Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
AD 265
1 338629
System for dete_ inin~ the angular spin position of an object
spinning about an axis.
The invention relates to a system for dete ining the angular spin
position of a second object spinning about an axis, where a first
object emits elec~L. aP~etic waves and where the system is provided
with directional receiving antenna means fitted to the second
object, and with a receiving system which, using the receiving
antenna means, process in combination the carrier waves received to
obtain said angular spin position.
Such an arrangement is known from EP-A 0,239,156. This patent
particularly applies to a second object in the shape of a
projectile. In case of fired projectiles, such as shells, it is
often desirable to change the course during the flight. However,
since a shell spins about its axis along the tra;ectory, correction
of its course is effective only if at any random instant the
associated spin or roll position ~m(t) is well-known. Suitable
course correction means for this purpose are preferably based on
principles of the aerodynamics, the chemistry, the gas theory and
the dynamics. In this respect, considered are the bringing out of
damping fins or surfaces on the projectile's circumferential
surface, the detonation of small charges on the projectile, and the
ejection of a small mass of gas from the projectile.
According to the EP pstent specification this problem is solved by
transmitting signals consisting of at least two superimposed
phase-locked and polarised carrier waves having different
frequencies. These signals are transmitted by the first object.
Thus it is possible to obtain a reference signal by processing both
carrier waves in combination. This reference signal comprises phase
information of both carrier waves. By means of this reference
1 338629
signal, the 180 uncertainty can be eliminated. It is clear from
Fig. 1 of the EP patent that also a third carrier wave is present
for transmitting data to the projectile by means of the transmitter.
After this, for instance, the information on angle ~g is transmitted
upon which a correction is to be carried out by the pro~ectile.
For this purpose, the projectile itself dete_ ~neS the instantaneous
angular spin position ~m(t) and carries out a correction as soon as
~g ~ ~m(t)
The present invention has for its object to simplify and ~ ~Lvve the
above system and is characterised in that the received signals
comprise at least one first polarised carrier wave and a second
carrier wave, which comprises phase information of the first carrier
wave.
Contrary to the EP patent, according to the present invention, the
information for obtaining the reference signal is carried fully by
the second carrier wave. As a result, the receiving system of the
second object (the projectile) may be of a much simpler and thus
more cost-effective construction. Another advantage is that the
reference signal may be dete ~ned more accurately. Noreover, the
second carrier wave can be used to transmit other information (such
as ~g), resulting in a further cost reduction because there will be
no need for a third carrier wave.
According to a special embodiment of the invention, it is even
feasible to use the fins of a projectile as an antenna system. By
means of these fins, the first as well as the second carrier wave
can be received. This results in a further cost reduction, while
~ ".~ving the robustness of the system.
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According to another advantageous embodiment of the invention, the
orientation of the first object is lln~ ,_L~ant in the determination
of the angular spin position of the second object with respect to,
for instance, the earth surface. This is not possible in
conventional systems as the angular spin position of the second
object is determined with the first object as reference. In
conventional systems this implies that the orientation of the second
object with respect to the earth surface must be known and be kept
constant. If the first object is, for instance, a ship, a
transmitter and antenna unit of the first object, transmitting the
at least one polarised carrier wave, will have to be fitted on a
stabilised platform. Only then it is possible in conventional
systems to keep the polarisation direction of the transmitted
carrier waves with respect to space (the earth surface) constant.
The use of a stabilised platform however is rather expensive.
Moreover, the means must be available to measure and process the
position and orientation of the platform in order to obtain an
angular spin position of the second object with respect to space.
This renders the system inaccurate as well as more expensive.
In conventional systems, a polarised carrier wave around the second
object is obtained by transmitting a polarised carrier wave. This
has the disadvantage that a polarising transmitter and antenna unit
needs to be used. Such transmitter and antenna units have the
disadvantage that they are rather bulky and thus quite expensive.
