Optical fiber feeler gauge, micro-gap measurement system and measurement method

Abstract

The invention relates to the technical field of distance measurement, and discloses an optical fiber feeler gauge, a micro-gap measurement system and a micro-gap measurement method.The optical fiber feeler gauge comprises a sensor installation support, a first optical fiber and a second optical fiber, and an open groove penetrating through the surface of the sensor installation support is formed in one end of the sensor installation support; the optical fiber probe is arranged in the open groove and is composed of two single-mode optical fibers which are overlapped in parallel, and the optical fiber end faces of the sides, close to the end part of the sensor mounting bracket provided with the open groove, of the two single-mode optical fibers form 45-degree angles with the surfaces of the corresponding single-mode optical fibers respectively; and the included angle between the optical fiber end surfaces of the sides, close to the end part of the sensor mounting bracket provided with the slots, of the two single-mode optical fibers is 90 degrees. According to the invention, non-contact lossless dynamic measurement of the micro-gap in the ultra-precision manufacturing process can be realized, dynamic regulation and control of the micro-gap become possible, and technical support is provided for production and manufacturing of part of high-precision industrial products and sharp weapons and equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of distance measurement, and in particular to an optical fiber feeler gauge, a micro-gap measurement system and a measurement method. Background Art

[0002] Metal feeler gauges are commonly used to measure tiny gaps with depth. This method is a contact measurement method that can only measure the minimum value of the gap and cannot detect the gap value in real time. This results in the feeler gauge not being able to meet the requirements of non-destructive measurement that requires protecting objects on both sides of the gap from damage, and it is impossible to obtain the change of the gap with the depth during the insertion of the feeler gauge into the gap. At the same time, it is not suitable for real-time detection of the gap value during the assembly process. Therefore, how to design a non-contact feeler gauge for measuring the gap is an urgent problem to be solved. Summary of the invention

[0003] The present invention provides an optical fiber feeler gauge, an optical fiber feeler gauge and a measuring method. It is intended to construct a non-contact "optical fiber feeler gauge" based on a micro-optical fiber sensing structure, and use the optical frequency domain interference ranging principle and wavelength division multiplexing technology to simultaneously obtain the distances from the upper and lower surfaces of a gap to be measured to a sensor, and then use a simple geometric relationship to accurately measure the tiny gap value. The method can obtain the absolute distance of the gap value in real time, can realize real-time detection of the gap during the gap change process, and can also obtain the change of the gap with the depth during the insertion of the feeler gauge into the gap in real time. At the same time, laser ranging is used to realize non-contact measurement of objects on both sides of the gap, ensuring non-destructive measurement without damaging the surface to be measured.

[0004] The present invention is achieved through the following technical solutions:

[0005] An optical fiber feeler gauge, comprising:

[0006] A sensor mounting bracket, wherein a groove penetrating the surface of the sensor mounting bracket is formed at one end of the sensor mounting bracket;

[0007] The optical fiber probe is arranged in the groove and consists of two parallel and superimposed single-mode optical fibers. The optical fiber end faces of the two single-mode optical fibers on one side of the end of the sensor mounting bracket with the groove are respectively 45° to the surface of the corresponding single-mode optical fiber, and the angle between the optical fiber end faces of the two single-mode optical fibers on one side of the end of the sensor mounting bracket with the groove is 90°. The light beam in the single-mode optical fiber is refracted to the surface of the single-mode optical fiber through the optical fiber end face, and the surface is made to be a reference light reflecting surface, so that part of the light forms reference light and is reflected back to the optical fiber end face and refracted to the signal receiving end, and the other part of the light passes through the reference light reflecting surface to the inner wall of the gap to form signal light for interfering with the reference light. The signal light passes through the reference light reflecting surface to the optical fiber end face and is refracted to the signal receiving end, so as to realize the measurement of the distance from the two inner walls of the gap to the corresponding upper surface or lower surface of the optical fiber probe.

[0008] As an optimization, the sensor mounting bracket is a thin sheet, and the length direction of the slot is parallel to the length direction of the thin sheet.

[0009] As an optimization, the upper surface of the optical fiber probe is lower than the upper surface of the thin sheet, the lower surface of the optical fiber probe is higher than the lower surface of the thin sheet, and the optical fiber end face of the optical fiber probe on one side of the end of the sensor mounting bracket where the groove is opened is located inside the groove.

[0010] As an optimization, an extended surface of the optical fiber end face of one of the single-mode optical fibers close to the end of the sensor mounting bracket where the groove is formed is at 45° to the upper surface of the sensor mounting bracket, and an extended surface of the optical fiber end face of the other single-mode optical fiber close to the end of the sensor mounting bracket where the groove is formed is at 45° to the lower surface of the sensor mounting bracket.

