CN112224446B - High-speed coaxial dual-rotor blade tip distance measuring method based on phase distance measuring principle - Google Patents
High-speed coaxial dual-rotor blade tip distance measuring method based on phase distance measuring principle Download PDFInfo
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- G01S11/00—Systems for determining distance or velocity not using reflection or reradiation
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Abstract
The invention discloses a high-speed coaxial dual-rotor blade tip distance measuring method based on a phase distance measuring principle, which utilizes a measuring device to realize blade tip distance measurement; measuring device includes transmitting antenna, receiving antenna, radio frequency signal production circuit, RFID card and signal acquisition processing circuit, wherein, transmitting antenna, receiving antenna are pre-buried in the lower surface of last rotor point portion, the RFID card is pre-buried in the upper surface of lower rotor point portion, signal production circuit, signal acquisition processing circuit install in last rotor propeller hub center department, through laying the radio frequency cable on last rotor blade surface, be connected signal production circuit and transmitting antenna, be connected receiving antenna and signal acquisition processing circuit. The invention can solve the problem of measuring the blade distance in a non-contact manner, and can effectively ensure the operation safety of a rotor system of a coaxial helicopter and ensure the normal flight of the helicopter after the test flight of the helicopter.
Description
Technical Field
The invention relates to the technical field of test flight, in particular to a high-speed coaxial dual-rotor blade tip distance measuring method based on a phase distance measuring principle.
Background
The measuring technology of the blade tip distance is an important testing technology for the rotor safety monitoring of the coaxial double-rotor helicopter, the measuring accuracy of the blade tip distance directly influences the flight safety of the helicopter, and a non-contact measuring method is an optimal scheme for solving the measuring problem.
The phase ranging has high requirements on an analysis algorithm of signals, and is not applied to the field of helicopter blade ranging. The measuring method is applied to a helicopter rotor, the influence of large deformation, high vibration environment, dynamic balance and the like of the blade on a measuring device needs to be considered, and the method is not available at present; and the traditional method for measuring the pitch of the blade tip is difficult to realize dynamic measurement, so that the measurement result is not accurate enough.
Disclosure of Invention
The invention aims to provide a high-speed coaxial dual-rotor-wing tip distance measuring method based on a phase distance measuring principle, which is applied to a helicopter rotor wing under the premise of considering the influence of the rotor wing on a measuring device so as to solve the problem of accuracy of rotor wing tip distance measurement.
In order to realize the task, the invention adopts the following technical scheme:
a high-speed coaxial dual-rotor blade tip distance measuring method based on a phase distance measuring principle utilizes a measuring device to realize blade tip distance measurement; the measuring device comprises a transmitting antenna, a receiving antenna, a radio frequency signal generating circuit, an RFID card and a signal acquisition processing circuit, wherein the transmitting antenna and the receiving antenna are pre-embedded in the lower surface of the tip part of the upper rotor, the RFID card is pre-embedded in the upper surface of the tip part of the lower rotor, the signal generating circuit and the signal acquisition processing circuit are installed in the center of the hub of the upper rotor, the signal generating circuit is connected with the transmitting antenna through a radio frequency cable laid on the surface of the blade of the upper rotor, and the receiving antenna is connected with the signal acquisition processing circuit;
after the helicopter starts to rotate, when blades provided with measuring devices on the upper rotor and the lower rotor rotate to coincide up and down, a signal generating circuit on the blades of the upper rotor radiates electromagnetic signals through a transmitting antenna to activate an RFID card arranged on the surface of the blades of the lower rotor, the RFID card returns a receiving signal, the receiving signal is received by a receiving antenna and then is collected and processed by a signal collecting and processing circuit, and the strength of the measured receiving signal is converted into distance information.
Further, the process of processing the acquired signal in the signal acquisition circuit is as follows:
carrying out AD sampling on a received signal, converting the received signal into a digital signal, and obtaining an orthogonal variable of the received signal by using a frequency mixing technology; and performing low-pass filtering on the orthogonal variable, performing extraction after the low-pass filtering to obtain a signal containing a phase difference value, and obtaining the tip distance of the double rotors based on the signal.
Further, the strength of the measured received signal is converted into distance information, wherein the calculation formula of the pitch of the blade tip is as follows:
in the above-mentioned formula, the compound has the following structure,
λ is the signal wavelength, which is the phase difference between the transmitted and received signals.
Further, when the measured received signal strength is converted into distance information, if the ranging accuracy is Δ R, the following steps are performed:
where SNR represents the signal-to-noise ratio.
