RU2790640C1 - Way of measuring the initial velocity of high-speed projectiles with a laser fibre-optic system - Google Patents

Abstract

FIELD: testing and measuring equipment.

SUBSTANCE: invention relates to testing and measuring equipment and may be used to perform non-contact measurement of high-speed projectiles muzzle velocity, which is one of the most important ballistic characteristics of a weapon. Method is based on emission of electromagnetic energy in the direction of projectile movement, reception of electromagnetic energy reflected from the projectile by means of two optical telescopic systems, the angle between optical axes of which is known and invariable. Emissions received by each telescopic system with frequencies of (ƒ₀-ƒ_d1) and (ƒ₀-ƒ_d2) are summarized in optical summator and spectral composition of the resultant radiation is determined. The ƒ_d1 and ƒ_d2 Doppler frequencies are determined based on the obtained frequency spectra, from which the initial velocity of the projectile is determined.

EFFECT: invention obtains the signal frequency spectrum without performing analogue signal sampling, and to account for changes in the emission frequency of the single-frequency laser ƒ₀ during its operation.

1 cl, 8 dwg

Description

The invention relates to instrumentation and can be used for non-contact measurement of the muzzle velocity of a projectile, which is one of the most important ballistic characteristics of a weapon that affects its combat properties.

An analogue of this technical solution is a method for measuring the external ballistic characteristics of a projectile (patent RU 2515580 for the invention application: 2013112556/07 IPC G01S 13/58 (2006.01) published: 10.05.2014 Bull. No. 13).

The method is based on the radiation of electromagnetic energy in the direction of the projectile, the reception of electromagnetic energy reflected from the projectile, the conversion of an analog signal into digital form, the recording of signals in a memory block, the formation of a sequence of discrete values of its current velocity based on the implementation of the Doppler echo signal of the projectile, the calculation of the current velocity the initial speed of the projectile, taking into account the established delay in the start of its observation relative to the moment of departure from the gun barrel, evaluating the reliability of discrete values of the current speed of the projectile for each position in the obtained sequence of data contained in them, selecting, taking into account the results obtained in this sequence, a section containing predominantly reliable data, which determine the initial velocity of the projectile, while assessing the reliability of data on the current velocity of the projectile, criteria are used that take into account the specified requirements for the accuracy of measuring the initial velocity of the projectile, n when forming a section of the mentioned sequence for calculating the initial velocity of the projectile, the beginning of this section is determined by the presence of at least three consecutive positions with reliable data, and its end - by the presence of two or more positions with invalid data; the observation start delay time used in calculating the muzzle velocity of the projectile is the sum of the set delay and the total duration of the realization of the Doppler echo signal preceding the first position in the data section generated for calculating the muzzle velocity of the projectile; if there are single positions with unreliable data in the selected section of the sequence of discrete values of the current projectile speed, the data contained in such single positions are replaced by the average value of reliable data from two positions of this section directly adjacent to them, the reliability of the data on the current projectile speed is checked by exceeding the actual ratio the signal/noise of its value, which is necessary to ensure the specified accuracy of determining the initial velocity of the projectile, the reliability of data on the current velocity of the projectile is evaluated by changes in the values of the current velocity of the projectile, presented at adjacent positions in the resulting sequence, while first, zones are detected by the magnitude of these changes, containing unreliable data, and then, based on reliable data obtained from positions immediately adjacent to these zones, the expected speed values \u200b\u200bare determined for each position in the detected zone and each position is localized with insufficient correct data, and those positions are considered reliable, for which the analyzed changes in the values of the current velocity of the projectile do not exceed the value of the specified error in measuring the initial velocity of the projectile, determine the width of the spectrum of the Doppler echo signal, determine the area of the maximum section of the projectile by the width of the spectrum by the plane perpendicular to the line of sight of the projectile, according to a change in this area at each position, the magnitude of the nutation of the projectile is judged, additionally, in the spectrum of the Doppler echo signal, the harmonic frequencies of the secondary modulation of the echo signal caused by the asymmetry of the mass distribution of the projectile relative to its longitudinal axis are determined, calculated by the formula

angular velocity of rotation of the projectile around the longitudinal axis, where

f ₁ and f ₂ - frequencies corresponding to the maxima of the first pair harmonics of the secondary modulation of the Doppler echo signal.

In FIG. 1 shows a generalized scheme of the system for measuring the external ballistic characteristics of the movement of the projectile.

The operation of the system for measuring the external ballistic characteristics of the movement of the projectile functions as follows.