[0011] The present invention also discloses a micro-gap measurement system, comprising:

[0012] A broadband light source, for generating broadband light;

[0013] an optical wave transmission device for receiving the broadband light and transmitting the broadband light to the aforementioned optical fiber feeler gauge, and receiving and transmitting the reference light and the signal light returned from the optical fiber of the optical fiber feeler gauge;

[0014] The aforementioned optical fiber feeler gauge is used to connect to the optical wave transmission device via an optical fiber;

[0015] A spectrometer, used for collecting the reference light and the signal light in the optical fiber, so as to complete the interference and photoelectric conversion between the reference light and the signal light, and obtain a frequency domain interference signal;

[0016] The computer uses Fourier analysis to process the frequency domain interference signal to obtain the time difference between the reference light and the signal light, and calculates the distance between the optical fiber end face and the inner wall corresponding to the gap.

[0017] As an optimization, the light wave transmission device includes:

[0018] An optical fiber circulator, used for receiving the broadband light generated by the broadband light source and receiving and transmitting the reflected reference light and signal light;

[0019] The wavelength division multiplexer is used to split the broadband light into two light beams in terms of frequency / wavelength, and transmit the two light beams obtained after the splitting to two single-mode optical fibers corresponding to the optical fiber probe respectively.

[0020] As an optimization, the distance of the gap is specifically:

[0021] D=D1+D2+H;

[0022] Wherein, D is the distance of the gap, D1 is the distance from the upper surface of the optical fiber feeler gauge to the inner wall of the gap, D2 is the distance from the lower surface of the optical fiber feeler gauge to the inner wall of the gap, and H is the height of the optical fiber probe.

[0023] The present invention also discloses a measurement method based on the aforementioned optical fiber feeler gauge, comprising:

[0024] Sending a light beam emission instruction to control the broadband light source to emit broadband light to the optical fiber, and dividing the broadband light into two light beams in terms of frequency at the same time through a wavelength division multiplexer, thereby increasing a single measurement per unit time to two measurements, and the two light beams respectively pass through two single-mode optical fibers corresponding to the optical fiber probe and the inner wall of the gap to form a reference light and a signal light respectively;

[0025] Sending a frequency domain signal acquisition instruction to control the frequency domain signal acquisition device to acquire the reference light and the signal light, and respectively complete the interference and photoelectric conversion of the reference light and the signal light corresponding to the two light beams to obtain two frequency domain interference signals;

[0026] Using a calculator to perform Fourier analysis, the two frequency domain interference signals are processed respectively to obtain the time difference between the reference light and the signal light of the two light beams, and the distances from the reference light reflection surfaces of the two single-mode optical fibers to the inner wall of the gap are obtained respectively;

[0027] The distance of the gap is obtained by combining the stacking height of the two single-mode optical fibers and the distance from the reference light reflection surfaces of the two single-mode optical fibers to the inner wall of the gap.

[0028] As an optimization, the two light beams pass through two single-mode optical fibers of the optical fiber probe and the inner wall of the gap to form reference light and signal light respectively. The specific process is as follows:

[0029] The light beam in the single-mode optical fiber is refracted to the surface of the single-mode optical fiber through the optical fiber end face, and the surface is made to be a reference light reflecting surface, so that a part of the light forms a reference light and is reflected back to the optical fiber end face and refracted to the signal receiving end, and the other part of the light passes through the reference light reflecting surface to the inner wall of the gap and forms a signal light for interfering with the reference light.

[0030] As an optimization, the specific formula for the distance from the reference light reflecting surface to the inner wall of the gap is:

[0031] d = τ × c;

[0032] 2n

[0033] Where: τ is the transmission time difference between the reference light and the signal light, c is the speed of light in a vacuum, and n is the refractive index of the transmission medium.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The optical fiber feeler gauge, optical fiber feeler gauge and measurement method described in the present invention can realize non-contact and non-destructive dynamic measurement of tiny gaps in the ultra-precision manufacturing process, making dynamic regulation of tiny gaps possible, and providing technical support for the production and manufacturing of some high-precision industrial products and cutting-edge weapon equipment.

[0036] The optical fiber feeler gauge of the present invention does not contact the upper and lower surfaces of the gap during measurement, and can achieve non-contact measurement of the gap, which is more accurate than the technology of contacting one side or both sides;

[0037] The distance measurement of the present invention uses a wavelength division multiplexer to divide the spectrum of the broadband light into two parts, which solves the problem that all the spectrum components of the broadband light are used to test a distance information in the prior art, and the broadband light spectrum is not effectively utilized, and the cost and complexity of the multi-point distance measurement system can be greatly reduced;

[0038] The test system of the present invention can perform two distance measurements at the same time, so as to obtain the distances from the upper and lower surfaces of the gap to be tested to the sensor at the same time, and can avoid the measurement error caused by the distance information from the upper and lower surfaces to the sensor not being obtained at the same time during the dynamic change of the gap. This is a prerequisite for the method proposed by the present invention to realize non-contact dynamic testing of the gap.

