On-line rotor and stator axial clearance measuring device and method based on optical carrier microwave interference

Abstract

The invention discloses a rotor and stator axial clearance online measuring device and method based on optical carrier microwave interference. The measuring device comprises a broadband light source, a first polarization maintaining optical fiber, an electro-optical modulator, a second polarization maintaining optical fiber, an optical fiber circulator, a first single-mode optical fiber and a coated optical fiber probe which are connected in sequence, and the coated optical fiber probe directly faces the axial end face to be measured; a first port of the optical fiber circulator is connected with the second polarization maintaining optical fiber, a second port of the optical fiber circulator is connected with the first single-mode optical fiber, and a third port of the optical fiber circulator is sequentially connected with the second single-mode optical fiber, the photoelectric detector, the signal conditioning unit, the signal acquisition unit and the digital processing unit; the signal acquisition unit is connected with the micro-control unit, the micro-control unit is connected with the microwave frequency sweep signal generation unit, and the microwave frequency sweep signal generation unit is connected with the electro-optical modulator. According to the invention, non-contact on-line high-precision measurement of the axial clearance of the rotor and the stator of the aero-engine under the conditions of limited measurement space and complex signal leading-out path can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of non-contact distance measurement and specifically relates to an online measurement device and method for rotor-stator axial clearance based on optical carrier microwave interference. Background Art

[0002] The state parameters of core components in large rotating machinery, such as aircraft engines, steam turbines, and turbines, directly impact the equipment's operating status, efficiency, and safety. One of these core parameters is rotor-stator axial clearance. This clearance refers to the axial distance between the moving and stator blades within the rotating machinery. Too little clearance increases the risk of blade-to-blade collision, while too much clearance reduces the equipment's operating efficiency. Therefore, measuring and monitoring rotor-stator axial clearance is crucial.

[0003] Among existing methods for measuring small gaps within rotating machinery, the capacitive method uses sensors that are too large to be suitable for measuring axial gaps in confined environments, such as those involving axial clearance measurements. The eddy current method, commonly used in normal-temperature engine operating environments, is unsuitable for measuring axial gaps in high-temperature environments. The microwave method can be used for measurements in high-temperature environments, but its sensor outer diameter is also large, and due to the nonlinear effects of microwave components, achieving high accuracy is difficult. Fiber-optic measurement methods offer advantages such as small probes, high-temperature resistance, and immunity to electromagnetic interference, making them ideal for measuring rotor-stator axial gaps within rotating machinery. Among the reported fiber-optic measurement methods, the swept-frequency interferometry axial gap measurement method has a response speed limited by the sweep speed of the swept-frequency light source, and Doppler errors are present in dynamic measurements. The traditional phase-based axial gap measurement method, which uses electrical down-conversion, is still limited in accuracy by the nonlinear effects of microwave components, and reflected light from the end face of the fiber-optic sensor probe is difficult to eliminate, introducing additional errors. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an online measurement device and method for the rotor-stator axial gap based on optical carrier microwave interference. The present invention adopts an all-fiber Fizeau common optical path structure and a microwave scanning method, which can inherit the advantages of the fiber-optic axial gap measurement method and has the advantages of high measurement response speed and high precision.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] An online measurement device for rotor-stator axial clearance based on optical carrier microwave interferometry, characterized by comprising a broadband light source, a first polarization-maintaining optical fiber, an electro-optical modulator, a second polarization-maintaining optical fiber, an optical fiber circulator, a first single-mode optical fiber, and a coated optical fiber probe connected in sequence, wherein the coated optical fiber probe is facing the axial end face to be measured;

[0007] The first port of the optical fiber circulator is connected to the second polarization-maintaining optical fiber, the second port is connected to the first single-mode optical fiber, and the third port is connected to the second single-mode optical fiber, the photoelectric detector, the signal conditioning unit, the signal acquisition unit, and the digital processing unit in sequence;

[0008] The signal acquisition unit is connected to the micro control unit, the micro control unit is connected to the microwave frequency sweep signal generating unit, and the microwave frequency sweep signal generating unit is connected to the electro-optical modulator.

[0009] Furthermore, the end face of the coated optical fiber probe is coated with a semi-transparent and semi-reflective optical film.

