CONTROL AND OPTICAL INTERFEROMETRIC DISTANCE SENSOR

Abstract

The present invention reduces the shift in sampling times. A controller (110) is connected via an optical fiber cable (130) to a first sensor head (121) and a second sensor head (122), from which a light beam is emitted onto a target object, and includes: a light source (140); a first main interferometer (151) that generates a first main interference signal; a second main interferometer (152) that generates a second main interference signal; and an auxiliary interferometer (160) that generates an auxiliary interference signal.The controller (110) further includes: a first correction signal generation unit (171) that generates a first correction signal; a delay value generation unit that generates a delay value based on a length difference of the optical paths between an optical path length of a first optical waveguide (131) and an optical path length of a second optical waveguide (132); and a second correction signal generation unit (172) that generates a second correction signal to correct a sampling period of the second main interference signal based on the auxiliary interference signal and the delay value.

Description

TECHNICAL AREA

[0001] The present invention relates to a control system and an optical interferometric distance sensor. BACKGROUND OF THE INVENTION

[0002] In recent years, optical distance sensors that measure the distance to a target object without contact have become widespread. For example, a well-known optical interferometric distance sensor generates an interference light beam from a light beam emitted by a light source with a tuned wavelength, based on a reference light beam and a measurement light beam, and measures the distance to a target object based on this interference light beam.

[0003] An optical frequency-domain reflectometer known from the prior art includes: a tuned light source; an auxiliary interferometer that imparts a predetermined delay time difference to a portion of the output light from the tuned light source in order to generate interference and outputs the result as an auxiliary interference signal; a measuring interferometer that feeds a portion of the output light from the tuned light source into an optical waveguide to be measured, causes a reflected light beam from the optical waveguide to be measured and a portion of the output light from the tuned light source to interfere with each other, and outputs a measuring interference signal; a linearization unit that corrects the nonlinearity of the wavelength tuning of the tuned light source with respect to the measuring interference signal using the auxiliary interference signal;and a Fourier transform unit that performs a Fourier transform on an output signal of the linearization unit and outputs a signal in a frequency domain, wherein the linearization unit comprises a plurality of linearization units, each having a different delay time, and the Fourier transform unit comprises a weighted addition / Fourier transform unit for adding output signals of the plurality of linearization units with different weights and for outputting a Fourier-transformed result (see patent document 1). In this optical frequency domain reflectometer, the nonlinearity of the wave tuning over a wide range of the optical waveguide to be measured is corrected. LIST OF REFERENCE PATENT LITERATURE

[0004] Patent Document 1: JP 2017-181115 A SUMMARY OF THE TECHNICAL PROBLEM

[0005] On the other hand, an optical interferometric distance sensor with a controller and a multitude of sensor heads should cover measurement targets at different distances by changing the lengths of the optical waveguides connecting the controller and the sensor heads between the multitude of sensor heads.

[0006] However, if the optical waveguides in a main interferometer are of different lengths, there may be a shift in the sampling time between a signal from the main interferometer and a signal from an auxiliary interferometer, and a signal generated by interference of the two signals may cause a reduction in signal intensity (signal level).

[0007] The present invention was made in view of the circumstances described above and its object is to provide a control system and an optical interferometric distance sensor that are capable of reducing a shift in the sampling time. SOLUTION TO THE PROBLEM

[0008] A controller according to one aspect of the present disclosure is a controller connected via an optical fiber cable to a first sensor head and a second sensor head, from which a light beam is emitted onto a target object. The controller includes: a light source that projects a light beam while changing a wavelength; a first principal interferometer which, by being fed with the light beam projected by the light source, generates a first principal interference signal based on a first measurement light beam emitted from the first sensor head onto the target object and reflected by the target object, and a first reference light beam traveling along an optical path that differs at least partially from an optical path of the first measurement light beam;a second principal interferometer which, by being fed with the light beam projected from the light source, generates a second principal interference signal based on a second measurement light beam emitted from the second sensor head onto the target object and reflected by the target object, and a second reference light beam which travels along an optical path that differs at least partially from an optical path of the second measurement light beam;and an auxiliary interferometer which, by being fed with the light beam projected from the light source, generates an auxiliary interference signal based on two light beams traveling along different optical paths. The optical fiber cable includes: a first optical fiber connected to the first main interferometer, which carries a light beam from the first main interferometer to the first sensor head, and a light beam from the first sensor head to the first main interferometer;and a second optical waveguide, connected to the second main interferometer, transmits a light beam from the second main interferometer to the second sensor head and transmits a light beam from the second sensor head to the second main interferometer. The optical waveguide has an optical path length that differs from the optical path length of the first optical waveguide. The control system further includes: a first correction signal generation unit, which generates a first correction signal based on the auxiliary interference signal to correct one sampling period of the first main interference signal; a delay value generation unit, which generates a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide and the optical path length of the second optical waveguide;and a second correction signal generation unit which, based on the auxiliary interference signal and the delay value, generates a second correction signal to correct one sampling period of the second main interference signal.

[0009] According to this approach, the delay value is generated based on the optical path length difference between the first and second optical waveguides. The second correction signal, used to correct the sampling period of the second primary interference signal, is then generated based on the auxiliary interference signal and the delay value. This allows for the introduction of a delay in the second primary interference signal corresponding to the optical path length difference between the first and second optical waveguides. Consequently, this can reduce the shift in the sampling time of the second primary interference signal and the decrease in the signal intensity of the sampled digital signal.

[0010] In the aspect described above, the delay value generation unit can include a third optical waveguide that transmits an additional interference signal and has an optical path length based on the length difference of the optical paths.

[0011] According to this aspect, the third optical waveguide, which transmits an additional interference signal and has an optical path length based on the difference in optical path lengths between the first and second optical waveguides, is included. Thus, the delay value can be easily adjusted by changing the length of the optical path of the third optical waveguide.

[0012] In the aspect described above, the delay value generation unit can include a delay line which, in an auxiliary interferometer signal obtained by converting the auxiliary interference signal into an electrical signal, causes a delay in the time axis direction corresponding to the delay value and outputs the auxiliary interferometer signal to the second correction signal generation unit.

[0013] According to this aspect, the delay line is included, which imparts a time-axis delay to the auxiliary interferometer signal (obtained by converting the auxiliary interference signal into an electrical signal) corresponding to the delay value, and outputs the auxiliary interferometer signal to the second correction signal generation unit. Thus, the second correction signal generation unit can easily generate the second correction signal, which is an electrical signal, by outputting the auxiliary interferometer signal with the electrically induced delay.

[0014] In the aspect described above, the second correction signal generation unit can generate a pulse signal, which is the second correction signal, based on a signal obtained by causing a delay in the time axis direction in the auxiliary interferometer signal corresponding to the delay value, which is obtained by converting the auxiliary interference signal into an electrical signal.

[0015] According to this aspect, the second correction signal generation unit generates the pulse signal, which is the second correction signal, based on the signal obtained by applying a delay in the time axis direction to the auxiliary interferometer signal, which is obtained by converting the auxiliary interference signal into an electrical signal. In this way, it is possible to easily adjust (synchronize) the timing for sampling the second main interference signal.

[0016] The aspect described above may further include an AD converter unit that samples a second main interference signal based on the second correction signal, which is obtained by converting the second main interference signal into an electrical signal, and converts the second main interferometer signal into a digital signal.

[0017] In accordance with this aspect, the A / D converter unit is also included, which samples the second main interference signal based on the second correction signal. This second main interference signal is obtained by converting the second main interference signal into an electrical signal, and the second main interferometer signal is then converted into a digital signal. Accordingly, a configuration for converting the second main interferometer signal into a digital signal can easily be achieved, in which one sampling period has been corrected.

[0018] In the aspect described above, the delay value can be set so that an absolute value of a difference to a delay time of a light beam due to the length difference of the optical paths becomes smaller than a minimum sampling period in the AD converter unit.

[0019] According to this principle, the delay value is set so that the absolute value of the difference in the delay time of the light beam due to the length difference of the optical paths is smaller than the minimum sampling period in the A / D converter unit. In this way, a decrease in the signal intensity of the sampled digital signal can be reduced to a predetermined percentage or less, for example, 10% or less.

[0020] The aspect described above may further include a processing unit that measures a distance to the target object based on at least one of the first main interference signal or second main interference signal and the auxiliary interference signal.

[0021] According to this aspect, the processing unit is also included, which measures the distance to the target object based on at least one of the first main interference signals or the second main interference signal and the auxiliary interference signal. Accordingly, a configuration for measuring the distance to the target object can easily be achieved.

[0022] An optical interferometric distance sensor according to one aspect of the present disclosure is an optical interferometric distance sensor comprising a controller and an optical fiber cable configured to be connected to the controller. The controller includes: a light source that projects a beam of light while changing a wavelength; a first principal interferometer which, by being fed with the beam of light projected by the light source, generates a first principal interference signal based on a first measurement light beam emitted from a first sensor head onto a target object and reflected by the target object, and a first reference light beam traveling along an optical path that differs at least partially from an optical path of the first measurement light beam;a second principal interferometer which, by being fed with the light beam projected from the light source, generates a second principal interference signal based on a second measurement light beam emitted from a second sensor head onto the target object and reflected by the target object, and a second reference light beam which travels along an optical path that differs at least partially from an optical path of the second measurement light beam;and an auxiliary interferometer which, by being fed with the light beam projected from the light source, generates an auxiliary interference signal based on two light beams traveling along different optical paths. The optical fiber cable includes: a first optical fiber connected to the first main interferometer, which carries a light beam from the first main interferometer to the first sensor head, and a light beam from the first sensor head to the first main interferometer;and a second optical waveguide, connected to the second main interferometer, transmits a light beam from the second main interferometer to the second sensor head and transmits a light beam from the second sensor head to the second main interferometer. The optical waveguide has an optical path length that differs from the optical path length of the first optical waveguide. The control system further includes: a first correction signal generation unit, which generates a first correction signal based on the auxiliary interference signal to correct one sampling period of the first main interference signal; a delay value generation unit, which generates a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide and the optical path length of the second optical waveguide;and a second correction signal generation unit which, based on the auxiliary interference signal and the delay value, generates a second correction signal to correct one sampling period of the second main interference signal.