[0039] Existing patented sensing probes require additional reflective surfaces, are difficult to manufacture, are costly, and cannot be used for non-contact dynamic measurement of gaps. The fiber optic feeler gauge of the present invention has a simple structure and low cost. At the same time, the fiber optic feeler gauge of the present invention can be moved at will to achieve non-contact dynamic measurement of gaps, thereby enabling contour measurement of the upper and lower surfaces of the gap. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0041] Figure 1 is an overall schematic diagram of the optical fiber feeler gauge of the present invention;

[0042] Figure 2 is a schematic diagram of a single-mode optical fiber;

[0043] Figure 3 It is a schematic diagram of the structure of the optical fiber probe;

[0044] Figure 4 It is a structural schematic diagram of the mounting bracket;

[0045] Figure 5 for Figure 1 Schematic diagram of the local structure;

[0046] Figure 6 It is a structural schematic diagram of the micro-gap measurement system of the present invention;

[0047] Figure 7 It is the spectrum diagram after the light beam is split by the wavelength division multiplexer;

[0048] Figure 8 Schematic diagram of the gap measurement process;

[0049] Fig. 9 Schematic diagram of two-dimensional gap measurement.

[0050] Marks and corresponding parts names in the attached drawings:

[0051] 1-Sensor mounting bracket, 2-Fiber optic probe. DETAILED DESCRIPTION

[0052] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0053] This embodiment 1 provides a fiber optic feeler gauge, which is intended to construct a non-contact "fiber optic feeler gauge" based on a micro-fiber optic sensing structure, and uses the optical frequency domain interferometry ranging principle and wavelength division multiplexing technology to perform two distance measurements at the same time, so as to simultaneously obtain the distances from the upper and lower surfaces of the gap to be measured to the sensor, that is, to obtain the distances from the upper and lower surfaces of the gap to be measured to the sensor, and then use simple geometric relationships to accurately measure the tiny gap value. This method can obtain the absolute distance of the gap value in real time, can realize real-time detection of the gap during the gap change process, and can also obtain the change of the gap with the depth during the insertion of the feeler gauge into the gap in real time. At the same time, laser ranging is used to realize non-contact measurement of objects on both sides of the gap, ensuring non-destructive measurement without damaging the surface to be measured.

[0054] The basic principle of the gap measurement method proposed in the present invention is the principle of optical frequency domain interferometry. The "fiber feeler gauge" micro sensor is designed and manufactured using an optical fiber embedded structure. Two micro fiber optic folding probes are used to measure the distance between the upper and lower surfaces of the gap and the sensor respectively using lasers of different wavelength ranges, thereby realizing non-contact, non-destructive and dynamic measurement of small gaps. The specific implementation method is:

[0055] The "fiber optic feeler gauge" micro sensor that can measure the distance between the upper and lower surfaces of the gap simultaneously includes:

[0056] The optical fiber probe 2 is arranged in the slot and is composed of two parallel and superimposed single-mode optical fibers. The single-mode optical fiber here refers to an optical fiber without a coating layer. Figure 3 As shown, the optical fiber end faces of the two single-mode optical fibers on one side of the end of the sensor mounting bracket 1 where the groove is formed are respectively 45° to the surface of the corresponding single-mode optical fibers, and the angle between the optical fiber end faces of the two single-mode optical fibers on one side of the end of the sensor mounting bracket 1 where the groove is formed is 90°.

[0057] The single-mode optical fiber is a micro optical fiber folding light output probe. The optical fiber end face is polished 45 degrees. When the light wave is transmitted through the optical fiber and reaches the 45-degree optical fiber polishing surface, it is reflected due to the Fresnel effect, which changes the transmission direction of the light wave and realizes the 90-degree folding output of the light wave. Figure 2 shown.

[0058] Figure 2 The middle optical fiber is a common single-mode optical fiber with a diameter of 150μm. When in use, the coating layer is peeled off and the remaining diameter is 125μm. When in use, two 45° polished single-mode optical fibers are combined and bonded. The light-emitting part is as follows Figure 2 As shown in the figure, a micro optical fiber folding light emitting probe with upper and lower light emitting is formed. An optical fiber connector is made at the other end of the two single-mode optical fibers for connecting with the measurement system.

