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Publication numberUS3685159 A
Publication typeGrant
Publication dateAug 22, 1972
Filing dateDec 22, 1969
Priority dateJan 3, 1969
Also published asCA930216A, CA930216A1, DE1965559A1
Publication numberUS 3685159 A, US 3685159A, US-A-3685159, US3685159 A, US3685159A
InventorsErhard Rune Torsten Isidor
Original AssigneeBofors Ab
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method and system for establishing a correct lead when firing at a moving target
US 3685159 A
Abstract  available in
Images(2)
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Claims  available in
Description  (OCR text may contain errors)

United States Patent Erhard 51 Aug. 22, 1972 [54] METHOD AND SYSTEM FOR ESTABLISHING A CORRECT LEAD WHEN FIRING AT A MOVING TARGET [72] Inventor: Rune Torsten lsidor Erhard, Karlskoga, Sweden [73] Assignee: Aktiebolaget Bofors, Bofors, Sweden [22] Filed: Dec. 22, 1969 [21] Appl. N0.: 886,981

[30] Foreign Application Priority Data Jan. 3, 1969 Sweden ..96/69 [52] US. Cl. ..33/238, 89/41 AA [51] Int. Cl ..F4lg 3/08 [58] Field of Search ..33/49 R, 49 A, 49 B, 49 C; 89/37 A, 41 AA, 41 B, 41E

[56] References Cited UNITED STATES PATENTS 3,277,282 10/ I966 Kuhlenkamp ..33/49 C X 2,660,794 12/1953 Goertz et al. ..33/49 C 2,538,821 1/1951 Wheeler ..33/49 B 2,968,871 1/1961 Hammond, Jr ..33/49 B 3,135,053 6/1964 Newman et al. ..33/49 C Primary Examiner-William D. Martin, Jr. Attorney-Harte & Baxley [57] ABSTRACT The invention relates to a method and device for computing and providing a correct lead angle between. the direction of fire and the line of sight when firing a projectile at a moving target with a weapon and sight system in which the weapon and the sighting instrument are mechanically and/or electrically coupled to each other so as normally to move uniformly. The correct lead angle is computed during a predetermined limited time interval the length of which is proportional to the range to the target. During this computation interval the line of sight of the sighting instrument is maintained pointed directly at the moving target and the weapon is moved uniformly with the sighting instrument without any relative angular velocity between the line of sight of the sighting instrument and the direction of fire of the weapon, while simultaneously the angular velocity of the line of sight is integrated. At the end of the computation interval, over which the angular velocity of the line of sight is integrated, the direction of fire of the weapon and the line of sight of the sighting instrument are deflected from each other by an angle proportional to the result of the integration and in such a direction that the direction of fire of the weapon will lead the line of sight of the sighting instrument as seen in the direction of the target tracking.

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RUNE TORST'EN lS/DOR ERHARD A'rraklvtrs METHOD AND SYSTEM FOR ESTABLISHING A CORRECT LEAD WHEN FIRING AT A MOVING TARGET The present invention relates to a method and a device for providing a correct lead when firing projectiles at a moving target with a weapon and sight system including a weapon and a sight which are mechanically and/or electrically coupled to each other so that the direction of fire of the weapon and the line of sight of the sighting instrument normally move uniformly during the target tracking process. In particular the invention is related to vehicle carried weapons, as for instance weapons in tanks, where the weapon may be mounted on the vehicle so as to be movable in azimuth as well as elevation relative to the vehicle or alternatively be fixed in the vehicle, in which latter case the weapon is aimed by movement of the entire vehicle. However, the invention can also be used at stationary weapons. In particular the invention is related to such weapon and sight systems in which the sight is mounted on the movable portion of the weapon so that it participates in or at least is affected by the aiming of the weapon, but the invention can also be used in weapon and sight systems in which the weapon and sight are separate and can be individually aimed so that the aiming of the weapon does not directly affect the sight.

When firing at a moving target with a weapon and sight system of the type mentioned above the sight operator or gunner keeps the line of sight of the sighting instrument permanently pointed at the moving target and at the same time controls the weapon so that the direction of fire of the weapon moves uniformly with the line of sight. in a system where the sight is mounted directly on the aimable weapon the line of sight is generally pointed at the target by aiming of the weapon as such. As well known, however, at the moment when a projectile is to be fired a certain angular deflection must exist between the direction of fire of the weapon and the line of sight of the sighting instrument which is pointing at the target. The total necessary deflection angle consists primarily of two components, namely one component, the so called lead, which is required due to the movement of the target, and a second component, the so called superelevation, which is required due to the curved trajectory of the projectile. The total deflection angle includes generally also corrections or compensations for instance for the effects upon the fired projectile from wind forces, for the rotation of the projectile, etc. The present invention concerns primarily the computation of the lead angle necessary due to the movement of the target but touches also the computation of the other components of the total deflection angle between the direction of fire of the weapon and the line of sight at the moment of firing a projectile.

