Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
Method and device for measuring the muzzle velocity of
a projectile or the like
The invention relates to the subject of reducing the
overall length of a weapon barrel, particularly one
operated as a waveguide. A waveguide is a tube with a
characteristic cross-sectional form, which has a wall
that is a very good electrical conductor. Rectangular
and circular waveguides enjoy particularly widespread
technical use.
One method of operating the barrel as a circular
waveguide and measuring the Doppler velocity of the
projectile in the barrel can be found in EP 0 023 365
A2. The frequency of the signal in this case is above
the cutoff frequency of the waveguide mode concerned.
The electromagnetic wave that is formed here propagates
in the barrel and is reflected by the projectile. In
addition, there is a Doppler frequency shift that
depends on the instantaneous velocity. A muzzle
velocity for the projectile is then determined from
this.
DE 10 2006 058 375 Al, on the other hand, proposes the
use of the weapon barrel or launcher tube and/or parts
of the muzzle brake as a waveguide. However, this
waveguide is operated below the cutoff frequency of the
waveguide mode concerned.
DE 10 2008 024 574.7, which was not published prior to
this, addresses the same problem, wherein the
possibility of varying the distance between the
couplers and the individual choice of distance
depending on the mode selection of the waveguide (that
is to say > 0) is proposed. Different measuring devices
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ar e envisaged. If the receiving coupler is disposed
between the base of the projectile base and the
transmitting coupler, a measurement can be taken after
the projectile has passed. If the receiving coupler is
positioned between the projectile nose and the
transmitting coupler, the muzzle velocity is measured
before the projectile passes. The combination of the
two measuring methods is preferred, which means that at
least two receiving couplers are correspondingly
provided, while the transmitting coupler must then be
disposed between the two receiving couplers. The signal
generator (e.g. oscillator) generates a signal with a
constant mid-frequency, and is operated below the
waveguide's lowest cutoff frequency. A plurality of
waveguide modes (TEõ,, where m = 0, 1, 2_ and n = 1, 2,
3m) are excited by the geometry and nature of the
transmitting coupler (coil, dipole, etc.). The signal
generator produces either a carrier in the continuous-
wave mode (CW mode) or a modulated signal. The distance
between the transmitting coupler and the receiving
couplers in this case is chosen such that the received
signal is dominated by the single mode (n = 1) term.
However, this requires a specific waveguide or weapon
= barrel length to be observed.
Based on this principle, the invention addresses the
problem of being able to reduce the length of the
waveguide or =weapon barrel.
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Some embodiments of the invention relate to a method for
measuring the muzzle velocity of a projectile with a weapon
barrel or launcher tube and/or part of the muzzle brake operated
as a waveguide, involving the steps: generation of an
electromagnetic field by means of an oscillator, measurement of
the electromagnetic field of the weapon barrel or launcher tube
and/or part of the muzzle brake without the projectile to
determine a calibrating term, measurement of the electromagnetic
field in front of the projectile and/or behind the projectile to
determine an induced voltage over time, subtraction of the
calibrating term from the induced voltage to determine a
reflected electromagnetic field, determination of the muzzle
velocity from the measured signals, such that the reflected field
is broken down into coefficients, with which terms are formed,
wherein a muzzle velocity is calculated per term and by finding
the average of all muzzle velocities of the terms, the muzzle
velocity of the projectile is determined.
Some embodiments of the invention relate to a weapon barrel or
launcher tube and/or part of the muzzle brake, which is operated as a
waveguide to measure the muzzle velocity of a projectile, with an
oscillator, which is electrically connected to a transmitting coupler
via a signal supply to excite the weapon barrel or launcher tube
and/or part of the muzzle brake, and a receiving line to transfer the
signals measured at at least one receiving coupler to an evaluation
device to implement the method as described above, such that a
reduction in the distance between the transmitting coupler and the
receiving coupler to 0 mm is made possible.
The invention is based on the idea of shortening the measurement
arrangement by reducing the distance between the receiving and
transmitting couplers preferably to 0 mm. However, the
implementation of this
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concept is complicated by the fact that, when there is
less than a certain distance between the couplers, it
is no longer possible to determine individual terms,
but only so-called sum fields. This requires splitting
of said sum fields, in order to determine the muzzle
velocity vo therefrom.
Hence, similarly to DE 10 2008 024 574 Al, the source
field generated by the transmitting coupler is measured
first, in other words, when there is no projectile in
the waveguide. As is commonly known, when the
projectile passes the receiving coupler this produces a
characteristic, reflected sum signal, which is sampled
in time and read into an evaluation device. This sum
signal contains information on the velocity vo of the
projectile (6,z(t)), but said sum signal cannot be read
out directly. The induced voltage is therefore measured
to implement the basic idea underlying the invention
and the source field is subtracted from this. The
remaining reflected (electromagnetic) sum field is then
split into individual terms by software, so that a
plurality of velocities are determined over time. An
extremely accurate projectile velocity is then
determined from this by determining the average.
The shorter overall length of the measurement
arrangement reduces the risk posed by sabots being
detached within the measurement device, particularly
when using sub-caliber projectiles. Likewise, a weight
reduction is achieved, which increases the weapon's
stability. The measuring accuracy increases, as the
process is more resistant to vibration and shocks
during firing.
For munitions in the 35 mm caliber range, the
oscillator frequency may preferably fall within the 40
MHz to 80 MHz range, although it is not itself set to a
particular value. Different frequency ranges may be
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provided for different calibers. This frequency range
(40 MHz and 80 MHz) facilitates simple procurement of
components for this frequency range, particularly since
component tolerances have no effect on the measuring
process. In addition, only small electromagnetic
emissions are produced.
