EP0231161A2

EP0231161A2 - Apparatus for reducing projectile spread

Info

Publication number: EP0231161A2
Application number: EP87850027A
Authority: EP
Inventors: Hans Andersson; Kjell Albrektsson; Arne Franzén; Sven Eriksson; Per Raine
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1986-01-29
Filing date: 1987-01-28
Publication date: 1987-08-05
Also published as: SE8600380D0; EP0231161A3; SE8600380L

Abstract

The disclosure relates to an apparatus for reducing the spread of a hit pattern for an ammunition unit (2) in the form of a shell, projectile or the like, discharged in a ballistic trajectory from a launching device (1) towards a target (3) which is to be combated. The apparatus includes means (2') which are activated in response to the difference between the true position of the target and the point of impact of the shell for retardation thereof with the intention of increasing hit at least one of the trajectory parameters of the shell, preferably the muzzle velocity of the shell, an integral sensor (13, 14) for measuring corresponding trajectory parameters and a calculator unit (16) for calculating the point of impact on the basis of the thus measured value.

Description

TECHNICAL FIELD

The present invention relates to an apparatus for reducing the spread of a hit pattern for an ammunition unit in the form of a projectile shell or the like, discharged in a ballistic trajectory from launching device towards a target which is to be combated. the apparatus includes means which are activated in response to the difference between the true position of the target and the point of impact of the shell for arresting the travel of the shell for the purpose of increasing hit probability.

BACKGROUND ART

Swedish patent application No. 83.01651-9 discloses a method of reducing the spread of a hit pattern of a shell by calculating, on the basis of its muzzle velocity, its point of impact and by giving the shell a suitable braking command.
A conventional launching device, for example an artillery piece, may be employed, and the shell may be provided with a conventional propellant charge. The fire command post equipment must be provided with MV measurement equipment and the shell with a receiver to receive a braking command from the point of fire. In the example illustrated in the above-mentioned Swedish patent application, the command is transmitted to the shell in question via a radio link.
Although both the receiver and the braking means disposed in the shell may be of a comparatively simple nature, the apparatus will nevertheless be relatively complex as a whole because of the ground equipment in the form of MV measurement equipment, radar unit and radio link equipment required. Furthermore, there are tangible risks of disturbance to the system, primarily in the form of intentional jamming on the part of the enemy.

OBJECT OF THE PRESENT INVENTION

The object of the present invention is to realize an apparatus for reducing the spread of a hit pattern for an ammunition unit (shell, projectile or the like) which is insensitive to disturbances and requires less highly-qualified ground equipment.' The invention is based on an autonomous or semi- autonomous system and is characterized in that the shell includes a memory unit for storing at least one of the trajectory parameters of the shell, an integral sensor for measuring corresponding trajectory parameters and a calculator for calculating the point of impact of the shell on the basis of the parameter values thus measured.
Like the apparatus according to the above-mentioned Swedish patent application, the shell is given greater range compared with the shells in a conventional artillery system, such that the nominal point of impact is placed between 1.0 and 1.5 per cent beyond the target position. The shell is then corrected by retardation to a higher hit probability.
In one advantageous embodiment of the present invention, the measured trajectory parameter consists of the muzzle velocity (MV) of the shell which is compared with a preprogrammed level within the shell. As opposed to the procedure in the prior art apparatus, the MV measurement is affected fully autonomously.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The nature of the present invention and its aspects will be more readily understood from the following brief description of the accompanying drawings, and discussion of one embodiment of the present invention relating thereto.
In the accompanying drawings:

Fig. 1 is a schematic diagram of an artillery system employing the present invention;
Fig. 2 illustrates the ground equipment of the present invention;
Fig. 3 schematically illustrates a shell with sensor;
Fig. 4 illustrates means for the inductive transfer of nominal values of trajectory parameters; and
Fig. 5 is a block diagram of the electronics included in the system.

