Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With time interval measuring means
Patent
1992-09-15
1993-11-02
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With time interval measuring means
367906, F41J 506
Patent
active
052589625
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with an apparatus for determination of the trajectory or the direction of the trajectory or movement of a projectile, or, more specifically, the approach direction, the velocity, and the distance of a specified target.
Several indicator devices of this kind are known in the prior art, which more or less accurately give the distance from the trajectory of a projectile to a target, to which the corresponding apparatus is assumed to be attached, see for example the International application WO79/00452, applicant Swedair AB, and the art described and cited therein. In this document is also described how it is possible to determine the approach direction of the projectile as well as its trajectory. The trajectory direction is in many cases the important information, and even an approximate indication of the direction can be of great value. This is for example the case when an aircraft is being fired upon, when the said information can be used to choose a suitable passage for retreat. The present invention, in one of its embodiments, is particularly well suited to this type of indication when one or more projectiles having approximately the same trajectory direction pass near a target.
From the International Application WO 87/05706 for MS Instruments PLC a measuring apparatus is previously known for measurement of the position of a projectile moving at supersonic speed. Therein two groups or clusters are provided, each comprising three transducers and all being fixedly mounted in space, in such a way that all pressure transducers of both clusters are positioned in a single vertical plane, this plane forming a target area. By means of time measurements only, or, more particularly, the time difference between those time instances when a pressure wave generated by a projectile hits the respective transducer, a straight line is determined for each group of transducers passing through the point, at which said projectile passes through the vertical target plane. Any information of the velocity of sound and the projectile is not required. A fourth transducer can be added to each transducer cluster and be positioned at a distance from its associated cluster in a direction located approximately along the trajectory of the projectile, this trajectory obviously being assumed to be perpendicular to said target plane. From the time measurement obtained from this fourth pressure transducer the velocity of the projectile can be calculated.
According to the invention a varying number of pressure transducers, which for example all are rigidly attached to the target, may be used. To approximately indicate the approach direction of the projectiles it may be sufficient to use only four transducers, geometrically arranged in a suitable way, specifically they should not be located in the same plane. A more accurate determination of the trajectory direction is possible if several rounds in a salvo are detected. An alternative possibility is to set up a larger number of pressure transducers, located together in groups of four, which may then directly provide the trajectory direction for a single projectile, and also its actual trajectory.
In the general case always one or more, preferably three groups of at least four transducers are used according to the invention. These pressure transducers are generally completely movable, for instance they may be located rigidly attached to a moving target. In addition, primarily the trajectory direction is determined, that is the direction of the segment of said trajectory, from which the pressure wave sensed by the pressure transducers is generated. In contrast to the International application for MS Instruments PLC the positions of the above straight lines are not determined. Instead more complex relations are utilized which in an optimal way make use of the time data measured and the information known in advance of the position and movement of the pressure transducers.
In the target indication system, described in detail in the above mentioned document WO79/00
REFERENCES:
patent: 4323993 (1982-04-01), Soderblom et al.
patent: 4805159 (1989-02-01), Negendank et al.
Pihulic Daniel T.
Techsonic Aerosystems AB
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