GB2188507A

GB2188507A - Target detection mechanism

Info

Publication number: GB2188507A
Application number: GB08706715A
Authority: GB
Inventors: Horst-Ulf Schottelius
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1986-03-22
Filing date: 1987-03-20
Publication date: 1987-09-30
Anticipated expiration: 2007-03-20
Also published as: GB2188507B; GB8706715D0; FR2596162B2; FR2596162A2; DE3609774C2; DE3609774A1

Abstract

A target detection mechanism 3 for a guided missile 1, which is to be able to home-in on a target object, detected at a displacement angle (a), in accordance with the principles of collision-course or proportional navigation, uses overlapping detector elements 11 on the longitudinal axis 10 of the missile. Its design allows a compact and insensitive construction and a favourable ray path with respect to the geometry of the head 2 of the missile 1. Optical system 8 projects an image of the target object (35, Fig. 1) into the detector plane 9 the output of whose detectors 11 gives the angle alpha <1> of the line-of-site 15 to the target object (35, Fig. 1). Preferably the ray path through the lens 8 is reflected by mirror 30 so that the detector plane 9 lies close to the longitudinal axis 10. Alternatively the detector plane may be perpendicular to the missile axis (Fig. 1). <IMAGE>

Description

SPECIFICATION A target detection mechanism This invention relates to a target detection mechanism in a missile.

Such a target detection is known for steering an anti-aircraft missile on approaching a target. This target detection mechanism is to be equally usable in missiles which approach a flying object substantially horizontally or substantially vertically at up to several times supersonic speed, so that the flying object may be intercepted by the missile and thus combatted by its combat charge.

It is known for such a target detection mechanism to be equipped with an annular infra-red detector element which is incorporated into a spin-stabilised missile concentrically to its longitudinal axis and which is arranged in the beam path of a Cassegrainshaped hollow-mirror deflecting optical system. The centre region of the ring detector is insensitive to radiation. Accordingly, a thermally radiating target object does not activate the detector element if its projection (image) by way of the optical system lies in the insensitive centre region; and the missile moves in its instantaneous spatial orientation along its axis towards the target object.

If, however, the target object migrates (wanders) out of this axis, i.e. the target projection or image becomes displaced radially away from the centre into the radiation-sensitive part of the detector element, homing-in by a steering mechanism in the form of a transmitted transverse impulse is effected in an orientation which once more annuls this radial migration of the target projection (image), i.e. the longitudinal axis of the missile is again aligned in the direction of the target object.

What tends to be disadvantageous with such previously known target detection mechanisms is more especially that only a target pursuit navigation, in other words target approach in the manner of a drag or dog curve, is possible. Thus, sufficient probability for adequate approach of the amti-aircraft missile to the target object that is to be intercepted is afforded only if both missile and target are moving on approximately the same course in the same direction and the missile is travelling considerably faster than the flying object (target) that is to be combatted.If, on the other hand, on setting in operation the target detection mechanism, the paths of movement of missile and target intersect at not too great a distance in a relatively obtuseangled manner (of even if an approaching object is to be intercepted by the defence missile in a head-on attack) manoeuvring possibilities along a target tracking (pursuit) course are, as is well known, not sufficient in the event of close target proximity, because then severe flight or course manoeuvres become necessary; which leads to flight instabilities of the defence missile and/or to a loss of a target hit, i.e. to the target being passed by at too great a distance for the effect of the intercepting warhead to be successful.Generally, with this previously known target detection mechanism, only a very narrow and constructionally rigidly preset (fixed) target detection angle as well as the spatial conejacket-surface scanning during rigid or fixed coupling to the spin of the missile is disadvantageous. This is because it is not possible, prior to first-time target detection or after loss of a given target detection, to search a sector of space, lying ahead, for the whereabouts of the target object; and manoeuvring during advancing of the point-of-impact, i.e. in accordance with the rules of collisioncourse or proportional navigation, is likewise not feasible with the previously known mechanism.