According to an especially cost-effective embodiment of the
inventionr however, a transmitter and antenna unit is used which
transmits carrier waves re~ch~ng up to and around the second object
but also up to and interfering with the earth surface. Moreover, the
transmitter and antenna unit of the first object is thus arranged
that the frequency of the first carrier wave to be transmitted is
` 1 338629
24005-166
relatively low, i.e. around 50 kHz. These technical measures
result in a carrier wave of which the electric field component is
vertically disposed with respect to the earth surface. The latter
is entirely independent of the orientation of the transmitter and
antenna unit. Similarly, the magnetic field component of the
first carrier wave is horizontally disposed with respect to the
earth surface. This results in the enormous advantage of being
able to measure the rotation of the angular spin position of the
second object with respect to the earth surface. Moreover, there
is no need to fit the transmitter and antenna unit, when used on a
ship, on to a stabilised platform.
The above also results in much simpler and cheaper
embodiment of the transmitter and antenna unit, because said
system needs not be suitable for the generation of polarised
carrier waves with an accurately defined polarisation direction.
Moreover, determination and calculation of the angular spin
position are also simpler and cheaper as the orientation of the
first object is of no importance.
The invention will now be described in more detail with
reference to the accompanying drawings, of which:
Fig. la is a schematic representation of a first embodiment
of a complete system for the control of a projectile functioning
as the second object, taking into account an apparatus according
to the invention;
Fig. lb is a schematic representation of a projectile
controlled by the system of Fig. la;
Fig. 2 represents a special embodiment of the system where
. , , ~
` -- ~
1 3 3 8 6 2 9 24005-166
the system is arranged in such a way that the orientation and
position of the antenna unit of the system may remain
undetermined.
Fig. 3 is a schematic representation of two perpendicularly
disposed loop antennas placed in an electromagnetic field;
Fig. 4 is a schematic representation of two perpendicularly
disposed dipole antennas placed in an electromagnetic field;
Fig. 5 is a diagram of a magnetic field at the location of
the loop antennas;
Fig. 6 shows a schematic representation of the receiving
system included in a projectile to determine the angular spin
position of the projectile;
Fig. 7 is a first embodiment of a unit from Fig. 6;
Fig. 8 is a second embodiment of a unit from Fig. 6;
Fig. 9 is a diagram of an electric field at the location of
the dipole antennas;
Fig. 10 is an embodiment of the projectile with dipole
antennas;
Fig. lla is a schematic representation of a second embodiment
of a complete system for the control of a projectile functioning
as the first object, taking into account an apparatus according to
the invention; and
Fig. llb is a schematic representation of a projectile
controlled by the system of Fig. lla.
In Fig. 1 it is assumed that a projectile 1 functioning
as second object has been fired to hit a target 2. The target
trajectory is tracked from the ground with the aid of target
,- ~ 5
1 338629
24005-166
tracking means 3. For this purpose, use may be made of a
monopulse radar tracking unit operable in the K-band or of pulsed
laser tracking means operable in the far infrared region. The
trajectory of projectile 1 is tracked with comparable target
tracking means 4. From the information of supplied target
positions determined by target tracking means 3 and from supplied
projectile positions determined by target tracking means 4,
computing means 5 determines whether any course corrections of the
projectile are necessary. To make a course correction, the
projectile is provided with gas discharge units 6. Since the
projectile rotates about its axis, a course correction requires
the activation of a gas discharge unit at the instant the
projectile assumes the correct position. To determine the correct
position, carrier waves sent out by a transmitter and antenna unit
7 functioning as first object are utilised. Computing means 5
determines the desired projectile angular spin position ~g at
which a gas discharge should occur with respect to the
electromagnetic field pattern of the carrier waves at the
projectile position.
5a
.,
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The position and attitude of the transmitter and antenna unit 7 serve
as reference for this purpose. This is possible, because the field
pattern and the pro~ectile position in this field are known.