[0059] The sensor mounting bracket 1 has a groove at one end thereof which penetrates the surface of the sensor mounting bracket 1. Figure 4 As shown; in this embodiment, the sensor mounting bracket 1 is a thin sheet, and the length direction of the slot is parallel to the length direction of the thin sheet, so that it is convenient to insert the sensor mounting bracket 1 into the gap and measure the distance of the gap.

[0060] For example, the thickness along the Z direction is 0.3 mm, the length along the Y direction is 50 mm, and the width along the X direction is 5 mm. At the same time, a groove is made in the Y direction, the groove position is in the middle of the sheet, the groove width is 0.13 mm, and the depth is 0.3 mm.

[0061] Furthermore, the micro-fiber folded light output probe and the sensor mounting bracket 1 are assembled and installed to form a fiber optic feeler gauge. During installation, the micro-fiber folded light output probe for outputting light from top to bottom is placed in the center of the slot of the sensor bracket and fixed with glue. For example, the sensor mounting bracket 1 has a height of 0.3mm and a width of 0.13mm, and the probe has a height of 0.25mm and a width of 0.125mm. After installation, it can ensure that the fiber optic probe 2 is located inside the groove and is not easily damaged during use. The schematic diagram of the light output position of the fiber optic feeler gauge after installation is shown in the figure below. Figure 5 As shown, the overall schematic diagram of the optical fiber feeler gauge is as follows Figure 1 The fiber optic feeler gauge uses spectral interference technology, and the light beams on the measurement system link are all propagated in the optical fiber, which is not easily affected by electromagnetic interference.

[0062] The light beam in the single-mode optical fiber is refracted to the surface of the single-mode optical fiber through the optical fiber end face, and the surface is made to be a reference light reflection surface, so that a part of the light forms a reference light and is reflected back to the optical fiber end face and refracted to the signal receiving end, and the other part of the light passes through the reference light reflection surface to the inner wall of the gap to form a signal light for interfering with the reference light, and the signal light passes through the reference light reflection surface to the optical fiber end face and is refracted to the signal receiving end, so as to measure the distance from the two inner walls of the gap to the corresponding upper surface or lower surface of the optical fiber probe 2. In this embodiment, the extended surface of the optical fiber end face on one side of the end of the sensor mounting bracket 1 where the groove is provided is 45 degrees to the upper surface of the sensor mounting bracket 1, and the extended surface of the optical fiber end face on the other side of the single-mode optical fiber near the end of the sensor mounting bracket 1 where the groove is provided is 45 degrees to the lower surface of the sensor mounting bracket 1. That is, let the surface of the sensor mounting bracket 1 be the upper surface and the lower surface, then the extended surface of the optical fiber end face of one single-mode optical fiber is at 45° with the upper surface of the sensor mounting bracket 1, and the extended surface of the optical fiber end face of the other single-mode optical fiber is at 45° with the lower surface of the sensor mounting bracket 1, as shown in FIG. Figure 3 and 5 shown.

[0063] In this embodiment, the upper surface of the optical fiber probe 2 is lower than the upper surface of the thin sheet, the lower surface of the optical fiber probe 2 is higher than the lower surface of the thin sheet, and the optical fiber end face of the optical fiber probe 2 on the side of the end of the sensor mounting bracket 1 where the groove is opened is located inside the groove.

[0064] Therefore, the embodiment of the present invention transmits a light beam in a straight line to the optical fiber end face at an angle of 45°, and reflects part of the light beam to the corresponding inner wall of the gap through the optical fiber end face to form reflected light for reflecting back to the optical fiber through the optical fiber end face, so as to measure the distance from the inner wall of the gap to the reflecting surface, thereby avoiding the defect of the prior art that a contact feeler gauge is used for gap measurement, so that real-time detection of the gap during the gap change process cannot be achieved, and the change of the gap with the depth during the insertion of the feeler gauge into the gap cannot be obtained in real time.

[0065] Embodiment 2 further discloses a micro-gap measurement system, comprising:

[0066] A broadband light source, for generating broadband light;

[0067] an optical wave transmission device for receiving the broadband light and transmitting the broadband light to the aforementioned optical fiber feeler gauge, and receiving and transmitting the reference light and the signal light returned from the optical fiber of the optical fiber feeler gauge;

[0068] The aforementioned optical fiber feeler gauge is connected to the optical wave transmission device via an optical fiber;

[0069] A spectrometer, used for collecting the reference light and the signal light in the optical fiber, so as to complete the interference and photoelectric conversion between the reference light and the signal light, and obtain a frequency domain interference signal;

[0070] The computer uses Fourier analysis to process the frequency domain interference signal to obtain the time difference between the reference light and the signal light, and calculates the distance between the optical fiber end face and the inner wall corresponding to the gap.

