Optical device for measuring the roll angle of a projectile

Details Optical device for measuring the roll angle of a projectile Optical device for measuring the roll angle of a projectile

1992-04-20

1993-11-09

Lobo, Ian J.

Aeronautics and astronautics

Missile stabilization or trajectory control

Remote control

F41G 700

Patent

active

052595676

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to the measurement of the roll angle of a projectile.


BACKGROUND OF THE INVENTION

The general evolution in threat and weapon systems raises the need for improving the performance of weapons by virtue of a guiding system whilst seeking a minimum cost.
It is particularly advantageous, then, to reduce as far as possible the amount of sophisticated equipment loaded on board an expendable guided projectile (computer, homing head, inertial unit, proximity fuse etc.) by transferring the maximum number of functions to the firing station alone.
The guidance of a guided weapon launched by a conventional or electromagnetic gun and set into a rotation movement about its axis, may be performed with the aid of gas-generating lateral impellers, the operation of which is actuated when they are oriented in the desired direction. This requires knowing at any instant the roll angle of the projectile.
This function of angular measurement of the roll is generally ensured by an inertial unit (rate-gyro) loaded on board the projectile, which inertial unit is expensive and expendable. Furthermore, this inertial unit becomes difficult to design and to construct in the case of a projectile launched by an electromagnetic gun where the acceleration at the start may reach 200,000 g.
It is known how to measure the roll angle of a projectile with the aid of a catadioptric system equipped with a polarizer disposed at the rear of the projectile, with a light source illuminating the rear of the projectile and a light analyzer calculating the roll angle of the projectile from the polarisation direction of the light flux reflected by the rear of this projectile. However, this measurement has the drawback of exhibiting an ambiguity of .pi..


BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to enable ambiguity in an optical measurement of the roll angle of a projectile to be removed with the aid of components loaded on board the projectile which are robust, reliable and inexpensive.
The subject of this invention is an optical device for measuring the roll angle of a projectile launched by launching means located in a firing station. This device comprises, at the rear of the projectile, a catadioptric system equipped with a polarizer and, at the firing station, a light source which is laterally offset in relation to the firing axis of the projectile and whose beam illuminates the rear of the projectile, and a light-flux analyzer calculating, from the polarization direction of the light flux reflected by the rear of the projectile, the roll angle of the latter. It is noteworthy in that it furthermore comprises a reflector dihedron which is positioned along the side of the projectile and turned towards the rear of the latter with its edge normal to the rotation axis of the roll of the projectile and which reflects the light beam from the source back to the light-flux analyzer once per turn of the roll of the projectile when the light source is not occulted from it by the body of the projectile.
The catadioptric system may be a reflector trihedron.
The light-flux analyzer comprises a first optical receiver which is sensitive to the intensity of the light flux and which receives the light flux reflected by the projectile by the agency of a polarizer constituting a polarization analyzer, a second optical receiver which is also sensitive to the intensity of the light flux and which is directly exposed to the light flux reflected by the projectile, a turbulence-compensating circuit splitting the signal supplied by the first optical receiver from the signal supplied by the second optical receiver and a circuit for estimating the roll angle of the projectile employing the signal supplied by the turbulence-compensating circuit.
Other characteristics and advantages of the invention will emerge from the description of embodiments given by way of example. This description will be made hereinbelow, with respect to the drawing in which:


BRIEF DESCRIPTION OF THE FIGURES

FIG.

REFERENCES:
patent: 3757632 (1973-09-01), Bellinger
patent: 3963195 (1976-06-01), Coxe et al.
patent: 4003659 (1977-01-01), Conard et al.
patent: 4072281 (1978-02-01), Miller, Jr. et al.
patent: 4097007 (1978-06-01), Fagan et al.
patent: 4219170 (1980-08-01), Esker
patent: 5039029 (1991-08-01), Taylor et al.

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