[0023] According to this approach, the delay value is generated based on the optical path length difference between the first and second optical waveguides. The second correction signal, used to correct the sampling period of the second primary interference signal, is then generated based on the auxiliary interference signal and the delay value. This allows for the introduction of a delay in the second primary interference signal corresponding to the optical path length difference between the first and second optical waveguides. Consequently, this can reduce the shift in the sampling time of the second primary interference signal and the decrease in the signal intensity of the sampled digital signal. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0024] According to the present invention, the shift in the sampling time can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic external view illustrating in outline a displacement sensor 10 according to the present disclosure. Fig. Figure 2 is a flowchart illustrating a method for measuring a target object T with the displacement sensor 10 according to the present disclosure. Fig. Figure 3 is a functional block diagram illustrating in outline a sensor system 1 in which the displacement sensor 10 is used according to the present disclosure. Fig. Figure 4 is a flowchart illustrating a method for measuring the target object T with the sensor system 1, in which the displacement sensor 10 is used according to the present disclosure. Fig. Figure 5A is a diagram illustrating a principle for measuring the target object T with the displacement sensor 10 according to the present disclosure. Fig. Figure 5B is a diagram illustrating another principle of measuring the target object T with the displacement sensor 10 according to the present disclosure. Fig. Figure 6A is a perspective view illustrating a schematic configuration of a sensor head 20. Fig. Figure 6B is a schematic representation illustrating the internal structure of the sensor head 20. Fig. Figure 7 is a block diagram to illustrate signal processing in a controller 30. Fig. Figure 8 is a flowchart illustrating a procedure for calculating a distance to the target object T, which is executed by a processing unit 59 in the controller 30. Fig. 9A is a diagram illustrating a state in which a frequency conversion is performed to convert a waveform signal (voltage versus time) into a spectrum (voltage versus frequency). Fig. 9B is a diagram illustrating a state in which a distance conversion is performed to convert a spectrum (voltage versus frequency) to a spectrum (voltage versus distance). Fig. 9C is a diagram illustrating a condition in which a peak is detected based on the spectrum (voltage versus distance) and a distance value corresponding to the peak is calculated. Fig. Figure 10 is a schematic diagram illustrating in outline a configuration of an optical interferometric distance sensor 100 according to an embodiment of the present invention. Fig. Figure 11 is a schematic representation illustrating in outline a configuration of another optical interferometric distance sensor 101 according to the embodiment of the present invention. Fig. Figure 12 is a diagram illustrating the sampling times of a first principal interferometer signal and a second principal interferometer signal. Fig. Figure 13 is a diagram illustrating the relationship between the signal intensity of the second main interferometer signal converted into a digital signal and a time difference Δt. Fig. Figure 14 is a schematic diagram illustrating an example of a specific configuration of an auxiliary interferometer 160 and its subsequent stage when three sensor heads are provided. Fig. Figure 15 is a schematic diagram illustrating another example of a specific configuration of the auxiliary interferometer 160 and its subsequent stage when three sensor heads are provided. Fig. Figure 16 is a diagram illustrating variants of interferometers that generate an interference light beam using a measuring light beam and a reference light beam. DESCRIPTION OF THE EXECUTION FORMS

[0025] Each preferred embodiment of the present invention is described in detail below with reference to the drawings. It should be noted that each embodiment described below represents only a specific example of the implementation of the present invention and is not intended to limit the design of the present invention. To facilitate understanding of the description, the same components are designated with the same reference numerals in the drawings wherever possible, and duplicate descriptions may be omitted. Overview of a displacement sensor

[0026] First, a displacement sensor according to the present disclosure is described in its basic features.

[0027] Fig. Figure 1 is a schematic external view illustrating in outline a displacement sensor 10 according to the present disclosure. As in Fig. Figure 1 illustrates that the displacement sensor 10 includes a sensor head 20 and a controller 30 and measures a displacement of a target object T (a distance to the target object T).

[0028] The sensor head 20 and the control unit 30 are connected to each other by an optical fiber 40, and a lens 21 is attached to the sensor head 20. The control unit 30 comprises a display unit 31, a setting unit 32, a section 33 for an external interface (I / F), a section 34 for the connection to the optical fiber, and an external storage unit 35, and further includes a measurement processing unit 36.

[0029] The sensor head 20 illuminates the target object T with a light beam emitted by the controller 30 and receives a light beam reflected from the target object T. The sensor head 20 includes a reference surface that reflects a light beam emitted by the controller 30 and received via the optical fiber 40, causing the light beam to interfere with the light beam reflected from the target object T as described above.

[0030] Although the objective lens 21 is attached to the sensor head 20, it is configured to be attachable and detachable. The objective lens 21 can be replaced by an objective lens with a suitable focal length, which depends on the distance between the sensor head 20 and the target object T, or a variable focal length objective lens can be used.

[0031] Furthermore, during the installation of the sensor head 20, the sensor head 20 and / or the target object T can be installed in such a way that the target object T is positioned accordingly in a measurement region of the displacement sensor 10 by irradiating the target object T with a guide light beam (visible light beam).

[0032] The optical fiber 40 is connected to the connecting section 34 located on the controller 30 and extends from it, connecting the controller 30 and the sensor head 20. Accordingly, the optical fiber 40 is configured to guide a light beam emitted by the controller 30 to the sensor head 20 and also to guide a light beam returning from the sensor head 20 to the controller 30. Various optical fibers of different lengths, widths, materials, or the like can be used as the optical fiber 40, as long as they can be connected to and disconnected from the sensor head 20 and the controller 30.

[0033] The display unit 31 includes, for example, a liquid crystal display, an organic EL display, or the like. The display unit 31 shows a setting value of the displacement sensor 10, the amount of light received from a rear light beam by the sensor head 20, and a measurement result such as a displacement of the target object T (a distance to the target object T) measured by the displacement sensor 10.

[0034] At the setting unit 32, for example, the settings required for measuring the target object T are made by a user operating a mechanical button, a touch panel, or the like. All or some of the required settings can be made in advance or via an external connection device (not illustrated) connected to the external I / F section 33. Furthermore, the external connection device can be wired or wireless via a network.

[0035] Here, the external I / F section 33 includes, for example, Ethernet (registered trademark), RS232C, an analog output, and the like. The external I / F section 33 can be connected to another connection device so that the necessary settings can be made from the external connection device, or the measurement results from the displacement sensor 10 and the like can be output to the external connection device.

[0036] The settings required for measuring the target object T can be made by the controller 30 by retrieving the data stored in the external storage unit 35. The external storage unit 35 is, for example, an additional storage device such as a USB (Universal Serial Bus) memory card, on which the settings required for measuring the target object T are stored in advance.

[0037] The measurement processing unit 36 ​​in the controller 30 includes, for example, a wavelength-tuned light source that projects a light beam with a constantly changing wavelength, a light receiving element that receives a backlight beam from the sensor head 20 and converts the backlight beam into an electrical signal, a signal processing circuit that processes the electrical signal, and the like. Various processes are carried out in the measurement processing unit 36 ​​via the control unit, the storage unit, and the like, so that ultimately, based on the backlight beam from the sensor head 20, a displacement of the target object T (a distance to the target object T) is calculated. These processes are described in detail below.

[0038] Fig. Figure 2 is a flowchart illustrating a method for measuring the target object T with the displacement sensor 10 according to the present disclosure. As in Fig. As illustrated in point 2, the procedure includes steps S11 to S14.

[0039] In step S11, the sensor head 20 is installed. For example, a guide light beam is emitted from the sensor head 20 onto the target object T, so that the sensor head 20 is installed in a suitable position with reference to the guide light.

[0040] In particular, the amount of light received from a rear light beam by the sensor head 20 can be displayed on the display unit 31 of the controller 30, and a user can adjust the orientation of the sensor head 20, the distance (height position) to the target object T, and the like, while checking the amount of light received. Basically, the amount of light reflected from the target object T is large when the sensor head 20 can emit a light beam perpendicular (at an angle closer to the perpendicular) to the target object T, and the amount of light received from the rear light beam by the sensor head 20 is also large.

[0041] The objective lens 21 can be replaced by a lens having a suitable focal length, which depends on the distance between the sensor head 20 and the target object T.

[0042] Furthermore, if suitable settings cannot be made for measuring the target object T (e.g., if the required amount of light received for the measurement cannot be obtained, the focal length of the objective lens 21 is unsuitable, or similar), the user can be notified accordingly by displaying an error, a message about incomplete settings, or similar on the display unit 31 or by sending a message to an external communication device.

[0043] In step S12, various states are set for the measurement of the target object T. For example, the user operates the setting unit 32 of the controller 30 to set calibration data (e.g., a linearity correction function) that applies only to the sensor head 20.

[0044] Furthermore, various parameters can be set. For example, a sampling time, a measuring range, a threshold value to determine whether a measurement result is normal or abnormal, and the like can be set. Additionally, a measurement period can be set according to the properties of the target object T, such as its reflectance and material, and a measurement mode or similar can be set according to the material of the target object T.

[0045] The measurement states and the various parameters are set by actuating the setting unit 32 in the control unit 30, but can also be set from an external connection device or by retrieving data from the external storage unit 35.

[0046] In step S13, the target object T is measured by the measuring head 20 installed in step S11 according to the measurement states and various parameters set in step S12.

[0047] Specifically, in the measurement processing unit 36 ​​of the controller 30, a light beam from the light source with a tuned wavelength is projected, a backlight beam from the sensor head 20 is received by the light receiving element, and frequency analysis, distance conversion, peak detection, and the like are performed by the signal processing circuit, whereby a displacement of the target object T (a distance to the target object T) is calculated. Specific details of the measurement processing are described later.

[0048] In step S14, the measurement result measured in step S13 is output. For example, the displacement of the target object T (the distance to the target object T) measured in step S13 or the like is displayed on the display unit 31 in the controller 30 or output to an external connection device.

[0049] Furthermore, the determination of whether the displacement of the target object T measured in step S13 (the distance to the target object T) is within a normal range or abnormal, based on the threshold set in step S12, can be displayed or output as a measurement result. Additionally, the measurement states set in step S12, the various parameters, the measurement mode, and the like can be displayed or output together. Overview of a system that includes the displacement sensor

[0050] Fig. Figure 3 is a functional block diagram illustrating the basic features of a sensor system 1 in which the displacement sensor 10 is used according to the present disclosure. As in Fig. As illustrated in Figure 3, the sensor system 1 includes the displacement sensor 10, a control device 11, a control signal input sensor 12, and an external connection device 13. The displacement sensor 10 is connected to the device 11 and the external connection device 13, for example, via a communication cable or an external connection cable (e.g., with an external input line, an external output line, and a power supply line), and the device 11 and the control signal input sensor 12 are connected to each other via a signal line.

[0051] As with reference to Fig. 1 and Fig. As described in section 2, the displacement sensor 10 measures the displacement of the target object T (the distance to the target object T). The displacement sensor 10 can then output the measurement result or similar information to the control device 11 and the external connection device 13.

[0052] The control device 11 is, for example, a programmable logic controller (PLC) and gives the displacement sensor 10 different instructions when the displacement sensor 10 measures the target object T.

[0053] For example, the control device 11 can output a measurement time signal to the displacement sensor 10 based on an input signal from the control signal input sensor 12, which is connected to the control device 11, or output a zero reset command signal (a signal to set the current measured value to 0) or the like to the displacement sensor 10.

[0054] The control signal input sensor 12 outputs an ON / OFF signal to the control device 11, indicating the time at which the displacement sensor 10 measures the target object T. For example, the control signal input sensor 12 can be installed near a production line on which the target object T is transported, and detect that the target object T has reached a predetermined position, and output an ON / OFF signal to the control device 11.

[0055] The external connection device 13 is, for example, a PC that can be operated by the user to make various settings for the displacement sensor 10.

[0056] As a concrete example, a measurement mode, an operating mode, a measurement period, a material of the target object T and the like are set.

