GB1580836A

GB1580836A - Apparatus for automatically harmonising a plurality of instruments

Info

Publication number: GB1580836A
Application number: GB2294377A
Authority: GB
Original assignee: Eltro GmbH and Co
Current assignee: Eltro GmbH and Co
Priority date: 1976-06-04
Filing date: 1977-05-31
Publication date: 1980-12-03
Also published as: FR2353871B1; FR2353871A1

Description

(54) APPARATUS FOR AUTOMATICALLY HARMONISING A PLURALITY OF INSTRUMENTS (71) We, ELTRO G.M.B.H. GESELL SCHAFT FUR STRAHLUNGS TECHNIK, a German limited liability company, of 6900 Heidelberg 1, Kurpfalzring 106, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to an apparatus for automatically harmonising a plurality of instruments operating in different wavelength ranges and coupled to one another mechanically by adjustable support means.

It is known for example from German Auslegeschrift No. 23 22 017 that a slight mark projector can be used for axial harmonisation. Furthermore, Application P 2550 941.5 describes sight mark projectors for various wavelengths which can be used for harmonising optoelectonic units within a system. These units are connected rigidly to one another. In this case, harmonisation of the system is effected by manual adjustment of the individual units to the sight mark of the joint sight mark projector or sight mark projection unit.

From the Franco-German "Milan" Weapons system it is furthermore known, by means of the broad-band collimator in the day vision channel and in the infra-red goniometer, to project a simulated aiming spot through the common inlet window, so that the day vision channel and the infrared goniometer can be aligned independently of each other, using a fixed mark in the vision channel and an electrical deviation signal from the goniometer.

Alignment of the two axes with respect to each other is carried out when the aiming spot shown in the centre of the line in the day vision channel no longer produces any electrical deviation signal in the infra-red goniometer. This alignment is performed manually, but checking is possible only by attaching the collimator. Rapid automatic alignment is not needed because axial alignment is maintained, even under the severe environmental conditions of military use, by the rigid structural connection of the two channels; furthermore, routine checking by means of the collimator is carried out only at relatively long intervals.

The invention is based on the problem of automatically aligning the optical axes of two or more opto-electronic instruments working in different wavelength ranges, the instruments being set up as separate units and which can be rapidly and mechanically coupled by special precision support means, e.g. dovetail mountings, the intention being that the accuracy of alignment can be checked as requred.

According to this invention, there is provided an apparatus comprising two or more separate optical instruments mechanically connectable to and detachable from each other and operating in different wavelength ranges, a first one of the instruments having an angle sensing device to provide an electrical signal at its output indicative of the angular deviation of rays incident thereon from the optical axis of the device, and a second instrument having a test mark projector and an image reproduction unit optically coupled to the first instrument, the output of the angle sensing device being connectable to means for displacing the image of the image reproduction unit formed in the first instrument so that an output signal caused by deviation of rays from the test marker projector from the axis of the device gives rise to an adjustment in the position of the said image to compensate for mechanical misalignment of the first and second instruments with respect of each other.

Thus, an add-on opto-electronic unit can be advantageously mounted on an existing opto-electronic unit with a rapidly separable support. This is important in view of the requirements laid down by the Military in respect of weight, speed of assembly and dismantling of such instruments, and also in respect of providing the most rugged possible coupling under severe environmental conditions. The test mark projector, for example, constitutes an auxiliary unit which has to be separately transportable and which, in the case of equipment for infantry use, represents an additional burden for the soldiers if the wish is to carry out an axial alignment check after each change of position. The mechanical mounting of the equipment to be aligned is such as to provide a rough orientation of the individual optical axes.

However, the accuracy of this orientation is such that any fine alignment which may still be necessary to achieve angular adjustments is confined to the milliradian range. The joint mounting panel is, however, on grounds of weight, so constructed that the alignment is not in general maintained when the unit is removed and then refitted; and even if the unit remains fitted, and shock, vibration, or any violent fluctuation in temperature would produce an upset.

It is true that the installation could then be aligned manually with the help of an external test mark projector, but this would be time-consuming. An additional difficulty is that the two units have no common inlet aperture so that the test mark projector has to be constructed for two separately located apertures.

In accordance with the invention, a test mark projector similar to that described in German Application No. P 25 50 941.5, which, for a unit working in the various wavelength ranges, projects test marks through a common diaphragm in the image field of a common catoptric objective, and then through a series of optical elements via the relevant inlet pupil to the optoelectronic instruments which are to be aligned. The test mark projector may be associated with an auxiliary opto-electronic unit which is flanged onto the existing optoelectronic installation. This is because it is often essential that the existing unit is not modified but is merely provided with a means of supporting the auxiliary unit.

However, the test mark projector may also be integrated into the existing unit and an additional apparatus provided to image the test mark into the instrument which is to be flanged on. With regard to automation, it is of advantage for the existing unit to have a day vision channel with a fixed sight mark and a goniometer channel. The two channels are aligned with respect to each other, the goniometer channel being aligned to the central point of the sight mark, the deviation of heat image spots being indicated by cartesian co-ordinates in the image field by electrical signals which can be used directly for processing to achieve automatic alignment.

