GB2236925A

GB2236925A - Measuring rotational position of missile

Info

Publication number: GB2236925A
Application number: GB9015862A
Authority: GB
Inventors: Hans-Joachim Leus; Josef Osthues; Otto Gaede; Helmut Neff
Original assignee: Tzn Forschung & Entwicklung; Rheinmetall GmbH
Current assignee: Tzn Forschung & Entwicklung; Rheinmetall Industrie AG
Priority date: 1989-10-14
Filing date: 1990-07-19
Publication date: 1991-04-17
Also published as: GB9015862D0; FR2653231A1; DE3934363A1

Abstract

A sensor for measuring the rotational position of a ballistic projectile rotating about its longitudinal axis using the plane of polarisation of a guide beam 6 is described. A magnetic field sensor (10) being provided with a circuit (11) providing time gating reference impulses (34) which define an above or below relative position of the projectile used in conjunction with the peak value of the guide beam to unambiguously define the roll position. The output (30) of the analyser (8, 9) is converted to peak pulses (31) having 180 DEG ambiguity. The magnetometer (10) output (32) provides the gating pulses (33) to select the correct peak pulses (34), (18). <IMAGE>

Description

:21:21 3 c C-D:2-1 ES 1 TITLE is 1 Guiding Ballistic Pro-jActilea 408 12-

/wsy This invention relates to guiding ballistic projectiles, more particularly to a means for generating impulses enabling the roll position to be determined.

For trajectory correction of ballistic projectiles using particularly a guide beam control or command control system, the roll position in relation "to the flight path must be accurately known. The correction is often effected by one or more impulse transmissions using suitable impulse generators (pyrotechnical impulses, hot t-%old-gas generators and the like). Accurate impulse correction calls for a reference signal (reference impulse) which determines the angle prevailing at any instant between the impulse generator and a reference plane.

In the case of powered projectiles not flying ballistically the reference may be defined, for example, by the position and direction of acceleration due to gravity and determined by acceleration sensors, micropendulums or the like. This method cannot be adopted in the case of missiles and projectiles having a ballistic trajectory, because the flight thereof is "weightless" 0 0 40812/wsy and in this state it is not possible to measure any force in order to determine the direction taken by gravitational acceleration.

U.S. 4 347 996 makes known a method of measuring the roll position by means of polarised radiation. This known device, however, does not enable the roll position to be clearly determined, for owing to the ambiguity of the output signal the exclusive use of the polarisation process only enables a reference plane to be established. The process is only suitable as a means of measuring the roll rate.

U.S. 4 328 938 makes known a system for determining the roll position with the use both of a magnetic sensor and an electrostatic sensor. This system suffers from the disadvantage that the required measurement of the electrostatic earth field is extremely difficult and imprecise. A method of this kind is not applicable in practice, because the field intensities may be very small. This normally leads to unacceptable errors in determining the roll position.

This invention seeks to provide means for producing reference signals or reference impulses for accurately determining the roll position of a ballistic projectile.

According to this invention there is provided means for generating reference impulses enabling the roll J.

3 - ZO 408 12/wsy position of a projectile rotating about its longitudinal axis to be determined, wherein a transmitting system associated with the projectile firing device emits polarised radiation which is received by a sensor on the projectile, the sensor having a means for determining the peak value of the received sensor signal, the projectile including a magnetic field sensor to determine the direction of the Earth's magnetic field and a time gating device to establish a time range over the relevant maximum or minimum value of the output signal of the magnetic field sensor, and an AND function means to derive from the peak signal over the gated signal time range an output signal forming the reference impulse.

This invention is thus based on the combined use of polarised radiation, which is necessary in any case for beam following guidance, taking into account the direction of the earth's magnetic field (for above/below) decision. This latter is determined by means of a magnetic field detector situated in the projectile.

This invention is further described with reference to embodiments shown by way of examples in the drawings, wherein:- Figure 1 shows an armoured vehicle with optical beam following guidance of a projectile, Figure 2 shows a laser systerri for guidance and for 1 0 W 408 12 /wsy determining the roll position, Figure 3 shows a first example of a means in accordance with this invention for determining the roll position reference signals, Fig ures 4a to 4e show the signals present in the means of Figure 3, and Figure 5 shows a second example of a means according to the invention.

Figure 1 shows an armoured vehicle 1 having a laser system 2 located on a positionally stabilised platform 3. A projectile 4 with a sensor system 5 has just been fired. The polarisation plane 6 of the radiation emitted by the laser system 2 is fixed as a result of the positionally stabilised platform 3.

In Figure 2 the constructional elements of the laser system 2 are shown scherriatically with the laser system 2 21 serving to comprising essentially a laser 20, a lens spread the beam and a polarisation filter serving to determine the polarisation plane 6. The polarisation plane is fixed and is ensured by the stabilised platform 3 (Figure 1).

Figure 3 shows the sensor system 5 as well as a magnetic field sensor 10 and a circuit 11 for determining the roll position reference signals.