[0057] When setting the measurement mode, an “internal synchronous measurement mode” is selected, in which the measurement is started periodically within the control device 11, an “external synchronous measurement mode” in which the measurement is started in response to an input signal from outside the control device 11, or similar.

[0058] When setting the operating mode, an “operating mode” in which the target object T is actually measured, a “setting mode” in which a state for the measurement of the target object T is set, or the like, is selected.

[0059] The measurement period is the time span during which the target object T is measured and can be adjusted according to the reflectance of the target object T. Even if the reflectance of the target object T is low, it can still be measured adequately by setting a correspondingly long measurement period.

[0060] For the target object T, a “rough surface mode” is selected, which is suitable in the case where diffuse reflection as a component of the reflected light beam is relatively large, a “reflective surface mode” is selected in the case where specular reflection as a component of the reflected light beam is relatively large, or a “standard mode” which lies between these modes.

[0061] In this way, the target object T can be measured with higher accuracy by adjusting the reflectance and material of the target object T accordingly.

[0062] Fig. Figure 4 is a flowchart illustrating a method for measuring the target object T with the sensor system 1, in which the displacement sensor 10 is used according to the present disclosure. As in Fig. As illustrated in Figure 4, the procedure is a procedure for the external synchronous measurement mode described above, which includes steps S21 to S24.

[0063] In step S21, sensor system 1 detects the target object T that is to be measured. Specifically, the control signal input sensor 12 detects that the target object T has reached a predefined position on a production line.

[0064] In step S22, the sensor system 1 gives an instruction to measure the target object T, detected in step S21, with the displacement sensor 10. Specifically, the control signal input sensor 12 outputs an ON / OFF signal to the control device 11 to give an instruction to measure the target object T detected in step S21, and the control device 11 outputs a measurement time signal to the displacement sensor 10 based on the ON / OFF signal to instruct the displacement sensor 10 to measure the target object T.

[0065] In step S23, the target object T is measured by the displacement sensor 10. Specifically, the displacement sensor 10 measures the target object T based on the measurement instruction received in step S22.

[0066] In step S24, the sensor system 1 outputs the measurement result measured in step S23. In particular, the displacement sensor 10 displays the result of the measurement processing on the display unit 31 or outputs the result via the external I / F section 33 to the control device 11, the external connection device 13, or the like.

[0067] With reference to Fig. Section 4 described the method for the external synchronous measurement mode, in which the target object T is measured when it is detected by the control signal input sensor 12, 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 time signal based on a preset period is generated to instruct the displacement sensor 10 to measure the target object T.

[0068] Next, a principle for measuring the target object T with the displacement sensor 10 is described according to the present disclosure.

[0069] Fig. Figure 5A is a diagram illustrating the principle for measuring the target object T with the displacement sensor 10 according to the present disclosure. As in Fig. As illustrated in Figure 5A, the displacement sensor 10 includes the sensor head 20 and the controller 30. The sensor head 20 includes the objective lens 21 and a variety of collimator lenses 22a to 22c. The control unit 30 includes the light source 51 with tuned wavelength, an optical amplifier 52, a plurality of isolators 53 and 53a to 53b, a plurality of optocouplers 54 and 54a to 54e, an attenuator 55, a plurality of light receiving elements (e.g. photodetectors (PD)) 56a to 56c, a plurality of amplifier circuits 57a to 57c, a plurality of analog-to-digital (AD) converter units (e.g. analog-to-digital converters) 58a to 58c, a processing circuit (e.g. a processor) 59, a balance detector 60 and a correction signal generation unit 61.

[0070] The tuned-wavelength light source 51 projects laser light whose wavelength is tuned. For example, with the tuned-wavelength light source 51, a mode jump is less likely to occur when a method for modulating a vertical-wavelength surface-emitting laser (VCSEL) with a current is applied, because the resonator length is short and the wavelength can be easily changed, so the tuned-wavelength light source 51 can be obtained at low cost.

[0071] The optical amplifier 52 amplifies a light beam projected from the light source 51 with a tuned wavelength. The optical amplifier 52 can be, for example, an erbium-doped fiber amplifier (EDFA) or an optical amplifier for 1550 nm.

[0072] The insulator 53 is an optical element that allows the incident light beam to pass through in one direction and can be arranged immediately after the light source 51 with tuned wavelength to prevent the influence of noise generated by a reflected light beam.

[0073] As described above, the light beam projected by the light source 51 with a tuned wavelength is amplified by the optical amplifier 52, passes through the insulator 53, and is split by the optocoupler 54 into a main interferometer and an auxiliary interferometer. For example, with a ratio of the light beam splitting into the main interferometer and the auxiliary interferometer by the optocoupler 54b, 90% or more of the light beam can be split into the main interferometer.

[0074] The light beam split into the main interferometer is further split by the optocoupler 54a of a first stage in the direction of the sensor head 20 and in the direction of the optocoupler 54b of a second stage.

[0075] The light beam, split by the optocoupler 54a of the first stage towards the sensor head 20, emerges from a front end of an optical waveguide in the sensor head 20, passes through the collimator lens 22a and the objective lens 21, and strikes the target object T. The front end (end face) of the optical waveguide then serves as a reference surface, and the light beam reflected from the reference surface and the light beam reflected from the target object T interfere with each other to produce an interference light beam. The interference light beam returns to the optocoupler 54a of the first stage and is then received by the light receiving element 56a to be converted into an electrical signal.

[0076] The light beam split by the optocoupler 54a of the first stage towards the optocoupler 54b of the second stage passes through the insulator 53a to the optocoupler 54b of the second stage and is further split by the optocoupler 54b of the second stage towards the sensor head 20 and towards the optocoupler 54c of a third stage. Similar to the first stage, the light beam split by the optocoupler 54b towards the sensor head 20 is guided from the front end of the optical waveguide in the sensor head 20 through the collimator lens 22b and the objective lens 21 and strikes the target object T.The front end (end face) of the optical waveguide then serves as a reference surface, and the light beam reflected from the reference surface and the light beam reflected from the target object T interfere with each other to generate an interference light beam. This interference light beam returns to the optocoupler 54b of the second stage and is then split by the optocoupler 54b towards the insulator 53a and towards the light receiving element 56b. The light beam split by the optocoupler 54b towards the light receiving element 56b is received by the light receiving element 56b and converted into an electrical signal.On the other hand, the insulator 53a transmits the light beam from the optocoupler 54a of the preceding stage to the optocoupler 54b of the subsequent stage and blocks the light beam from the optocoupler 54b of the subsequent stage to the optocoupler 54a of the preceding stage, so that the light beam split by the optocoupler 54b in the direction of the insulator 53a is blocked.

[0077] The light beam split by the optocoupler 54b of the second stage towards the optocoupler 54c of the third stage passes through the insulator 53b to the optocoupler 54c of the third stage and is further split by the optocoupler 54c of the third stage towards the sensor head 20 and towards the attenuator 55. Similar to the first and second stages, the light beam split by the optocoupler 54c towards the sensor head 20 is guided from the front end of the optical waveguide in the sensor head 20 through the collimator lens 22c and the objective lens 21 and strikes the target object T.The front end (end surface) of the optical waveguide then serves as a reference surface, and the light beam reflected from the reference surface and the light beam reflected from the target object T interfere with each other to generate an interference light beam. This interference light beam returns to the third-stage optocoupler 54c and is then split by the optocoupler 54c towards the insulator 53b and towards the light-receiving element 56c. The light beam split by the optocoupler 54c towards the light-receiving element 56c is received by the light-receiving element 56c and converted into an electrical signal.On the other hand, the insulator 53b transmits the light beam from the optocoupler 54b of the preceding stage to the optocoupler 54c of the subsequent stage and blocks the light beam from the optocoupler 54c of the subsequent stage to the optocoupler 54b of the preceding stage, so that the light beam split by the optocoupler 54c in the direction of the insulator 53b is blocked.

[0078] It should be noted that the light beam which is split by the optocoupler 54c of the third stage in a direction other than the direction to the sensor head 20 is not used for measuring the target object T and is therefore preferably attenuated by the attenuator 55, such as an end cap, so that it is not reflected and sent back.

[0079] As described above, the main interferometer is an interferometer with three stages of optical paths (three channels), each of which has a length difference of the optical paths equal to twice the distance (circle) from the front end (end face) of the optical waveguide of the sensor head 20 to the target object T and generates three interference light beams according to the respective length difference of the optical paths.

[0080] The light receiving elements 56a to 56c receive the interference light beams from the main interferometer as described above and generate electrical signals corresponding to the received amounts of light.

[0081] The amplifier circuits 57a to 57c amplify the electrical signals output by the light receiving elements 56a to 56c.

[0082] The analog-to-digital converter (ADC) units 58a to 58c receive the electrical signals amplified by the amplifier circuits 57a to 57c and convert the electrical signals from analog to digital signals (AD conversion). The ADC units 58a to 58c perform the ADC conversion based on a correction signal from the correction signal generation unit 61 in the auxiliary interferometer.

[0083] To correct the non-linearity of the wavelength of the light source 51 with tuned wavelength at the time of sampling, the auxiliary interferometer detects an interference signal and generates a correction signal called the K-clock.

[0084] Specifically, the light beam split by the optocoupler 54 to the auxiliary interferometer is further split by the optocoupler 54d. The optical paths of the split light beams are configured to have length differences, for example, by using optical waveguides of different lengths between the optocoupler 54d and the optocoupler 54e. An interference light beam, dependent on the length differences of the optical paths, is output by the optocoupler 54e. The balance detector 60 then receives the interference light beam from the optocoupler 54e, removes noise by determining the difference between the interference light beam and an opposite-phase signal, amplifies the optical signal, and converts it into an electrical signal.

[0085] Both the 54d optocoupler and the 54e optocoupler can split a light beam in a 50:50 ratio.

[0086] The correction signal generation unit 61 determines the non-linearity of the wavelength of the light source 51 with tuned wavelength at the time of sampling based on the electrical signal of the balance detector 60, generates a K-clock corresponding to the non-linearity and outputs the K-clock to the AD converter units 58a to 58c.

[0087] Due to the non-linearity of the wavelength of the light source 51, which has a tuned wavelength at the time of sampling, the intervals between the waves of the analog signals input to the A / D converter units 58a to 58c in the main interferometer are not equal. In the A / D converter units 58a to 58c, a sampling time is corrected based on the K-clock described above, and an A / D conversion (sampling) is performed so that the intervals between the waves become equal.

[0088] Since the K-clock is a correction signal used for sampling the analog signals of the main interferometer, as described above, the K-clock must have a higher frequency than the analog signals of the main interferometer. Specifically, the length difference of the optical paths between the optocoupler 54d and the optocoupler 54e in the auxiliary interferometer can be adjusted to be greater than the length difference of the optical paths between the front end (end face) of the optical waveguide and the target object T in the main interferometer, or the frequency can be multiplied by the correction signal generation unit 61 (e.g., by eight) to obtain the higher frequency.

[0089] The processing unit 59 acquires the digital signals obtained through nonlinearity correction and analog-to-digital conversion by the analog-to-digital converter units 58a to 58c, and calculates a displacement of the target object T (a distance to the target object T) based on these digital signals. Specifically, the processing unit 59 converts the digital signals by frequency conversion using a Fast Fourier Transform (FFT) and analyzes the converted digital signals to calculate the distance. The process in the processing unit 59 is described in detail below.

[0090] Since high-speed processing is required in the processing unit 59, the processing unit 59 is often implemented by an integrated circuit such as a field-programmable gate array (FPGA).

[0091] Furthermore, the main interferometer provides three stages of optical paths. The sensor head 20 sends a measurement light beam from each of the optical paths to the target object T, and based on an interference light beam (backlight beam) received from each of the optical paths, a distance to the target object T or the like is measured (multi-channel). The number of channels in the main interferometer is not limited to three stages, but can be one, two, four, or more.

[0092] Fig. Figure 5B is a diagram illustrating another principle for measuring the target object T with the displacement sensor 10 according to the present disclosure. As in Fig. As illustrated in Figure 5B, the displacement sensor 10 includes the sensor head 20 and the controller 30. The sensor head 20 includes the objective lens 21 and the multiple collimator lenses 22a to 22c. The control unit 30 includes the light source 51 with tuned wavelength, the optical amplifier 52, the plurality of insulators 53 and 53a to 53b, a plurality of optocouplers 54 and 54a to 54j, the attenuator 55, the plurality of light receiving elements (e.g., photodetectors (PDs)) 56a to 56c, the plurality of amplifier circuits 57a to 57c, the plurality of analog-to-digital (AD) converter units (e.g., analog-to-digital converters) 58a to 58c, the processing unit (e.g., a processor) 59, the balance detector 60, and the correction signal generation unit 61. The in Fig. The displacement sensor 10 shown in Figure 5B has a different configuration than the one in Figure 5B. Fig. 5A illustrated displacement sensor 10, primarily by providing optocouplers 54f to 54j, and the principle with the other configuration is compared to Fig. 5A described in detail.

[0093] The light beam projected by the light source 51 with a tuned wavelength is amplified by the optical amplifier 52, passes through the insulator 53, and is split by the optocoupler 54 into a main interferometer side and an auxiliary interferometer side. The light beam split to the main interferometer side is further split by the optocoupler 54f into a measurement light beam and a reference light beam.

[0094] As in Fig. As described in section 5A, the measuring light beam is emitted by the optocoupler 54a of the first stage in such a way that it passes through the collimator lens 22a and the objective lens 21 and strikes the target object T and is reflected by the target object T. Fig. 5A The front end (the end face) of the optical waveguide serves as a reference surface, and the light beam reflected from the reference surface and the light beam reflected from the target object T interfere with each other to produce an interference light beam. However, in Fig. 5B the reference surface from which the light beam is reflected is not provided. That is, unlike Fig. 5A the light beam reflected from the reference surface is in Fig. 5B is not generated, and the measuring light beam reflected from the target object T returns to the optocoupler 54a of the first stage.

[0095] Similarly, the light beam split by the first-stage optocoupler 54a towards the second-stage optocoupler 54b is emitted by the second-stage optocoupler 54b in such a way that it passes through the collimator lens 22b and the objective lens 21, strikes the target object T, is reflected by the target object T, and returns to the second-stage optocoupler 54b. The light beam split by the second-stage optocoupler 54b towards the third-stage optocoupler 54c is emitted by the third-stage optocoupler 54c in such a way that it passes through the collimator lens 22c and the objective lens 21, strikes the target object T, is reflected by the target object T, and returns to the third-stage optocoupler 54c.

[0096] On the other hand, the reference light beam divided by the optocoupler 54f is further divided by the optocoupler 54g into the optocouplers 54h, 54i and 54j.

[0097] In the optocoupler 54h, the measuring light beam reflected by the target object T and emitted by the optocoupler 54a and the reference light beam emitted by the optocoupler 54g interfere with each other to generate an interference light beam, and the interference light beam is received by the light receiving element 56a to be converted into an electrical signal.In other words, the light beam is split by the optocoupler 54f into the measuring light beam and the reference light beam, the interference light beam is generated according to a length difference of the optical paths between the optical path of the measuring light beam (the optical path along which the measuring light beam travels from the optocoupler 54f through the optocoupler 54a, the collimator lens 22a and the objective lens 21, is reflected by the target object T and reaches the optocoupler 54h) and the optical path of the reference light beam (the optical path along which the reference light beam travels from the optocoupler 54f through the optocoupler 54g and reaches the optocoupler 54h), and the interference light beam is received by the light receiving element 56a to be converted into an electrical signal.

[0098] Similarly, in the optocoupler 54i, an interference light beam is generated according to a length difference of the optical paths between the optical path of the measuring light beam (the optical path along which the measuring light beam travels from the optocoupler 54f through the optocouplers 54a and 54b, the collimator lens 22b and the objective lens 21, is reflected by the target object T and reaches the optocoupler 54i) and the optical path of the reference light beam (the optical path along which the reference light beam travels from the optocoupler 54f through the optocoupler 54g and reaches the optocoupler 54i), and the interference light beam is received by the light receiving element 56b to be converted into an electrical signal.

[0099] In the optocoupler 54j, an interference light beam is generated according to a length difference of the optical paths between the optical path of the measuring light beam (the optical path along which the measuring light beam travels from the optocoupler 54f via the optocouplers 54a, 54b, and 54c, the collimator lens 22c, and the objective lens 21, is reflected by the target object T, and reaches the optocoupler 54j) and the optical path of the reference light beam (the optical path along which the reference light beam travels from the optocoupler 54f through the optocoupler 54g and reaches the optocoupler 54j). The interference light beam is received by the light receiving element 56c to be converted into an electrical signal. It should be noted that the light receiving elements 56a to 56c can be, for example, equilibrium photodetectors.

[0100] As described above, the main interferometer includes three stages of optical paths (three channels) and generates three interference light beams according to a length difference of the optical paths between the measurement light beam reflected by the target object T and fed into each of the optocouplers 54h, 54i and 54j and the reference light beam fed into each of the optocouplers 54h, 54i and 54j via the optocouplers 54f and 54g.

[0101] The length difference of the optical paths between the measuring light beam and the reference light beam can be adjusted so that it is different for the three channels, for example by setting different optical path lengths between the optocoupler 54g and each of the optocouplers 54h, 54i and 54j.

[0102] Then, based on the interference light beam received from each of the channels (multi-channel), a distance to the target object T and the like is measured. Sensor head structure

[0103] Now the structure of the sensor head of the displacement sensor 10 will be described.

[0104] Fig. Figure 6A is a perspective view illustrating a schematic configuration of the sensor head 20, and Fig. Figure 6B is a schematic diagram illustrating an internal structure of the sensor head.

[0105] As in Fig. Figure 6A illustrates that the sensor head 20 contains the objective lens 21 and the collimator lenses in a lens holder 23. For example, the size of the lens holder 23 is chosen such that the length of one of the sides surrounding the objective lens 21 is approximately 20 mm and the length in the direction of the optical axis is approximately 40 mm.

[0106] As in Fig. As illustrated in Figure 6B, an objective lens 21 and three collimator lenses 22a to 22c are mounted in the lens holder 23. The optical waveguide is configured such that the light beam is guided via an optical waveguide array 24 to the three collimator lenses 22a to 22c, and the light beams that have passed through the three collimator lenses 22a to 22c strike the target object T via the objective lens 21.

[0107] As described above, the optical waveguide, the collimator lenses 22a to 22c and the optical waveguide array 24 together with the objective lens 21 are held by the lens holder 23 and form the sensor head 20.

[0108] The lens holder 23, from which the sensor head 20 is made, can be made of a metal (e.g. A2017) that has high strength and can be machined with high accuracy.

[0109] Fig. Figure 7 is a block diagram illustrating signal processing in controller 30. As shown in Fig. As illustrated in Figure 7, the control unit 30 includes a variety of light receiving elements 71a to 71e, a variety of amplifier circuits 72a to 72c, a variety of AD converter units 74a to 74c, a processing unit 75, a differential amplifier circuit 76 and a correction signal generation unit 77.

[0110] In control unit 30, as in Fig. Figure 5A illustrates that the light beam projected by the light source 51 with tuned wavelength is split by the optocoupler 54 into the main interferometer and the auxiliary interferometer signal, and a main interference signal and an auxiliary interference signal obtained from the respective interferometers are processed, thereby calculating a distance value to the target object T.

[0111] The multitude of light-receiving elements 71a to 71c corresponds to those in Fig. 5A, illustrated by light receiving elements 56a to 56c, each receives main interference signals from the main interferometer and outputs the signals as current signals to the amplifier circuits 72a to 72c.

[0112] The multitude of amplifier circuits 72a to 72c converts the current signals into voltage signals (IV conversion) and amplifies the voltage signals.

[0113] The large number of AD converter units 74a to 74c correspond to those in Fig. 5A illustrated AD converter units 58a to 58c and converts the voltage signals into digital signals based on a K-clock of the correction signal generation unit 77 to be described below (AD conversion).

[0114] The processing unit 75 corresponds to the one in Fig. 5A illustrated processing unit 59, converts the digital signals of the AD converter units 74a to 74c into frequencies using FFT and analyzes the frequencies to calculate a distance value to the target object T.

[0115] The multitude of light-receiving elements 71d to 71e and the differential amplifier circuit 76 correspond to that in Fig. Figure 5A illustrates the equilibrium detector 60, each of the light receiving elements 71d and 71e receives the interference light beam in the auxiliary interferometer, one of them outputs a phase-inverted interference signal, and the interference signal is amplified and converted into a voltage signal, whereby noise is removed by obtaining a difference between the two signals.

[0116] The correction signal generation unit 77 corresponds to the one in Fig. The correction signal generation unit 61, shown in Figure 5A, binarizes the voltage signal with a comparator, generates a K-clock, and outputs the K-clock to the A / D converter units 74a to 74c. Since the K-clock must have a higher frequency than the analog signals of the main interferometer, the frequency can be multiplied by the correction signal generation unit 77 (e.g., by eight) to obtain the higher frequency.

[0117] Fig. Figure 8 is a flowchart illustrating a procedure for calculating a distance to the target object T, which is executed by the processing unit 59 in the controller 30. As shown in Fig. As illustrated in section 8, the procedure includes steps S31 to S34.

[0118] In step S31, the processing unit 59 performs a frequency conversion to convert a waveform signal (voltage versus time) into a spectrum (voltage versus frequency) using the FFT described below. Fig. 9A is a diagram illustrating a state in which frequency conversion is performed to convert a waveform signal (voltage versus time) into a spectrum (voltage versus frequency). ∑t=0N−1f(t)exp(−i2ΠωtN)=f(ω) N: NUMBER OF DATA POINTS

[0119] In step S32, the processing unit 59 performs a distance conversion to convert the spectrum (voltage versus frequency) into a spectrum (voltage versus distance). Fig. 9B is a diagram illustrating a state in which distance conversion is performed to convert a spectrum (voltage versus frequency) to a spectrum (voltage versus distance).