The lead angle necessary due to the movement of the target is dependent on the angular velocity of the target relative to the site of the weapon, this angular velocity being equal to the angular velocity of the line of sight if the sighting instrument is mounted on or located close to the weapon and the line of sight is maintained permanently pointed at the target, the range to the target and the mean velocity of the projectile fired at the target. For computing the necessary lead angle it is known in the art to measure the angular velocity of the line of sight continuously during the target tracking and on the basis of this angular velocity, after low-pass filtering thereof, and a continuously measured value for the range to the target to let a computer continuously compute the lead angle required due to the movement of the target; the deflection angle between the line of sight and the direction of fire of the weapon being continuously adjusted into agreement with said computed value. However, a device operating according to this principle becomes comparatively complicated. Further the sight operator must maintain the line of sight continuously pointed at the target, as any error in the target tracking will give cause to an error in the computation of the lead angle and this error will remain for a time which is dependent on the time constant for the low-pass filtering of the measured angular velocity of the line of sight. Consequently it is not possible for the sight operator to judge when a sufficient accuracy in the computation of the lead angle has been achieved after an error in the target tracking. Further, every change in the velocity or the direction of movement of the target will give cause to a disturbance in the computation of the lead angle and this disturbance will not be eliminated until after a time unknown to the sight operator.

A system is also known in the prior art, in which the lead angle necessary due to the movement of the target is provided in that during a predetermined limited time interval, at the beginning of which the direction of fire of the weapon as well as the line of sight of the sighting instrument are pointing directly at the target and have the same angular velocity, the line of sight is given an angular velocity which is only a predetermined fraction of the angular velocity of the weapon so that during this time interval a continuously increasing deflection angle is created between the direction of fire of the weapon and the line of sight. At the end of the time interval, when the line of sight and the direction of fire are once more given the same angular velocity, the accumulated deflection angle is equal to the lead angle required due to the movement of the target. This method has the advantage that it requires only a comparatively simple computing device and that the sight operator must keep the line of sight exactly pointed at the target only at the beginning and that the end of the predetermined limited time interval in order to produce a correct lead angle. However, at the beginning of such time interval the line of sight is suddenly given a smaller angular velocity than before, wherefore it cannot be avoided that the sight operator loses the target with the line of sight. Consequently the sight operator must during the limited time interval return the line of sight onto the target so that it is accurately pointed at the target at the end of the time interval. It has been found that this is a very difficult task for the sight operator, as the predetermined limited time interval must be comparatively short, of the order of 1 to 2 seconds. The reason for this is partly than one wishes to fire a projectile at the target as soon as possible and partly that the target must move with constant velocity and in an unchanged direction during the time interval if the computation of the lead angle is to be correct. Further, in a system of this type it is comparatively difficult to .introduce the other necessary components of the total deflection angle between the direction of fire and the line of sight,

such as the superelevation and the compensations for wind forces, the projectile rotation, etc.

An object of the present invention is therefore to provide a method and a device for providing a correct lead when firing at a moving target with a weapon and sight system of the type mentioned in the foregoing,

which method puts substantially smaller demands on the skill and the reaction speed of the sight operator and which requires only a simple device with a comparatively small number of components for the computation of the lead angle necessary due to the movement of the target and which device may also be modified by addition of a comparatively small number of additional components to compute also the deflection angle components necessary for the super-elevation, wind compensation, compensation for the projectile rotation, etc.

Also in the method according to the invention the lead angle necessary due to the movement of the target is computed during a predetermined limited time interval and the method is characterized in that the line of sight is maintained pointed directly at the target and the direction of fire of the weapon is moved uniformly with the direction of the line of sight without any relative velocity between the direction of fire and the line of sight while the angular velocity of the line of sight is integrated over a predetermined time interval, and that after the integration interval the line of sight and the direction of fire are displaced relative each other by an angle proportional to the result of the integration and in a direction such that the direction of fire will lead the line of sight as seen in the direction of the movement of the line of sight.