Further, in order to avoid ambiguity of the phase range, the following relationship is required:
h is the distance between the transmitting antenna and the RFID card in a static state, L is the distance between the transmitting antenna and the RFID card after relative movement, and thetamaxThe maximum deviation angle between the transmitting antenna and the RFID card during rotation.
Further, the received signal is divided into three zones according to the movement of the paddle wing: an approach zone, an overlap zone, and a distance zone; in the approach area, the upper and lower blades move in opposite directions, and the Doppler velocity is positive; the frequency of the received signal is consistent with that of the transmitted signal in the overlapping area, and when the area is far away, the energy amplitude of the received signal begins to decrease; and measuring the time of the overlapping area through the RSSI, and comparing the phases of the received signal and the transmitted signal in the area to obtain the phase difference value of the overlapping area, thereby calculating the distance value between the upper blade and the lower blade.
Furthermore, the transmitting antenna and the receiving antenna both adopt FPC form, the antenna wiring adopts a spiral winding mode, the space size is 80mm multiplied by 40mm multiplied by 14mm, the weight is 5 g, and the inductance value is 1.5 uH.
Furthermore, during calculation, the residence time is set to be 0.5ms, as the overlapping interval needs to be calculated, during judgment, a threshold value is obtained by combining an actually measured value, 1ms intervals are respectively obtained at the left and the right of the overlapping interval, and calculation is started when the blade delays for 1ms after passing through the overlapping area;
the period of a transmitted signal is 5ns, 4 periods are taken as a group of PRFs, 8 PRFs are taken as a frame, the first four periods are 1111 periods, and the last four periods encode No. 1-4 paddles according to the serial numbers;
calculating distance for testing phase delay, and completing multiplication and FIR filtering only in time domain; and after the phase is calculated, converting the phase and distance conversion value by adopting a table look-up method.
Compared with the prior art, the invention has the following technical characteristics:
the invention can solve the problem of measuring the blade distance in a non-contact manner, and can effectively ensure the operation safety of a rotor system of a coaxial helicopter and ensure the normal flight of the helicopter after the test flight of the helicopter.
Drawings
FIG. 1 is a schematic view of the layout structure of the measuring device of the present invention;
FIG. 2 is a schematic diagram of a waveform of a transmitted signal;
FIG. 3 is a waveform diagram of a received signal;
FIG. 4 is a waveform plot of a received signal;
FIG. 5 is an equivalent circuit diagram of an antenna;
FIG. 6 is a schematic diagram of a transmitting antenna and a receiving antenna;
FIG. 7 is a schematic diagram of HFSS simulation; wherein (a) is an electric field screenshot, and (b) is a magnetic field screenshot;
FIG. 8 is a schematic block diagram of a transmit chain;
FIG. 9 is a functional block diagram of a receive chain;
FIG. 10 is a digital quadrature mixing schematic;
FIG. 11 is a schematic of a parallel FIR;
FIG. 12 is a schematic diagram of transmission and reception;
FIG. 13 is a wavelength phase mapping diagram;
fig. 14 is a graph of accuracy versus signal-to-noise ratio.
Detailed Description
The phase ranging principle is to analyze the phase of the received signal and compare or calculate with the phase of the transmitted signal to realize ranging, and the principle is as follows,
as shown below, let the transmitted signal be located at point a, the target be located at point B, and the distance R between the two be:
wherein the content of the first and second substances,
ω0for the initial phase and angular velocity of the transmit signal, the phase difference between the transmit signal and the echo signal is as follows:
thereby, it can push:
wherein f is0For the carrier frequency, C is the signal velocity, as can be seen from the above equation, if measured
The R value can be obtained.
From the measurement technology, the phase ranging technology is adopted to realize higher precision, but it can be seen that the phase ranging technology is suitable for the measurement of the phase of the object
When the phase difference does not exceed 2 pi, the measurement of the phase difference is not fuzzy, otherwise, the speed ambiguity needs to be solved through a multi-carrier frequency technology, and the implementation is complex.
The invention provides a high-speed coaxial dual-rotor blade tip distance measuring method based on a phase distance measuring principle, wherein the composition and the layout mode of a measuring device are shown in figure 1:
measuring device includes transmitting antenna, receiving antenna, radio frequency signal produces the circuit, RFID card and signal acquisition processing circuit, wherein, transmitting antenna, receiving antenna pass through sticky form pre-buried in the lower surface of last rotor point portion, the RFID card is pre-buried in the upper surface of lower rotor point portion through sticky form, signal production circuit, signal acquisition processing circuit installs in last rotor propeller hub center department, through laying the radio frequency cable on last rotor blade surface, be connected signal production circuit and transmitting antenna, be connected receiving antenna and signal acquisition processing circuit.