[0120] In step S33, the processing unit 59 calculates a distance value corresponding to a peak based on the spectrum (voltage versus distance). Fig. 9C is a diagram illustrating a condition in which a peak is detected based on the spectrum (voltage versus distance) and a distance value corresponding to the peak is calculated. As in Fig. As illustrated in Figure 9C, the peaks are detected based on the spectra (voltage versus distance) in the three channels and the distance values ​​corresponding to the respective peaks are calculated.

[0121] In step S34, processing unit 59 calculates the average of the distance values ​​calculated in step S33. Specifically, processing unit 59 averages the distance values ​​because the peaks are detected based on the spectra (voltage versus distance) in the three channels, and the distance values ​​corresponding to the peaks are calculated in step S33. It then outputs the averaged calculation result as the distance to the target object T.

[0122] In step S34, when averaging the distance values ​​calculated in step S33, processing unit 59 prefers to average the distance values ​​such that the signal-to-noise ratio (S / R) is equal to or greater than a threshold. For example, if a peak based on a spectrum (voltage versus distance) is detected in one of the three channels, but the S / R ratio is below the threshold, a spectrum-based distance value is determined to be unreliable and is not adopted.

[0123] The present disclosure is described in detail below in the form of specific embodiments, with a focus on characteristic configurations, functions, and properties. An optical interferometric distance sensor described below corresponds to the one referred to in Fig. 1 to Fig. 9 described displacement sensor 10, and all or part of the basic configurations, functions and features included in the optical interferometric distance sensor are common to the configurations, functions and features described in the with reference to Fig. 1 to Fig. The displacement sensor 10 described in 9 is included. Design configuration of the optical interferometric distance sensor

[0124] Fig. Figure 10 is a schematic diagram illustrating the basic configuration of an optical interferometric distance sensor 100 according to an embodiment of the present invention. As shown in Fig. As illustrated in Figure 10, the optical interferometric distance sensor 100 includes a controller 110 and an optical fiber cable 130 that connects the controller 110 and a sensor head 121. The optical interferometric distance sensor 100 can further include the first sensor head 121 and the second sensor head 122.

[0125] The control unit 110 includes a light source 140 with tuned wavelength, an optical divider unit 111, a main interferometer 150, an auxiliary interferometer 160, first photodiodes (PD) 112 and 113, amplifier circuits 114 and 115, second photodiodes (PD) 116 and 117, a first correction signal generation unit 171, a second correction signal generation unit 172, A / D converter units 181 and 182 and a processing unit 118.

[0126] The optical fiber cable 130 is an optical fiber assembly comprising multiple optical fibers. The optical fiber cable 130 is configured to be attachable to and detachable from the controller 110, the first sensor head 121, and the second sensor head 122. For example, the optical fiber cable 130 includes a first optical fiber 131 and a second optical fiber 132. The first optical fiber 131 has an optical path length proportional to a length L1, and the second optical fiber 132 has an optical path length proportional to a length L2. The length L1 of the first optical fiber 131 is set based on the distance to a target object T1, and the length L2 of the second optical fiber 132 is set based on the distance to a target object T2.The measurement target object T2 is assumed to be an object that is located at a different distance than the measurement target object T1, i.e., in the distance shown in . Fig. Figure 1 illustrates this at a greater distance. The optical path length of the second optical waveguide 132 therefore differs from the optical path length of the first optical waveguide 131 and is longer than the optical path length of the first optical waveguide 131.

[0127] The tuned-wavelength light source 140 projects a light beam with a continuously changing wavelength. That is, the wavelength of the light beam projected by the tuned-wavelength light source 140 is constantly changing. The light beam projected by the tuned-wavelength light source 140 is fed to the main interferometer 150 and the auxiliary interferometer 160 via the optical splitter unit 111, which includes, for example, an optocoupler. In the tuned-wavelength light source 140, the wavelength is continuously controlled by changing the magnitude of an input current. A triangular wave or a sawtooth wave is primarily used as the input current waveform.

[0128] The main interferometer 150 has a multitude of optical paths (a multitude of channels) and closes in the in Fig. 10 illustrated examples include a first main interferometer 151 and a second main interferometer.

[0129] The first main interferometer 151 is connected to the optical waveguide 131 of the optical waveguide cable 130, guides the light beam projected by the light source 140 with tuned wavelength via the optical waveguide 131 to the first sensor head 121 and directs a backlight beam from the first sensor head 121 to the first photodiode 112.

[0130] In particular, the light beam guided from the first main interferometer 151 to the sensor head 121, representing the target object T, is directed to the target object via, for example, a collimator lens and an objective lens arranged in the first sensor head 121. The light beam reflected from the target object T then returns to the first sensor head 121.

[0131] A portion of the light beam directed from the first principal interferometer 151 to the first sensor head 121 is reflected as the first reference light beam, for example, from a reference surface provided at the front end of the first optical waveguide 131. The first measurement light beam and the first reference light beam interfere with each other to generate an interference light beam (also referred to as the "first principal interference signal"), which depends on a length difference of the optical paths between the first measurement light beam and the first reference light beam.

[0132] In this way, the light beam projected from the light source 140 with a tuned wavelength is supplied to the main interferometer 150, and it generates the first main interference signal based on the first measurement light beam emitted from the first measuring head 121 to the target object T and reflected by the target object T, and the first reference light beam, which travels along an optical path that differs at least partially from the optical path of the first measurement light beam. Since the light beam projected from the light source with a tuned wavelength is supplied and the main interference signal is generated, the first main interferometer 150, including the measuring head 121, can be referred to as the first main interferometer.

[0133] The second main interferometer 152 is connected to the second optical waveguide 131 of the optical waveguide cable 130, guides the light beam projected by the light source 140 with tuned wavelength via the second optical waveguide 132 to the second sensor head 122 and directs a backlight beam from the second sensor head 122 to the first photodiode 113.

[0134] In particular, the light beam directed from the second main interferometer 152 to the second sensor head 122 is guided as a second measuring light beam via, for example, a collimator lens and an objective lens arranged in the second sensor head 122 to the target object T. Then the light beam reflected from the target object T returns to the second sensor head 122.

[0135] A portion of the light beam directed from the second principal interferometer 152 to the second sensor head 122 is reflected as a second reference light beam, for example, from a reference surface provided at the leading end of the second optical waveguide 132 or the like. The second measurement light beam and the second reference light beam interfere with each other to produce an interference light beam (also referred to as the "second principal interference signal"), the length of which depends on a difference in the optical paths between the second measurement light beam and the second reference light beam.

[0136] In this way, the light beam projected by the wavelength-controlled light source 140 is supplied to the second principal interferometer 152, and it generates the second principal interference signal based on the second measurement light beam emitted by the second sensor head 122 to the target object T and reflected by the target object T, and the second reference light beam, which travels along an optical path that differs at least partially from the optical path of the second measurement light beam. Since the light beam projected by the tuned wavelength light source is supplied and the second principal interference signal is generated, the second principal interferometer 152, including the second sensor head 122, can be referred to as the second principal interferometer.

[0137] The first photodiode 112 receives the first main interference signal generated by the first main interferometer 151 and converts it into an electrical signal. The electrical signal converted by the first photodiode 112 is, for example, a current signal. The first photodiode 113 receives the second main interference signal generated by the second main interferometer 152 and converts it into an electrical signal. The electrical signal converted by the first photodiode 113 is also, for example, a current signal.

[0138] Amplifier circuit 114 amplifies the electrical signal input from the first photodiode 112 with a predetermined gain. When a current signal is input from the first photodiode 112, amplifier circuit 114 converts the current signal into a voltage signal (also known as "IV conversion") and amplifies the voltage signal. The amplified electrical signal is output to the analog-to-digital converter (ADC) unit 181. Amplifier circuit 115 amplifies the electrical signal input from the first photodiode 113 with a predetermined gain. When a current signal is input from the first photodiode 113, amplifier circuit 115 converts the current signal into a voltage signal and amplifies the voltage signal. The amplified electrical signal is output to the ADC unit 182.

[0139] A light beam projected from the light source 140 with a tuned wavelength is fed to the auxiliary interferometer 160. The beam is split by the optical splitter unit 111, generating an auxiliary interference signal based on two light beams traveling along optical paths of different lengths. Specifically, the light beam is split into two beams by the first optocoupler 161, each traveling along an optical path of different lengths. These two beams are then combined by the second optocoupler 162 to interfere, producing an auxiliary interference signal based on the optical path length difference. This auxiliary interference signal propagates through the optical waveguide 163 to the second photodiode 116 and through the optical waveguide 164 to the second photodiode 117.

[0140] Optical waveguide 163 has an optical path length proportional to a length L1r, and optical waveguide 164 has an optical path length proportional to a length L2r. Optical waveguide 164 of the present embodiment corresponds to an example of the “delay value generation unit” of the present invention. Optical waveguide 164 of the present embodiment also corresponds to an example of the “third optical waveguide” of the present invention.

[0141] The optical waveguide 164 is configured to generate a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132.

[0142] In particular, the optical waveguide 164 transmits an additional interference signal and has an optical path length based on the difference in optical path lengths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132. The auxiliary interferometer signal transmitted via the optical waveguide 164 to the second photodetector 117 is therefore an auxiliary interferometer signal delayed by the optical waveguide 164 (hereinafter also referred to as the "delayed auxiliary interferometer signal").Since the optical waveguide 164 transmits an additional interference signal as described above and has an optical path length based on a length difference of the optical paths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132, a delay value can be easily set by changing the optical path length of the optical waveguide 164.

[0143] The second photodiode 116 receives the auxiliary interferometer signal propagating through the optical waveguide 163 of the auxiliary interferometer 160 and converts the auxiliary interferometer signal into an electrical signal (hereinafter also referred to as the "auxiliary interferometer signal"). The electrical signal converted by the second photodiode 116 is, for example, a current signal. The second photodiode 117 receives the auxiliary interferometer signal transmitted through the optical waveguide 164 of the auxiliary interferometer 160 and converts the auxiliary interferometer signal into an electrical signal (hereinafter also referred to as the "delayed auxiliary interferometer signal"). The electrical signal converted by the second photodiode 116 is, for example, also a current signal.

[0144] Each electrical signal output by the second photodiodes 116 and 117 can be amplified by an amplifier circuit (not illustrated) with a predetermined gain. In this case, the amplifier circuit outputs the amplified electrical signal to the first correction signal generation unit 171 and the second correction signal generation unit 172.

[0145] The correction signal generation unit 171 is configured to generate a first correction signal (also referred to as the "first K-clock signal" or simply the "first K-clock") based on the auxiliary interference signal. The first correction signal is a signal used to correct the sampling period of the first principal interference signal generated by the first principal interferometer 151. Since the auxiliary interference signal, like the first principal interference signal, is nonlinear due to the nonlinearity of the wavelength at the time of tuning, the first correction signal generation unit 171 can generate a first correction signal for suitable sampling and analog-to-digital conversion of the analog signal of the first principal interference signal—that is, a first K-clock signal—by exploiting the nonlinearity of the wavelength at the time of tuning based on the auxiliary interference signal.