To overcome these disadvantages, in our Patent Specification No. GB 2166314 it has already been proposed to vary the target displacement (angle) or line-of-sight angle to a target object (related to the longitudinal axis and axis of motion of the missile); a so-called zoom optical system (i.e. a multi-lens optical system having a mechanically adjustable focal length) is used, which projects an image of the target object deleted at the instantaneous line-of-sight angle onto a detector element which is arranged radially outside the common axis of the missile and of the zoom objective in the ray path behind the optical system.The effective zoom focal length which is adjustable by means of a motor, i.e. the instantaneous mechanical setting (adjustment) of the zoom objective, is, in accordance with the given radiation-geometrical zoom conditions, a measure of the instantaneous line-of-sight angle. If the target object migrates (wanders) transversely to the longitudinal axis, or if a sector of space lying ahead is to be searched for the presence of a target object, swivelling of the line-of-sight angle (of the line of sight relative to the longitudinal axis of the missile) is effected by varying the zoom focal-point setting.This is because, by reason of zoom imaging principles, each zoom setting adjustment in accordance with the instantaneous radial displacement of the target object from the longitudinal axis of the missile leads to radial displacement of the target projection (image) in the detector plane and thus to the stimulation of the detector element which is arranged there at a fixed radial distance from the longitudinal axis.

Thus, a rapid target search in a large space angle is made possible; and a target-object projection onto two radially overlapping and mutually offset or staggered detector elements allows, in a particularly simple manner, homing-in on the target object in accordance with proportional navigation, because the missile merely has to be so steered that at all times the region of overlap of both radially mutually offset detector elements is covered uniformly by the target projection (image); with constriction or narrowing of the line-of-sight angle in accordance with the target approach.

An aim of the present invention is, whilst in general retaining the aforementioned application-orientated advantages for the target search steering, to further develop the apparatus of the target detection mechanism so that seemingly simpler conditions for variation and evaluation of the line-of-sight result and/or, despite restricted space factors in the narrowly-elongated head of a supersonic missile, to provide possibilities for the apparatus correction of ray-geometric error effects in the course of the target-object imaging.

According to the present invention there is provided in a missile, a target detection mechanism having a line-of-sight displacement angle, inclined ahead relative to the longitudinal axis of the missile, with regard to a target object that is to be homed-in on and which is projected by way of a collecting optical system into a detector plane, for example in accordance with GB Patent Specification No. GB 2166314 characterised in that an adjusting mechanism is provided for a detector-element re-adjustment in the detector plane and/or for the successive interrogation of several detector elements.

The present invention is based on the realisation that it is, for target projection (imaging) onto the detector plane under variable line-ofsight angles, not necessary to realise the nonlinear control characteristic and the mechanical construction (relatively sensitive to disturbance) of a zoom objective; all the more so since the optical components thereof (which are for example transmissive for thermal radiation and which are crucial for image reproduction quality) are really costly with respect to the necessary production accuracy.Instead, a single-member collecting optical system can be used, which system would appear to no longer experience any mechanical variations of any kind in the ray path, if one allows, in accordance with the radial target displacement, a radial displacement, variable from the longitudinal axis, of the target projection (image) in the detector plane and evaluates the instantaneous radial distance as a measure of the instantaneous angle of the line-of-sight to the target object.

The linear displacement of the detector element in the detector plane can be effected by means of a simple electromagnetic linear actuator, for instance in the form of a moving-coil adjusting member, since, contrary to the conditions in the case of a zoom objective, now several lenses no longer have to be shifted in non-linear mutual dependency. Thus, no optical element has to be moved, but in the detector plane the given displacement of the target projection (image) is sought from a reference position.

An axially and radially compact construction of the target detection mechanism with seemingly minimum mechanical stress factors through rotation-dependent centrifugal forces may be provided if a deflection mirror is arranged in the ray path of the optical mechanism between the collecting lens and the detector plane. This is because then the deflection mirror can assume such an inclination relative to the optical plane through the lens that the detector plane no longer extends radially away from the longitudinal axis of the missile, but instead lies in it or at least close to it.Moreover, then the lens may be offset radially out of the longitudinal axis and, what is more, be angled somewhat relative to the parallel (line) to the longitudinal axis of the missile, something which, in view of the reproduction distortions caused by the dome of the missile head, yields very favourable geometric ray entry or passage conditions. The optical system angled relative to the perpendicular line onto the longitudinal axis provides the result known 'per se' that the focal point of the target reproduction (image) no longer travels on a parallel line to the longitudinal axis of the missile if the detected target object migrates radially, but (in the two-dimensional projection) along a detector plane inclined in a ramp-shaped manner relative to the longitudinal axis.This inclination can, however, be compensated for again, i.e. the detector plane can be orientated into or parallel to the longitudinal axis, if the deflection mirror is employed with an appropriate compensating inclination in the ray path behind the collecting lens.