When the combat button is pressed, the device 1 for measuring external ballistic characteristics is simultaneously launched and the throwing device 2 is triggered, while at the moment the projectile 4 exits the barrel bore, the induction sensor 3 is triggered. In Fig. 2 shows a block diagram of a device for measuring the external ballistic characteristics of the projectile movement. The Doppler radar 5 emits electromagnetic energy in the direction of the projectile, the signal reflected from the projectile is fed to the first input of the key 6, the second input of which receives the signal from the output of the delay line 7, the input of which receives the signal from the output of the inductive sensor 3. The choice of the delay time is determined by the need to measure the initial velocity of the projectile, since it is at the moment of the shot that the moment when the projectile velocity reaches its maximum value is observed. The signal from the output of the key 6 through the analog-to-digital converter 8 is fed to the input of the memory block 9, where it is recorded.

In FIG. Figure 3 shows a block diagram of the analyzer of the reliability of the measured data, as well as determining the width of the spectrum and the angular velocity of the projectile.

The processing of the received data is carried out in the data processing unit 10, while the analysis of the reliability of the data is carried out in the analyzer 14 of the reliability of the data (Fig. 3).

The data reliability analyzer 14 selects a section containing increased reliable data, while the beginning of the section is determined by the presence of at least three successive positions with reliable data, and its end is determined by the presence of two or more positions with invalid data, which determine the initial velocity of the projectile .

In FIG. 4 shows a graph of projectile velocity over time. Calculations of the initial speed of the projectile are carried out at the time t ₀ =t _set +t _∑ , where t _set is the set delay, t _∑ is the total duration of the Doppler echo signal realization preceding the first position in the data section formed to calculate the initial speed of the projectile. If there are single positions with unreliable data in the selected section of the sequence of discrete values of the current projectile velocity, the data contained in such single positions is replaced by the average value of reliable data from two positions of this section immediately adjacent to them.

Thus, the data validity analyzer 10 (FIG. 2) provides a sampling of the area of increased data reliability and provides a validation of the current speed, while the speed is determined in accordance with the expression

where Δf is the Doppler frequency, λ is the wavelength, Δϕ is the viewing angle. From the output of the analyzer 14 data validity signals are fed to the inputs of the block 15 to determine the width of the spectrum and block 16 to determine the angular velocity of the projectile.

In addition, the signal from the output of the analyzer 14 reliability (Fig. 3) of the data is input to the indicator 11 of the speed of the projectile. Block 15 for determining the width of the spectrum provides:

- calculation of the fast Fourier transform (FFT) modulus:

where yk=y(k/F _d ) the input signal y(t) digitized by the analog-to-digital converter, F _d is the sampling frequency of the original signal, N is the number of FFT samples, S _n is the actual amplitude of the n-th spectral harmonic, the frequency of which can be define as:

- determination of the threshold value:

- дисперсия шума, значение которой можно вычислить, проанализировав БПФ выходного сигнал радиолокатора при отсутствии движущихся объектов в его зоне видимости на соответствие закону распределения Релея;where Р _lt is the probability of a false alarm, which in practice is usually taken equal to 10 ^-5 ,

- noise dispersion, the value of which can be calculated by analyzing the FFT of the output signal of the radar in the absence of moving objects in its visibility zone for compliance with the Rayleigh distribution law;

- zeroing of harmonics that did not exceed the value of the threshold S _then and are in the region of the expected Doppler frequencies:

where f _exp.min , f _exp.max - the lower and upper boundaries of the region of expected Doppler frequencies, respectively,

- determination of the width of the signal spectrum:

where f _c.min is the lower limit of the signal spectrum, f _c.max is the upper limit of the signal spectrum, Δf is the width of the signal spectrum (Fig. 5);

- determination by the width of the spectrum of the area of the maximum section of the projectile by a plane perpendicular to the line of sight of the projectile,

- determination of the value of the nutation of the projectile by changing the given area at each position.

In FIG. 5 shows the amplitude-frequency characteristic of the signal reflected from the projectile.

The signal from the output of the block 15 to determine the width of the spectrum is input to the indicator 12 of the width of the spectrum. Block 16 determines the angular velocity of rotation of the projectile determines the angular velocity of rotation of the projectile relative to the longitudinal axis for the selected area of measurement. The disadvantage of this method is the dependence of the accuracy of measuring the initial velocity of the projectile on the angle between the trajectory of the projectile and the direction of observation.