[0010] The present invention also provides an online measurement method for the rotor-stator axial clearance, comprising:

[0011] The broadband laser generated by the broadband light source passes through the first polarization-maintaining optical fiber to reach the electro-optic modulator;

[0012] The microwave frequency sweep signal generating unit generates a microwave modulation signal to modulate the intensity of the broadband laser passing through the electro-optical modulator;

[0013] The laser intensity-modulated by the electro-optical modulator passes through the second polarization-maintaining optical fiber, the optical fiber circulator, the first single-mode optical fiber and the coated optical fiber probe in sequence;

[0014] After the intensity-modulated laser light passes through the optical film of the coated fiber probe, a portion of the laser light is directly reflected back to the first single-mode fiber as the reference light; the other portion of the laser light passes through the optical film and is incident on the axial end face to be measured as the measurement light.

[0015] The axial distance of the measuring light is The light passes through the axial gap space to reach the axial end face to be measured, and part of the light after diffuse reflection by the axial end face to be measured is received by the coated optical fiber probe, and then enters the first single-mode optical fiber;

[0016] The measuring light and the reference light generate microwave interference, and the microwave interference signal passes through the second single-mode optical fiber and is received by the photodetector. The microwave interference signal output by the photodetector is de-DCed and amplified by the signal conditioning unit;

[0017] While controlling the microwave sweep signal generating unit to sweep the frequency, the microcontroller unit controls the signal acquisition unit to collect the output signal of the signal conditioning unit at each frequency point, and transmits the collected data to the data processing unit, and estimates the frequency of the signal through the frequency estimation algorithm, thereby calculating the size of the axial gap to be measured.

[0018] Furthermore, when the micro control unit controls the microwave frequency sweep signal generating unit to perform frequency sweep, an amplitude variation curve can be obtained.

[0019] Furthermore, the electric field of the broadband laser generated by the broadband light source is expressed as:

[0020] ;

[0021] Where, represents the electric field of broadband laser; represents the magnitude of the electric field; represents the angular frequency of the light wave; represents the phase of the light wave, and t represents time;

[0022] The microwave modulation signal generated by the microwave sweep signal generating unit is expressed as:

[0023] ;

[0024] Where, Indicates the modulation index, its value ranges from 0 to 1; Represents the angular frequency of the microwave modulation signal; Indicates the phase of the microwave modulated signal;

[0025] The intensity modulation response of the electro-optic modulator can be expressed as:

[0026] ;

[0027] The electric field of the optical signal modulated by the electro-optic modulator is expressed as:

[0028] ;

[0029] The measuring light and the reference light have different optical paths, and their electric fields are expressed as:

[0030] ;

[0031] Where, and are the electric fields of the measurement light and the reference light, and are the optical path lengths of the measuring light and the reference light, respectively, expressed as:

[0032] ;

[0033] Where, represents the refractive index of the optical fiber, represents the refractive index of air, Indicates the length of the optical fiber, Indicates the axial clearance to be measured;

[0034] Then the electric fields of the measurement light and the reference light are expressed as:

[0035] ;

[0036] Where, and represents the reflectivity of the measured light and the reflected light, respectively; W represents the transmission optical path of the optical fiber components other than the optical fiber; and c represents the speed of light;

[0037] The measurement light and reference light are broadband lasers. Assume that the spectrum width of the broadband laser is , the spectral range is arrive , then the optical power received by the photodetector is expressed as:

[0038] ;

[0039] When the spectral width of the broadband light source used is wide enough, its coherence length is much smaller than the optical path difference between the measuring light and the reference light, that is, the axial gap to be measured, and the second cross-multiplication integral term in the formula can be ignored;

[0040] The total optical power received by the photodetector is expressed as:

[0041] ;

[0042] After the DC is removed and amplified by the signal conditioning unit, the microwave interference signal S received by the photodetector is expressed as:

[0043] ;

[0044] The amplitude and phase of the signal are expressed as:

[0045] ;

[0046] Where g is the amplification gain, and Expressed as:

[0047] ;

[0048] The signal collected by the signal acquisition unit is the amplitude of the microwave interference signal S, that is:

[0049] ;

[0050] The data is transmitted to the data processing unit, and the frequency of the signal is estimated by the frequency estimation algorithm, which is expressed as:

[0051] ;

[0052] The axial clearance size is calculated as follows:

[0053] ;

[0054] In the formula, the speed of light and the refractive index of air is a constant.

