GB2339009A

GB2339009A - Aligning an aircraft sight

Info

Publication number: GB2339009A
Application number: GB9915725A
Authority: GB
Inventors: Hans-Joachim Lehmeier
Original assignee: LFK Lenkflugkoerpersysteme GmbH
Current assignee: LFK Lenkflugkoerpersysteme GmbH
Priority date: 1998-07-03
Filing date: 1999-07-05
Publication date: 2000-01-12
Anticipated expiration: 2019-07-05
Also published as: FR2780773A1; GB2339009B; GB9915725D0; DE19829710A1

Description

2339009 Aligning an aircraft sight The present invention relates to a

method for the preparation for the fully automatic harmonization of the lines of sight of a sighting device and a homing head in a weapons system that is installed on an aircraft.

Usually, harmonization of the lines of sight of a sighting device and a homing head in an aircraft weapons system, for example a he 1 i copter -mounted weapons system, is effected manually. For this, a target board provided with markings is set up. It is to be of an appropriate size in order to cover the visual field of both the sighting device and the homing-head simulator (HHS) used for the harmonization, since the principle of manual harmonization is based on the parallelism of the lines of sight of a sighting device and a homing-head simulator. In a first step, the operator/marksman aligns the sighting device with a suitable marking which is to represent the target.

With a given known spacing (horizontally and vertically) between the sighting device and the projector barrel, it is possible to determine the desired position of the homing-head simulator line of sight in the non-loaded state (no homing-head simulator in the projector barrel) on the target board.

Subsequently, the projector barrel is loaded with the homing-head simulator and the deviation of the current position of the homing-head simulator line of sight from the desired value is determined by means of an adjusting laser provided on the projector.

Such conventional methods and apparatus for determining the steering angles for the harmonization of the lines of sight of a sighting device and a homing head in a helicopter-supported weapons system have the disadvantage, however, precisely that the harmonization is effected manually and therefore is very time consuming and inaccurate.

The invention is therefore intended to provide a method and an apparatus for the preparation for the fully automatic harmonization of the lines of sight of a sighting device and a homing head in a weapons system that is installed on an aircraft that make harmonization possible in a fully automatic manner and with a high level of accuracy.

In accordance with one aspect of the invention there is provided a method for the preparation for the fully automatic harmonization of the lines of sight of a sighting device and a homing head in a weapons system that is installed on an aircraft, having the steps:

is alignment of a sighting device of an aircraft, standing on the ground, with a target point; alignment of a homing head with the same target point; recordal and storage by an image-processing unit of the deviations that occur thereby as correction values for later use; determination of the steering angles for the alignment of the homing head in a fully automatic manner by causing the lines of sight of the sighting device and the homing head to intersect at the target, and thus determination of the correction values of the harmonization angles.

In another aspect the invention provides an apparatus for the preparation for the fully automatic harmonization of the lines of sight of a sighting device and a homing head in a weapons systems that is installed on an aircraft, having: a device for the alignment of a sighting device of an aircraft, standing on the ground, with a target point; a device for the alignment of a homing head with the same target point; an image-processing unit for the recordal and storage of the deviations that occur thereby as correction values for later use; and a device for the fully automatic determination of the steering angles for the alignment of the homing head that causes the lines of sight of the sighting device and the homing head to intersect at the target, and thus for the determination of the correction values of the harmonization angles.

Fully automatic and accurate harmonization of the lines of sight of a sighting device and a homing head in a helicopter-supported weapons system is thus achieved.

For a better understanding of the invention embodiments of it will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic representation of the squint angle Jsquint in azimuth; and Figure 2 shows a diagrammatic representation of the squint angle esquint in elevation.

It is often necessary for a weapons systems to be operational on carrier helicopters for a long period.