67 1 i 1 40812/wsy The sensor system mainly comprises a lens 7 serving to focus the laser beam, a polarisation filter 8 and a laser detector 9. The laser detector 9 is connected to the input 14 of an AND gate 15 via an amplifier 12 and a peak value detector 13. The magnetic field sensor 10 is likewise connected with an input 14' of the AND gate 15 via a comparator 17. It is important that the magnetic field sensor should be positioned in the projectile 4 in such a way that the lines of flux of the earth's magnetic field are intersected at a finite angle, that is not parallel to the field. Furthermore, the field-sensitive plane of the magnetic field sensor and the plane of the polarisation filter must coincide.

The method of operation of the circuit shown in Figure 3 is described in more detail with reference to Figure 4.

As the polarisation plane 6 is kept constant and the polarisation filter 8 rotates with the projectile, the light intensity signal occurring at the input of the laser light detector takes the form I (t) = JO. coo2 -c (1) 1 with T = CJ t, wherein CJ is the angular rotation rate of the projectile, t the time and Io the signal peak which 1 i. 0 0 40812/wsy occurs when the planes of the two polarisation filters 22 (Figure 2) and 8 (Figure 3) coincide.

A corresponding voltage signal 30, shown in Figure 4a, therefore occurs at the oUtput of the laser light detector 9.

The signal obtained at the output of the laser light detector 9 is amplified by means of the amplifier 12 and conveyed to the peak value detector 13. Figure 4b shows the peak value signal 31 (impulse sequence) occurring at the output of the peak value detector 13 fed to the input 14 and the AND gate 15.

Figure 4c gives the voltage characteristics 32 at the output of the magnetic field sensor 10. The rotation results in an output signal of the form

U (H, t) = Uo cos ( -f + 19) (2) The angle 0 depends on the direction taken by the earth's magnetic field and by the projectile. it therefore causes a phase difference between Equation (1) and Equation (2), according to the direction of the projectile.

The output signal of the magnetic field sensor 10 is conveyed via the amplifier 16 to the comparator 17 for determining the sign of the magnetic field and then to

1 - 7 40812/wsy the input 14 of the AND gate 15.

Figure 4d shows the output signals 33 of the comparator 17 and the signals prevailing at the input 14'. The comparator 17 thus'forms time gated values. For this purpose a constant threshold value voltage is applied at one input of the comparator 17. If the output signal 32 of the magnetic field sensor 10 is now conveyed to the other input of the comparator a constant voltage value is produced at the output for as long as the voltage remains below the threshold value.

At the output 18 reference impulses occur which determine the definite position of the projectile (above or bp-low). These signals are shown in Figure 4e. The diagram does not include the possible phase shift of the output signals of the two sensor channels.

The invention is not limited to the example described in the foregoing. The optical measuring device, for instance, can be replaced by a millimetre wave measuring device. In this case the laser system 2 must be replaced by a millimetre wave antenna which either emits linear polarised waves direct or is connected by the aid of an additional polarisation filter. The receiving sensor system 5 must be equipped accordingly, a millimetre wave sensor being used in place of the laser light detector.

40812/wsy A Figure 5 shows a further example of the invention, the peak value detector, the comparator and the AND gate being replaced by a microprocessor. In this case likewise an amplifier 12 is uied for the amplification of the signals of the reception sensor 9, which are then digitalised in an analogue/digital converter and conveyed to the microprocessor 41. Accordingly, the signals of the magnetic field sensor 10 likewise are again first of all amplified in the amplifier 16, then digitalised in an analogue/digital converter 42 and conveyed to the microprocessor 41. The process of determining the maximum value, determining the gate value and the AND function is then effected using software in the microprocessor 41.

1 0 0

Claims

40812/wsy 1. Means for generating reference impulses enabling the roll position of a projectile'rotating about its longitudinal axis to be determined, wherein a transmitting system associated with the projectile firing device emits polarised radiation which is received by a sensor on the projectile, the sensor having a means for determining the peak value of the received sensor signal, the projectile including a magnetic field sensor to determine the direction of the Earth's magnetic field and a time gating device to establish a time range over the relevant maximum or minimum value of the output signal of the magnetic field sensor, and an AND function means to derive from the peak signal over the gated signal time range an output signal forming the reference impulse.
2. Means in accordance with Claim 1, wherein the transmitting system comprises a laser and a polarisation f ilter.
3. Means in accordance with Claim 1 or 2, wherein the means for determining the peak values, the time gating range and the AND function comprise modules being a peak value detector, comparator and an AND gate.

- 10 40812/wsy
4. Means in accordance with Claim 1 or 2, wherein the means for determining the peak values, the time gating range and the AND function is a microprocessor.
5. Means for generating reference impulses for steering ballistic projectiles substantially as described herein and exemplified by the drawings.
6. A ballistic projectile constructed and arranged to function as described herein and exemplified with reference to the drawings.

Published 1991 atIbe Patent Office. State House. 66/71 High Holbom. London WCIR47P. Further copies Tnay be obtained from Sales Bramb. Unit 6. Nine Mile Point, Cwmielinfach. Cross Keys. NewporL NP1 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent.