RU2757929C1 - Method for measuring initial velocity of projectile by laser fiber-optic system - Google Patents

Abstract

FIELD: checkout technique.

SUBSTANCE: invention relates to control and measuring equipment and can be used for non-contact measurement of the initial velocity of a projectile, which is one of the most important ballistic characteristics of a weapon that affects its combat properties. To do this, electromagnetic energy is emitted in the direction of the projectile movement, receive electromagnetic energy reflected from the projectile by two optical telescopic systems with Doppler frequencies ƒ_d1 and ƒ_d2. At the same time, the angle α between the optical axes of telescopic systems is known and unchanged. The received radiation from each of the telescopic systems is combined with the laser radiation in two optical mixers, receiving signals with different radiation frequencies after the first mixer (ƒ₀-ƒ_d1) and (ƒ₀-ƒ_d2) after the second mixer. Then the signals after the first mixer and after the second mixer are summed in the third mixer, receiving a signal with a difference frequency (ƒ_d1-ƒ_d2). Initial velocity of the projectile is determined by the formula:

,

where λ is the laser wavelength and corresponding frequency ƒ₀; (ƒ₀-ƒ_d1) is the difference radiation frequency after the first mixer; (ƒ₀-ƒ_d2) is the difference radiation frequency after the second mixer; (ƒ_d1-ƒ_d2) is the difference radiation frequency after the second mixer.

EFFECT: increased accuracy of measuring the initial velocity of the projectile at small angles between the optical axes of telescopic systems.

1 cl, 7 dwg

Description

The invention relates to instrumentation and can be used for non-contact measurement of the initial velocity of a projectile, which is one of the most important ballistic characteristics of a weapon, which 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 invention, application: 2013112556/07 IPC G01S 13/58 (2006.01), published: 05/10/2014. Bull. No. 13).

The method is based on emitting electromagnetic energy in the direction of the projectile movement, receiving electromagnetic energy reflected from the projectile, converting an analog signal into digital form, recording signals into a memory unit, generating a sequence of discrete values of its current velocity based on realizations of the projectile's Doppler echo signal, and calculating from the current velocity the initial velocity of the projectile, taking into account the established delay in the beginning of its observation relative to the moment of departure from the gun barrel, evaluating the reliability of discrete values of the current projectile velocity for each position in the obtained sequence of data contained in them, highlighting, taking into account the results obtained in this sequence, a section containing mainly reliable data, by which the initial velocity of the projectile is determined, 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, p When forming a section of the above 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 unreliable data; used in calculating the initial velocity of the projectile, the observation start delay time is the sum of the set delay and the total duration of the Doppler echo signal implementation preceding the first position in the data section formed for calculating the initial velocity of the projectile; in the presence of single positions with unreliable data in the selected section of the sequence of discrete values of the current velocity of the projectile, the data contained in such single positions is replaced by the average value of reliable data from two immediately adjacent positions of this section, the reliability of the data on the current velocity of the projectile is checked by exceeding the actual ratio signal / noise of that value, which is necessary to ensure the specified accuracy of determining the initial velocity of the projectile, the reliability of the data on the current velocity of the projectile is assessed by the changes in the values of the current velocity of the projectile, presented at adjacent positions in the obtained sequence, while the zones are first detected by the magnitude of these changes, containing invalid data, and then, using valid data obtained from positions immediately adjacent to these zones, determine the expected speed values for each position in the detected zone and localize each position with an invalid the correct data, and those positions 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 Doppler echo signal spectrum, determine the area of the maximum cross section of the projectile by the plane perpendicular to the line of sight of the projectile from the spectrum width, according to the change in this area at each position is judged on the magnitude of the nutation of the projectile, additionally in the spectrum of the Doppler echo signal, the frequencies of the harmonics 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

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

f _bp = (f ₁ -f ₂ ) / 2,

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

The operation of the device for measuring the external ballistic characteristics of the projectile functions as follows (Fig. 1).

When the combat button is pressed, the device 1 for measuring the external ballistic characteristics is simultaneously launched and the throwing device 2 is triggered, while at the moment the projectile 4 leaves the bore, the induction sensor 3 is triggered. The Doppler radar 5 emits electromagnetic energy in the direction of movement of the projectile, reflected from the projectile the signal 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, to the input of which the signal from the output of the induction sensor 3 is received (Fig. 2). The choice of the delay time is due to the need to measure the initial velocity of the projectile, since it is at the moment of the shot that the moment is observed when the velocity of the projectile reaches its maximum value. The signal from the output of the key 6 through the analog-to-digital converter 8 is fed to the input of the memory unit 9, where it is recorded. The processing of the obtained data is carried out in the data processing unit 10, while the analysis of the data reliability is carried out in the data reliability analyzer 14 (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 consecutive positions with reliable data, and its end - by the presence of two or more positions with unreliable data, which determine the initial velocity of the projectile ...