After the helicopter starts to rotate, when blades provided with measuring devices on the upper rotor and the lower rotor rotate to coincide up and down, a signal generating circuit on the blades of the upper rotor radiates electromagnetic signals (transmitting signals) through a transmitting antenna, an RFID card arranged on the surface of the blades of the lower rotor is activated, the RFID card returns a receiving signal, the receiving signal is received by a receiving antenna and then is collected and processed by a signal collecting and processing circuit, and the strength of the measured receiving signal is converted into distance information.
The waveform of the transmitted signal is a continuous wave, which aims at ensuring that the transmitted waveform and the radiation power do not change at all during the high-speed rotation of the rotor wing, as shown in figure 2; when the high-speed Doppler transmission device works, the blades move oppositely, so that the frequency of a received signal is increased when the upper and lower blades approach at a high speed due to the Doppler effect, and the frequency of the received signal is decreased when the upper and lower blades are far away at a high speed. Meanwhile, under the condition of signal space attenuation, when the upper and lower layers of blades approach at high speed, the amplitude of the received signal becomes high, and the amplitude of the signal far from the upper and lower layers of blades becomes low, as shown in fig. 3, the received signal should be an amplitude modulation and frequency modulation continuous wave signal.
Let the system signal frequency be f0So as to calculate the period T of the transmitting signal to be 1/f0The wavelength lambda and the test distance d plus or minus delta m, and selecting proper f according to the test distance0Analysis is carried out to ensure that when the double blades are overlapped, the phase delay of the transmitting signal and the receiving signal does not exceed 2 pi, namely, distance ambiguity cannot be generated.
As shown in fig. 4, the received signal is divided into three regions according to the movement of the paddle wing: approach zone, overlap zone and distance zone.
In the approach area, the upper and lower blades move in opposite directions, the Doppler velocity is positive, and the received signal is the frequency rise. When the upper and lower blades are overlapped, the energy of the received signal is the highest and is at the amplitude peak value, the opposite movement speed is 0 due to the overlapping of the upper and lower blades, and the frequency of the received signal is consistent with that of the transmitted signal in the overlapping area. When the upper and lower blades are far away from the area, the energy amplitude of the received signal begins to decrease, the upper and lower blades are far away from the area, the Doppler velocity is negative, and the received signal is the frequency decrease.
At the moment, the RSSI and the phase ranging are combined, namely the time of an overlapping area is measured through the RSSI, the phase of a received signal in the area is compared with that of a transmitted signal, the phase difference value of the overlapping area is obtained, and the distance value between the upper blade and the lower blade is calculated.
Through the analysis of actual working conditions, the low-frequency operation is selected, the magnetic coupling is used for near-distance transmission, the influence of space and external interference signals on measurement can be avoided, the self acting distance is limited, and the influence on other equipment is avoided. And when the range finding, through the phase place range finding of overlap region, improved the precision of range finding greatly, also avoid the influence that the paddle warp and bring when rotatory simultaneously.
One, transmitting antenna and receiving antenna
From maxwell's equations, the strength E of the electric field and the magnetic field strength H depend on three main parameters, namely:
(1) a time variable t.
(2) The distance variable r between the radiation source has three items of 1/r, 1/(r2) and 1/(r 3).
(3) The product kr, has a value of kr 2 pi/λ.
And the space regions of the antenna define three space regions, namely a near field space, a middle field space and a far field space according to the test distance value and the wavelength lambda. The distinction is made according to whether the value of r is greater or less than:
thus, the far field (Fraunhofer region) is
The area of space of (a) is,
the midfield (Fresnel zone) is the spatial region where r ═ λ,
the near field (Rayleigh region) is
The spatial region of (a).
According to the method of the invention, the measuring device works in the near field area during the test, and the Biot-Laplace law and the Biot-Savart law mainly play a role in the area, because the working frequency of the antenna is f0In the low frequency region, the radio frequency signal is transmitted by adopting an inductive coupling mode, in order to reduce the weight, the FPC mode is adopted, and the antenna wiring adopts a spiral winding mode, as shown in figure 5. The space size is 80mm x 40mm x 14mm, only 0.9mm space in height is needed, and the weight is about 5 g. The inductance value is about 1.5 uH.