In order to achieve this, mechanical tolerances between the sighting device, provided on the carrier, and the projectors laterally flange-mounted on the carrier must be determined by means of an ammunition simulator (equal in weight and size to a real missile) located therein and compensated for in order to guarantee the vectoring or lining-up process in the battlefield. In this connection, vectoring is a process in which the homing head of the missile, for example a PARS3-missile or an ATA ammunition, is aligned with the target detected by the sighting device.

Embodiments of the invention are intended to provide a harmonization procedure that is provided specifically for this purpose in a fully automatic manner.

The fundamental principle of harmonization can be exemplified as follows: the sighting device of a helicopter standing on the ground is aligned with a lorry approximately loom away from it. The homing-head simulator is now likewise to be aligned with the same target point. Since mechanical tolerances usually exist, this is only successful to a certain extent.

The deviations present are recorded by an image processing unit and are stored. They are used as correction values for later use.

The present method in accordance with the invention makes it possible to realize this harmonization principle, in particular the determination of the steering angles for the alignment of the homing-head simulator, in a fully automatic manner. Previously, in particular, there was no possibility of being able to cause the lines of sight of the sighting device and the homing-head simulator to intersect at the target at short distances (approximately 50m to loom) during the harmonization.

Basing considerations on the measured configuration (rest position of the carrier helicopter on the ground, position of an artificial target at a distance of approximately loom in front of the carrier helicopter, pre-inclination of the mast of the sighting-device flange, projector incidence), in the first instance the input variables for a parallelization unit are determined by means of geometrical relationships and corresponding transformations of coordinates. Processing the input variables for the parallelization unit results in the output values of the parallelization unit, the so called steering or control values, aligning the line of sight of the homing-head simulator with the target at the intended distance.

If the line of sight of the homing-head simulator intersects the line of sight of the sighting device at the target, there are no longer any tolerances.

otherwise, mechanical tolerances exist that can be identified by an image-processing unit.

Before being fed to the parallelization unit, the input variables are fed to a processing device which processes the input variables in such a way that instead of a parallelization of the lines of sight a convergence of the lines of sight is achieved.

The processing unit calculates the squint or oblique angle, that is, the angle at which a sighting device at the location of the homing-head simulator (HHS) would view the target. For this calculation, the following assumptions are made:

1. The plane on which the target and the helicopter stand is substantially flat and without an incline; 2. The spacing of the target plane from the helicopter is known and so too is the pre-inclination of the mast of the sighting device; 3. The helicopter is aligned in such a way that its longitudinal axis penetrates the surface of the target circumference; 4. All the angle specifications for the calculations are in rad; and 5. The system of coordinates used by the vectoring processor (AP) complies with the provisions of the information sheet Luftfahrtnorm (Aeronautical Standard) LN 9300.

In Figures 1 and 2 a projection onto the (110) plane (x-y-plane) is shown in azimuth (Figure 1) and elevation (Figure 2), the projection representing said assumptions which enter into the calculation of the squint angles. In this connection, in Figure 1 1squint denotes the squint angle in azimuth, VF denotes the angle between the optical axis of the sighting device (OAV) or sighting-device camera and the sighting-device flange and Z\YLM denotes the lateral deflection of the sighting device in the target plane. Furthermore, in Figure 2 Osquint denotes the squint angle in elevation, GVr denotes the angle between the optical axis of the sighting device (OAV) or sighting-device camera and the sighting-device flange and LZLKW denotes the vertical deflection of the sighting device in the target plane.

The origin of the reference-giving system of coordinates is fixed in the sighting device, the alignment of the axis being parallel to those of the carrier.

In this representation in accordance with Figures 1 and 2, the optical axis of the sighting device can be considered to be an arrow which rotates on a spherical shell (circle drawn with a continuous line) about the sighting-device head in azimuth and elevation. This arrow penetrates the image plane with an interspacing L (L = distance from the sighting device to the target), that is, at that point at which the target is located.