At the same time by way of the alignment of the deflection mirror the minimum limiting angle of the line-of-sight swivel can be adjusted practically parallel to the longitudinal axis of the missile although the ray geometry does not extend in the axis through the nose of the missile (which for constructional reasons would not be possible, at least for thermal reasons would be undesirable and optically, on account of extreme reproduction distortions, would be inexpedient). Finally, the use of the deflection mirror is also advantageous insofar as a relatively small displacement of the target-object image in the detector plane corresponds to a large angle of swivel of the line-of-sight, something which, despite axially compact construction, means a large detection region with high resolution.

The present invention thus yields, more especially in a further development with bending of the ray path behind the optical system by way of a deflection mirror, a constructional realisation of the target detection mechanism which (with ray-geometrically optimum passage of the line-of-sight through the slim dome of the projection tip) avoids expensive zoom constructions and complicated inert or sluggish mechanical mechanisms for the specific adjustment of a multi-lens zoom objective. The target detection mechanism has, relative to a realisable zoom, a larger angular detection region, i.e. overall it opens up a greater optimum possibility for integration into the slim supersonic anti-aircraft missile. With respect to the requirements of the solid angle scanning, the same possibilities are afforded with the arrangement shown in Patent Specification No.GB 2166314, as regards the rotation of the target-object reproduction about the longitudinal axis of the missile onto mutually overlapping detector elements. Since now the seemingly simplest possible optical system, which no longer has to be adjusted mechanically, is provided, a rotation relative to the missile can be undertaken without mechanical problems by rotation of the compact structural unit consisting of optical system (collecting lens together with deflection mirror) together with the detector elements.

Also with respect to the possibilities of reducing the actual rotation by peripherally (circumferentially) mutually offset detector elements and/or optical systems, the same measures as employed in GB 2166314 can be applied; to which, to avoid repetitions, reference is made here in its full content, and the description in patent specification No. GB 2166314 is incorporated herein by reference.

Additional alternatives and further developments as well as further features and advantages of the present invention will be apparent from the claims and, from the following description, by way of example only, of two preferred embodiments of a target detection mechanism in a missile in accordance with the present invention which are shown in a highly simplified manner in the drawings along with a restriction to that which is apparently essential for understanding the present invention.

FIGURE 1 shows the first basic embodiment, and illustrates the beam-geometric function of the target detection mechanism and FIGURE 2 shows, in axial longitudinal section through a missile, the second, preferred embodiment of the target detection mechanism.

The missile 1 shown in the drawings in chain-dotted lines is more especially intended to approach flying objects at supersonic speed and to combat them by means of its combat charge. For homing-in on the target once detected in location-technology manner, for example optronically, at a displacement angle a from the missile and longitudinal axis of motion 10, the missile head 2 is equipped with a target detection mechanism 3.The signal-processing circuit 4 thereof supplies, in accordance with the instantaneous displacement angle a, steering commands 6 to a missile steering mechanism (not shown in the drawings), in order (depending on the desired kinematics for combatting the target 35) to orientate the missile longitudinal axis 10 in accordance with a target tracking course or, preferably, on collision course in accordance with proportional navigation, while the distance between the target 35 and the missile 1 is reduced.

