein: The light projection channel and the at least one of the plurality of light receiving channels are formed of optical fibers for propagating the measurement light and the reference light.

11. The optical interferometric ranging sensor according to claim 1, wherein: The light projecting channel and the at least one of the plurality of light receiving channels are configured to include a first optical fiber for propagating the measurement light and a second optical fiber for propagating the reference light.

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