[0146] To generate a suitable first correction signal in the first correction signal generation unit 171, the nonlinearity of the first main interference signal received by the first photodiode 112 must be adequately detected by the first correction signal generation unit 171. For this purpose, it is advantageous to align the characteristics (nonlinearities) of the first main interference signal and the auxiliary interference signal, i.e., to synchronize the timing of the first main interference signal and the auxiliary interference signal.

[0147] The second correction signal generation unit 172 is configured to generate a second correction signal (also referred to as the "second K-clock signal" or simply the "second K-clock") based on the auxiliary interference signal and the delay value. This second correction signal is used to correct the sampling period of the second main interference signal generated by the second main interferometer 152. Since the auxiliary interference signal, like the second main interference signal, is nonlinear due to the nonlinearity of the wavelength at the time of tuning, the second correction signal generation unit 172 can generate a second correction signal for suitable sampling and analog-to-digital conversion of the analog signal of the second main interference signal—i.e., a second K-clock signal—by determining the nonlinearity of the wavelength at the time of tuning based on the auxiliary interference signal.

[0148] As described above, a delay value is generated based on the optical path length difference between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132. A second correction signal for correcting the sampling period of a second main interference signal is generated based on an auxiliary interference signal and the delay value. This makes it possible to generate a delay that corresponds to the optical path length difference between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132 in the second main interference signal. Accordingly, a shift in the sampling time of the second main interference signal and a decrease in the signal intensity of a sampled digital signal can be reduced.

[0149] In particular, the second correction signal generation unit 172 is configured to generate a second correction signal based on a delayed auxiliary interferometer signal. That is, the second correction signal is generated based on a signal obtained by delaying an auxiliary interferometer signal in the time-axis direction. This auxiliary interferometer signal is obtained by converting an auxiliary interference signal into an electrical signal. The delay is a time value corresponding to the delay value described above.

[0150] To generate a suitable second correction signal in the second correction signal generation unit 172, the nonlinearity of the second main interference signal received by the first photodiode 113 must be correctly detected by the second correction signal generation unit 172. For this purpose, it is advantageous to align the characteristics (nonlinearities) of the second main interference signal and the delayed auxiliary interference signal, i.e., to synchronize the first main interference signal and the auxiliary interference signal in time.

[0151] The second correction signal generation unit 172 can generate a pulse signal, which is a second correction signal, based on a signal obtained by applying a delay in the time-axis direction to an auxiliary interferometer signal corresponding to the delay value described above. This auxiliary interferometer signal is obtained by converting an auxiliary interference signal into an electrical signal. In this way, the timing for sampling the second main interference signal can be easily tuned (synchronized).

[0152] As in the case of the second correction signal generation unit 172, the first correction signal generated by the first correction signal generation unit 171 can be a pulse signal.

[0153] The A / D converter unit 181 is configured to sample a main interference signal, obtained by converting a main interference signal into an electrical signal, based on the first correction signal, and to convert the main interferometer signal into a digital signal. In the first main interference signal input to the A / D converter unit 181, the intervals of the waves in the analog signal are not equal. The A / D converter unit 181 samples the analog signal of the first main interference signal and converts it with a sampling period (sampling interval) that is corrected based on the first correction signal described above, i.e., the first K-clock signal, so that the intervals of the waves in the first main interference signal become equal.

[0154] The A / D converter unit 182 is configured to sample a second main interference signal, obtained by converting a second main interference signal into an electrical signal, based on the first correction signal, and to convert this second main interferometer signal into a digital signal. In the second main interference signal input to the A / D converter unit 182, the intervals of the waveforms in the analog signal are not equal. The A / D converter unit 182 samples the analog signal of the second main interference signal and converts it with a sampling period (sampling interval) that is corrected based on the second correction signal described above, i.e., the second K-clock signal, so that the intervals of the waveforms in the second main interference signal become equal.

[0155] As described above, the AD converter unit 182 samples the second main interference signal, which is obtained by converting the second main interference signal into an electrical signal, based on the second correction signal, and converts the second main interferometer signal into a digital signal, so that a configuration to convert the second main interferometer signal into a digital signal in which the sampling period has been corrected can be easily configured.

[0156] The processing unit 118 is configured to calculate a distance to the target object T based on the first main interference signal generated by the first main interferometer 151, or the second main interference signal generated by the second main interferometer 152, and the auxiliary interference signal generated by the auxiliary interferometer 160.

[0157] In particular, the processing unit 118 is configured to calculate a distance to the target object T based on the first main interference signal received by the first photodiode 112 and amplified by the amplifier circuit 114, the second main interference signal received by the first photodiode 113 and amplified by the amplifier circuit 115, and the auxiliary interference signal received by the second photodiodes 116 and 117.

[0158] In particular, since a non-linear analog signal based on the first main interference signal is converted into a digital signal with a sampling period that is corrected by the first correction signal based on the auxiliary interference signal in the AD converter unit 181, the processing unit 118 converts the digital signal into a frequency using FFT or the like, analyzes the frequency and calculates a distance value to the target object T.

[0159] Furthermore, since a non-linear analog signal based on the second main interference signal is converted into a digital signal with a sampling period that is corrected by the second correction signal based on the auxiliary interference signal and the delay amount in the A / D converter unit 182, the processing unit 118 converts the digital signal into a frequency using FFT or the like, analyzes the frequency and calculates a distance value to the target object T.

[0160] As described above, the processing unit 118 calculates a distance to the target object T based on at least one of the first main interference signal generated by the first main interferometer 151, or the second main interference signal generated by the second main interferometer 152, and the auxiliary interference signal generated by the auxiliary interferometer 160, so that a configuration for calculating a distance to the target object T can easily be obtained.

[0161] Fig. Figure 11 is a schematic representation illustrating the basic configuration of another optical interferometric distance sensor 101 according to the embodiment of the present invention. Fig. 11 are components that are related to those of the in Fig. The optical interferometric distance sensor 100 illustrated in Figure 10 is identical or similar to the components shown, designated with the same or similar reference symbols, and the description of these components is omitted where appropriate. Furthermore, the same processes and effects are achieved by the same components as those of the optical interferometric distance sensor shown in Figure 10. Fig. The 10 illustrated optical interferometric distance sensor 100 is not mentioned separately.

[0162] As in Fig. As illustrated in Figure 11, the optical interferometric distance sensor 101 includes the controller 110, the first sensor head 121, and the second sensor head 122, and further comprises the optical fiber cable 130 that connects the controller 110 to the first sensor head 121 and the second sensor head 122. The controller 110 of the in Fig. The optical interferometric distance sensor 101 illustrated in 11 differs from the control 110 of the in Fig. 10 illustrated optical interferometric distance sensor 100 by the fact that the optical waveguide 164 is not present and a delay line 191 is present.

[0163] A light beam projected from the wavelength-matched light source 140 and split by the optical splitter 111 is fed to the auxiliary interferometer 160 of the controller 110. This beam generates an auxiliary interference signal based on two light beams traveling along optical paths with different path lengths. Specifically, the light beam is split into two beams by the first optocoupler 161, each traveling along an optical path with a different path length. These two beams are then combined by the second optocoupler 162 to interfere, generating an auxiliary interference signal based on the path length difference. This auxiliary interference signal propagates through the optical waveguide 163 and is directed to the second photodiode 116.On the other hand, a remaining connection of the second optocoupler 162 is connected to an optical waveguide which encloses a coreless end cap or is connected to an attenuator.

[0164] The second photodiode 116 receives a second interference signal propagating through the optical waveguide 163 of the auxiliary interferometer 160 and converts this second interference signal into an auxiliary interferometer signal, which is an electrical signal. The electrical signal converted by the second photodiode 116 is, for example, a current signal. The electrical signal output by the second photodiode 116 can be amplified by an amplifier circuit (not illustrated) with a predetermined gain. In this case, the amplifier circuit outputs the amplified electrical signal to the first correction signal generation unit 171 and the delay line 191.

[0165] The delay line 191 is configured to introduce a delay into the auxiliary interferometer signal, which is obtained by converting the auxiliary interference signal into an electrical signal. This delay corresponds to a delay value in the time axis direction, and the auxiliary interferometer signal is output to the second correction signal generation unit 172. Similar to the delay value of the optical waveguide 164, the delay value of the delay line 191 is also set based on a length difference of the optical paths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132. The delay line 191 of the present embodiment corresponds to an example of the "delay value generation unit" of the present invention.The delay line 191 outputs the signal in which the delay was effected, i.e. the delayed auxiliary interferometer signal, to the second correction signal generation unit 172.

[0166] The delay line 191 includes an electronic component that causes a delay in the propagation of an electrical signal, such as a delay line. It should be noted that the structure, type, number, and the like of the electronic components of the delay line 191 are not restricted, as long as they cause a delay of an auxiliary interference signal.

[0167] As described above, the delay line 191 causes a delay corresponding to a delay value in the time axis direction in an auxiliary interferometer signal obtained by converting an auxiliary interference signal into an electrical signal, and outputs the auxiliary interferometer signal, in which the delay is caused electrically, to the second correction signal generation unit 172, so that the second correction signal generation unit 172 can easily generate a second correction signal, which is an electrical signal. Sampling time of the first main interferometer signal and the second main interferometer signal

[0168] Fig. Figure 12 is a diagram illustrating the sampling times of a first principal interferometer signal and a second principal interferometer signal. Fig. Figure 12 illustrates, in the upper part, the signals during sampling of the first main interferometer signal based on the first interference signal of the first main interferometer 151, and in the lower part, the signals during sampling of the second main interferometer signal based on the second interference signal of the second main interferometer 152. Unless explicitly stated otherwise, the following example describes the signals based on the signal shown in Figure 12. Fig. 10 illustrated optical interferometric distance sensor 100, and the description for the case of use of the in Fig. The illustrated optical interferometric distance sensor 101 is omitted.

[0169] As in the upper part of Fig. As illustrated in Figure 12, the sampling of the first main interferometer signal with the first correction signal, which is generated based on an auxiliary interferometer signal obtained by converting an auxiliary interference signal into an electrical signal, is started at time 11. Then the first main interferometer signal is sampled with a period corrected by the first correction signal and converted into a digital signal.

[0170] On the other hand, as in the lower part of Fig. Figure 12 illustrates that the second main interferometer signal is not generated at time t1, but at time t2 (t2 > t1). This time difference (hereinafter also referred to as the "delay time t12") is a delay time of a light beam caused by a length difference of the optical paths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132.

[0171] The optical fiber 164 of the in Fig. The optical interferometric distance sensor 100, illustrated in Figure 10, generates a delay value tdelay in the second main interferometer signal in response to this delay time t12. The delay value tdelay is represented by the following equation (1), where the length L1r of the optical waveguide 163, the length L2r of the optical waveguide 164, and a speed of light c are used. tdelay=|L2r−L1r| / c

[0172] The sampling of the second main interferometer signal, along with the second correction signal (generated based on the delay value tdelay) and the auxiliary interferometer signal (obtained by converting the auxiliary interference signal into an electrical signal), is started at time t2. The second main interferometer signal is then sampled with a period corrected by the second correction signal and converted into a digital signal.