As according to the method of the invention the lead angle required due to the movement of the target is computed during a predetermined limited time interval, the sight operator has only to ascertain that the line of sight is accurately pointing at the target at the beginning and at the end of such time interval in order to achieve a correct computation. As a matter of fact the computation will be correct if the direction of the line of sight relative to the target is the same both at the beginning and at the end of the measuring interval. Thus the computation error is proportional to the difference between the tracking errors at said two instants. As the sight operator himself determines the instant when the computation interval is started and easily can be informed about the end of the computation interval, the sight operator can easily judge whether the computation carried out during the limited computation interval has been sufficiently accurate. Should this not be the case he can immediately start a new computation interval. As according to the method of the invention the line of sight is pointing directly at the target and has an angular velocity equal to the angular velocity of the target at the beginning of the measuring interval and at this instant no sudden compulsory change outside the control of the sight operator is imposed upon the angular velocity of the line of sight, it is very easy for the sight operator to track the target during the computation interval and to ascertain that at the end of the computation interval the line of sight is accurately aimed at the target. Thus in contrast to the prior art system for computation of the lead angle during a predetermined limited time interval which has been described in the foregoing, no disturbance whatsoever is imposed upon the target tracking at the beginning of the computation interval, which disturbance it would be necessary for the sight operator to eliminate before the end of the computation interval. Therefore, the computation interval can be short without insurmountable demands being put upon the skill of the sight operator. It is advantageous to have a short computation interval partly because this permits an early firing of a projectile against the target and partly as the target must move with a constant velocity and in an unchanged direction from the beginning of the computation interval to the instant of impact of the fired projectile if the computed lead angle is to be valid. The length of the integration interval may be constant, in which case at the end of the integration interval the line of sight and the direction of fire are displaced relative each other by an angle equal to the product of the result of the integration and a computed value for the time of flight of the fired projectile.

Alternatively the integration interval may have a length proportional to the computed time of flight of the projectile, in which case the direction of fire and the line of sight are displaced relative each other by an angle directly corresponding to the result of the integration.

However, the length of the integration interval is preferably made equal to a constant times the range to the target, in which case at the end of the integration interval the line of sight and the direction of fire are displaced relative each other by an angle proportional to the result of the integration divided by a computed value for the mean velocity of the projectile fired against the target. In this case the device for the computation of the necessary deflection angle between the direction of fire and the line of sight can be given an especially simple and component-saving design, in particular if the device is adapted to compute not only the lead angle necessary due to the movement of the target but also other components of the total deflection angle, such as the superelevation, wind compensation, compensation for the projectile rotation, etc.

Since, generally, the weapon and sight can be directed in azimuth as well as in elevation and also the target is moving in azimuth as well as elevation, the computation of the total lead angle is in conventional manner divided into a computation of the lead angle in azimuth and another computation of the lead angle in elevation, these two computations being of course carried out simultaneously. Correspondingly the device for performing this computation and for displacing the line of sight and the direction of fire of the weapon relative each other in agreement with the computed lead angle consists in principle of two portions, one for the azimuth components and the other for the elevation components of the movements of the weapon and the sighting instrument respectively.

In the following the invention will be further described with reference to the accompanying drawing, which illustrates by way of example a weapon and sight system in which the invention is incorporated. in the drawing:

FIG. 1 is a schematical perspective view of a weapon and sight system provided with a device according to the invention, in which system the sight is mounted on the weapon so as to participate in the aiming thereof;

FIG. 2 is a block diagram of the device according to the invention incorporated in the weapon and sight system in FIG. 1 for computing the required lead angle and of the devices necessary for the aiming of the weapon and for the introduction of the computed lead angle between the direction of fire of the weapon and the line of sight; and

FIG. 3 is a diagram illustrating the angular positions of the target, the line of sight and the direction of fire as functions of time during the target tracking.

Before the device illustrated in the drawing is described in detail, a short discussion of the mathematical expressions on which the computation of the various components of the total deflection angle is based will be given. In this discussion following symbols are used:

D range to the target w the angular velocity of the target relative to the site of the weapon and thesight w the angular velocity of the line of sight v the muzzle velocity of the projectile v,,,=the mean velocity of the projectile during the time of flight t, the time of flight of the projectile the lead angle necessary due to the movement of the target 4),, superelevation necessary due to the curved trajectory of the projectile Provided that the line of sight is maintained pointed at the target, one has obviously w,, w For the time of flight of the projectile one has tg= l nl (2) As well known the mean velocity of the projectile can be expressed by the series f m r=( m (4) As well known the necessary superelevation 4),, can be approximated by the series where k k and k are constants and in which series generally one or two terms give a sufficient accuracy.

For the computation of other components of the total deflection angle that may be necessary, as for instance compensations for the wind and the projectile rotation, expressions may be used similar to the expression (5) given above for the superelevation 1 as well known in the art.

It shall be pointed out here that all the components of the total necessary deflection angle between the direction of fire and the direction to the target that are to be computed are inversely proportional to the mean velocity v of the projectile, a fact that is made use of for simplifying the design of the device according to the invention.

FIG. 1 shows as an example only and very schematically a weapon and sight system including a gun with a barrel 1 which in conventional manner is mounted for elevation on a gun mount 2 upon a rotatable platform 3. Thus the barrel 1 can be directed in elevation as well as in azimuth relative to a supporting member not illustrated in the drawing, which may for instance consist of a vehicle, such as a tank, in which case the platform 3 is replaced with the gun turret of the tank. In the illustrated embodiment of the invention the barrel 1 is directed in azimuth, by means of a servomotor M1 and in elevation by means of a servomotor M2. A

tachogenerator T1 is coupled to the servomotor M1 for generating an electric signal proportional to the angular velocity in azimuth of the barrel 1 and thus of the direction of fire. In similar manner a tachogenerator T2 is coupled to the servomotor M2 for generating an electric signal proportional to the angular velocity in elevation of the barrel 1 and thus of the direction of fire.