[0055] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0056] 1. This invention overcomes the shortcomings of traditional axial clearance measurement methods such as capacitance method, eddy current method, and microwave method, and solves the problems of low response speed and insufficient accuracy of existing fiber-optic measurement methods. It achieves non-contact, online, high-precision measurement of the axial clearance of aircraft engine rotors and stators under conditions of limited measurement space and complex signal extraction paths.

[0057] 2. The optical path of the measurement device and method of the present invention is based on the Fizeau common optical path structure. The optical path structure is simple, and the common path of the measurement light and the reference light can reduce the drift in the optical path caused by temperature changes and vibrations.

[0058] 3. The present invention introduces a measurement method of optical carrier microwave interferometry, which realizes the superposition and interference of microwave signals in the optical path, eliminating the need for microwave devices and avoiding the reduction of measurement accuracy caused by the nonlinearity of microwave devices;

[0059] 4. The present invention introduces a microwave sweep frequency measurement method to convert the phase identification related to the axial gap into frequency identification, which has better anti-interference performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic structural diagram of the measuring device of the present invention.

[0061] Figure 2 It is a curve diagram of amplitude change.

[0062] Reference numerals: 1- broadband light source, 2- first polarization-maintaining fiber, 3- electro-optic modulator, 4- second polarization-maintaining fiber, 5- fiber circulator, 6- first single-mode fiber, 7- coated fiber probe, 8- axial end face to be measured, 9- second single-mode fiber, 10- photodetector, 11- microcontroller unit, 12- microwave sweep signal generating unit, 13- signal conditioning unit, 14- signal acquisition unit, 15- digital signal processing unit DETAILED DESCRIPTION

[0063] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0064] Example 1

[0065] like Figure 1As shown, this embodiment provides an online measurement device for the rotor-stator axial gap based on optical carrier microwave interferometry, comprising a broadband light source 1, a first polarization-maintaining optical fiber 2, an electro-optical modulator 3, a second polarization-maintaining optical fiber 4, an optical fiber circulator 5, a first single-mode optical fiber 6, and a coated optical fiber probe 7, which are connected in sequence. The coated optical fiber probe 7 is facing the axial end face 8 to be measured;

[0066] The first port of the optical fiber circulator 5 is connected to the second polarization-maintaining optical fiber 4, the second port is connected to the first single-mode optical fiber 6, and the third port is connected in sequence to the second single-mode optical fiber 9, the photodetector 10, the signal conditioning unit 13, the signal acquisition unit 14, and the digital processing unit 15;

[0067] The signal acquisition unit 14 is connected to the micro control unit 11 , the micro control unit 11 is connected to the microwave frequency sweep signal generating unit 12 , and the microwave frequency sweep signal generating unit 12 is connected to the electro-optical modulator 3 .

[0068] Example 2

[0069] This embodiment provides a measurement method based on the above-mentioned rotor-stator axial clearance online measurement device, which is specifically as follows:

[0070] (1) The broadband laser generated by the broadband light source 1 passes through the first polarization-maintaining fiber 2 and reaches the electro-optic modulator 3. The electric field of the laser can be expressed as:

[0071] ;

[0072] Where, represents the electric field of broadband laser; represents the magnitude of the electric field; represents the angular frequency of the light wave; Represents the phase of the light wave.

[0073] (2) The microwave modulation signal is generated by the microwave sweep signal generating unit 12 to modulate the intensity of the broadband laser passing through the electro-optical modulator. The microwave modulation signal generated by the microwave sweep signal generating unit 12 can be expressed as:

[0074] ;

[0075] Where, Indicates the modulation index, its value ranges from 0 to 1; Indicates the angular frequency of the modulation signal; Indicates the phase of the modulating signal.

[0076] The intensity modulation response of the electro-optic modulator can be expressed as:

[0077] ;

[0078] Then the electric field of the optical signal modulated by the electro-optical modulator 3 can be expressed as:

[0079] ;

[0080] (3) The laser intensity modulated by the electro-optical modulator passes through the second polarization-maintaining fiber 4, the optical fiber loop 5, the first single-mode optical fiber 6 and the coated optical fiber probe 7 in sequence;

[0081] Because the end face of the coated optical fiber probe 7 is coated with a semi-transparent and semi-reflective optical film, after the intensity-modulated laser passes through the optical film, part of the laser is directly reflected back to the first single-mode optical fiber 6 as reference light; part of the laser passes through the optical film and enters the axial gap space as measurement light.