The solid displacement angle a thus defines the instantaneous target detection axis 15 or line-of-sight from the target 35 to the missile head 2; namely to the centre 17 of an optical system 8, behind which in the ray path 7 at least one detector element 11 is arranged in a detector plane, which plane extends, for instance, in accordance with FIGURE 1 radially with respect to the longitudinal axis 10 of the missile.For a typical mean target detection distance 16 between the instantaneous target distance plane 21 (orientated transversely to the longitudinal axis 10 of the projectile, and the centre 17 of the optical system) the detector plane 9 lies approximately at the spacing of the focal length 13 behind the optical system; so that the target 35 is reproduced or imaged by way of the optical system 8, in the case of these ray-geometric spacing conditions, in the detection plane 9 as a spot. The radial spacing 12 of the spot from the longitudinal axis 10 of the missile is, by virtue of the ray geometry, proportional to the transverse displacement 20 of the target 35 from the longitudinal axis 10 of the missile. If, in the relative course of target approach, this focus condition is no longer fulfilled, target imaging in the detection plane 9 becomes correspondingly more out of focus.

The instantaneous distance 12 of the target projection (image) in the detector plane 9 is thus a measure of the instantaneous target displacement angle a. For the determination thereof, either several detector elements 11 or pairs of elements can be arranged radially with respect to the longitudinal axis 10 of the missile side-by-side in the detector plane 9, which elements are interrogated successively for the existence of a detector output signal 24; or alternatively only a single detector element 11 or pair is provided, which is displaceable radially with respect to the longitudinal axis 10 of the missile in the detector plane 9.

For the determination of the instantaneous radial distance 12 of the projection of the target 35 onto the detector plane 9, an adjusting mechanism 36 is provided which causes either the successive interrogation of the several detector elements 11 arranged side-by-side or else the mechanical displacement of one detector element 11 or respective (detector) pair, until the instantaneous projection spot is reached, in other words an output signal 24 appears. This position is supplied by a position transmitter 37 as instantaneous line-ofsight angle information a' to the signal processing circuit 4, which circuit then issues to the missile stee ring mechanism a steering command 6 for swinging-in the longitudinal axis 10 of the missile in the direction of the target 35 (possibly taking into account a preset lead angle).

If, line-of-sight to the target 35 is lost for any reason, for instance because of environmental influences on the instantaneous flight path, interrogation of the detector plane 9 for the instantaneous position of the target image (in other words the interrogation of the detector elements 11 lying side-by-side or the mechanical displacement of a single detector element 11) is periodically repeated until a detector element 11 once again lies in the ray path 7 and therefore supplies an output signal; which signal causes the adoption of the new angle information a' into the signal processing circuit 4 and possibly, in the appropriate circumstances, an interruption of the search operation of the adjusting mechanism 36.

FIGURE 2 shows an embodiment of a target detection mechanism 3 which is preferable in apparatus respects. In FIGURE 2 in the optical mechanism a deflection optical system 30 (mirror) lies in the ray path 7 behind the convergent or collecting lens 8. In this way there results, with a small overall axial length of target detection mechanism 3, a desirably long (since it is bent) ray path 7. The detector plane 9 can be formed axially-parallel in the, or in the vicinity of, the longitudinal axis 10 of the missile. As compared with the nondeflected ray path 7 in accordance with FIG URE 1 there results, for the same amount of projection-spot shift in the detector plane 9, an enlarged region of the line-of-sight angle a which can be covered, in other words a greater angular location resolution can be achieved during search and tracking of the target 35 (FIGURE 1).In addition to this, of advantage is the ray-path deflection, because now the optical system 8 does not have to be arranged in the longitudinal axis 10 of the missile. This is because the tip (very highly thermally stressed on supersonic flight) of the missile head or nose 2 is not readily suitable for incorporation of the measuring-technology for detection of energy, emitted by the target 35, in the radiation spectrum in which the optical system 8 and the detector element 11 work.The optical system 8 now thus offset radially relative to the longitudinal axis 10 of the missile now also no longer needs-contrary to the basic conditions shown in FIGURE 1-to be aligned with its main plane transverse to the longitudinal axis 10 of the missile, because angles of tilt of the main plane can be so precisely compensated for by an appropriate swivelling of the deflection mirror 30 that the focal point of the targt projection (image) into the detector plane travels parallel to the longitudinal axis 10 of the missile (or into this axis) if the transverse target distance 20 (see FIGURE 1) changes.With this angle compensation provided by way of the angle of incidence of the deflection mirror 30, an optical system 8 swivelled relative to the perpendicular to the longitudinal axis 10 of the missile would lead to displacement of the focal point in a detector plane 9 rising in a wedge-shaped manner relative to the longitidunal axis of the missile, which would necessitate a guidance (more expensive or complex in apparatus respects) on shifting of a detectorelement pair 11-11.An angle of the optical system 8 relative to the radial line to the longitudinal axis 10 of the missile has, furthermore, the advantage that the mean displacement angle a of the line-of-sight 15 intersects more steeply with the dome 31 (curved in practice in a three-dimensional non-linear manner) of the missile head 2, which leads, compared to an acute-angled entry through the dome 31, to reduced errors in target imaging.