As shown in FIG. 2, the azimuth motor M1 for the barrel 1 is supplied with a control signal through a servo-amplifier F1 and a comparator Cl from a signal generator S1, such as a potentiometer, which is coupled to a manually, by the gunner, operated control lever 5 which is universally pivoted in a pivot and gearing mechanism 4. The signal generator S1 is coupled to the lever 5 in such a way that it generates a signal proportional to the deviation angle of the lever 5 from a neutral position in a predetermined first direction. The output signal from the tachogenerator T1 is fed back in opposition to the comparator C 1. Consequently the servomotor M1 is rate coupled, wherefore the gunner by means of the control lever 5 can impart an angular velocity to the barrel 1 proportional to the deviation of the control lever 5 from its neutral position in the first direction.

In a similar manner the elevation servomotor M2 for the barrel 1 is supplied with a control signal through a servoamplifier F2 and a comparator C2 from a signal generator S2 which is coupled to the control lever 5 so as to generate an electric signal proportional to the deviation angle of the lever 5 from its neutral position in a second direction which is perpendicular to the first direction. The output signal of the tachogenerator T2 is fed back in opposition to the comparator C2, whereby the servomotor M2 imparts an angular velocity in elevation to the barrel 1 proportional to the deviation angle of the control lever 5 from its neutral position in said second direction.

The weapon and sight system shown in FIG. 1 includes also a sighting instrument 6 mounted on a portion of the gun which can be directed in azimuth as well as in elevation. In the drawing the sighting instrument illustrated only very schematically as the specific type or design of the sight is of no fundamental importance for the invention. Thus for instance the sight may be a suitable conventional optical sight, a radar sight or a laser sight. It is only important that the gunner can continuously determine the position of the line of sight through the sighting instrument relative to the direction to a target viewed through the sight. In the illustrated embodiment it has been assumed for the sake of simplicity that the sight 6 has a line of sight which is fixed relative to the sight casing and that the sight casing together with the line of sight can be rotated in azimuth relative to the direction of the barrel 1, that is the direction of fire of the weapon, by means of a servomotor M3 and in elevation by means of a servomotor M4. However, the sighting instrument may of course also be of a type having a line of sight which is movable in azimuth and elevation relative to the sight casing, for instance by means of movable optical members, such as mirrors, prisms or hairline crosses. In this case the sight casing is mounted stationary on the layable portion of the gun and the servomotors M3 and M4 are coupled to those members in the sighting instrument itself by means of which the line of sight can be moved in azimuth and elevation respectively relative the sight casing. The two servomotors M3 and M4 have predetermined starting positions in which the line of sight for the sighting instrument 6 is parallel to the direction of the barrel 1. As long as the servomotors M3 and M4 are not rotated from these starting positions during a target tracking process the line of sight remains consequently stationary relative to the direction of fire of the gun and parallel thereto. By viewing a moving target through the sighting instrument 6 and controlling the azimuth motor M1 and the elevation motor M2 respectively for the barrel 1 a gunner can consequently continuously maintain the line of sight as well as the barrel aimed directly at the moving target. During this process the signal produced by the tachogenerator Tl will be proportional to the azimuth angular velocity of the line of sight and thus also of the moving target, whereas the signal produced by the tachogenerator T2 will be proportional to the elevation angular velocity of the line of sight and thus of the moving target.

An electric signal generator Pl, such as a potentiometer, is coupled to the servomotor M3 for generating a signal proportional to the rotation angle of the servomotor M3 from its starting position. In similar manner a signal generator P2, for instance a potentiometer, is coupled to the servomotor M4 so as to generate a signal proportional to the rotation angle of the servomotor M4 from its starting position.

Further, a range meter 7 is provided, which in the illustrated embodiment is mounted on the sighting instrument so as to have its measuring direction parallel to the line of sight. This range meter may be of any conventional type, such as a radar range meter, a laser range meter or some kind of optical range meter. It is only important that it produces information about the range to the target being tracked either in the form of an electric, digital or analog signal or in the form of a rotation angle of a mechanical shaft.

As shown in FIG. 2, the servomotor M3 for the azimuth movement of the sight 6 relative to the barrel 1 is supplied with a control signal from an amplifier F3 through a comparator C3. The output signal from the potentiometer P1 coupled to the servomotor M3 is fed back in opposition to the comparator C3. Thus the servomotor M3 is position-coupled and will consequently rotate its shaft by an angle directly proportional to the control signal supplied from the amplifier F3 and inversely proportional to the signal feeding the potentiometer Pl; the latter signal being derived from an amplifier F5 as will be described in further detail in the following. In a similar manner the servomotor M4 for the elevation movement of the sight 6 relative to the barrel 1 is connected to a servoarnplifier F4 through a comparator C4. The output signal from the potentiometer P2 is fed back in opposition to the comparator C4, whereby the shaft of the servomotor M4 is rotated by an angle directly proportional to the magnitude of the signal from the amplifier F4 and inversely proportional to the signal feeding the potentiometer P2, said latter signal being also derived from the amplifier F5.

As explained in the foregoing, the two servomotors M3 and M4 are used for deflecting the line of sight of the sighting instrument 6 in azimuth and elevation respectively relative to the direction of the barrel 1 and thus the direction of fire by angles corresponding to the computed, totally required deflection angles in azimuth and elevation respectively.

For computing the lead angles in azimuth and elevation respectively required due to the movement of the target two integrators l1 and I2 are provided. These integrators may, through switching means K1, be supplied with the output signals form the tachogenerators T1 and T2 respectively which are coupled respectively to the azimuth motor M1 and the elevation motor M2 for the barrel 1.

As mentioned in the foregoing, the signal from the tachogenerator T1 is proportional to the azimuth angular velocity of the barrel 1 and thus also to the azimuth angular velocity w, of the line of sight, whereas the signal from the tachogenerator T2 is proportional to the elevation angular velocity w,, of the barrel 1 and thus of the line of sight, provided that the two servomotors M3 and M4 for the sight 6 are stationary in their starting positions so that the line of sight is parallel to and stationary relative the direction of the barrel 1. The integrated signals on the output terminals of the integrators I1 and I2 can, through additional switching means K2, be connected to the amplifier F3 and the amplifier F4 respectively. Further switching means K3 are provided for temporary short-circuiting each of the integrators I1 and I2, whereby the integrated signals on the output terminals of the integrators are eliminated and a new integration can be started.

The switching means K1, K2 and K3 may be mechanical contacts on a relay or solid state switches and are actuated from a timing device T, which may be of any conventional type, such as an electric timing circuit or an electromechanical timer. The time span of the timing device T can be adjusted or set from the range meter 7 in agreement with the measured range D to the target so that the time span becomes equal to a constant times the range D to the target. In their inactivated state all switches K1, K2 and K3 are in the positions shown in the drawing. The timing device T can be started by temporary closure of a switch 8 which is manually operated by the gunner. When the timing device T starts it closes the switches Kl for the input signals to the integrators I1 and I2. When the timing device T runs out it reopens the switches K1 and closes the switches K2 so that the integrated signals on the I output terminals of the integrators I1 and I2 are applied to the amplifiers F3 and F4. The timing device T can thereafter be caused to reopen the switches K2 if and when the gunner temporarily closes an additional manually operated switch 9. When the switches K2 then open the switches K3 are closed temporarily, whereby the integrators I1 and 12 are short circuited and the integrated signals on their output terminals are eliminated.

The range meter 7 supplies information about the range also to a number of analog multipliers for generating signals proportional to D, D D etc. dependent on the demand for accuracy in the computation. In the illustrated embodiment of the invention there are only two such multipliers which consist of potentiometers P3 and P4. The potentiometer P3 is supplied with a reference voltage, which for the sake of simplicity is assumed to have the value 1, whereas the potentiometer P4 is supplied with the output voltage from the potentiometer P3. The output voltage from the potentiometer P3 is consequently proportional to the range D to the target, whereas the output voltage from the potentiometer P4 is proportional to D2. The output voltages from these two potentiometers P3 and P4 are supplied to separate inputs of the amplifier F5, which on an additional input is also supplied with a voltage proportional to the muzzle velocity v for a fired projectile. The input voltages are summed and amplified in the amplifier F5 with the polarities and constants given in the expression (3) so that the output signal from the amplifier F5 is proportional to the mean velocity v,,, for the projectile. As the signal from the amplifier F5 is supplied to the two potentiometers P1 and P2, which generate the feed-back signals for the servomotors M3 and M4, the rotation angles of these servomotors, when control signals from the amplifiers F3 and F4 are applied to the servomotors, will be inversely proportional to the mean velocity v,, of the projectile.

The output signals from the potentiometers P3 and P4 are also supplied to separate inputs on an amplifier F6, in which the two input signals are summed and amplified with the constants K and k given in the expression (5) so that the output signal from the amplifier F6 becomes proportional to 4),, v,,,, that is the product of the required superelevation (1),, and the mean velocity v,,, of the projectile. The output signal from the amplifier F6 can be applied to the amplifier F4 through a switch K4.

In similar manner the output signals from the two potentiometers P3 and P4 are supplied to separate inputs of an additional amplifier F7, which sums and amplifies the two input signals in such a way that the output signal from the amplifier becomes proportional to the product of the mean velocity v of the projectile and the deflection angle components necessary for compensation of, for instance, wind forces and the rotation of the projectile. The output signal from the amplifier F7 can be supplied to the amplifier F3 through a switch K5.