The transmitting antenna is consistent with the receiving antenna, the center of the mounting position is opposite to the center of the mounting position, and the transmitting antenna is mounted at the wingtip. Respectively introducing a transmitting signal and a receiving signal, establishing an annular pcb wiring in HFSS software, and artificially intercepting a plane distribution value of electric field intensity and magnetic field intensity at a certain distance from a coil, wherein model diagrams of the plane distribution value are shown in (a) and (b) of 7, the electric field intensity is stronger at a feed source, and the magnetic field intensity is stronger at the center.
Two, a transmit chain and a receive chain
The principle of the transmission chain is as the figureAs shown in fig. 8, the main functions and indexes of the transmission link are as follows: generating a high-stability low-phase-noise clock signal required by DA through a crystal oscillator; production of f by DA0The transmitting signal passes through a final amplifier and outputs a 1dB compression point reaching 17dBm @ f0Transmitting signal output power of 10dBm and reserving power adjustment allowance; generating a transmitting signal through a DDS, and performing phase modulation at fixed time; and (3) transmitting link thermal noise signal-to-noise ratio analysis: the noise power is equal to-174 +10log (B) + Gain + NF ═ 100dBm, and the thermal noise signal-to-noise ratio reaches 110 dB.
The transmit link waveform is periodic to produce phase modulation for generating phase encoding for airfoil identification.
The quality of the crystal oscillator directly determines the precision and stability of the frequency of the final output waveform and the phase noise of the output signal. Meanwhile, because the crystal oscillator is a temperature and vibration sensitive device, the stability of the crystal oscillator at a wide temperature and the performances of noise, stray and the like under vibration need to be fully considered in the initial model selection, and a margin needs to be reserved for related indexes.
The crystal oscillator of the type utilizes a constant temperature bath to keep the temperature of a crystal oscillator constant, can reduce the variation of the output frequency of the oscillator caused by the ambient temperature variation to the minimum, and generally keeps the common frequency stability of the constant temperature crystal oscillator at 2 multiplied by 10-7(ii) a The annual ageing rate is less than +/-100 ppb; stray is less than or equal to-80 dBc; harmonic wave is less than or equal to-30 dBc; the phase noise level of the crystal oscillator is typically-150 dBc/Hz at 1 KHz. The harsh requirements of the system on environment and phase noise can be met.
The principle of the receiving link is shown in fig. 9, and the receiving link has the following main functions and indexes: generating a high-stability low-phase-noise clock signal required by AD through a crystal oscillator; the high-gain low-noise amplifier is selected as the first stage of a receiving link, the maximum input power is not less than 13dBm, therefore, the first stage cannot be burnt out due to coupling between transmitting and receiving, the output 1dB compression point is at least 12dBm, the power entering the ADC after passing through the acoustic meter is not more than 12dBm, and the ADC chip cannot be damaged.
Third, delay time and blade identification
In the calculation, the residence time is set to 0.5 ms. Because the overlapping interval needs to be calculated, the threshold is taken by combining with the measured value during the judgment, and because the interval of 1ms is respectively taken at the left and the right of the overlapping interval, because of the rotating speed problem, the transmitting antenna and the receiving antenna have no overlapping area completely at 1ms, and the coupling signal is sharply reduced. At this time, the calculation was started at a delay of about 1ms after the blade passed through the overlap region.
Because the period of the transmitted signal is 5ns, 4 periods are taken as a group of PRFs, 8 PRFs are taken as a frame, the first four periods are 1111 (phase encoding), and the last four periods encode No. 1-4 paddles according to the serial numbers (0000, 0001, 0010, 0011). The received signals determine the order of the paddles. These time-consuming events all occur within 500us of the overlap region.
Because the distance is calculated for testing the phase delay, multiplication and FIR filtering are completed only in the time domain, the working clock of the processor is 100MHz, the multiplication time is 160ns, and the FIR filtering delay is as follows: (n-1)/2 fs-15 ns. After the phase is calculated, the phase and distance conversion value is converted by adopting a table look-up method, so that the calculation time can be reduced; the delay is about 20ns, including 1ms before the overlap region, 500us after the overlap region, and 1ms after the overlap region, plus a calculated delay of about 195 ns. Namely, after passing through the overlapping area, the time required for processing is 1ms +195ns, and the distance value is obtained and sent out.