[0173] The delay value tdelay generated by the optical waveguide 164 is preferably set such that the absolute value of a deviation from the delay time t12 of the light beam due to the length difference of the optical paths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132 becomes smaller than a minimum sampling period Tsmin in the AD converter unit 182.

[0174] In other words, the delay value tdelay is set such that a time difference Δt between the delay time t12 of the light beam and the delay amount tdelay satisfies the following equation (2). Δt=|t12−tdelay| <Tsmin

[0175] Ratio between the signal intensity of the second main interferometer signal converted into a digital signal and the time difference

[0176] Fig. Figure 13 is a diagram illustrating the relationship between the signal intensity of the second main interferometer signal converted into a digital signal and the time difference Δt. Fig. 12. The signal intensity of the second main interferometer signal, which is converted into a digital signal, is normalized under the assumption that the signal intensity at a time difference Δt of 0 is considered the reference value “1”. The in Fig. 12 illustrated examples are based on the one in Fig. The optical interferometric distance sensor 100 shown in Figure 10 is described, and the description when using the sensor shown in Figure 10 is further detailed. Fig. The optical interferometric distance sensor 101 shown in Figure 11 is omitted.

[0177] If at the in Fig. Figure 10 illustrated optical interferometric distance sensor 100 the length L1 of the first optical waveguide 131 2 [m], the distance between the first sensor head 121 and the target object T1 1 [m], the distance between the second sensor head 122 and the target object T2 1 [m], the length L2 of the second optical waveguide 132 10 [m], the refractive index of the first optical waveguide 131 and the second optical waveguide 132 1.5 and the speed of light c 3 × 10 8 If the speed is [m / s], then the delay time t12 is calculated as 8 × 10 -8[s] calculated. If the optical interferometric distance sensor 100 includes the A / C converter units 181 and 182, which have a maximum sampling time of 100 [MHz], the minimum sampling period Tsmin in the A / C converter units 181 and 182 is 1 × 10 -8 [s]. These values ​​are substituted into equation (2) described above, and the delay value tdelay is set to 7 × 10 -8 [s] or more and 9 × 10 -8 [s] or less set.

[0178] As in Fig. As illustrated in Figure 13, the decrease in the signal intensity of the second main interferometer signal converted into a digital signal can be reduced to 10 [%] or less if the delay value tdelay is set to 7 × 10 -8 [s] or more and 9 × 10 -8[s] or less. For example, if the length L1r of the optical waveguide 163 of the auxiliary interferometer 160 is 1 [m], the length L2r of the optical waveguide 164 of the auxiliary interferometer 160 is set to 14 [m].

[0179] In this way, if the delay value tdelay is set such that the absolute value of a deviation from the delay time t12 of the light beam due to the length difference of the optical paths between the optical path length of the first optical waveguide 131 and the optical path length of the second optical waveguide 132 becomes smaller than the minimum sampling period Tsmin in the A / D converter unit 182, the decrease in the signal intensity of the sampled digital signal can be reduced to a predetermined percentage or less, for example 10% or less.

[0180] In the present embodiment, an example has been described in which each of the optical interferometric distance sensors 100 and 101 has two sensor heads, and the guide waveguide cable includes two guide waveguides connecting the respective sensor heads to the controller 110. However, the optical interferometric distance sensor is not limited to this. The optical interferometric distance measurement can include three or more sensor heads and a guide waveguide cable with the same number of sensor heads. For the sake of simplicity, in the case where the optical interferometric distance sensor includes three sensor heads and a guide waveguide cable with two guide waveguides, a configuration of the controller 110, in particular a configuration of the auxiliary interferometer 160 and the subsequent (downstream) stage, is described below. Specific configuration of an auxiliary interferometer and its subsequent stage when three sensor heads are provided

[0181] Fig. Figure 14 is a schematic diagram illustrating an example of a specific configuration of the auxiliary interferometer 160 and the subsequent stage thereof when three sensor heads are provided, and Fig. Figure 15 is a schematic diagram illustrating another example of a specific configuration of the auxiliary interferometer 160 and the subsequent stage thereof when three sensor heads are provided.

[0182] As in Fig. As illustrated in Figure 14, a light beam projected from the wavelength-matched light source 140 is supplied to the auxiliary interferometer 160 and split by the optical splitter unit 111. This generates an auxiliary interferometer signal based on two beams traveling along optical paths of different optical path lengths. Specifically, the light beam is split into two beams traveling along optical paths of different optical path lengths by the first optocoupler 161. The two beams are then combined by the second optocoupler 162 to interfere with each other, generating an auxiliary interference signal based on the length difference of the optical paths. The auxiliary interference signal propagates through the optical waveguide 163 and is directed to the second photodiode 116, and it propagates through the optical waveguide 164 and is directed to the second photodiode 117.Furthermore, the auxiliary interference signal generates a delay value as in the guide waveguide 164. The auxiliary interference signal propagates through the guide waveguide 165 and is directed to the second photodiode 119. The guide waveguide 165, the second photodiode 119, receives the auxiliary interferometer signal, which propagates through the guide waveguide 165 of the auxiliary interferometer 160, and converts the auxiliary interferometer signal into an electrical signal (hereinafter also referred to as the "delayed auxiliary interferometer signal").

[0183] A third correction signal generation unit 173 is configured to generate a third correction signal (also referred to as a "third K-clock signal" or simply a "third K-clock") based on the auxiliary interference signal and the delay value. The third correction signal is a signal used to correct the sampling period of a third principal interference signal generated by a third principal interferometer (not illustrated). The third correction signal generation unit 173 can generate a third correction signal to correctly sample the analog signal of the third principal interference signal, i.e., a third K-clock signal, and perform an analog-to-digital conversion on it by capturing the nonlinearity of the wavelength at the time of sampling based on the auxiliary interference signal.

[0184] As in Fig. As illustrated in Figure 15, a light beam projected from the light source 140 with a tuned wavelength is supplied to the auxiliary interferometer 160 and split by the optical splitter unit 111. This generates an auxiliary interferometer signal based on two light beams traveling along optical paths of different optical path lengths. Specifically, the light beam is split into two light beams traveling along optical paths of different optical path lengths by the first optocoupler 161. The two light beams are then combined by the second optocoupler 162 to interfere with each other, generating an auxiliary interference signal based on the length difference of the optical paths. The auxiliary interference signal propagates through the optical waveguide 163 and is directed to the second photodiode 116.On the other hand, a remaining connection of the second optocoupler 162 is connected to an optical waveguide, which may enclose a coreless end cap or be connected to an attenuator.

[0185] The second photodiode 116 receives a second interference signal propagating through the optical waveguide 163 of the auxiliary interferometer 160, converts the second interference signal into an auxiliary interferometer signal, which is an electrical signal, and outputs the auxiliary interferometer signal to the first correction signal generation unit 171 and the delay line 191.

[0186] The delay line 191 is configured to introduce a delay into the auxiliary interferometer signal, obtained by converting the auxiliary interference signal into an electrical signal. This delay corresponds to a time-axis delay value, and the auxiliary interferometer signal is output to the second correction signal generation unit 172. The delay line 191 outputs the signal in which the delay has been introduced—that is, the delayed auxiliary interferometer signal—to the second correction signal generation unit 172 and to a delay line 192. Similarly, the delay line 192 is configured to introduce a delay into the auxiliary interferometer signal, obtained by converting the auxiliary interference signal into an electrical signal. This delay corresponds to a time-axis delay value, and the auxiliary interferometer signal is output to the third correction signal generation unit 173.The delayed auxiliary interferometer signal is fed from the delay line 191 into the delay line 192, and the further delayed auxiliary interferometer signal is output to the third correction signal generation unit 173. Modification example of an interferometer

[0187] In the embodiment described above, the optical interferometric distance sensor 100, 101 uses a Fizeau interferometer which generates a reference light beam by using the leading end of the optical waveguide as a reference surface in the main interferometer 150, but the interferometer is not limited to this.

[0188] Fig. Figure 16 is a diagram illustrating variations of interferometers that generate an interference light beam using a measurement light beam and a reference light beam. Fig. 16(a) In the optical path passing through the main interferometer 150, an interference light beam is generated based on a length difference of the optical paths between a reference light beam, which uses the front end (the end face) of the optical waveguide as a reference surface, and a measurement light beam emitted by the sensor head and reflected by a measurement target object T. This represents the configuration of the main interferometer 150 of the optical interferometric distance sensor 100, 101 of the embodiment described above (Fizeau interferometer), and the reference surface can be configured to reflect a light beam through the difference in refractive index between the optical waveguide and the air (Fresnel reflection).A reflective coating may be applied to the front end of the optical waveguide, or a non-reflective coating may be applied to the front end of the optical waveguide, and a reflective surface such as a lens may be arranged separately.

[0189] In Fig. 16(b) An optical measurement path Lm for guiding a measurement light beam to the target object T and an optical reference path Lr for guiding a reference light beam in the optical path passing through the main interferometer 150 are formed, and a reference surface is arranged at the front end of the optical reference path Lr (Michelson interferometer). A reflective coating may be applied to the front end of the optical waveguide at the reference surface, or a non-reflective coating may be applied to the front end of the optical waveguide, and a mirror or similar device may be arranged separately. In this configuration, an interference light beam is generated by providing a length difference in the optical paths between the optical path length of the optical measurement path Lm and the optical path length of the optical reference path Lr.

[0190] In Fig.16(c) An optical measurement path Lm for guiding a measurement light beam to the measurement target T and an optical reference path Lr for guiding a reference light beam in the optical path passing through the main interferometer 150 are formed, and a balance detector is arranged on the optical reference path Lr (Mach-Zehnder interferometer). In this configuration, an interference light beam is generated by providing a length difference of the optical paths between the optical measurement path Lm and the optical reference path Lr.

[0191] As described above, the main interferometer is not limited to the Fizeau interferometer described in the embodiment and can, for example, be a Michelson interferometer, a Mach-Zehnder interferometer, or any interferometer, a combination of these interferometers, or other configurations, as long as an interference light beam can be generated by adjusting the length difference of the optical paths between a measurement light beam and a reference light beam. Similarly, the auxiliary interferometer (not illustrated) can be a Fizeau interferometer, a Michelson interferometer, a Mach-Zehnder interferometer, or any interferometer, a combination of these interferometers, or other configurations, as long as an interference light beam can be generated by adjusting the length difference of the optical paths between a measurement light beam and a reference light beam.