[0071] In this embodiment, the light wave transmission device includes:

[0072] An optical fiber circulator, used for receiving the broadband light generated by the broadband light source and receiving and transmitting the reflected reference light and signal light;

[0073] The wavelength division multiplexer is used to split the broadband light into two light beams in terms of frequency / wavelength, and transmit the two light beams obtained after the splitting to two single-mode optical fibers corresponding to the optical fiber probe 2 respectively.

[0074] In the traditional frequency interference test method, all spectral components of broadband light are used to test a distance information, and the effective use of the broadband light spectrum is not achieved. In the present invention, a wavelength division multiplexer is used to divide the spectrum of broadband light into two parts. The wavelength division multiplexer used has one input port and two output ports. The input end is connected to broadband light with a spectral range of 1525nm to 1565nm. Output port 1 outputs broadband light with a wavelength of 1525nm to 1543nm, and output port 2 outputs broadband light with a wavelength of 1547nm to 1565nm. The spectrum of the broadband light is multiplexed, and the receiving end processes the two parts of the spectrum separately to achieve simultaneous measurement of two optical fiber probes.

[0075] The wide spectrum light is divided by wavelength division multiplexing technology, and the distance between the upper and lower surfaces is measured at the same time using different wavelength ranges; the measurement of different gap values ​​is achieved by synchronously solving the frequency interference signals in different spectral ranges. The system structure diagram is shown in the figure. Figure 6 shown.

[0076] The broadband laser first passes through the fiber circulator, and then passes through the wavelength division multiplexer to split the broadband light source into two. The spectrum after division is as follows: Figure 7 As shown, the split spectrum enters the upper and lower micro-fiber probes 2 respectively, and after being turned 90°, the distance between the feeler gauge and the upper and lower surfaces of the gap is measured respectively. The gap value is obtained after calculation. The schematic diagram of the measurement process is shown in Figure 8 shown.

[0077] like Figure 7 As shown, since the thickness of the sensor mounting bracket 1 is greater than the thickness of the micro-fiber folded light-emitting probe, there is a gap between the upper and lower surfaces of the fiber optic feeler gauge and the light-emitting surface of the fiber optic probe 2, and the gap values ​​are h1 and h2 respectively. At the beginning of the distance measurement, the wide-spectrum laser (light beam) is divided into two parts, one of which enters the "upper" fiber optic probe 2 (i.e., the upper single-mode optical fiber), and the laser is reflected by a 45° inclined surface and then emitted perpendicularly to the optical fiber. Due to reflection on the emission surface, a reference light is formed and returns along the original path. The remaining emitted light hits the upper surface of the gap and forms a signal light that returns along the original path. Assuming that the amplitudes of the two reflected light beams (reference light and signal light) are equal, the mathematical expression of the amplitude of the reference light wave participating in the interference in the frequency domain is E ref (t) can be expressed as:

[0078] E ref (t) = E 0 cos(2πf 0 t+φ r ) (1)

[0079] Where: E ref (t) is the reference light amplitude, f 0 is the frequency of the light wave component, φ r is the initial phase of the reference light wave.

[0080] Similarly, the mathematical expression of the amplitude of the signal light wave participating in the interference in the frequency domain is E prb (t) can be expressed as:

[0081]

[0082] Where: E prb (t) is the signal light amplitude; f 0 is the frequency of the light wave component; τ is the transmission time difference between the two light wave signals (reference light and signal light); φ p is the initial phase of the signal light wave; R is the relative coefficient of the reflected signal light of the measured target (i.e. the ratio of the signal light intensity to the reference light intensity).

[0083] When the spectrometer detects the spectrum, the photoelectric conversion process is a square rate detection. Therefore, the square of equations (1) and (2) can be added to obtain f 0 The component interference field spectral intensity is as follows:

[0084]

[0085] Wherein, η is a constant coefficient including factors such as photoelectric conversion efficiency.

[0086] Since the photoelectric conversion elements in the frequency domain signal acquisition instrument cannot respond to the hundreds of terahertz level of f 0 And higher frequency time-varying signals, so their average value is 0, so the last three terms of equation (3) can be omitted and rewritten as:

[0087]

[0088] From equation (4), we can see that the intensity of the frequency domain interference field is not only related to the reflectivity R of the light wave signal and the initial phase angle φ r ,φ p It is not only related to the light wave frequency f and the transmission time difference τ, and the transmission time difference τ is the period of the interference signal. Therefore, the frequency domain interference field intensity distribution collected by the spectrum analyzer can be written as:

[0089]

[0090] By performing Fourier analysis on the frequency domain interference signal described in formula (5), the transmission time difference τ of the two light waves can be obtained, and then the distance d between the reference light reflection surface and the measured surface can be calculated as follows:

[0091]

[0092] In the formula: τ is the transmission time difference between the two light wave signals, c is the speed of light in a vacuum, and n is the refractive index of the transmission medium.