In the illustrated embodiment of the invention the two switches K4 and K5 are actuated by the timing device T so as to close and open simultaneously with the switches K2.

The device described above operates in the following manner. In the starting state for a target tracking operation all switches Kl to K2 are in the open positions shown in FIG. 2, wherefore no control signals are supplied to the servomotors M3 and M4 and the line of sight for the sighting instrument 6 consequently is parallel to and stationary relative the direction of the barrel 1. By means of the control lever 5 the gunner aims the barrel 1 and thus also the line of sight directly at the target and follows subsequently the target with the line of sight. The angular movement of the barrel and the line of sight will consequently be equal to the angular movement of the target. In the diagram in FIG. 3 the angular positions of the target, the line of sight and the barrel are shown as functions of the time during a target tracking operation. The angular position of the target is represented by the solid curve, whereas the angular position of the line of sight is represented by the dotted curve and the angular position of the barrel, that is of the direction of fire, is represented by the dash-dot curve. Further it is assumed that during all the time the target is moving with a constant angular velocity, wherefore the angular position of the target is a linear function of the time. During the above described initial stage of the target tracking operation the direction to the target, the line of sight and the direction of fire are obviously moving together uniformly. At an instant when the gunner has the line of sight aimed as accurately as possible at the target and judges that the target will during the immediate future probably move with unchanged velocity and direction, the gunner initiates the process for computing the required lead angle in that he closes the switch 8 temporarily (FIG. 2). In the diagram in FIG. 3 this instant is indicated by 1-,.

When the switch 8 closes, the timing device T starts its operation and closes simultaneously the two switches K1. Thus the two integrators I1 and I2 start to integrate the signal proportional to the azimuth angular velocity w, of the line of sight and the signal proportional to the elevation angular velocity w,, of the line of sight respectively. The starting of the lead angle computation does not affect the two servomotors M3 and M4 for the sighting instrument, wherefore these servomotors remain stationary. Neither are the servomotors M1 and M2 for the gun affected by the starting of the lead angle computation. Consequently the gunner meets no difficulties whatsoever in maintaining the line of sight aimed directly at the target.

When the time span 1' of the timing device T is finished, there exists consequently an integrated signal on the output terminal of the integrator II which is proportional to the product of the azimuth angular velocity w, of the line of sight and the range D to the target, and on the output terminal of the integrator I2 an integrated signal proportional to the product of the elevation angular velocity w of the line of sight and the range D to the target because the time span 1- of the timing device T is equal to a constant times the range D to the target as determined by the range meter 7. In the diagram in FIG. 3 the end of the computation period is indicated by 7 As described in the foregoing there exists on the output terminal of the amplifier F6 permanently a signal proportional to the product of the desired superelevation d) and the mean velocity v,,, of the projectile, whereas on the output terminal of the amplifier F7 a signal is present which is proportional to the product of the mean velocity v, of the projecnle and the correction angles necessary due to, for instance, wind forces, projectile rotation, etc.

At the instant 1- when the timing device T runs out, the switches K2, K4 and K5 and simultaneously the switches K1 are opened, whereby the integration in the integrators I1 and I2 is interrupted. The integrated signals on the output terminals of the integrators and the signals on the output terminals of the amplifiers F6 and F7 are consequently applied to the servoamplifiers F3 and F4 for respectively the azimuth motor M3 and the elevation motor M4 of the sighting instrument. Thus the motors M3 and M4 will rotate the sight 6 and deflect the line of sight relative to the direction of the barrel 1, that is relative to the direction of fire, in azimuth and elevation respectively by angles which are directly proportional to the magnitudes of the control signals supplied to the amplifiers F3 and F4 respectively and inversely proportional to the signal supplied from the amplifier F5 to the potentiometers P1 and P2 respectively. The latter signal is, as mentioned in the foregoing, proportional to the computed mean velocity v of the projectile. As is obvious from the expressions (4) and (5) and the discussion connected therewith, the two servomotors M3 and M4 will deflect the line of sight from the direction of the barrel, that is from the direction of fire, in azimuth and elevation respectively by a total angle corresponding to the total desired deflection angle for the firing of a projectile against the target, that is both the lead angle required due to the movement of the target as well as the required superelevation and the required correction angles for wind forces, projectile rotation, etc. In the diagram in FIG. 3 this total deflection angle is designated by 4),. As can be seen in FIG. 3, the line of sight is deflected from the direction of fire in such a direction that the line of sight will lag the direction of fire as seen in the direction of the target tracking. The deflection of the line of sight will be carried out substantially momentarily, as the two servomotors M3 and M4 have only to rotate the sighting instrument 6 which has a very small weight.