Another analogue is (patent RU 2715994 for the invention application: 2019127089 IPC G01S 13/58 (2006.01) published: 05.03.2019 Bull. No. 7) In this method, the laser radiation propagates in the direction of the projectile, and the electromagnetic energy reflected from the projectile is received by two optical telescopic systems with Doppler frequencies ƒ _d1 and ƒ _d2 , and the angle α between their optical axes is known and unchanged. In this case, the radiation from each of the telescopic systems is added to the laser radiation in two optical mixers, and the initial velocity of the projectile is determined by the formula:

where λ ₀ is the laser wavelength and its corresponding frequency ƒ ₀ ; (ƒ ₀ -ƒ _d1 ) - difference frequency of radiation after the first mixer; (ƒ ₀ - ƒ _d2 ) - difference frequency of radiation after the second mixer. This provision is explained as follows. The frequency of the radiation reflected from the projectile when using the Doppler effect depends on the speed of the moving projectile and the angle ϕ between the projectile velocity vector V and the direction of observation. In this case, the Doppler shift of the radiation frequency ƒ _D , is related to the initial velocity of the projectile by the relation:

where λ ₀ is the wavelength of the electromagnetic radiation of the laser; ϕ is the angle between the projectile velocity vector V and the direction of observation. The velocity measurement error due to the error in setting the angle Δϕ between the shaft axis and the observation direction ϕ can be found by differentiating relation (1) with respect to ϕ.

Dividing ΔV by V from formula (1), we obtain the relative error:

As follows from this formula, the relative error in measuring the initial velocity of the projectile is determined by the angle between the velocity vector of the projectile V and the direction of observation. At observation angles ~ 90°, the error tends to infinity. In the field, this error can be significant. So at ϕ=10° and the absolute error of setting the angle between the axis of the barrel and the direction of observation Δϕ=1°, the relative error in measuring the muzzle velocity of the projectile will be 17.6%. To eliminate this component of the error, it is proposed that the radiation scattered and reflected by the projectile be received by two telescopic optical systems, with a known and constant angle α between their optical axes. In this case, the Doppler frequency shift of the radiation will be:

After optical mixing of laser radiation with a frequency ƒ ₀ corresponding to the wavelength λ, with radiation corresponding to the Doppler frequency shifts ƒ _d1 and ƒ _d2, the frequency difference is obtained:

Δƒ ₁ =ƒ ₀ -ƒ _d1 and Δƒ ₂ =ƒ ₀ -ƒ _d2

From the last relations we obtain a system of two equations:

In these equations, the quantities ƒ ₀ , α are known, and Δƒ ₁ and Δƒ ₂ are measured. Solving a system of two equations, excluding the parameter ϕ from these equations, we obtain:

As follows from the last relationship, the initial velocity of the projectile does not depend on the angle ϕ, and the angle α can be constructively set with any predetermined accuracy.

In FIG. 6 shows a block diagram of a laser system for measuring the muzzle velocity of a projectile, which operates as follows. Laser radiation 17 is directed to the projectile. The laser radiation reflected from the projectile with Doppler frequencies is received by two optical telescopic systems 18 and 19, the angle between the optical axes of which is equal to α. The received radiation is fed into optical mixers - 20 together with laser radiation 17 with a frequency ƒ ₀ . After the mixers 20, signals with difference frequencies Δƒ ₁ =ƒ ₀ - ƒ _d1 and Δƒ ₂ =ƒ ₀ - ƒ _d2 are sent to photodetectors installed in the Doppler echo signal processing unit 21, which processes the signals and calculates the initial velocity of the projectile according to the last formula .

The disadvantage of the described method is the small frequency difference ƒ _d1 and ƒ _d2 determined, in accordance with the formulas, a small angle α. A small angle is necessary to ensure the intersection of the optical axes of two telescopic systems in the projectile movement zone, with a small distance between the optical axes of two adjacent lenses of telescopic systems.

The closest (prototype) method is (patent RU 2757929 for invention application: 2020138819 IPC G01S 5/00 (2006.01) published: 10/25/2021, Bull. No. 30.)

In FIG. Figure 7 shows a block diagram of a laser fiber-optic system for measuring the initial velocity.

To do this, electromagnetic energy is emitted in the direction of the projectile, electromagnetic energy reflected from the projectile is received by two optical telescopic systems with frequencies Δƒ ₁ =ƒ ₀ - ƒ _d1 and Δƒ ₂ =ƒ ₀ - ƒ _d2 . In this case, the angle α between the optical axes of telescopic systems is known and unchanged.