Accorting to a special embodiment of the invention, use of the
position and orientation of the transmitter and antenna unit 7 as a
reference is obviated. This is especially advantageous when the
orientation of transmitter and antenna unit 7 is sub~ect to v~- ^nt,
for instance, when it is placed on a ship (see Fig. 2). Antenna
unit 7 of Fig. 2 is arranged in such a way that the transmitted
carrier wave reaches up to and around the projectile and that the
carrier wave reaches down to the earth surface. Moreover, the
frequency of the transmitted carrier wave is relatively low with
respect to conventional systems. The result of the above is that
the electric field component E of the carrier wave is vertically
polarised and that the magnetic field component is horizontally
polarised with respect to the earth surface. The polarisation
reaches greater heights as the frequency ~O becomes lower and as the
antenna unit is placed closer to the earth surface.
As a result of these technical measures, the earth surface behaves
as a flat conducting metal plate. The advantage is that the
polarisation is independent of the orientation of antenna unit 7.
Angles ~m(t) and ~g(t) can then be determined with the earth
surface as a reference.
Antenna unit 7 is of an especially simple and cost-effective type,
viz. a single wire. No use is made, as for conventional systems, of a
stabilised platform onto which the antenna unit is fitted. Antenna
unit 7 will therefore continuously change orientation as a result of
the roll of the ship. Antenna unit 7 is also not suitable for
transmitting polarised carrier waves, having as an advantage that the
length of the antenna unit 7 can be limited. In this case, antenna
unit 7 concerns a communication antenna already present on the ship.
1 33~`~2~
The calculated value ~g is transmitted by means of transmitter 8.
For this purpose, transmitter 8 may be provided with its own antenna,
as shown in Fig. 1, but may also use the c- ~cation antenna of the
transmitter and antenna unit as shown in Fig. 2.
A receiver g, accommodated in the pro~ectile, receives from receiving
antenna means 10 the value of ~g transmitted by transmitter 8. The
received value ~g is supplied to a comparator 12 via line 11.
A receiving system 13, fed with the antenna signals of two perpendi-
cularly disposed directional antennas contained in receiving antennameans 10, dete ~neS the instan~neo~s pro~ectile position ~m(t) with
respect to the elecLL~ a~etic field at the location of the
directional loop antennas. The instantaneous value ~m(t) is supplied
to comparator 12 via line 14. When the condition ~m(t)- ~g has been
fulfilled, comparator 12 delivers a signal S to activate the gas
tischarge unit 6. At this moment a course correction is made.
Thereafter this entire process can be repeated if a second course
correction is required.
It should be noted that it is also possible to make the desired course
corrections without the use of second target tracking means 4.
The target tracking means 3 thereto measures the target tra~ectory.
From the measuring data of the target tra~ectory the computing
means 5 makes a prediction of the rest of the target tra~ectory.
Computing means 5 uses this predicted data to calculate the direction
in which the pro~ectile must be fired. The pro~ectile tra~ectory is
calculated by computing means 5 from the pro~ectile ballistic data.
The target tracking means 3 keeps tracking the target 2. If it is
found that target 2 suddenly deviates from its predicted tra~ectory,
computing means 5 calculates the pro~ectile course correction
to be made. It is thereby assumed that the pro~ectile follows its
calculated tra~ectory. If the pro~ectile in flight nears the target,
this target will also get in the beam of the target tracking means 3.
1 338629
From this moment onward it is possible to track both the target and
the projectile trajectories, permitting computing means 5 to make
some pro~ectile course corrections, if necessary. As a result, any
deviations from the calculated projectile tra~ectory, for example
due to wind, are corrected at the same time.
It is also possible to eliminate the second tracking means 4 with the
application of a time-sharing system. In such a case, the target and
the pro~ectile tra~ectories are tracked alternately by means of
target tracking means 3. Any course corrections of the pro~ectile are
made analogously, as described hereinbefore.
Fig. 3 and Fig. 4 show the two perpendicularly disposed directional
antennas 15 and 16, forming part of the receiving antenna means 10.