[0093] When the above principle is applied to gap measurement, the optical fiber feeler gauge does not contact the two surfaces of the gap between the gaps. During the distance measurement process, the upper and lower single-mode optical fibers measure the upper and lower inner walls of the gap respectively, and the reference light reflection surface is the end face of the optical fiber inside the gap sensor.

[0094] The distance d is the distance from the optical fiber's light-emitting surface to the surface to be measured. In actual use, the thickness of the sensor (fiber optic feeler gauge) needs to be calibrated. The calibration process is as follows: First, cover the upper surface of the "fiber optic feeler gauge" with a flat reflective surface. At this time, the test distance d = h1. Then, cover the lower surface of the fiber optic feeler gauge with a flat reflective surface. At this time, the test distance d = h2. Finally, the sensor thickness H = h1 + h2 + 0.25 is calculated, and the unit is mm. Therefore, during use, the distance from the upper surface of the gap to the upper surface of the fiber optic feeler gauge is D1 = d1-h1, and the distance from the lower surface of the gap to the lower surface of the fiber optic feeler gauge is D2 = d2-h2. The gap value D = D1 + D2 + H = d1 + d2 + 0.25, and the unit is mm.

[0095] Embodiment 3 further discloses a measurement method based on the aforementioned optical fiber feeler gauge, the execution subject is the micro-gap measurement system of embodiment 2, including:

[0096] Sending a light beam emission instruction to control the broadband light source to emit broadband light to the optical fiber, and dividing the broadband light into two light beams in terms of frequency at the same time through a wavelength division multiplexer, wherein the two light beams pass through two single-mode optical fibers corresponding to the optical fiber probe 2 and the inner wall of the gap to form a reference light and a signal light respectively;

[0097] Send a frequency domain signal acquisition instruction to control the frequency domain signal acquisition device to collect the reference light and the signal light, and respectively complete the interference and photoelectric conversion of the reference light and the signal light corresponding to the two light beams to obtain two frequency domain interference signals; in this embodiment, the two light beams respectively pass through the two single-mode optical fibers of the optical fiber probe 2 and the inner wall of the gap to form the reference light and the signal light respectively. The specific process is as follows:

[0098] The light beam in the single-mode optical fiber is refracted to the surface of the single-mode optical fiber through the optical fiber end face, and the surface is made to be a reference light reflecting surface, so that a part of the light forms a reference light and is reflected back to the optical fiber end face and refracted to the signal receiving end, and the other part of the light passes through the reference light reflecting surface to the inner wall of the gap and forms a signal light for interfering with the reference light.

[0099] Using a computer to perform Fourier analysis, the two frequency domain interference signals are processed respectively to obtain the time difference between the reference light and the signal light of the two light beams, and the distances from the reference light reflection surfaces of the two single-mode optical fibers to the inner wall of the gap are obtained respectively;

[0100] The distance of the gap is obtained by combining the stacking height of the two single-mode optical fibers and the distance from the reference light reflection surface of the two single-mode optical fibers to the inner wall of the gap. The specific formula for the distance from the reference light reflection surface to the inner wall of the gap is:

[0101]

[0102] Where: τ is the transmission time difference between the reference light and the signal light, c is the speed of light in a vacuum, and n is the refractive index of the transmission medium.

[0103] Finally, the specific formula of the gap distance measured by the micro-gap measurement system is:

[0104] D=D1+D2+H;

[0105] Wherein, D is the distance of the gap, D1 is the distance from the upper reflective surface of the optical fiber feeler gauge to the inner wall of the gap, D2 is the distance from the lower reflective surface of the optical fiber feeler gauge to the inner wall of the gap, and H is the height of the optical fiber probe 2.

[0106] refer to Figure 2 As shown, the light beam generated by the wide spectrum light source is input from port 1 of the optical fiber circulator, and the light beam output from port 2 enters the wavelength division multiplexer (which plays the role of splitting and combining beams and can connect two single-mode optical fibers), and its output light is sent to the optical fiber probe 2 by the transmission optical fiber. The optical fiber probe 2 is glued in the slot of the sensor mounting bracket 1, and the glue can be set between the optical fiber probe 2 and the horizontal inner wall of the slot. The reference light and the signal light are reflected by the upper surface and the lower surface of the measured gap, respectively. The optical fiber probe 2 collects the reflected reference light wave and the detection light wave signal, and reversely passes through the transmission optical fiber and the wavelength division multiplexer to input the port 2 of the optical fiber circulator, and then outputs from the port 3 to the spectrometer, completing the interference, photoelectric conversion and collection of the reference light and the signal light. The frequency domain interference signal of the spectrometer is obtained by the computer, and then the transmission time difference is obtained by Fourier analysis, and then the distance information between the reference light reflection surface and the measured surface is calculated.