There shall now be located at the position of the homing-head simulator, that is, offset by AL in the x direction (AL = difference between distances between the sighting-device and the target and the homing-head simulator and the target), by dAZ or -dA. in the y-direction (dAz = interspacing between the sighting device and the homing-head simulator in the y direction) and by dEl in the z-direction (dE1 interspacing between the sighting device and the homing-head simulator in the z-direction), a second imaginary sighting device, the optical axis of which, again considered to be a rotating arrow, penetrates the image plane likewise at the position of the target (circle drawn in broken lines). The model of an imaginary sighting device originates from the question:

At what angle would a sighting device at the location of the homing-head simulator view the target? These angles represent precisely the so-called squint angles.

This state of affairs can be formulated using corresponding rotation matrixes as a basis therefor. The matrixes generally have the following form:

cos V/ sin V/ 0' Rotation matrix in azimuth [Vfl= -sinV/cosVO 0 0 1) (cosO 0 -sinO Rotation matrix in elevation [61= 0 1 0 sinO 0 cosO) The system of coordinates required for the calculation of the squint angles is stored with its origin in the sighting-device head of the real sighting T device and its viewing direction is towards (1,0,0) that is, in the x-direction of the longitudinal axis of the helicopter. For the real sighting device, in consideration of the pre-inclination of the mast em (= angle of the pre-inclination of the mast of the sighting device) (=-40=-0.0698 rad) and also the Cardan angles (angles between the sighting-device camera and the sighting-device flange) Vr and OVF (in azimuth and elevation) from the target the following transformation equation now holds good:

L") ( X 0 1 Ovrl I OF] I em] Y (1a) 0.' Z) or correspondingly X) L' Y OMI 7 1 Orl 7 1 evr] 0 (1b) Z. 0 In this connection the index T stands for the transpose. L' denotes the radius of a sphere about the real sighting device, the shell of which penetrates the target at the distance L (L';->L). After multiplying out the expressions in brackets, Equation (1b) obtains the following form:

X ') ( L'(cos Om cos VvF cos OvF- sin Om sin OvF) Y L'sin VvF cos VvF Z,' X(-sint9mcosV/vF cos OvF- cos 6kf sin OrF), (2) The first component of the vector, the spacing of the point of penetration in the target plane, is known and equal to L. Thus L', as well as the components y and z, are also given. Put together this reads:

X = L (3a) (cosOmcosVvFcos9vF- sin Om sin OvF) (3b) Y= L(sin Vf vF cos OvF) (3c) (cos Om cos VvF cos OvF - sin Om sin OvF) L(- sin Om cos VfvF cos OvF - cos Om sin OvF) (3d) (cos Om cos VlvF cos OvF - sin Om sin OvF) The position of the imaginary sighting device is shifted in relation to the origin of coordinates of the real sighting device by the translation vector T. In the case of a translation, a vector V is transformed in the system of coordinates of the real sighting device into a vector a in the system of coordinates of the imaginary sighting device in accordance with Equation (4) 5 "!=g.sighting device Vrea2 sighting derice -7 (4) In the present case, the shift vector is AL N T= sign(dA.,)dA, (5) dEi For sign(dAz) sign(dAz) = + I for the right - hand projector (6) -I for the left - hand projector holds good.

The point at which the spherical shell of the imaginary sighting device intersects the spherical shell of the real sighting device occurs in the target T plane at the location of the target (x,y,z). For the imaginary sighting device at the position of the homing-head simulator the following transformation equation therefore results, with L" denoting the radius of the sphere about the imaginary sighting device:

x o Osquint] 11squintl lem] Y _T O L Z) J x- AL [esquintl hfsquintl [E)MI Y - S'gn(dA')dA' Z - IdEl (7) and x- AL Lit y - sign(dA.,)dA.- [eM] T 11Vsqu:Lnt1'1 lesquint iT 0 z-dEi 0 L"(coSOM COS Vsquint COS Osquint -sin Om sin Osquint) L if sin Vsquint COS Osquint Lit (- sin Om COS Vsquint COS Osquint - COS Om sin Osquint), (8) Equation (8) represents a non-linear system of equations with three unknowns, the solution of which cannot generally be specified in a closed form. An exact solution can only be found numerically, yet does depend greatly upon the choice of "good" initial conditions and is thus not necessarily given. If during the harmonization, however, one is not restricted to small sighting-device angles, various simplifications of Equation (8) result. Using a lorry with a length of approximately lom and a height of 4m as a basis, with rough estimates for the orders of magnitude of the squint angles to be expected the following would result:

estimate 01 = arctan(5m/100m) = 0.04996 (9a) squmt estimate - 4m 2m e squint Z -arctan ( 100 0.05992 and 0.01999 respectively (9b) To a good approximation it is thus justifiable in Equation (8) to replace the cosine terms with 1 and the sine terms with their argument. If the values of (X, Y, Z) T, which have already been determined, are used further, the following system of equations is obtained:

x-AL ') ( L"(cos Om - Osquint sin Om y - sign(dA,)dA, L 11 Vsquint zdEl,-P(sin0m+Osquintcos0m, (10) The magnitudes which are sought can be extracted therefrom:

(dyj - z)sine, + (L-AL)cosE), (11a) y - sign(dA,)dA squint- L (11b) dEi z E)squint Lit - sin OM)_ Cos OM x/ y, and z are known from Equations 3a, 3c and 3d. The squint angles which have been calculated cause the parallelization unit to be correctly supplied with input data, yet the calculated commanded homing-head Cardan angles must still be processed for the homing-head simulator or the vectoring processor respectively, because the homing-head simulator or the vectoring p rocessor operates in an image plane with translations and first converts these into angles. In the case of translatory movements, the sequence is of no significance, yet this is not so in the case of rotations, as executed in the case of the homing-head Cardan framework. The conversion of the homing-head angles into variables suitable for the homing-head simulator or the vectoring processor (AP) respectively will be discussed briefly in the following.

The transformation of a vector in the system of the homing-head simulator into the system of the sighting device is effected by the successively executed rotations E)SK (E)Sy = angle of the projector incidence in relation to the helicopter)(E)LF + em =incidence of the homing-head simulator or the homing head in relation to the helicopter, eLF harmonization roll angle between the projector and the sighting-device flange in elevation), eSL,k (commanded angle homing-head projector in elevation) and VSL,k (commanded angle homing-head projector in azimuth) and also a translation T (see Equation (5) or Ll 11) X 0 ['VSL,k] [()SL,k] IeS. I Y (12a) and x-AL Lill y - sign(dA.)dA. = [eS.] T eSL"K T [SL,IK T 0 z-dE 1 0 (12b) with the expressions in brackets multiplied out, the following equations are obtained from Equation (12a) and (12b) respectively:

x-AL=L'" (cos (E)SK + E)SL,K) COSVSL,K) (13a) y-sign(dAz)dAz = L'sinSL,r, (13b) z-dEl =-L'" (sin (E)SK + sinE)SL,F,) COSVSL,r,) (13c) From the requirement x = L-AL at the location of the target position there follows: 5 x= (L-6L) =L'" (cos (E)Sr' + E)SL,r,) C04SL,K) (14a) Lffl= (L - AL) COS(AK + aL, K)COS VAL, K (14b) (L - AL) tan VSL, K ign(dAz) dAZ COS(OSK + OSL, K) (14c) z=-(L-6L)tan(E) SIK + E) SL, K) + dE I (14d) The angles that are suitable for a target homing head simulator and the vectoring processor respectively and which the fire control computer (FCC) has to deliver are then determined to give AP arctan Y (15a) VSL AL)2 + ZI E)AP Z SL arctan AL)' (15b) VSL, es,= commanded azimuth or elevation angle of the homing-head camera in relation to the projector.