Fourth, signal processing
The signal processing of the measuring device adopts a digital orthogonal sampling method, and can keep the information of the amplitude, the phase and the like of the complex envelope of the signal, so the measuring device has wide application in the field of signal processing. The digital quadrature sampling method is a method for directly sampling the low and middle frequency band signals and obtaining quadrature signals through digital signal processing. The principle of digital quadrature mixing is shown in fig. 10:
the received signal is a narrowband signal represented by:
x(t)＝a(t)cos(ωot+θ(t))
after AD sampling, the signal becomes a digital signal:
x(n)＝a(n)cos(ωon + θ (n)), where n ═ k/fsAnd k is 0, 1, 2.
By mixing techniques, the quadrature variance of the signal can be obtained, and the digital signal quadrature mixing can be expressed as:
where x (t) is the received signal, sin (2 π f)0n) and cos (2 π f)0n) is the signal of the phase shift of 90 degrees of the transmitting signal and the transmitting signal, and the phase difference value of the transmitting signal and the receiving signal can be obtained after the orthogonal product of the transmitting signal and the transmitting signal.
After quadrature mixing, low pass filtering is carried out to filter out redundant frequencies. Low-pass filtering followed by decimation, where filtering and decimation may be performed simultaneously; for a causal FIR system, its equations can be simplified as:
wherein, M is the filter coefficient length, if the multi-path parallel processing of the multi-phase filtering is adopted, and N is the number of paths of FIR filtering in parallel, then:
if the decimation 4 operation is to be implemented, the above equation is further analyzed, and as shown in fig. 11, the filtered signal only contains the phase difference signal: cos [ theta (n) ] and sin [ theta (n) ]
And obtaining corresponding distance information through the obtained phase difference signal. Because of the adoption of the high-stability crystal oscillator and the full-coherent signals, the method can achieve higher phase precision.
Fifth, error analysis
The transmit signal is represented as:
the received signal is represented as:
wherein, ω is0Is a digital angular frequency, f0Is the frequency of the carrier wave,
to an initial phase, R0The distance from the transmitting antenna to the RFID card, i.e., the distance between the tips of the blades, and c is the signal speed.
It can be seen that the distance from transmission to reception can be inferred by the phase difference between the transmitted and received signals.
Order to
The distance measurement formula is
Assuming that the distance measurement accuracy is Δ R equal to 0.01m, it should satisfy
Assuming noisy echoes of
The accuracy of the estimate of the phase in the noisy echo can be expressed as
Wherein SNR is A2/σ2Is the signal to noise ratio.
Since the phase change rate is extremely high during estimation, it can be considered as instantaneous phase estimation, so
In summary, if the phase estimation precision satisfies the requirement of the distance measurement precision, the method includes
It is possible to obtain:
the larger the signal wavelength, the higher the SNR requirement; in a certain SNR, the smaller the wavelength, the higher the ranging accuracy.
As shown in fig. 12, satisfies
In order to measure the phase without blurring, and simultaneously satisfy,
thus it has
H is the distance between the transmitting antenna and the RFID card in a static state, L is the distance between the transmitting antenna and the RFID card after relative movement, and thetamaxThe maximum offset angle between the transmitting antenna and the RFID card during rotation.
FIG. 13 shows the wavelength requirement of the rotation angle between-30 and +30 degrees, and the wavelength range is 1.15-2 m.
Fig. 14 shows the SNR requirement for achieving Δ R of 0.01m at different wavelengths. It can be seen from the figure that the signal-to-noise ratio requirement is between 27-33dB in the wavelength range of 1.15-2 m.
In the device, the receiving-transmitting noise ratio analysis comprises the following steps:
when a low-phase-noise crystal oscillator is adopted, the output power of the crystal oscillator can reach-70 dBc at 10Hz, and the output power of the crystal oscillator is 7dBm, so the signal-to-noise ratio introduced by the phase noise is about 7- (-63+10) ═ 60 dB.
DDS generation f0The signal-to-noise ratio of the transmitted signal is much greater than 40dB, so thermal noise is a major factor to be considered in the transceiver chain. After the signal-to-noise ratio of the transmitted signal is input to a receiving link, the signal-to-noise ratio is deteriorated by 12.35dB, still can reach 97.65dB, and is far larger than 40 dB.
The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equally replaced; such modifications and substitutions do not depart from the spirit and scope of the embodiments of the present application, and they should be construed as being included in the present application.