The received radiation from each of the telescopic systems is added to the laser radiation in two optical mixers, receiving signals with Doppler difference frequencies after the first mixer ƒ _d1 and ƒ _d2 after the second mixer. Then the signals after the first mixer and after the second mixer are summed in the third mixer, obtaining a signal with a difference frequency (ƒ _d1 -ƒ _d2 ). The initial velocity of the projectile is determined by the formula:

where λ is the laser wavelength and its corresponding frequency ƒ ₀ ;

ƒ _d1 - difference frequency of radiation after the first mixer;

ƒ _d2 - difference frequency of radiation after the second mixer;

(ƒ _d1 -ƒ _d2 ) - difference frequency of radiation after the third mixer.

In the last ratio, the optical signal with a frequency ƒ _d1 -ƒ _d2 =ƒ ₀ -Δƒ ₁ -ƒ ₀ -Δƒ ₂ is the result of mixing optical signals after the first and second mixers in the third mixer, which is quite simple to register.

Laser fiber-optic system for measuring the initial speed (Fig. 7), contains:

17 - single-frequency laser; 18, 19 - receiving telescopic systems; 20.1, 20.2, 20.3 - first, second and third optical mixers; 21 - Doppler echo signal processing unit with photodetectors. The system works as follows. The radiation of the laser 17 is directed to the trajectory of the projectile. Laser radiation reflected from the projectile with frequencies Δƒ ₁ =ƒ ₀ -ƒ _d1 and Δƒ ₂ =ƒ ₀ -ƒ _d2 is received by two optical telescopic systems 18 and 19, the angle between the optical axes of which is equal to α. The received radiation is fed into the first 20.1 and second 20.2 optical mixers. At the same time, the optical mixers 4.1 and 20.2 receive laser radiation 17 with a frequency ƒ ₀ . After mixers 20.1 and 20.2, optical signals with difference frequencies ƒ _d1 and ƒ _d2 are sent to the third mixer 20.3. Optical signals with difference frequencies Δƒ ₁ after the first mixer and ƒ _d1 -ƒ _d2 after the third mixer fall on two photodetectors installed in the Doppler echo processing unit 21, which processes the signals and calculates the initial velocity of the projectile according to the formula:

Doppler echo processing involves converting analog signals to digital signals using analogue digital transducers.

The disadvantage of this method is the complexity of digital registration of high frequencies Δƒ ₂ at high initial projectile velocities.

So at a projectile speed V=1000 m/sec. ϕ=0, α=0.2°, ƒ _d2 =1.290322580.6 GHz, and at projectile velocity V=2000 m/sec. ϕ=0, α=0.2°, ƒ _d2 =2.580645161.3 GHz.,

The required sampling frequency F _d of Doppler signals ƒ _d2 is determined by the Kotelnikov theorem in accordance with the relation:

Therefore, at the initial velocity of the projectile equal to V=2000 m/sec., the sampling frequency F _d of the Doppler signals must be at least F _d =2ƒ _d2 =2*2.581=5.162 GHz.

Carry out the conversion of an analog signal with a frequency of 5.162 GHz. digitally is quite a technical challenge. Another disadvantage of this method is the possible change in the frequency of radiation of a single-frequency laser ƒ ₀ during the operation of the system, which will lead to an error in measuring the initial velocity of the projectile. So when changing the laser wavelength (λ=1550 nm) by Δλ=1.0 pm, the frequency change will be Δƒ ₀ =125 MHz, which will lead to an error in measuring the projectile velocity ΔV≈10%.

The technical objective of the invention is:

• Obtaining the frequency spectrum of the signal without analog signal sampling;

• Accounting for changes in the radiation frequency of a single-frequency laser ƒ ₀ during its operation

The essence of the invention is based on the radiation of electromagnetic energy in the direction of the projectile, the reception of electromagnetic energy reflected from the projectile by two optical telescopic systems with a known and unchanged angle α between their optical axes. A distinctive part of the invention is that received by each telescopic system of radiation with frequencies (ƒ ₀ -ƒ _d1 ) and (ƒ ₀ -ƒ _d2 ) and part of the laser radiation with a frequency ƒ ₀ summarize, determine the spectral composition of the resulting radiation and the spectral composition is found laser radiation frequency ƒ ₀ at the time of measuring the velocity and Doppler frequency ƒ _d1 and ƒ _d2 , from which the initial velocity of the projectile is calculated:

where λ is the laser wavelength and its corresponding frequency ƒ ₀ .