Calculations of the initial velocity of the projectile are carried out at time t ₀ = t _back + t _Σ , where t _back is the set delay, t _Σ is the total duration of the Doppler echo signal implementation preceding the first position in the data section formed to calculate the initial velocity of the projectile (Fig. . 6). 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 with the average value of reliable data from two immediately adjacent positions of this section. Thus, the reliability analyzer 10 (Fig. 4) of the data provides a sample 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 observation angle.

From the output of the data reliability analyzer 14, the signals are fed to the inputs of the block 15 for determining the spectrum width and block 16 for determining the angular velocity of rotation of the projectile.

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

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

where y _k = 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 is can be defined 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 _лт - the probability of a false alarm, which in practice is usually taken equal to 10 ^-5 ,

- the variance of the noise, 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 do not exceed the threshold S _pore and are in the area of expected Doppler frequencies:

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

- determination of the signal spectrum width:

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

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

The signal from the output of the block 15 for determining the spectrum width is fed to the input of the spectrum width indicator 12. Block 16 for determining the angular velocity of rotation of the projectile provides for the determination of 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.

The closest (prototype) method is (patent RU 2715994 for invention, application: 2019127089 IPC G01S 13/58 (2006.01), published: 03/05/2019. Bull. No. 7).

In this method, the laser radiation propagates in the direction of the projectile movement, 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 summed up with 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 the 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 velocity vector of the projectile 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 ratio:

where λ ₀ is the wavelength of the electromagnetic radiation of the laser; ϕ is the angle between the velocity vector of the projectile V and the direction of observation.

The error in measuring the velocity caused by the error in setting the angle Δϕ between the axis of the trunk and the direction of observation 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 formula (3), the relative measurement error of 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 viewing angles of ~ 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 ∆ϕ = 1 °, the relative error in measuring the initial 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, one} obtains:

Substituting (4) into (5), a system of two equations (6) and (7) is obtained:

In these equations, the quantities ƒ ₀ , α are known, and Δƒ ₁ and Δƒ _{2 are} measured. Solving the system of two equations, excluding the parameter ϕ from these equations, one obtains:

As follows from expression (8), 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.

The device for measuring the initial velocity of the projectile (Fig. 6) operates as follows. The laser radiation reflected from the projectile with Doppler frequencies is received by two optical telescopic systems 2 and 3, the angle between the optical axes, which is equal to α. The received radiation is fed into optical mixers - 4 together with the radiation of the laser 1 with a frequency ƒ ₀ . After the mixers 4, the signals with the difference frequency are sent to the photodetectors installed in the Doppler echo signal processing unit 5, which processes the signals and calculates the initial velocity of the projectile according to the formula (8).

The disadvantage of the described method is the small difference in frequencies ƒ _d1 and ƒ _d2 determined, in accordance with formulas (4), by a small angle α. A small angle is necessary to ensure the intersection of the optical axes of two telescopic systems in the area of movement of the projectile, with a small distance between the optical axes of two adjacent lenses of telescopic systems. For example, in order to ensure the intersection of the optical axes of two telescopic systems in the projectile movement zone, at a distance of ~ 30 meters from the installation site of the receiving system, the angle α should be 0.2 ° ÷ 10.5 °, with a distance between the optical axes of two adjacent lenses of telescopic systems ~ 100 mm. tg 0.2 ° = 100 / 30,000 = 0.0035.

At a projectile speed V = 1000 m / s. ϕ = 0, α = 0.2 °, ƒ _d 1 = 1290322580.6 Hz, ƒ _d2 = 1290314719.5, and the frequency difference calculated by formulas (5) will be ƒ _d1 -ƒ _d2 = 7861 Hz, which is 0 , 0006% of ƒ _d1 .

At the same angles ϕ and α, as well as the velocity of the projectile V = 1001 m / s.

ƒ _d1 = 1291612903.2 Hz, ƒ _d2 = 1291605153.5 Hz, ƒ _d1 -ƒ _d2 = 7750 Hz.

