Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With plurality of transducers
Patent
1987-11-12
1989-12-05
Steinberger, Brian S.
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With plurality of transducers
367127, 367906, 273372, G01S 518
Patent
active
048857254
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to apparatus for measuring the position of a projectile travelling at a supersonic velocity.
2. Prior Art
When a supersonic projectile travels through a medium such as the atmosphere it creates a conical shock wave. This shock wave can be detected and used to determine the position of the projectile. Arrangements for detecting shock waves are known and have several Applications. One such Application is in determining the co-ordinates of a bullet as it passes through a given area, e.g. a conventional target on a shooting range. One known apparatus of this type is described in United Kingdom Patent Specification No. 1371173. The arrangement described in this Specification includes a pair of steel bars which are located so that their longitudinal axes lie at an angle to each other. The bars are disposed near the target so that they lie generally in the same plane as the target area or close to that plane. Each bar carries a pair of transducers, one at each end thereof. A projectile such as a bullet passing through the target generates a shock wave which expands and strikes each bar. The shock wave then propagates along each bar to the respective transducers. The apparatus is arranged to measure the arrival times of the shock wave at the transducers and to evaluate from those measured times the point at which the shock wave struck each bar. From this information the position of the bullet can be evaluated. This type of apparatus provides relatively accurate position information but has limitations. In the case of a rifle range both bars need to be below ground level at the target area so that the sensor cannot be struck by the bullets. Because one of the bars is usually upright, the depth required below ground can sometimes make installation difficult. In addition the area covered by the sensor array is limited and outside this area the only information available is that the shot is off target in a certain direction. Another type of system such as that described in United Kingdom Patent Specification No. 2083177 uses an array of transducers which detect the shock wave directly. However known arrangements which use an array of transducers suffer from the fact that the calculation of the projectile position usually involves the velocity of sound in air and the projectile velocity. The projectile velocity can be measured but this will introduce some errors. In addition the velocity of sound in air varies with temperature. Whilst the temperature at ground level can be measured this is not always an accurate representation of the temperature at the transducers. This type of apparatus has been found to be less accurate than apparatus which uses the bar type detector referred to above.
DESCRIPTION OF THE INVENTION
One form of the present invention provides apparatus for sensing the position of supersonic projectiles which uses arrays of transducers but which does not require knowledge of the velocity of sound for the position calculation process.
According to a first aspect of the present invention there is provided apparatus for determining the position of a projectile travelling at a supersonic velocity comprising a plurality of transducers, said transducers being so arranged and disposed that they form two triangular groups which are adjacent to and which lie in or generally parallel to the plane of a target area through which the projectile passes, each transducer being arranged to convert the mechanical impulse of a shock wave from the projectile into an electrical signal or signals, and processing means arranged to receive said electrical signals and to compute from said signals the direction of the projectile from each group of sensors. Knowing the position of each group of sensors relative to the target area it is possible to calculate from the direction information the position at which the projectile passes through the target. Because the apparatus essentially determines two directions the evaluation of the position becomes independent of the velocit
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patent: 3778059 (1973-12-01), Rohrbaugh et al.
patent: 4261579 (1981-04-01), Bowyer et al.
patent: 4307292 (1981-12-01), Knight et al.
patent: 4350882 (1982-09-01), Phillips
patent: 4351026 (1982-09-01), Phillips
McCarthy Brian D.
Regan Bernard J.
MS Instruments public limited company
Steinberger Brian S.
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