When carrying out the harmonization the vectoring processor (AP) sends back measured-angle miss distances:

A MAP A /trkp in which case the rMeasured, A C2tepasured, 'Vmeasured, determined miss distances are understood to be the difference between the rated value and the actual value. However, during the harmonization test it is not known into what proportions the harmonization errors are quantitatively broken down so it is possible to proceed with absolute justification on the assumption that it is exclusively the sighting device that is producing the errors (position of the target in the sighting-device image = actual value, position of the target in the homing-head simulator image = desired value). The roll proportion (that is, the roll angle between the projector and the sighting-device flange) Llff""P rmeasured. as required above, is not to be considered further. Thus the rest of the analysis is restricted to the azimuth and elevation angle respectively.

Since the angle errors in the sighting-device image (planar system of coordinates) have been determined, they must further be transformed into corresponding sighting-device Cardan angles (sphere coordinates) in consideration of the sequence of rotation of the sighting-device Cardan framework. This is effected in that the fire control computer first converts the angles L 71AP and L "-" respectively, measured by the Omeasured Uie-asured vectoring processor, into lengths Ly and Lz and therefrom calculates the suitable sighting-device Cardan angles by way of Equation (2). Analogously to Equations (15a) and (15b):

Ay Ay MAP arctan =arctan Y,measured _2 2) fX + A? f+AZ (16a) 0-kP -arctan AZ =-arctan Az measured + AY2 (16b) NIX + AY 2 hold good.

There follows from this:

(1+tan2(AV/,IP d)) )AP - measur Lz=Ltan UEmeasured) (i+t=2(A AP 2 an t9AP Vf.easured) tan (A measured (17a) Ly=tan (Z AP __[L2 + A Z 2 fmAeasured) (17b) The correlation of Ay and Az with the sightingdevice Cardan angles follows from Equations (3c) and (3d):

Ly LsinA VVFCOSA OVF (COS OMCOSA VVFCOSA OVF - sin OmsinA OvF) (18a) LZ L(- sin Om COS A VlvF cos A OvF - COS Om sin A OvF) (cos Om COS A VlvF COS A OvF - sin Om sin A OvF) (18b) Since the angle miss distances to be expected will presumably be very small, it is possible to arrange that ZVF, Z E)VF <<1, cos LVF = 1, cos AeVF = 1, sin Lvr = ZVF and sinLE)VF = LE)VF. As a result, the above system of equations obtains the following form:

Ly = LA VvF.

(cosOm - sinOmA OvF) (19a) Az= L(- sin Om - COS OmA OvF (COS Ou - sin OmA OvF) (19b) The solution in accordance with the Cardan angles produces:

Ae Az cos Om + L sin Om vF - Az sin Om - L cos Om (20a) AVF = Ay(cos Om sin OmA OvF) L (20b) The values from Equations (17a) and (17b) are to be used for Ay and Az. Since the vectoring-processor measured values are already in the system of the is sighting-device flange, no further transformation needs to be effected. It is merely necessary to note that the correction values are to be inverse to the error miss distances determined. Thus the correction values of the harmonization angles are given by:

AV LF _'"VVF (21a) AeLF -Aev. (21b).

As the final step in the harmonization procedure, the fire control computer must store the values of Equations (21a) and (21b) -

Claims

1. A method for automatic harmonization of the lines of sight of a sighting device and a homing head in a weapons system installed on an aircraft, having the steps:

alignment of a sighting device of the aircraft, as it is standing on the ground, with a target point; alignment of the homing head with the same target point; recordal and storage by an image-processing unit of any deviations occurring as correction values for later use; and determination of the steering angles for the alignment of the homing head in a fully automatic manner, and thus of the correction values for the harmonization angles, by causing the lines of sight of the sighting device and the homing head to intersect at the target.