The instantaneous position of the detector element 11 which supplies an output signal 24, in other words the instantaneous target displacement angle a, is again determined by means of a position transmitter 37.

Shifting of the detector element 11 or interrogation of detector elements arranged sideby-side is, in the embodiment in accordance with FIGURE 2, caused, for example, by means of an electro-magnetic linear path transmitter or actuator, along the lines of a moving-coil actuator 38, which is controlled by the adjusting mechanism 36.

As described in detail in British Patent Specification No. GB 2166314 again provision can be made for the fact that in the detector plane 9 two mutually offset but mutually overlapping detector elements 11 are provided, in order to be able to determine, for the derivation of steering commands 6 for proportional navigation, the line-of-sight final speed or rotation quota (Sichtliniendrehrate), in other words the temporal migration of the acquired target 35. In this connection, of advantage is the ray deflection by way of the mirror 30, since the (inner) line-of-sight 15 can be so orientated by way of the mirror position that it extends parallel to the longitidunal axis 10 of the missile; whereby an offset angle of the target detection mechanism 3 is avoided, although the ray path of the optical system 8 is not concentric with the longitudinal axis 10 of the missile.

The representation in the drawings shows the angular conditions projected onto a vertical plane parallel to the longitudinal axis 10 of the missile. In practice, the displacement angle a is a solid angle. This is, as described in more detail in Patent Specification No. GB 2166314, covered by a rotation of the detector element 11 about the longitudinal axis 10 of the missile, in that each line-of-sight 15 is the generatrix of a pointed-cone jacket surface with an aperture angle a in accordance with the beam geometry of the optical system 8.

These conditions occur if the described target detection mechanism 3 (with target spot projection displaceable radially in accordance with FIGURE 1 or parallel to the axis in accordance with FIGURE 2, in the detector plane 9) is incorporated fixedly into a rotating missile 1.

In order, however, to be independent of any missile spin, for example because this does not have the constant or desirable time-dependent angular velocity-because the effective detector rotation frequency is to be controllable independently of the behaviour of the missile, or because a spin-stabilised missile 1 is not even provided-in accordance with the conditions in Patent Specification No. GB 2166314 here too provision is made for installing a motor 29 for rotation of the detector plane 9 concentrically about the longitudinal axis 10 of the missile.An angle transmitter 25 supplies, for the instantaneous position of each detector element 11 relative to a reference radius in the missile 1 fixed relative to the missile body, an item of rotaryposition information b' to the signal processing circuit 4, so that this issues a steering command 6 to the steering mechanism of the missile. The optical mechanism consisting of lens 8 and mirror 30 can be incorporated in a manner fixed relative to the missile body, if in the detector plane 9 mutually overlapping fields of view emerge, for example because several lenses 8 are provided peripherally mutually offset. In apparatus respects it can, however, be simpler to construct the entire mechanism 3 consisting of lens 8, mirror 30 and detectorelement pair 11-11 as a rotating unit with a common holder or mounting support 39.

Finally, in FIGURE 2-as set forth in more detail in Patent Specification No. GB 2166314it can be expedient to fashion, coaxially with the longitudinal axis of the missile, several such units 3 peripherally mutually offset with overlapping pairs of detector elements 11-11, with which in each case a deflection mirror 30 and a lens 8 is associated.This allows imbalances to be avoided, and makes possible a high resolution upon detection of the relative movement (line-of-sight speed or rotation quota-Sichtliniendrehrate) between missile 1 and target 35 despite only moderate angular frequemcy of the rotary motor 29, because the target 35 is detected in the target distance plane 21 by the pairs (here overlapping one another in axialiy-parallel manner and being peripherally consecutive) of detector elements 11-11 in the ray path 7 and thus rapidly in succession.