DESCRIPTION OF PREFERRED EMBODIMENT

Fig. 1 is a schematic illustration of an artillery system for combating a target, for example a ship. The artillery system includes an artillery piece 1 for discharging a shell 2 in a ballistic trajectory towards the target 3. In the figure, the target 3 indicates either the true position of the target or the aim-off point towards which the weapon must be aimed when fighting a moving target. The artillery piece may be of conventional type but is provided with a simple supplementary device, as will become more clearly apparent below. The calibre of the shells may be, for example, of the order of magnitude of between 7.5 and 15.5 cm.
The position of the target is continually tracked ano measured using fire control radar 4. The fire control radar includes a calculator 5 for calculating the movement of the target and predicting the target position. The calculator 5 emits values for alignment and aiming of the artillery piece 1 towards a point 6 located beyond the aim-off point 3 of the target in relation to the piece 1, preferably between 1.0 and 1.5 per cent further off than the aim-off point.
However, because of disturbances from the ambient environment and deficiencies in the manufacture of the round, every shell trajectory is unique and the true point of impact of the shell is marked 6' in Fig. 1. According to the present invention, a calculation is affected of this point of impact and, in response to the difference between the true position 3 of the target and the point of impact 6', a retardation is effected of the shell with the intention of increasing hit probability. The brake means mounted on the shell have been symbolically marked 2' in Fig. 1.
The often wholly dominant factor in the tine-of-shot spread of the shells is the so-called MV spread, i.e. the variation in the muzzle velocity of each shell discharged. Consequently, in the example illustrated below the measured trajectory parameter consists of the muzzle velocity of the shell. The MV measurement system is based on the principle that a light detector in the shell passes through two ground-located or gun-fixed light curtains. The distance between the light curtains is known and the passage time is measured.
In Fig. 2, two gun-fixed light curtains in the form of two LEDs or alternatively laser diodes 7, 8 are shown disposed on a stay 9 mounted on the barrel 10 of the gun placed in mutually known distance relationship A. The distance A between the LEDs may, for example, be 1 m.
In its outer appearance, the shell 2 is fully conventional and comprises a nose cap 11 and a warhead 12. The nose cap includes a measurement sensor in the form of a conical mirror 13, a light detector 14 and a translucent band 15 which extends about the circumference of the shell. when the shell, which is laid and discharged in the conventional manner, leaves the muzzle of the gun, it passes the two gun-fixed light curtains 7 and 8. The measurement sensor of the shell detects light inlets at right angles to the axis of the snell and the passage time between the light curtains is registered. The muzzle velocity is measured and is compared with a value preprogrammed in the shell. For the elevation of the weapon on this particular discharge, the difference in muzzle velocity gives a range modification which is calculated from a stored memory table for MV - elevation - range. The calculated range modification is subsequently employed to calculate, from a similarly preprogrammed table, the retardation point to hit the target.
The table covers retardation time, elevation, range. Account must also be taken of the trajectory distance which has been intentionally laid beyond the target. This distance may, appropriately, be set at 1.2 per cent of the shell range and is programmed in the shell as an elevation-dependent variable.
When the retardation point has been calculated in relation to preprogrammed and entered flight time, nothing will happen until the retardation time point has been achieved according to a clock integrated in the'shell, at which point the shell is retarded, for example, by shedding the nose section. Thereafter, the explosive charge is initiated upon impact with the target (or possibly in the water) in a conventional manner.
The electronics of the shell are based on a 1-chip microprocessor 16, see Fig. 5. The peripheral electronics required may, for the most part, consist of custom-designed circuits which can be manufactured to small scale, be current-miserly in design and be extremely insensitive to the ambient environment. When the shell, on discharge, passes the light curtains, the light detector 14 emits two pulses which are allowed to pass through a threshold circuit 17 in order, firstly, to generate digital signals and, secondly, to be discriminate filtered from background noise. The distance (t) between the pulses is a measurement of the muzzle velocity. The pulses are registered in a counter 18 which, thus, contains a value which is a measurement of the muzzle velocity. With the assistance of an oscillator 19, the microprocessor compares the MV in the counter 10 with the preprogrammed MV value.
The shell is "informed" of the data of the contemplated trajectory, for example elevation and trajectory time by a temporal equipment disposed on the piece. Transmission may be effected inductively, thus obviating contact problems. Fig. 4 illustrates a simple sketch of inductive transmission from a transmitter winding 20 through the intermediary of the shell case 21' to a receiver winding 21 within the shell. The receiver winding 21 is connected, through the intermediary of a temporal memory, to the microprocessor, see Fig. 5. The values for calculation of current retardation time are stored in the temporal memory, see above. Through the intermediary of a drive step 23, a retardation command is issued to the retardation devices or braking means of the shell.
The inductive receiver winding 21 is connected to a primary power supply source 24 which, in its turn is connected, via a diode, to a voltage stabilization device 25. A thermal battery 26 is connected, via a further diode, to the input of the above-mentioned voltage stabilization device.
The design of the retardation or braking means proper is not material to the inventive concept as herein disclosed and will not, therefore, be described in greater detail here. However, the requisite retardation correction may suitably be realized in that one or more parts of the nose cone of the shell are shedded in order to increase the air resistance, see Fig. 4 in the above-mentioned Swedish patent application No. 83.01651-9.
The example described above has taken account of but one ballistic parameter, namely the muzzle velocity. However, it will be obvious to a person skilled in this art that account may also be taken, in the spread of shots, also of other ballistic trajectory parameters such as: trajectory time, trajectory angle, trajectory retardation, trajectory angle of velocity, speed of rotation and the like. In order to reduce the spread in trajectory retardation, the trajectory retardation may be measured by an accelerometer and the trajectory retardation deviation be thus determined. The microprocessor may then calculate a new retardation time point from the measured muzzle velocity and retardation.
However, it is possible to reduce the spread in retardation without the need-of carrying out any specific measurement of the trajectory retardation. For example, the shells may be manufactured according to the method which is disclosed in our copending Swedish patent application . Such a high- precision manufacture of the shells as therein disclosed can greatly reduce mass imbalances. By also effecting weight rectification of the shell, it has been assessed that the spread of trajectory retardation of the shell can be reduced from 0.5 per cent to approx. 0.2 per cent.
The present invention should not be considered as restricted to those embodiments described above and shown on the drawings, many modifications being conceivable without departing from the spirit and scope of the appended claims.