The antennas may comprise a B field or an E field. If two B fielt
antennas are applied (such as represented in Fig. 3), the magnetic
field c o~e~ts B of an elec~l. apnetic field are detected.
If two E field antennas are applied (such as represented in Fig. 4),
the electric field c _.onents E of an elec~,- Q~netic field are
detected. If one B field and one E field antenna are used, one
subc ,_ ^nt of field component E and one subc. .onent of field
c ,~onPnt B are detected. Because field cs ,~.^nts E and B are
connected to eachother via the so-called relation of Maxwell,
measuLe --t of at least one of the components E or B, or of one
s~bc~ , ^nt of the E c _, ent and one subcomponent of the B
will suffice.
For measuring the B component, a loop antenna can be used, while
a dipole antenna may be used for measuring the E component.
An x,y,z coordinate system is coupled to one of the loop antennas.
The propagation direction v of the projectile is parallel to the
z-axis. The magnetic field c ,~.^nt B, transmitted by transmitter
8 has the magnitude and direction B(rO) at the location of the
1 338629
loop antennas. Here rO is the vector with the transmitter ant the
antenna unit 7 as origin and the origin of the x,y,z coordinate
system as end point. The magnetic field c ,~.^nt B(rO) can be
resolved into a component B(rO)// (parallel to the z-axis) and
the component B(rO)l (perpendicular to the z-axis). Only the
components B(rO)l can generate an induction voltage in the two
loop antennas. Therefore, as reference for the determination of ~m(t)
use is made of B(rO)l. In this case, ~m(t) is the angle between the
x-axis and B(rO)l, see Fig. 5. Since the computing means is
capable of calculating v from the supplied pro~ectile positions r,
computing means 5 can also calculate B(rO)l from B(rO) and define ~g
with respect to this c ~o~^nt.
Fig. 6 is a schematic representation of the receiving system 13.
In the embodiment of system 13 in Fig. 6 it is assumed that the
transmitter sends out an elecL~ .^etic field consisting of a
polarised carrier wave with frequency ~O. The magnetic field
cc ,_ ^nt Bl(rO) can be defined as
~
Bl(rO) ~ (a sin ~Ot)e, where _ _ ~ e (1)
The magnetic flux ~15 through the loop antenna 15 can be defined as:
~15 = (a sin ~ot).S.cos ~m(t) (2)
In this formula, S is equal to the area of the loop antenna 15.
The magnetic flux ~16 through loop antenna 16 can be tefined as:
~16 ~ (a sin ~Ot).S.sin ~m(t) (3)
The induction voltage in loop antenna 15 is now equal to:
indl5 -e dt ~ -e(a wO cos ~ot).S.cos ~ (t) +
d~m
+ -e(a sin ~Ot).S.sin ~m(t)- dt (4)
1 338629
Here ~ is a constant which is dependent upon the used loop antennas
d~
15, 16. Since the projectile speed of rotation dt is much smaller
than the angular frequency ~O, it can be approximated that:
indl5 -~(a ~O cos ~Ot)~o(t).s.cos ~ (t) -
e (A cos ~ot).cos ~m(t) (5)
Similarly, for loop antenna 16:
Vind ~ (A cos ~ot).sin ~m( ) (6)
Transmitter 8 also transmits an elecLL. ag~etic wave E where:
E(t) ~ G(t) cos ~lt with G(t) - D.(l - ~ wot).
In this formula, D is a constant and ~ the modulation depth, so
< ~ < 1. Also, ~1 ~0- According to this embodiment, frequency
~1 is FM- -d~ ted to comprise the information concerning ~g.
The elec~,. a~etic wave is therefore modulated with cos ~ot and
thus comprises phase information of the signal transmitted by
antenna unit 7. Receiving antenna means lO is provided with an
antenna 17 for the reception of signal E(t). Antenna 17 is linked
with a reference unit 18, which generates a reference signal Uref
from the received signal E(t), with
U - C cos ~ t . (7)
ref o
Here C is a constant which is dependent upon the specific embodiment
of reference unit 18. The Uref signal is supplied to mixers 20 and
21 via line 19.