As can be seen in FIG. 3, the introduction of the total computed deflection angle qb, between the line of sight and the direction of fire causes that the line of sight is moved away from the target. Consequently the gunner must as soon as possible return the line of sight onto the target by means of the control lever 5 the barrel 1 and thus also the line of sight. During this process the barrel, that is the direction of fire, and the line of sight move of course uniformly so that the mutual total deflection angle dz, between them is maintained. As soon as the gunner has returned the line of sight onto the target a projectile can be fired. Of course also several projectiles can be fired using the same deflection angle between the direction of fire and the line of sight. If, however, the gunner should wish to perform a new computation of the necessary lead angle before a new projectile is fired, he can do this by closing the switch 9 temporarily. This causes the switches K2, K4 and K5 to be reopened, whereby the servomotors M3 and M4 return the line of sight to a position parallel to the direction of the barrel ll. At the same time the integrators I1 and I2 are temporarily short-circuited by the switches K3 so that the integrated signals on the output terminals of the integrators are eliminated. Thereafter the gunner can start a new computation of the lead angle by closing the switch 8 in the manner described in the foregoing.

One disadvantage of the device according to the invention which has been described above is that at the end of the computation interval the line of sight is momentarily moved away from the target, whereby the gunner loses the target and has to return the line of sight onto the target by means of the control lever 5 before a projectile can be fired. This makes the task of the gunner more difficult and at the same time the firing of a projectile is delayed.

However, this disadvantage can be eliminated by a modification of the device according to the invention in which, as illustrated by dotted lines in FIG. 2, each of two servomotors M3 and M4 for the sight 6 is coupled to a signal generator T3 and T4 respectively, for instance a tachogenerator, generating a signal proportional to the rate of rotation of the associated servomotor. The signal form the tachogenerator T3 coupled to the azimuth motor M3 of the sight is applied as an additional control signal to the azimuth servomotor Ml of the barrel 1 with such a polarity that this additional control signal assists the control signal form the signal generator S1 coupled to the lever 5. In similar manner the signal from the tachogenerator T4 coupled to the elevation motor M4 of the sight is applied as an additional control signal to the elevation servomotor M2 of the barrel 1. Thus when the two servomotors M3 and M4 for the sighting instrument are started for introducing the computed deflection angle in azimuth and elevation respectively between the line of sight and the direction of fire of the barrel 1, the barrel will, due to the above described modified arrangement, be given an increased azimuth angular velocity and elevation angular velocity respectively. The magnitude of this increase exactly corresponds to the azimuth angular velocity and the elevation angular velocity respectively that are imparted to the line of sight by the servomotors M3 and M4 relative to the barrel 1. In this way the line of sight will be maintained pointed at the target without the gunner having to operate the control lever 5, whereas the barrel 1, that is the direction of fire, is moved forward in the direction of the target tracking by an angle corresponding to the computed total deflection angle.

In the foregoing the invention has been described with reference to a weapon and sight system in which the sighting instrument is mounted on the layable portion of the weapon so that the gunner can keep the line of sight pointed at the target by controlling the servomotors laying the weapon. However, the invention can also be used in weapon and sight systems in which the weapon and the sighting instrument are separate and individually layable relative to a support, as for instance the ground. In this case, however, the gunner must, by means of a control lever, control the servomotors laying the sighting instrument relative to the support so that the line of sight is maintained pointed at the target, while the direction of fire of the weapon is caused to move uniformly with the line of sight in that the servomotors laying the weapon are supplied with control signals derived from position detectors coupled to the servomotors of the sighting instrument. The servomotors belonging to the lead angle computer (corresponding to the servomotors M3 and M4 in FIG. 2) are in this case not coupled to either the sighting instrument or the weapon but rotate instead position signal generators which generate signals proportional to the computed total deflection angle in azimuth and elevation respectively. At the end of the computation interval these signals are applied to the servomotors laying the weapon as additional control signals, whereby the direction of fire of the weapon is deflected from the line of sight in the direction of the target tracking by the computed total deflection angle.

In the embodiment of the invention described by way of example it has also been assumed that the direction of fire of the weapon and the line of sight are parallel during the target tracking and the integration interval. Fundamentally this is not necessary. Thus for instance at the beginning of the computation interval there may exist a deflection angle between the direction of fire of the weapon and the line of sight corresponding to those deflection angle components that are independent of the movement of the target, such as the superelevation and compensations for wind forces and the projectile rotation. It is essential, however, that during the computation interval the direction of fire of the weapon and the line of sight move uniformly without any mutual angular velocity relative each other so that the target tracking process is not affected by any disturbances during the computation interval.