[0082] The measuring light passing through the optical film travels an axial distance of The light passes through the axial gap space and reaches the axial end face 8 to be measured. Part of the light after diffuse reflection by the axial end face 8 is received by the optical fiber probe 7 and enters the first single-mode optical fiber 6.

[0083] The measuring light and the reference light have different optical paths, and their electric fields can be expressed as:

[0084] ;

[0085] Where, and are the optical path lengths of the measurement light and the reference light, respectively:

[0086] ;

[0087] Where, represents the refractive index of the optical fiber, represents the refractive index of air, Indicates the length of the optical fiber, Indicates the axial clearance to be measured.

[0088] Then the electric fields of the measurement light and the reference light can be expressed as:

[0089] ;

[0090] Where, and They represent the reflectivity of the measuring light and the reflected light respectively, W represents the transmission optical path of the optical fiber components other than the optical fiber, and c represents the speed of light.

[0091] (4) The measuring light and the reference light undergo microwave interference, pass through the second single-mode optical fiber 9, and are received by the photodetector 10.

[0092] The measurement light and reference light are broadband lasers. Assume that the laser spectrum width is , the spectral range is arrive , then the light power received by the photodetector can be expressed as:

[0093] ;

[0094] When the spectral width of the broadband light source is sufficiently wide, its coherence length is much smaller than the optical path difference between the measurement light and the reference light, i.e., the axial gap to be measured. The second cross-product integral term in the formula can be ignored.

[0095] The total optical power received by the photodetector can be expressed as:

[0096] ;

[0097] (5) The photodetector 10 transmits the received signal to the signal conditioning unit 13, and the signal conditioning unit 13 removes DC and amplifies the signal.

[0098] The signal received by the photodetector can be expressed as:

[0099] ;

[0100] The amplitude and phase of the signal can be expressed as:

[0101] ;

[0102] Where g is the amplification gain, and It can be expressed as:

[0103] ;

[0104] (6) The microcontroller unit (MCU) 11 controls the microwave sweep signal generating unit 12 to sweep the frequency. At the same time, at each frequency point, the microcontroller unit (MCU) controls the signal acquisition unit 14 to collect the output signal of the signal conditioning unit 13. Since the microwave signal frequency is too high, the signal collected by the signal acquisition unit is is the amplitude of the microwave interference signal S, that is:

[0105] ;

[0106] When the microcontroller unit (MCU) 11 controls the microwave sweep signal generating unit 12 to sweep the frequency, a similar Figure 2 The amplitude change curve is shown.

[0107] (7) The data is transmitted to the data processing unit 15, and the frequency of the signal is estimated by the frequency estimation algorithm, which can be expressed as:

[0108] ;

[0109] From this, the axial clearance size can be calculated and expressed as:

[0110] ;

[0111] In the formula, the speed of light and the refractive index of air is a constant.

[0112] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, those skilled in the art may make various specific modifications based on the teachings of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. An online measurement device for rotor-stator axial clearance based on optical carrier microwave interferometry, characterized in that: It comprises a broadband light source (1), a first polarization-maintaining optical fiber (2), an electro-optical modulator (3), a second polarization-maintaining optical fiber (4), an optical fiber circulator (5), a first single-mode optical fiber (6), and a coated optical fiber probe (7) connected in sequence, wherein the coated optical fiber probe (7) is facing the axial end face (8) to be measured; The first port of the optical fiber circulator (5) is connected to the second polarization-maintaining optical fiber (4), the second port is connected to the first single-mode optical fiber (6), and the third port is connected in sequence to the second single-mode optical fiber (9), the photoelectric detector (10), the signal conditioning unit (13), the signal acquisition unit (14), and the digital processing unit (15); The signal acquisition unit (14) is connected to the microcontrol unit (11), the microcontrol unit (11) is connected to the microwave frequency sweep signal generating unit (12), and the microwave frequency sweep signal generating unit (12) is connected to the electro-optical modulator (3).

2. The on-line measurement device for rotor-stator axial clearance based on optical carrier microwave interferometry according to claim 1, characterized in that: The end face of the coated optical fiber probe (7) is coated with a semi-transparent and semi-reflective optical film.