Signal Vind (t) is also applied to mixer 20 via line 22.
The output signal of mixer 20 is applied to low-pass filter 24 via
line 23. The output signal U24(t) of the low-pass filter 24 (the
t~
c~ Eone~t of frequency dt ) is equal to:
11 1 338629
U (t) = AC cos ~ (t) (8)
In a fully analogous way, signal Vind (t) is fed to mixer 21 via
line 25. The output signal of mixer 21 is fed to a low-pass filter
27 via line 26. Output signal U27(t) of the low-pass filter 27 is
equal to:
U27(t) e 2 sin ~m(t) (9)
From formula (8) and (9) and for a given U24(t) and U27(t), it is
simple to determine ~m(t)~ To this effect, signals U24(t) and U27(t)
are sent to a trigonometric unit 30 via lines 28 and 29. In response
to these signals, trigonometric unit 30 generates ~m(t)~
Trigonometric unit 30 may, for instance, function as a table
look-up unit. It is also possible to have the trigonometric unit
functioning as a computer to generate ~m(t) via a certain algorithm.
Fig. 7 represents an embodiment of reference unit 18. Antenna signal
E(t) is supplied to a b~ndpass filter 32 via line 31. B~ndpflss
filter 32 only passes signals with a frequency of arount ~1 Signal
B(t) will therefore not be passed. Signal E(t) is subsequently
supplied to an AM demodulator 34 via line 33 to obtain Uref on
line 19. The reference unit may be additionally provided with an
FN demodulator 35 and a bit demodulator 36. In that case, signal
E(t) is also used as an information rh~nnel. The information is
FM modulated and transmitted with signal E(t). This enables the
required angle ~g to which the correction of the pro~ectile is to be
carried out to be received, FM demodulated and bit demodulated from
signal E(t). In this case, receiver 9 of Fig. 1 is not required
because reference unit 18 determines ~g by itself.
Fig. 8 represents a special embodiment of reference unit 18.
According to this embodiment, the task of antenna 17 is replaced by
both antennas 15 and 16. For this purpose, reference unit 18 is
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12
provided with two b~ndp~ss filters 32A and 32B having the same
function as the bandp~ss filter of Fig. 7. The output signal of
b~ndp~ss filter 32B is supplied to a 90 phase shifter 37. The
output signal of the phase shifter is supplied via line 38 to
~j in~ unit 40. Owing to the 90 phase shifter 37, the signals when
summed will supplement each other and an output signal will be
obtained having a constant amplitude. The output signal of s~ ~ng
unit 40 is equal to the signal on line 33 as described in Fig. 7.
The output signal of &- ~ng unit 40 is processed by means of an
AM demodulator 34, FM demodulator 35 and bit demodulator 36 in the
same way as described for Fig. 7.
In Fig. 3 the directional antennas are represented as two loop
antennas. However, it is also possible to use two perpendicularly
disposed dipole antennes. In that case, the E field instead of the
B field of the electromagnetic field is measured. Because the E
field and the B field are connected via the well-known relation of
Naxwell, the principle of the invention remains the same. The dipole
antennas are preferably positioned perpendicularly to the surface of
the former loop antennas (see Fig. 4).
Fig. 4 represents, besides the B field, also the E field. In this
case, the E field instead of the B field as represented in Fig. 3
now functions as reference for measuLc - t of the instantaneous
angular position ~'m(t) of the projectile. A first dipole antenna is
for this purpose positionet parallel with the x axis, while a second
dipole antenna is positioned parallel with the y axis.
The E field at the dipole antennas is described by E(rO). The
E field can be disintegrated into two components E(rO)// and E(rO)
_ _
as represented in Fig. 9. Only the E(rO)l component will generate a
voltage in the dipole antennas.