This provision is explained as follows. The optical signals received by each telescopic radiation system with frequencies ƒ ₀ -ƒ _d1 and ƒ ₀ -ƒ _d2 and part of the laser radiation with a frequency ƒ ₀ are summed, and the resulting radiation is analyzed, for example, with an ultra-high resolution infrared spectrometer. The frequencies ƒ ₀ -ƒ _d1 , ƒ ₀ -ƒ _d2 and ƒ ₀ are found from the frequency spectra obtained in the ultra-high resolution infrared spectrometer. Having determined these radiation frequencies, calculate the Doppler frequencies ƒ _d1 \u003d ƒ ₀ -ƒ _d1 -ƒ ₀ and ƒ _d2 \u003d ƒ ₀ -ƒ _d2 -ƒ ₀ , by which the initial velocity of the projectile is determined:

New features that have significant differences in method are the following set of actions:

1. Radiations received by each telescopic radiation system with frequencies ƒ ₀ -ƒ _d1 and ƒ ₀ -ƒ _d2 and part of the laser radiation with a frequency ƒ ₀ are summed. The resulting radiation is analyzed, for example, with an ultra-high-resolution infrared optical spectrum analyzer, and the frequencies ƒ ₀ -ƒ _d1 and ƒ ₀ -ƒ _d2 and ƒ ₀ are determined from the obtained frequency spectra.

2. Doppler frequencies are calculated: ƒ _d1 =ƒ ₀ -ƒ _d1 -ƒ ₀ and ƒ _d2 =ƒ ₀ -ƒ _d2 -ƒ ₀ .

3. The initial velocity of the projectile is determined by the formula:

The claimed method is the result of scientific research and experimental work.

The figure 8 shows the scheme of the experiments, where:

17 - single-frequency laser;

18, 19 - receiving telescopic systems;

20 - optical adder;

21 - Doppler echo processing unit;

22 - ultra-high resolution infrared optical spectrum analyzer.

The device for measuring the initial velocity of the projectile contains a single-frequency laser 17, the radiation of which is directed to the trajectory of the projectile. The laser radiation reflected from the projectile with Doppler frequencies ƒ ₀ -ƒ _d1 and ƒ ₀ -ƒ _d2 is received by two optical telescopic systems 18 and 19. The received radiation by telescopic systems 18, 19 and part of the laser radiation are sent to the optical adder (mixer) 20, after which the resulting radiation is fed to an ultra-high-resolution infrared optical spectrum analyzer 22. The received frequency signals are fed to a Doppler echo processing unit 21, which calculates the muzzle velocity of the projectile.

Thus, the use of the proposed invention allows you to simultaneously obtain three frequency spectra. These are the signals ƒ ₀ -ƒ _d1 and ƒ ₀ -ƒ _d2 received by each telescopic system and laser radiation with a frequency ƒ ₀ . The Doppler frequencies and the initial velocity of the projectile are determined from the obtained frequency spectra.

All system components are standard for telecommunication applications.

Used sources of information:

1. A method for measuring the external ballistic characteristics of a projectile (patent RU 2515580 for the invention application: 2013112556/07, IPC G01S 13/58 (2006.01) published: 10.05.2014 Bull. No. 13).

2. A method for measuring the initial velocity of a projectile (patent RU 2715994 for invention application: 2019127089, IPC G01S 13/58 (2006.01) published: 05.03.2019 Bull. No. 7).

3. A method for measuring the initial velocity of a projectile with a laser fiber optic system (patent RU 2757929 for invention application: 2020138819 IPC G01S 5/00 (2006.01) published: 10/25/2021, Bull. No. 30).

Claims (3)

A method for measuring the initial velocity of high-speed projectiles with a laser fiber-optic system, which consists in the emission of electromagnetic energy in the direction of movement of the projectile, the reception of radiation reflected from the projectile by two optical telescopic systems, with a known and constant angle α between their optical axes, characterized in that each telescopic radiation system with frequencies (ƒ ₀ -ƒ _d1 ) and (ƒ ₀ -ƒ _d2 ) and part of the laser radiation with a frequency ƒ ₀ are summarized, the spectral composition of the resulting radiation is determined and the frequency of the laser radiation ƒ ₀ is found from the spectral composition at the time of measuring the speed and frequency Doppler ƒ _d1 and ƒ _d2 , which calculate the initial velocity of the projectile:

, where λ is the laser wavelength corresponding to the frequency ƒ ₀ .

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