[0192] It should be noted that the embodiment described above is provided for a better understanding of the present invention and is not intended to limit its scope. The present invention can be modified / improved without departing from its core principles, and it also includes equivalents thereof. In other words, variations obtained by a person skilled in the art through a corresponding design modification of the embodiment are also included within the scope of the present invention, provided that the variations include the features of the present invention. For example, the elements included in the embodiment, as well as the arrangement, material, condition, shape, size, etc., of the individual elements, are not limited to the elements listed as examples and can be modified accordingly.The embodiment shown is for illustrative purposes only, and it is understood that partial substitutions or combinations of configurations illustrated in different embodiments are permissible and are also included within the scope of the present invention, as long as they include the features of the present invention. Supplementary Note 1

[0193] A controller (110) connected via an optical fiber cable (130) to each of a first sensor head (121) and a second sensor head (122), from which a light beam is emitted to a target object, the controller comprising: a light source (140) that projects a beam of light and thereby changes a wavelength; a first principal interferometer (151) which, by being fed with the light beam projected from the light source (140), generates a first principal interference signal based on a first measurement light beam emitted from the first sensor head (121) to the target object and reflected by the target object, and a first reference light beam which travels along an optical path that differs at least partially from an optical path of the first measurement light beam; a second principal interferometer (152) which, by being fed with the light beam projected from the light source (140), generates a second principal interference signal based on a second measurement light beam emitted from the second sensor head (122) onto the target object and reflected by the target object, and a second reference light beam which travels along an optical path that differs at least partially from an optical path of the second measurement light beam; an auxiliary interferometer (160) which, by being supplied with the light beam projected from the light source (140), generates an auxiliary interference signal based on two light beams traveling along different optical paths; and a processing unit (118) that measures a distance to the target object based on at least one of the first main interference signal or the second main interference signal and the auxiliary interference signal, including the optical fiber cable (130) a first optical waveguide (131) which is connected to the first main interferometer (151) and transmits a light beam from the first main interferometer (151) to the first sensor head (121) and transmits a light beam from the first sensor head (121) to the first main interferometer (151), and a second optical waveguide (132) which is connected to the second main interferometer (152), transmits a light beam from the second main interferometer (152) to the second sensor head (122) and transmits a light beam from the second sensor head (122) to the second main interferometer (152), wherein the second optical waveguide (132) has an optical path length that differs from the optical path length of the first optical waveguide (131), and wherein the control (110) further includes a first correction signal generation unit (171) that generates a first correction signal to correct one sampling period of the first main interference signal based on the auxiliary interference signal, a delay quantity generation unit that generates a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide (131) and the optical path length of the second optical waveguide (132), and a second correction signal generation unit (172) that generates a second correction signal to correct one sampling period of the second main interference signal based on the auxiliary interference signal and the delay value. Supplementary Note 8

[0194] An optical interferometric distance sensor (100) that includes: a controller (110); and a fiber optic cable (130) connected to the controller (110), including the control (110) a light source (140) that projects a beam of light and thereby changes a wavelength, a first principal interferometer (151) which, by being fed with the light beam projected from the light source (140), generates a first principal interference signal based on a first measurement light beam emitted from a first sensor head (121) onto the target object and reflected by the target object, and a first reference light beam which travels along an optical path that differs at least partially from an optical path of the first measurement light beam; a second principal interferometer (152) which, by being fed with the light beam projected from the light source (140), generates a second principal interference signal based on a second measurement light beam emitted from a second sensor head (122) onto the target object and reflected by the target object, and a second reference light beam which travels along an optical path that differs at least partially from an optical path of the second measurement light beam, and an auxiliary interferometer (160) which, by being supplied with the light beam projected from the light source (140), generates an auxiliary interference signal based on two light beams traveling along different optical paths, including the optical fiber cable (130) a first optical waveguide (131) which is connected to the first main interferometer (151) and transmits a light beam from the first main interferometer (151) to the first sensor head (121) and transmits a light beam from the first sensor head (121) to the first main interferometer (151), and a second optical waveguide (132) which is connected to the second main interferometer (152), transmits a light beam from the second main interferometer (152) to the second sensor head (122) and transmits a light beam from the second sensor head (122) to the second main interferometer (152), wherein the second optical waveguide (132) has an optical path length that differs from an optical path length of the first optical waveguide (131), and the control (110) further includes a first correction signal generation unit (171) that generates a first correction signal to correct one sampling period of the first main interference signal based on the auxiliary interference signal, a delay value generation unit that generates a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide (131) and the optical path length of the second optical waveguide (132), and a second correction signal generation unit (172) that generates a second correction signal to correct one sampling period of the second main interference signal based on the auxiliary interference signal and the delay value. REFERENCE MARK

[0195] 1 Sensor system; 10 Displacement sensor; 11 Control device; 12 Control signal input sensor; 13 External connection device; 20 Sensor head; 21 Objective lens; 22a Collimator lens; 22b Collimator lens; 22c Collimator lens; 23 Lens holder; 24 Optical fiber array; 30 Control unit; 31 Display unit; 32 Adjustment unit; 33 External I / F section; 34 Optical fiber connection section; 35 External storage unit; 36 Measurement processing unit; 40 Optical fiber; 51 Wavelength tuning light source; 52 Optical amplifier; 53, 53a, 53b Insulator; 54, 54a, 54b, 54c, 53d, 54e, 54f, 54g, 54h, 54i, 54j Optocoupler; 55 Attenuator; 56a, 56b, 56c Light receiving element; 57a, 57b, 57c Amplifier circuit; 58a, 58b, 58c AD converter unit; 59 Processing unit; 60 Balance detector; 61 Correction signal generation unit; 71a, 71b, 71c, 71d, 71e Light receiving element; 72a, 72b, 72c Amplifier circuit; 74a, 74b, 74c A / D converter unit; 75 Processing unit; 76 Differential amplifier circuit; 77 Correction signal generation unit; 100, 101 Optical interferometric distance sensor; 110 Control unit; 111 Optical divider unit; 112, 113 First photodiode; 114, 115 Amplifier circuit; 116, 116, 119 Second photodiode; 118 Processing unit; 121 First sensor head; 122 Second sensor head; 130 Optical fiber cable; 131 First optical fiber; 132 Second optical waveguide; 140 Light source with wavelength tuning; 150 Main interferometer; 151 First main interferometer; 152 Second main interferometer; 160 Auxiliary interferometer; 161 First optocoupler; 162 Second optocoupler; 163 Optical waveguide; 164 Optical fiber; 165 Optical fiber; 171 First correction signal generation unit; 172 Second correction signal generation unit; 173 Third correction signal generation unit; 181, 182 A / D converter unit; 191, 192 Delay line; Lm Optical measurement path; Lr Optical reference path; T, T1, T2 Target object; t1 Time; t2 Time; t12 Delay time; Tsmin Sampling period relative to voltage; Δt Time difference QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2017-181115 A

[0004]

Claims

[1] Controller connected via an optical fiber cable to a first sensor head and a second sensor head, from which a light beam is emitted onto a target object, the controller comprising: a light source configured to project a beam of light while changing its wavelength; a first principal interferometer which, by being fed with the light beam projected from the light source, is configured to generate a first principal interference signal based on a first measurement light beam emitted from a first sensor head onto a measurement target object and reflected by the measurement target object, and a first reference light beam which travels along an optical path that differs at least partially from an optical path of the first measurement light beam; a second principal interferometer which, by being fed with the light beam projected from the light source, is configured to generate a second principal interference signal based on a second measurement light beam emitted from a second sensor head onto the target object and reflected by the target object, and a second reference light beam traveling along an optical path that differs at least partially from an optical path of the second measurement light beam; and an auxiliary interferometer which, by being fed with the light beam projected from the light source, is configured to generate an auxiliary interference signal based on two light beams traveling along different optical paths, including the fiber optic cable a first optical waveguide connected to the second main interferometer, transmits a light beam from the first main interferometer to the first sensor head and transmits a light beam from the first sensor head to the first main interferometer, a second optical waveguide connected to the second main interferometer, transmits a light beam from the second main interferometer to the second sensor head and transmits a light beam from the second sensor head to the second main interferometer, wherein the second optical waveguide has an optical path length that differs from the optical path length of the first optical waveguide, and the control further includes a first correction signal generation unit configured to generate a first correction signal to correct one sampling period of the first main interference signal based on the auxiliary interference signal, a delay value generation unit configured to generate a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide and the optical path length of the second optical waveguide, and a second correction signal generation unit configured to generate a second correction signal to correct one sampling period of the second main interference signal based on the auxiliary interference signal and the delay value. [2] Control according to claim 1, wherein the delay value generation unit includes a third optical waveguide with an optical path length based on the length difference of the optical paths, configured to transmit the auxiliary interference signal. [3] Control according to claim 1, wherein the delay value generation unit includes a delay line which causes a delay in the time axis direction corresponding to the delay value in an auxiliary interferometer signal obtained by converting the auxiliary interference signal into an electrical signal and outputs the auxiliary interferometer signal to the second correction signal generation unit. [4] Control according to claim 1, wherein the second correction signal generation unit generates a pulse signal, which is the second correction signal, based on a signal obtained by applying a delay in the time axis direction corresponding to the delay value in an auxiliary interferometer signal obtained by converting the auxiliary interference signal into an electrical signal. [5] Control according to claim 1, further comprising an AD converter unit configured to sample a second principal interference signal obtained by converting the second principal interference signal into an electrical signal based on the second correction signal, and to convert the second principal interferometer signal into a digital signal. [6] Control according to claim 5, wherein the delay value is set such that an absolute value of a difference to a delay time of a light beam due to the length difference of the optical paths is smaller than a minimum sampling period in the AD converter unit. [7] Control according to claim 1, further comprising a processing unit configured to measure a distance to the target object based on at least one of the first principal interference signal or second principal interference signal and the auxiliary interference signal. [8] Optical interferometric distance sensor, comprising: a control system; and a fiber optic cable connected to the controller, including the control system a light source configured to project a beam of light while changing its wavelength, a first principal interferometer which, by being fed with the light beam projected from the light source, is configured to generate a first principal interference signal based on a first measurement light beam emitted from a first sensor head onto a measurement target object and reflected by the measurement target object, and a first reference light beam which travels along an optical path that differs at least partially from an optical path of the first measurement light beam, a second principal interferometer which, by being fed with the light beam projected from the light source, is configured to generate a second principal interference signal based on a second measurement light beam emitted from a second sensor head onto the target object and reflected by the target object, and a second reference light beam which travels along an optical path that differs at least partially from an optical path of the second measurement light beam, and an auxiliary interferometer which, by being fed with the light beam projected from the light source, is configured to generate an auxiliary interference signal based on two light beams traveling along different optical paths, including the fiber optic cable a first optical waveguide connected to the second main interferometer, transmits a light beam from the first main interferometer to the first sensor head and transmits a light beam from the first sensor head to the first main interferometer, a second optical waveguide connected to the second main interferometer, transmits a light beam from the second main interferometer to the second sensor head and transmits a light beam from the second sensor head to the second main interferometer, wherein the second optical waveguide has an optical path length that differs from the optical path length of the first optical waveguide, and the control further includes a first correction signal generation unit configured to generate a first correction signal to correct one sampling period of the first main interference signal based on the auxiliary interference signal, a delay value generation unit configured to generate a delay value based on a length difference of the optical paths between the optical path length of the first optical waveguide and the optical path length of the second optical waveguide, and a second correction signal generation unit configured to generate a second correction signal to correct one sampling period of the second main interference signal based on the auxiliary interference signal and the delay value.

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