[0107] Since the z-direction height of the optical fiber probe 2 is smaller than the z-direction thickness of the sensor mounting bracket 1 and the glue is disposed between the optical fiber probe 2 and the horizontal inner wall of the slot, it is only necessary to determine the z-direction height of the optical fiber probe 2 .

[0108] After the formal measurement, the specific formula of the gap distance measured by the micro-gap measurement system is:

[0109] D=D1+D2+H.

[0110] For example, the optical fiber feeler gauge of the present invention is used Figure 5As shown, the sensor mounting bracket 1 is made of ceramic thin sheet, with a thickness of 0.3mm along the Z direction, a length of 50mm along the Y direction, and a width of 5mm along the X direction. At the same time, a groove is cut in the Y direction, the groove position is in the middle of the thin sheet, the groove width is 0.13mm, and the depth is 0.3mm. The schematic diagram of the mounting bracket is shown in Figure 5 The slotted position of the mounting bracket is used to mount the upper and lower light-emitting micro optical fiber probe 2, and the structural diagram is shown in FIG. Figure 3 As shown, the upper and lower light-emitting micro-fiber probe 2 is composed of Figure 2 The two single-mode optical fibers shown are ground at 45°. Figure 6 The dual-channel multiplexed micro-gap measurement system shown in the figure realizes the collection and processing of the gap value, wherein the wide-spectrum laser first passes through the fiber circulator, and then passes through the wavelength division multiplexer to split the wide-spectrum light source into two, and the split spectrum enters the upper and lower probes of the "fiber feeler gauge" sensor respectively, and the signal light passes through the upper and lower surfaces of the feeler gauge after being turned 90° and then returns along the original path, interfering with the reference light returned from the optical fiber light output surface, and after passing through the spectrometer, the interference fringes formed in the frequency domain are collected, and then the period of the interference fringes is calculated segmentally through Fourier transform, thereby obtaining the delay time of the signal light and the reference light on the upper and lower surfaces, and finally the delay time of the upper and lower surfaces is obtained through formula 6. Figure 8 The distance information d1 and d2 from the light-emitting surface of the optical fiber to the surface of the gap to be measured is shown. Finally, the gap value to be measured D=d1+d2+0.25 is calculated through simple geometric relationships, and the unit is mm. In implementation, the "fiber optic feeler gauge" sensor is fixed on a precision displacement platform with a fiber optic feeler gauge sensor fixture, and the displacement platform is adjusted to allow the feeler gauge to be located in the gap to be measured. The displacement platform is moved toward the depth of the gap to slowly move the feeler gauge deeper into the gap. At the same time, the gap value is calculated and recorded in real time, and the gap values ​​at different positions are measured to achieve two-dimensional measurement of the gap. The test structure diagram is shown in Fig. 9 shown.

[0111] In summary, the embodiments of the present invention develop a micro-optical fiber gap sensor and a measurement system based on the principle of spectral interference, thereby realizing the measurement of tiny gaps in confined spaces.

[0112] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An optical fiber feeler gauge, characterized in that: include: A sensor mounting bracket, wherein a groove penetrating the surface of the sensor mounting bracket is formed at one end of the sensor mounting bracket; The optical fiber probe is arranged in the groove and consists of two parallel and superimposed single-mode optical fibers. The optical fiber end faces of the two single-mode optical fibers on one side of the end of the sensor mounting bracket with the groove are respectively 45° to the surface of the corresponding single-mode optical fiber, and the angle between the optical fiber end faces of the two single-mode optical fibers on one side of the end of the sensor mounting bracket with the groove is 90°. The light beam in the single-mode optical fiber is refracted to the surface of the single-mode optical fiber through the optical fiber end face, and the surface is made to be a reference light reflecting surface, so that part of the light forms reference light and is reflected back to the optical fiber end face and refracted to the signal receiving end, and the other part of the light passes through the reference light reflecting surface to the inner wall of the gap to form signal light for interfering with the reference light. The signal light passes through the reference light reflecting surface to the optical fiber end face and is refracted to the signal receiving end, so as to realize the measurement of the distance from the two inner walls of the gap to the corresponding upper surface or lower surface of the optical fiber probe.