3. A method for online measurement of rotor-stator axial clearance, based on the device for online measurement of rotor-stator axial clearance according to any one of claims 1 or 2, characterized in that: The broadband laser light generated by the broadband light source (1) reaches the electro-optic modulator (3) through the first polarization-maintaining optical fiber (2); A microwave frequency sweep signal generating unit (12) generates a microwave modulation signal to modulate the intensity of the broadband laser passing through the electro-optical modulator (3); The laser light intensity-modulated by the electro-optical modulator (3) passes through the second polarization-maintaining optical fiber (4), the optical fiber circulator (5), the first single-mode optical fiber (6), and the coated optical fiber probe (7) in sequence; After the intensity-modulated laser light passes through the optical film of the coated optical fiber probe (7), a portion of the laser light is directly reflected back to the first single-mode optical fiber (6) as reference light; another portion of the laser light passes through the optical film and is incident on the axial end face to be measured (8) as measurement light; The axial distance of the measuring light is The light passes through the axial gap space to reach the axial end face (8) to be measured, and part of the light after diffuse reflection from the axial end face (8) to be measured is received by the coated optical fiber probe (7) and then enters the first single-mode optical fiber (6); The measurement light and the reference light generate microwave interference, the microwave interference signal passes through the second single-mode optical fiber (9) and is received by the photodetector (10), and the microwave interference signal output by the photodetector (10) is de-DCed and amplified by the signal conditioning unit (13); The microcontrol unit (11) controls the microwave sweep signal generating unit (12) to sweep the frequency, and at each frequency point, controls the signal acquisition unit (14) to acquire the output signal of the signal conditioning unit (13), and transmits the acquired data to the data processing unit (15), and estimates the frequency of the signal through a frequency estimation algorithm, thereby calculating the size of the axial gap to be measured.

4. The method for online measurement of rotor-stator axial clearance according to claim 3, characterized in that: When the micro control unit (11) controls the microwave frequency sweep signal generating unit (12) to perform frequency sweep, an amplitude variation curve can be obtained.

5. The method for online measurement of rotor-stator axial clearance according to claim 3, characterized in that: The electric field of the broadband laser generated by the broadband light source (1) is expressed as: ； Where, represents the electric field of broadband laser; represents the magnitude of the electric field; represents the angular frequency of the light wave; represents the phase of the light wave, and t represents time; The microwave modulation signal generated by the microwave sweep signal generating unit (12) is expressed as: ； Where, Indicates the modulation index, its value ranges from 0 to 1; Represents the angular frequency of the microwave modulation signal; Indicates the phase of the microwave modulated signal; The intensity modulation response of the electro-optic modulator can be expressed as: ； The electric field of the optical signal modulated by the electro-optic modulator (3) is expressed as: ； The measuring light and the reference light have different optical paths, and their electric fields are expressed as: ； Where, and are the electric fields of the measurement light and the reference light, and are the optical path lengths of the measuring light and the reference light, respectively, expressed as: ； Where, represents the refractive index of the optical fiber, represents the refractive index of air, Indicates the length of the optical fiber, Indicates the axial clearance to be measured; Then the electric fields of the measurement light and the reference light are expressed as: ； Where, and represents the reflectivity of the measured light and the reflected light, respectively; W represents the transmission optical path of the optical fiber components other than the optical fiber; and c represents the speed of light; The measurement light and reference light are broadband lasers. Assume that the spectrum width of the broadband laser is , the spectral range is arrive , then the optical power received by the photodetector is expressed as: ； When the spectral width of the broadband light source used is wide enough, its coherence length is much smaller than the optical path difference between the measuring light and the reference light, that is, the axial gap to be measured, and the second cross-multiplication integral term in the formula can be ignored; The total optical power received by the photodetector is expressed as: ； After the DC is removed and amplified by the signal conditioning unit (13), the microwave interference signal S received by the photodetector is expressed as: ； The amplitude and phase of the signal are expressed as: ； Where g is the amplification gain, and Expressed as: ； The signal collected by the signal collection unit (14) is the amplitude of the microwave interference signal S, that is: ； The data is transmitted to the data processing unit (15), and the frequency of the signal is estimated by the frequency estimation algorithm, which is expressed as: ； The axial clearance size is calculated as follows: ； In the formula, the speed of light and the refractive index of air is a constant.

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