Recording the change in frequency of 11 Hz at a frequency of 1.29 GHz is a rather difficult task.

The technical objective of the invention is to improve the accuracy of measuring the initial velocity of the projectile, at small angles between the optical axes of telescopic systems.

Let us rewrite relation (8) in the form:

We transform (9), for which we add and subtract ƒ _d1 in the numerator of the fraction. Then relation (9) will be written in the form:

Grouping the members in the last ratio, we get:

In relation (10), an 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. In this case, it is quite simple to register a change in frequency of 11 Hz at a frequency of ƒ _d1 -ƒ _d2 = 7750 Hz.

New features that have significant differences in the method is the following set of actions.

1. Radiation with a difference radiation frequency after the first mixer Δƒ ₁ = ƒ ₀ -ƒ _d1 and radiation with a difference radiation frequency after the second Δƒ ₂ = ƒ ₀ -ƒ _d2 are summed in the third mixer, obtaining a signal with a difference frequency (ƒ _d1 -ƒ _d2 ).

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

.

...

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

Figure 7 shows a diagram of the experiments, where:

1 - single frequency laser;

2, 3 - receiving telescopic systems;

4.1, 4.2, 4.3 - first, second and third optical mixers;

5 - block for processing Doppler echo signals with photodetectors.

The device for measuring the initial velocity of the projectile contains a single-frequency laser 1, the radiation of which is directed to the trajectory of the projectile. Reflected from the projectile laser radiation with Doppler frequencies ƒ _d1 and ƒ _{d2 is} received by two optical telescopic systems 2 and 3. Received radiation is fed into the first 4.1 and second 4.2 optical mixers. At the same time, the radiation of laser 1 with a frequency ƒ ₀ arrives at optical mixers 4.1 and 4.2. After mixers 4.1 and 4.2, optical signals with difference frequencies Δƒ ₁ and Δƒ _{2 are} sent to the third mixer 4.3. Optical signals with difference frequencies Δƒ ₁ after the first mixer and ƒd ₁ -ƒd ₂ after the third mixer fall on two photodetectors installed in the Doppler echo signal processing unit 5.

The device for measuring the initial velocity of the projectile operates as follows. The laser radiation reflected from the projectile with Doppler frequencies is received by two optical telescopic systems 2 and 3, the angle between the optical axes, which is equal to α. The received radiation is fed into the optical mixers 4 together with the radiation of the laser 1 with a frequency ƒ ₀ . After the first 4.1 and second 4.2 optical mixers, signals with difference frequencies

Δƒ ₁ = ƒ ₀ -ƒd ₁ and Δƒ ₂ = ƒ ₀ -ƒd ₂

are sent to the third optical mixer 4.3, the output of which will be an optical signal with a difference frequency ƒd ₁ -ƒd ₂ . Optical signals with difference frequencies Δƒ ₁ after the first mixer and ƒd ₁ -ƒd ₂ after the third mixer are sent to two photodetectors installed in the Doppler echo signal processing unit 5, which processes the signals and calculates the initial velocity of the projectile according to the formula:

.

...

Thus, the use of the proposed invention allows you to register a small change in frequency ƒd ₁ -ƒd ₂ and compensate for the effect of the angle between the trajectory of the projectile and the direction of observation on the accuracy of measuring the initial velocity of the projectile.

Claims (3)

A method for measuring the initial velocity of a projectile with a laser fiber-optic system, which consists in emitting electromagnetic energy in the direction of the projectile movement, receiving radiation reflected from the projectile by two optical telescopic systems, with a known and constant angle α between their optical axes, mixing the received radiation with each telescopic system with radiation laser in two optical mixers, subsequent conversion of optical signals into electrical ones and processing of mixing signals, characterized in that the optical signals with difference radiation frequencies after the first mixer (ƒ ₀ -ƒ _d1 ) and (ƒ ₀ -ƒ _d2 ) after the second mixer are summed into the third mixer, receiving a signal with a difference frequency (ƒ _d1 -ƒ _d2 ), and the initial velocity of the projectile is determined by the formula:

, where λ is the laser wavelength and the corresponding frequency ƒ ₀ ; ƒ _d1 is the Doppler frequency of the radiation reflected from the projectile and received by the first telescopic system; ƒ _d2 is the Doppler frequency of the radiation reflected from the projectile and received by the second telescopic system; Δƒ ₁ is the difference frequency of radiation after the first mixer.

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