Claims

1. An apparatus for reducing the spread of a hit pattern for an ammunition unit (2) in the form of a shell, projectile or the like discharged in a ballistic trajectory from a launching device_' (1) towards a target (3) to be combated, comprising means disposed to be activated in response to the difference between the true position of the target and the point of impact of the shell for retardation thereof with the intention of increasing hit probability, characterized in that the shell includes a memory unit for storage of at least one of the trajectory parameters of the shell, an integral sensor (13, 14) for measuring corresponding trajectory parameters, and a calculating unit (16) for calculating the point of impact on the basis of the thus measured value.

2. The apparatus as claimed in Claim 1, characterized in that the measured trajectory parameter consists of the muzzle velocity of the shell.

3. The apparatus as claimed in Claim 2, characterized in that the measurement sensor of the shell includes a conical mirror (13) and a light detector (14) disposed to detect light impingement at right angles to the axis of the shell from two ground or gun-fixed light curtains (7, 8) placed in a mutually known distance relationship (A).

4. The apparatus as claimed in Claim 3, characterized in that the light curtains (7, 8) consist of LEDs.

5. The apparatus as claimed in Claim 1, characterized in that the calculator unit of the shell consists of a microprocessor (16) which is operative to compare the value of the trajectory parameter measured by the measurement sensor of the shell with a preprogrammed nominal value of the same trajectory parameter stored in the memory unit of the microprocessor, and to emit, on the basis of the deviation, a retardation command to the braking means of the shell.

6. The apparatus as claimed in Claim 5, characterized in that the launching device (1) includes temporal equipment for the inductive transmission of the data of the contemplated shell trajectory, for example elevation and trajectory time, to an inductive receiver (21) and storage in a temporal memory (22) connected to the microprocessor (16) for calculating the current retardation time point.

7. The apparatus as claimed in Claim 2, characterized in that the shell includes one or more further measurement sensors for measuring further trajectory parameters, for example a measurement sensor for measuring the trajectory retardation of the shell, in which circumstance the calculation unit in the shell determines the deviation from a nominal value preprogrammed in the memory unit on the current trajectory parameter.

8. The apparatus as claimed in Claim 2, characterized in that the spread in trajectory retardation is restricted by means of precision manufacture of the shells, with the intention of reducing mass imbalances in the shells, for example by providing the shells with weight rectification means pursuant to our copending Swedish patent application .