Claims (8)
1. A high-speed coaxial dual-rotor blade tip distance measuring method based on a phase distance measuring principle is characterized in that the blade tip distance measuring method is realized by using a measuring device; the measuring device comprises a transmitting antenna, a receiving antenna, a radio frequency signal generating circuit, an RFID card and a signal acquisition processing circuit, wherein the transmitting antenna and the receiving antenna are pre-embedded in the lower surface of the tip part of the upper rotor, the RFID card is pre-embedded in the upper surface of the tip part of the lower rotor, the signal generating circuit and the signal acquisition processing circuit are installed in the center of the hub of the upper rotor, the signal generating circuit is connected with the transmitting antenna through a radio frequency cable laid on the surface of the blade of the upper rotor, and the receiving antenna is connected with the signal acquisition processing circuit;
after an upper rotor and a lower rotor of the helicopter start rotating, when blades provided with measuring devices on the upper rotor and the lower rotor rotate to coincide up and down, a signal generating circuit on the blades of the upper rotor radiates electromagnetic signals through a transmitting antenna, an RFID card arranged on the surface of the blades of the lower rotor is activated, a received signal returned by the RFID card is received by a receiving antenna and then is collected and processed by a signal collecting and processing circuit, and the strength of the measured received signal is converted into distance information.
2. The phase ranging principle-based high-speed coaxial dual-rotor blade tip distance measuring method according to claim 1, wherein the signal acquisition circuit processes the acquired signals by:
carrying out AD sampling on a received signal, converting the received signal into a digital signal, and obtaining an orthogonal variable of the received signal by using a frequency mixing technology; and performing low-pass filtering on the orthogonal variable, performing extraction after the low-pass filtering to obtain a signal containing a phase difference value, and obtaining the pitch of the double-rotor blade tip based on the signal.
3. The method of claim 1, wherein the measured received signal strength is converted to distance information, wherein the pitch R is the pitch R0The calculation formula of (2) is as follows:
in the above formula, the first and second carbon atoms are,
λ is the signal wavelength, which is the phase difference between the transmitted and received signals.
4. A method for measuring the pitch of a high-speed coaxial dual-rotor blade tip based on the phase distance measuring principle according to claim 1, wherein when the strength of the measured received signal is converted into distance information, if the distance measuring precision is Δ R, the following are provided:
where SNR represents the signal-to-noise ratio and λ is the signal wavelength.
5. A method for high speed coaxial dual rotor blade tip distance measurement based on the phase ranging principle as claimed in claim 1, wherein in order to make the phase ranging unambiguous, the following relationship is satisfied:
wherein H is the distance between the transmitting antenna and the RFID card in a static state, and thetamaxAnd lambda is the maximum offset angle of the transmitting antenna and the RFID card when the RFID card rotates, and is the signal wavelength.
6. A method for high speed coaxial dual rotor blade tip distance measurement according to claim 1 wherein the received signal is divided into three zones according to the movement of the blade: an approach zone, an overlap zone, and a distance zone; in the approach area, the upper and lower blades move in opposite directions, and the Doppler velocity is positive; the frequency of the received signal is consistent with that of the transmitted signal in the overlapping area, and when the area is far away, the energy amplitude of the received signal begins to decrease; and measuring the time of the overlapping area through the RSSI, and comparing the phases of the received signal and the transmitted signal in the area to obtain the phase difference value of the overlapping area, thereby calculating the distance value between the upper blade and the lower blade.
7. The method for measuring the pitch of the propeller tip of the high-speed coaxial dual-rotor based on the phase distance measuring principle according to claim 1, wherein the transmitting antenna and the receiving antenna are both in the form of FPC, the antenna wiring is in a spiral winding mode, the space size is 80mm x 40mm x 14mm, the weight is 5 g, and the inductance value is 1.5 uH.
8. The method for measuring the pitch of the blade tip of the high-speed coaxial double rotors based on the phase distance measuring principle according to claim 1, characterized in that in the calculation, the residence time is set to 0.5ms, because the overlapping interval needs to be calculated, in the judgment, the threshold value is taken by combining with the measured value, 1ms intervals are respectively taken at the left and the right of the overlapping interval, and the calculation is started when the blade is delayed by 1ms after passing through the overlapping interval;
the period of a transmitted signal is 5ns, 4 periods are taken as a group of PRFs, 8 PRFs are taken as a frame, the first four periods are 1111 periods, and the last four periods encode No. 1-4 paddles according to the serial numbers;
calculating distance for testing phase delay, and only completing multiplication and FIR filtering in a time domain; and after the phase is calculated, converting the phase and distance conversion value by adopting a table look-up method.
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