2. A method according to claim 1, in which the fully automatic determination of the steering angles for the alignment of the homing head includes the following steps, basing considerations on the measured configuration by means of geometrical relationships:

determination of the input variables for a parallelization unit; processing of the input variables for the parallelization unit in a processing device in such a way that instead of a parallelization of the lines of sight a convergence of the lines of sight is achieved so that the output values of the parallelization unit, that is, the steering angles, align the line of sight of the homing head with the target at the intended distance until the line of sight of the homing head intersects the line of sight of the sighting device at the target.

3. A method according to claim 1 or 2, having the further step:

storage of the correction values of the harmonization angles by the fire control computer after the determination of the steering angles.

4. A method according to one of claims 1 to 3, in which the correction values of the harmonization angles result from the following formulae:

'VLF = -'VVF AOLF =-Aev.F, with Azcos0m+ Lsinblvi 8 vF = Az sin Om - Lcos 6k AiVF Ay(cos Om - sin OmA OvF) L where AP E)AP VIleasured Az=L,tan(A measured) V(l_tanl(A AP)tM2 (A 'OAP red)) VI.easured '-meas AP J-2 Ay=tan (A measured) + Az' with:

LF and E)LF denoting harmonization angles in azimuth and elevation respectively between a projector and a sighting-device flange, ZWLF and AeLF a correction value for fLF and E)LF respectively, 14F and E)VF the angles between the optical axis (OAV) or sighting-device camera and the sighting-device flange in azimuth and elevation respectively, AVF and AeVF a correction value for JVF and evF respectively, E)M the angle of the pre-inclination of the sighting-device mast, L the distance between the sighting device and a target and A 71AP wmeasured and A"-'RP measured angle miss Ceasured distances in azimuth and elevation respectively.

5. An apparatus for the preparation for the fully automatic harmonization of the lines of sight of a sighting device and a homing head in a weapons systems that is installed on an aircraft, having:

a device for the alignment of the sighting device of the aircraft, while it is standing on the ground, with a target point; a device for the alignment of the homing head with the same target point; an image-processing unit for the recordal and storage of any deviations that occur as correction values for later use; and a device for the fully automatic determination of the steering angles for the alignment of the homing head that causes the lines of sight of the sighting device and the homing head to intersect at the target, and thus for the determination of the correction values of the harmonization angles.

6. An apparatus according to claim 5, in which the device for the fully automatic determination of the steering angles for the alignment of the homing head comprises the following devices:

a device which, basing considerations on the measured configuration by means of geometrical relationships, determines the input variables for a parallelization unit, a processing device for processing the input variables for the parallelization unit, wherein the processing device processes the input variables in such a way that instead of a parallelization of the lines of sight a convergence of the lines of sight is achieved so that the output values of the parallelization unit, that is, the steering angles, align the line of sight of the homing head with the target at the intended distance until the line of sight of the homing head intersects the line of sight of the sighting device at the target.

7. An apparatus according to claim 5 or 6, characterised in that the fire control computer is designed to store the correction values of the harmonization values after the determination of the steering angles.

8. An apparatus according to one of claims 5 to 7, characterised in that the parallelization unit determines the correction values of the harmonization angles from the following formulae:

AJLF = -AVVF AeLF -Aevp, with Azcos0m+ Lsin& '6vF Az sin Om - Lcos 6ki Ay(cos Om - sin OmA OvF) ZWVF L where IAP P measured Az=Ltan (AE)Imeasured) V (I _ tan2 (A AP 2 (A OA'P Kneaswed tan measured)) "P L2 + A? Ay=tan (Ameasured) with:

LF and OLF denoting harmonization angles in azimuth and elevation respectively between a projector and a sighting-device flange, Z\LF and zeLF a correction value for LF and eLF respectively, VF and OVF the angles between the optical axis (OAV) or sighting-device camera and the sighting-device f lange in azimuth and elevation respectively, LVF and L E)VF a correction value for IVVF and E)VF respectively, em an angle of the pre-inclination of the sighting-device mast, L a distance between the sighting device and a target and Z asured and LO-kP measured angle miss me measured distances in azimuth and elevation respectively.