The invention will be described in greater detail using
an exemplary embodiment with a drawing.
In this:
Fig. 1
is a measurement device for measuring the
velocity before the projectile,
Fig. 2
is a measuring device for measuring the
projectile velocity after the projectile,
Fig. 3
is a representation of the signal processing
steps in the two measuring processes.
In Figs. 1 and 2, 1 denotes a waveguide or a weapon
barrel or launcher tube and/or parts of the muzzle
brake, in which a transmitting coupler 2 is
incorporated. In Fig. 1 a receiving coupler 3 is spaced
away from the transmitting coupler 2 towards the barrel
mount. In Fig. 2 a receiving coupler 4 is spaced away
from the transmitting coupler 2 towards the muzzle. The
transmitting coupler 2 is electrically connected to an
oscillator 5. The two receiving couplers 3, 4 are in
turn connected to an evaluation device 6. A combination
of the arrangement of the two receiving couplers 3, 4
in a measurement setup 10 is preferred, but it is not a
condition. A projectile 7, the velocity vo of which is
to be measured, is projectile through the waveguide 1 /
weapon barrel. This arrangement is already known from
DE 10 2008 024 574.7, which is referred to here.
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The distance between the transmitting coupler 2 and the
respective receiving coupler 3, 4 is designated zK. The
positioning of the couplers 2, 3, 4 relative to one
another is determined as claimed in DE 10 2008 024
574.7 via an induced voltage of the oscillator 5, which
is calculated as claimed in the following formula:
Pi * ZK
a
UIND Al * lc!
In this case, UIND is the value of the induced voltage Al
and Al is the measurement amplitude, pi is a given
constant obtained directly from the solution of the
Maxwell equations of the measuring system 10, a is the
internal diameter of the waveguide 1. This internal
diameter a should be at least equal to or preferably
slightly greater than the weapon's barrel caliber. zk
defines the distance value between the transmitter 2
and the receiver 3, (4). This distance is determined
numerically and verified experimentally, such that of,
the terms ID', only the first term pi dominates. It is
permanently set in this case. This value is determined
for each diameter of the measurement device 10 / of the
waveguide 1 and is independent of the ammunition 7
used.
In order to now allow the overall length of the
waveguide 1 to be reduced, while at the same time
increasing the measurement accuracy of the Vo
measurement, signal processing as claimed in Fig. 3,
for example, is proposed.
The distance between the projectile base or projectile
nose and the receiving coupler 3 or 4 is designated
Az(t), where t is time. It is important to note that
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Lz(t) = 0 mm when the projectile base (nose) passes the
receiving coupler 3, 4.
To reduce the size of the available space, zk is now
reduced. The value will therefore differ from the given
value for single-mode operation. In other words, if a
smaller value is chosen for zk, this single-mode
operation will no longer dominate and the induced
voltage will once again have the formula
Pn * zK
a
UIND = An * e
n=
The terms in the above expression are constant over
time, and the individual terms decay in space at
different rates.
As the projectile 7 moves away from or approaches the
receiving coupler 3, 4, an induced voltage UIND is
measured, as described in greater detail in Fig. 3. The
first term "A" in this formula is constant over time
and may be used for calibration. It is preferably
measured continuously, but particularly shortly before
firing, in other words, when there is still no
projectile 7 in the waveguide 1. These values are
continuously stored, preferably in the shift register
of the evaluation unit 6. All changes in the constants,
which are caused, for example, by temperature effects
in the weapon, are eliminated by such a calibration. If
the profile of the signal UIND is now sampled in time
with the second term "B" upon firing, additional signal
processing can be carried out in accordance with Fig.
3.
Therefore, in a first step following measurement of the
induced voltage UIND (t), the calibration term "A" is
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subtracted from UIND. This leaves the so-called sum
field (reflected electromagnetic field) - the term "B".
The time profile of the sum field "B" is then broken
down into the coefficients Bm. These may be determined
using known curve fitting methods, taking account of
known optimization requirements, such as the least
squares method. The choice of optimization requirements
is influenced by the nature and level of the noise
which is present on the UIND signal.
The terms B1, B2, B3mBm can be formed in parallel with
the coefficient Bm, as pm and a (internal radius of the
waveguide 1) are known. The logarithm of each term is
then taken. With this mathematical operation, an offset
term is produced, which depends only on the known value
Bm and is compensated for by subtraction. As an interim
result, a further term with the known pm, a and vo =
Az(t) is produced. A muzzle velocity v01, v02, v03...vom is
thereby calculated per term 1, 2, 3mm. By finding the
average of all vol_m, the final result vo is determined.
Finding the average in this way means that vo is
determined with greater accuracy.
The proposed method allows the distance between the
transmitting coupler 2 and the receiving couplers 3, 4
to be reduced from zk to 0 mm, so that the waveguide can
be shortened at least in this area. In an ideal
scenario (zk = 0 mm), the transmitting coupler 2 should
be able to carry out the function of the receiving
coupler(s) 3, 4, so that the induced voltage is
directly measured at the transmitting coupler 2.
To simplify matters, further signal modifications, e.g.
using mixing methods for frequency reduction, may
precede the evaluation electronics 6 (not shown in
greater detail). To increase the evaluation speed, the
shift register should be sufficiently large in size for
values at measurement intervals of "per second" to be
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recorded, for example, so that all calibration data can
be used for the evaluation.