To summarise, a target detection mechanism (3) for a guided missile (1), which is to be able to home-in on a target object, detected at a displacement angle (a), in accordance with the principles of collision-course or proportional navigation, is (whilst retaining the functional advantages with respect to the use of detector elements (11) which are peripherally mutually offset about the longitudinal axis (10) of the missile but which mutually partially overlap in pairs transversely to this offset direction) to be designed in such a way that a more compact and more insensitive construction with a more favourable ray path with respect to the geometry of the head (2) of the guided body emerges.For this a collecting optical system (8) without focal-point variation is used and from the shift of the projection of the target object (35) into the detector plane (9) an item of angle information (a') regarding the line-of-sight (15) to the target object (35) is obtained. Preferably bending of the ray path through the lens (8) is effected at a deflection mirror (30) so that the detector plane (9) lies close to the longitudinal axis (10) and parallel to this.

It is to be understood that the scope of the present invention is not to be unduly limited by the particular choice of terminology and that a specific term may extend to, or be replaced by, any equivalent or generic term where sensible. Further it is to be understood that individual features, method or function related to the target detection mechanism or combinations thereof are important and might be patentable. Particularly important in this respect is the charactering portion of Claim 1 which may possibly be patentable 'per se' and form another aspect of the present invention.

Further according to the present invention there is provided a missile comprising a target detection mechanism having at least one detector element offset from the axis of the missile which, in use, detects a target at a lineof-sight displacement angle to the longitudinal axis of the missile by an image of the target being projected onto a detector plane by means of a collecting optical system, and in which an adjusting mechanism is provided for determining the instantaneous radial distance of the image in the detector plane.

Claims

1. In a missile, a target detection mechanism having a line-of-sight displacement angle, inclined ahead relative to the longitudinal axis of the missile, with regard to a target object that is to be homed in on and which is projected by way of a collecting optical system into a detector plane, for example in accordance with GB Patent Specification No. GB 2166314, characterised in that an adjusting mechanism is provided for a detector-element readjustment in the detector plane and/or for the successive interrogation of several detector elements.

2. A mechanism as claimed in Claim 1, in which the collecting optical system is arranged offset radially relative to the longitudinal axis of the missile and a deflection optical system is arranged in its ray path in front of the detector plane.

3. A mechanism as claimed in Claim 2, in which the detector plane is orientated parallel to the longitudinal axis of the missile.

4. A mechanism as claimed in Claim 2 or 3, in which the collecting optical system is inclined relative to the longitudinal axis of the missile.

5. A mechanism as claimed in any one of Claims 2 to 4, in which the deflection optical system with respect to the detector plane and the orientation of the collecting optical system has such an inclination that the line-of-sight in the case of a minimum displacement angle is orientated at least approximately parallel to the longitudinal axis of the missile.

6. A mechanism as claimed in any one of the preceding claims, in which in the region of the production of a target object, detected along the instantaneous line-of-sight, onto the detector plane, two mutually overlappingly adjacent detector elements are covered simultaneously.

7. A target detection mechanism as claimed in any one of Claims 2 to 6, in which in the detector plane, and mutually offset peripherally with respect to the longitudinal axis of the missile, several detector elements or pairs of mutually overlapping adjacent detector elements, in each case associated with an optical system, are provided.

8. A mechanism as claimed in any one of the preceding claims, in which the target-object projection rotates in the detector plane relative to the missile about its longitudinal axis.

9. A mechanism as claimed in Claim 8, in which also the optical system, held eccentrically to the longitudinal axis of the missile, rotates relative to the missile about its longitudinal axis.

10. A mechanism as claimed in any one of the preceding claims, in which for the detection of the instantaneous position of the target-object projection into the detector plane the adjusting mechanism is provided with a linear actuator, the position transmitter of which supplies an item of displacement angle information to a signal processing circuit for the issuance of steering commands.

11. A target detection mechanism substantially as herein described and illustrated with reference to FIGURE 1 or FIGURE 2 of the accompanying drawings.