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13
The E(rO)l field component can be expressed by:
E(rO)l - a' cos ~ot e (10)
_ _
with e e _ _ (11)
IE(rO)ll
Voltage V'15 in the dipole antenna parallel with the x axis is
equal to:
E(rO)l cos ~'m(t).h (12)
where hs is the length of the dipole antenna. In a fully analogous
way, voltage V'16 in the dipole antenna along the y asis is equal to
15 _ _
16 E(rO)l sin ~'m(t).h (13)
where hy is the length of the dipole antenna along the y axis.
Combination for fo- 1~s (11), (12) and (13) results in:
V'15 ~ a' hs cos ~ot-cos ~m(t) (14)
16 b hy cos ~Ot.sin ~' (t) (15)
Fully analogous to the description to fo_ 1~s (5) and (6), angle
~'m(t) can be determined from formulas (14) and (15) by means of
the reference signal of formula (7). Thus the instantaneous position
of the pro~ectile is determined, as the E field is known.
A special s ho~ ~ t of the dipole antennas is represented in
Fig. 10. Pro~ectile 41 in Fig. 10 is provided with two pairs of fins
42A, 42B, 43A and 43B. Fins 42A, 42B, like fins 43A, 43B, are
positioned at opposite angles, while fins 42A and 43A on the one
hand and 42B and 43B on the other hand are perpendicularly disposed.
14 1 338629
Fins 42A and 42B together form a first dipole antenna 15 and fins
43A and 43B form a second dipole antenna 16 perpendicularly
positioned to dipole antenna 15. In this case, the fins also
function, like antenna 18, for reception of the data signal.
ignals V 15~ V 16~ ~ m(t)~ Uref and ~g can be dete_ ~ned by means
of the fins as described above for Fig. 8.
It will be clear that it is not necessary to perpendicularly dispose
the dipole antennas, loop antennas and/or fins. Moreover, for the
sake of redun~ncy more than two antennas may be used. Thus for
instance six fins may be fitted at a 60 angle.
If one dipole antenna and one loop antenna are used which are not
perpendicularly disposed, the instantaneous angular spin position of
the ob~ect can also be dete_ ned. If one dipole antenna 15 is
parallel with a loop antenna 16 (parallel with the x axis), in a
fully analogous way as described above:
V'15 ~ a' hx cos ~ot.cos ~'m(t) (16)
20 Vind - A cos ~ot cos ~m( ) (17)
Because E and B are perpendicularly disposed:
~'m~t) ~ go _ ~m(t) (18)
Substitution of (18) in (16) will result in:
V~ e a' hx cos ~o(t) sin ~m( ) (19)
It will be clear that on the basis of fo l~s (19) and (17) the
value of ~m(t) can be dete ~ned as described above because
a', hx and A are also known.
It will be clear that the method for deteL ~n~n~ the angular spin
position of an object with the aid of an receiving system according
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to Fig. 6 can also be used if the projectile now functioning as the
first object is equipped with the transmitter ant antenna unit 7,
while the receiving system 13 now functioning as the second ob~ect
is installed, ~ointly with the loop or dipole antennas, on the
ground (see Fig. 11).
Fully analogous to Fig. 1, the first target tracking means 3,
the second target tracking means 4, and computing means 5 are used
to determine the angular spin position ~g of the projectile; this
requires a course correction of the projectile 1 to hit the target
2. To dete_ ~ne the angular spin position of the projectile, the
transmitter and antenna unit 7 is contained in the projectile 1.
With the use of the loop or dipole antennas located on the ground
and the receiving system 13, to which these antennas are mounted, it
is possible to dete_ ~ne ~m(t) in the same way as in Fig. 1, as here
a relative angular spin position of the projectile with respect to
the system 13 is concerned. The output signal ~m~t) of the system 13
is applied to comparator 12. If the condition ~m(t) - ~g is
fulfilled, the comparator delivers a control signal to transmitter
unit 8. This control signal is sent out for reception by the
receiver 9 in the projectile. In response to this, receiver 9
activates the gas discharge units 6. If a second course correction
is found to be necessary, this entire process can repeat itself.