Further, in the embodiment of the invention described in the foregoing the azimuth angular velocity and the elevation angular velocity of the line of sight are measured by means of tachogenerators coupled to the azimuth motor and the elevation motor of the weapon respectively. However, the angular velocities of the line of sight can of course also be measured in other ways, for instance by rate gyros mounted on a portion of the weapon which is directed in azimuth and elevation respectively. Such an arrangement will for instance be necessary if the weapon is stationary in a vehicle and is laid by movements of the entire vehicle.

What is claimed is:

1. In a weapon and sight system including an angularly rotatable weapon and sighting instrument with an angularly rotatable line of sight the method of providing a correct lead angle between the direction of fire of the weapon and the line of sight of the sighting instrument when firing a projectile from the weapon against a moving target comprising the steps of:

moving the line of sight of the sighting instrument so as to keep it pointing at the moving target;

rotating said weapon so as to move the direction of fire thereof uniformly with the movement of the line of sight of the sighting instrument without any relative angular velocity between the direction of fire and the line of sight;

continuously measuring the angular velocity of the line of sight;

integrating the angular velocity of the line of sight over a predetermined limited time interval;

at the end of said time interval substantially momentarily deflecting the direction of fire of said weapon and the line of sight of said sighting instrument from each other by an angle proportional to the integrated value of the angular velocity of the line of sight in such relative direction that the direction of fire of the weapon will lead the line of sight of the sighting instrument as seen in the direction of the angular movement of the target; and

subsequently continuing to move the direction of fire of said weapon uniformly with the movement of the line of sight of the sighting instrument until a projectile is fired against the target.

2. The method as claimed in claim 1, wherein said limited time interval is selected to be equal to the product of a constant and the range to the moving target, and at the end of the limited time interval the line of sight of the sighting instrument and the direction of fire of the weapon are deflected from each other by an angle proportional to the integrated value of the angular velocity of the line of sight divided by the mean velocity of a projectile fired at the target.

3. The method as claimed in claim 1, comprising the additional step at the end of said limited time interval of momentarily deflecting the line of sight of said sighting instrument and the direction of fire of said weapon from each other not only by said angle proportional to the integrated value of the angular velocity of the line of sight but also by a computed superelevation angle and computed correction angles for wind forces acting upon a projectile fired at the target and for the rotation of the projectile.

4. A weapon and sight system comprising:

an angularly rotatable weapon;

a sighting instrument with an angularly rotatable line of sight, said weapon and said sighting instrument being coupled to each other so that the line of sight of the sighting instrument and the direction of fire of the weapon normally move uniformly without any relative angular velocity;

first servo-drive means for angularly rotating the line of sight of said sighting instrument;

manually operable means for generating a manually variable control signal for said first servodrive means for tracking a moving target with the line of sight of the sighting instrument; and

lead angle computing means for providing a correct lead angle between the direction of fire of the weapon and the line of sight of the sighting instrument when firing a projectile at the target being tracked,

said lead angle computing means comprising means for measuring the angular velocity of the line of sight of the sighting instrument and producing a signal proportional thereto,

timing means for determining a time interval proportional to the range to the target being tracked,

means for initiating the operation of said timing means at a selected instant,

signal integrating means,

second servodrive means for angularly deflecting the direction of fire of said weapon and the line of sight of said sighting instrument from each other by an angle proportional to a control signal supplied to said second servo-drive means,

first switching means responsive to the operation of said timing means to apply said signal proportional to the angular velocity of the line of sight of the sighting instrument to the input of said signal integrating means during said time interval,

and second switching means responsive to the operation of said timing means to apply at the end of said time interval the output signal of said signal integrating means as a control signal to said second servo-drive means.

5. The weapon and sight system as claimed in claim 4, wherein said timing means is adapted to determine a time interval equal to the product of a constant and the range to the target being tracked, said second servodrive means including rotating servomotor means and signal generating means coupled to said servomotor means for generating a negative feed-back signal for said servomotor means proportional to the product of the angle of rotation of said servomotor means and a reference signal supplied to said signal generating means, and wherein said lead angle computing means comprise means for computing the mean velocity for a projectile fired at the target being tracked and producing a signal proportional to said mean velocity, said signal being supplied to said signal generating means as said reference signal.

6. A weapon and sight system as claimed in claim 5, wherein said first servo-drive means is adapted to angularly rotate said weapon, said sighting instrument is mounted on said weapon so as to participate in its movements, and said servomotor means of said second servo-drive means is adapted to angularly rotate the line of sight of the sighting instrument relative to the direction of fire of the weapon.

7. A weapon and sight system as claimed in claim 6, comprising second signal generating means coupled to said servomotor means of said second servo-drive means for generating a signal representing the rotation of said servomotor means, said signal being applied to said first servo-drive means for rotating said weapon as an additional control signal assisting said manually variable control signal.

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Classifications
U.S. Classification89/204, 89/41.17, 89/41.22
International ClassificationF41G3/00, F41G5/00, F41G3/06, F41G5/08
Cooperative ClassificationF41G3/06
European ClassificationF41G3/06