Also in accordance with the invention, in the case of a first optical unit without a goniometer which is to be mechanically coupled and automatically aligned with a second unit-the test mark projector is integrated into one installation and the goniometer into the other, the latter being mechanically rigidly connected and aligned to one of the axes which are to be aligned. Thus, the goniometer axis is used as a reference axis for alignment purposes. This can be effected if a test mark is depicted at infinity in the test mark projector through a back-illuminated circular aperture and a catoptric objective for all the wavelengths used for the various opto-electronic channels, the parallel beams being fed via optical elements to the relevant opto-electronic channels and depicted via the inlet pupil again as a spot in the particular image plane concerned.

Automatic axial alignment can be brought about by mounting a pair of rotating wedges in the path of parallel rays from the test mark projector, so that by appropriate rotation of the two wedges with respect to each other a defined angular deflection of the emergent beam from the projector is achieved, the axis of rotation coinciding with the projector axis. If the refraction index of the optical wedge material is constant for all optical wavelengths used, then the angular deflection will also be of the same magnitude and the test spots will be displaced by the same image field angle in all the optical channels which are to be aligned. If the wavelength ranges utilised are wide, wavelength dependency of the refraction index in the rotary wedge material may lead to different amounts of angular deflection, in which case, for angular deflection of the projection beam, it is expedient to use instead a plane mirror with a reflective behaviour which is unaffected by wavelength and which is pivotable about two axes at right-angles to each other. The individual projected beams are then fed via spectral dividers and optical deflector systems to the associated optical channels where the test spot is depicted in the respective image planes.

Advantageously, an electric bridge circuit is used for controlling the pair of rotating wedges or for pivoting the plane mirror about its axes of rotation, the bridge being balanced so that the adjusting elements are in their aligning position when the goniometer shows zero deviation, i.e.

when the test spot is in the centre of the coordinates. Therefore the test spot indicates in each individual channel the position of the goniometer axis in the image field, which axis thus constitutes the reference axis for the relevant channel. Due to the mechanical connection of the test mark projector to the optical channel of the auxiliary instrument, any variation in the position of the auxiliary instrument in relation to the existing installation containing the goniometer will result in the test spot moving off the centre of the goniometer co-ordinates, thereby giving rise to electrical deviation signals which lead to a follow-up control of the adjusting element, so that the test spots in the different channels are automatically adjusted to the new reference axis.

It is also possible for the test mark, produced by an illuminated diaphragm, to appear as a circular spot in the spectral range of the goniometer, but as a line or reticule in the other optical channels, the goniometer test spot lying at the point of intersection of the reticule. Then each of the optical channels can, by means of the aligning sight mark, be used as an aiming instrument with the goniometer axis acting as the sighting line. It is possible to check axial harmony if the goniometer test spot is imaged into the relevant sight and is shown at the point of intersection.

If there are no fixed spatial relationships for example between the image plane of the photographic field lens and the monitor of a television system or an electro-ocular, then it may be advantageous in one or more of the optical channels, for the test mark depicted in the objective image plane by the field lens to be capable of being displayed on the screen of the monitor or electro-ocular, this image being viewable via'the optical day vision channel equipped with a fixed or adjustable line mark, and furthermore for mechanical or electrical equipment to be provided so that the image of the monitor or electro-ocular can be so displaced and rotated that the representation of the test mark of the first channel coincides with a clearly defined position in respect of the sight mark of the day vision channel.

The electro-ocular and the test mark projector are preferably mechanically rigidly coupled to each other and for the pupil of the optical positioning element to be sufficiently large that with automatic alignment, the beams of test mark and screen image are refracted by the same angle.

It can also be expedient, after automatic axial alignment, to pivot a masking diaphragm into the path of the test mark projector beam so that the test mark disappears and the installation is free for observation and aiming purposes. In this connection, it is also important to provide the facility whereby at any time the alignment of the combined installation can be checked by observing the position of the test mark in respect of the fixed line mark by manual or automatic pivoting of the diaphragm.

Ideally, the rotating wedge prism unit is rigidly connected to the test mark projector and the electro-ocular. However, if a deflecting prism is required which is independent of the position of this prism unit and therefore also of the test mark projector, then a prism unit constructed as a triple speculum may be used.

It is desirable that a heat image produced by the auxiliary unit and imaged into the inlet pupil of the existing instrument should be depicted by a similarly provided image reproduction system and observed by a common ocular.

In use of the apparatus in accordance with the invention, the test mark projector is switched on and the deviation information, which arises in the form of electrical signals, is supplied by means of a goniometer, or a goniometer and a quadrant receiver, whereupon the electrical signals are converted into proportional voltages, stored, and called forward for proportional and positionallyaccurate displacement of the screen image, the test mark projector being switched off once displacement is completed. In this way, the image of that instrument with which the storage unit is associated can be rapidly and easily aligned onto the axis of the goniometer and the accuracy of the aligned picture checked.