2. The optical fiber feeler gauge according to claim 1, characterized in that: The sensor mounting bracket is a thin sheet, and the length direction of the slot is parallel to the length direction of the thin sheet.

3. The optical fiber feeler gauge according to claim 2, characterized in that: The upper surface of the optical fiber probe is lower than the upper surface of the sheet, the lower surface of the optical fiber probe is higher than the lower surface of the sheet, and the optical fiber end face of the optical fiber probe on the side of the end of the sensor mounting bracket where the groove is opened is located inside the groove.

4. The optical fiber feeler gauge according to claim 2, characterized in that: An extended surface of the optical fiber end face of one of the single-mode optical fibers near the end of the sensor mounting bracket where the groove is formed is at 45° to the upper surface of the sensor mounting bracket, and an extended surface of the optical fiber end face of the other single-mode optical fiber near the end of the sensor mounting bracket where the groove is formed is at 45° to the lower surface of the sensor mounting bracket.

5. A micro-gap measurement system, characterized in that: include: A broadband light source, for generating broadband light; An optical wave transmission device, for receiving the broadband light and transmitting the broadband light to the optical fiber feeler gauge according to any one of claims 1 to 3, and receiving and transmitting the reference light and the signal light returned from the optical fiber of the optical fiber feeler gauge; The optical fiber feeler gauge according to any one of claims 1 to 4, used for connecting to the optical wave transmission device via an optical fiber; A spectrometer, used for collecting the reference light and the signal light in the optical fiber, so as to complete the interference and photoelectric conversion between the reference light and the signal light, and obtain a frequency domain interference signal; The computer uses Fourier analysis to process the frequency domain interference signal to obtain the time difference between the reference light and the signal light, and calculates the distance between the optical fiber end face and the inner wall corresponding to the gap.

6. The optical fiber feeler gauge according to claim 5, characterized in that: The light wave transmission device comprises: An optical fiber circulator, used for receiving the broadband light generated by the broadband light source and receiving and transmitting the reflected reference light and signal light; The wavelength division multiplexer is used to split the broadband light into two light beams in terms of frequency / wavelength, and transmit the two light beams obtained after the splitting to two single-mode optical fibers corresponding to the optical fiber probe respectively.

7. A method for measuring an optical fiber feeler gauge according to any one of claims 1 to 4, characterized in that: include: Sending a light beam emission instruction to control the broadband light source to emit broadband light to the optical fiber, and dividing the broadband light into two light beams in terms of frequency at the same time through a wavelength division multiplexer, wherein the two light beams pass through two single-mode optical fibers corresponding to the optical fiber probe and the inner wall of the gap to form a reference light and a signal light respectively; Sending a frequency domain signal acquisition instruction to control the frequency domain signal acquisition device to acquire the reference light and the signal light, and respectively complete the interference and photoelectric conversion of the reference light and the signal light corresponding to the two light beams to obtain two frequency domain interference signals; Using a calculator to perform Fourier analysis, the two frequency domain interference signals are processed respectively to obtain the time difference between the reference light and the signal light of the two light beams, and the distances from the reference light reflection surfaces of the two single-mode optical fibers to the inner wall of the gap are obtained respectively; The distance of the gap is obtained by combining the stacking height of the two single-mode optical fibers and the distance from the reference light reflection surfaces of the two single-mode optical fibers to the inner wall of the gap.

8. The method for measuring an optical fiber feeler gauge according to claim 7, characterized in that: The distance of the gap is specifically: D=D1+D2+H; Wherein, D is the distance of the gap, D1 is the distance from the upper reflective surface of the optical fiber feeler gauge to the inner wall of the gap, D2 is the distance from the lower reflective surface of the optical fiber feeler gauge to the inner wall of the gap, and H is the height of the optical fiber probe.

9. The method for measuring an optical fiber feeler gauge according to claim 7, characterized in that: The two light beams pass through the two single-mode optical fibers of the optical fiber probe and the inner wall of the gap to form reference light and signal light respectively. The specific process is as follows: The light beam in the single-mode optical fiber is refracted to the surface of the single-mode optical fiber through the optical fiber end face, and the surface is made to be a reference light reflecting surface, so that a part of the light forms a reference light and is reflected back to the optical fiber end face and refracted to the signal receiving end, and the other part of the light passes through the reference light reflecting surface to the inner wall of the gap and forms a signal light for interfering with the reference light.

10. The optical fiber feeler gauge according to claim 7, characterized in that: The specific formula for the distance from the reference light reflecting surface to the inner wall of the gap is: Where: τ is the transmission time difference between the reference light and the signal light, c is the speed of light in a vacuum, and n is the refractive index of the transmission medium.

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