An advantageous further development of the invention provides for a heat image scene which can be imaged into at least one inlet pupil of the existing unit to be depicted via an image reproduction system together with a test spot corresponding to the wavelength range of this heat image scene and to be observed through a common ocular, and in that furthermore the goniometer test spot needed for automatic harmonisation is likewise imaged into the inlet pupil of the instrument, being then processed by the goniometer, the deviation of the test spot from the goniometer axis being fed into a storage unit via an electronic co-ordinates evaluator. In this way, the test spot representing the radiated heat and produced by the test mark projector, e.g. in the 10 ,um wavelength range, is reproduced in the heat image scene which is jointly imaged into the installation and depicted via the day display channel, in the same plane as the cross hairs. Since the aiming axis (day display channel) and the goniometer axis are rigidly aligned in the existing installation, the now visible heat test spot appears in the centre of the cross hairs following automatic displacement of the scene reproduced, by reason of the deviation signals from the goniometer. This test spot, which can also be switched on separately from the axial harmonising system for checking purposes, indicates that harmonisation is completed.

In addition, however, an advantageous further development of the invention also resides in the fact that a heat test spot, converted into an equi-positional test spot radiated in the spectral range of the goniometer, is fed into the goniometer to produce the electrical deviation signals, and by means of the corresponding deviation voltages, the screen image of an image reproduction unit which is constructed as an electro-ocular is correspondingly displaced until such time as the heat test spot lies on the goniometer axis and thus exhibits "zero" deviation.

The conversion of a heat test spot generated for example in the wavelength range of 10 ,um, into a test spot of equal position having a wavelength of, for example, 2.2 ,um, may be carried out by means of a radiant layer provided in the image tube of the electro-ocular to emit radiation in the spectral range of the goniometer, the test spot produced by the test mark projector being fed to the goniometer through deflecting and beam dividing optical elements. The transmission of the ascertained deviation signals may be effected via a plug-in connection made by connecting leads between the electronic co-ordinates evaluator and the storage unit.

The beam dividing optical element which transmits both the heat image scene and the goniometer test spot may be disposed in front of the inlet pupil of the existing installation. This has the advantage that a day locating system can also be used for daytime observation with a heat image instrument mounted on it.

An advantageous further development of the invention provides for the goniometer test spot imaged into individual optoelectronic channels to be faded in and out by means of a pivotable filter. Whereas the imaging facility makes it possible to check the alignment as such, the fading out prevents any interference in the guidance of a tracked flying object.

For conformity of the position of heat image scene and goniometer axis, it is from the structural point of view desirable for the goniometer to be integrated into the daytime locating system containing the day display channel and for the test mark projector, the image reproduction unit and the storage unit to be component parts of a night-time display unit containing the heat image device. Since the goniometer axis represents a reference axis for all the other optical axes, alignment of the heat image scene with this axis ensures that the latter also coincides with the other optical axes.

In accordance with the invention, the image reproduction unit may comprise an electro-ocular or image-reproducing matrix, a deflecting prism, and a projection lens, the matrix having at least one light-emitting diode, a plasma, liquid crystals or an optical display unit to reproduce the heat image.

Preferably, the image reproduction unit, the test mark projector and a prism system mounted in front of the latter are coupled to one another in an aligned arrangement and are grouped together as one harmonising unit.

Should there happen to be an alteration of the optical axes of the installation in respect of the harmonising unit, then the now visible test spot of the test mark projector, in other words the heat test spot, is no longer in the centre of the cross hairs of the installation. The test spot reproduced with the heat image scene can then, by displacement or rotation of the scene in the X-Y co-ordinates, be made to coincide with the cross hairs by the use of existing controls. This is effected in that the heat test spot can be manually or automatically adjusted by means of the goniometer deviation signals, and in fact after automatic harmonisation. This is most easily achieved by mechanical and/or electrical means provided on the heat image instrument. On the other hand, it is also possible for the image of the image reproduction unit with the heat test spot to be adjustable in relation to the cross hairs provided in the day display channel, by means of the quadrant receiver which produces the deviation voltages and which is rigidly mounted in the middle of the image plane of the day display channel. The deviation voltages arise in that there is a deviation of the now visible heat test spot in respect of the quadrant receiver and thus also in respect of the cross hairs. In this case, too, the deviation voltages are again processed true-to-scale, stored, and used for displacing the image of the image reproduction unit. The quadrant receiver can, still within the day display channel, be rigidly mounted in the image plane. It is also possible for the quadrant receiver to be rigidly mounted either on the image screen of a display tube and for this in turn to be rigidly mounted on the image plane of the cross hairs, or alternatively for the quadrant receiver to be rigidly mounted in an image plane reflected on a beam divider prism.

This latter possibility has the advantage that the image plane, which otherwise is the same in all three embodiments, can be rotated via the beam divider prism.

The invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a diagrammatic section of a locating system with day vision channel and infra-red goniometer together with an attached night vision instrument with heat image channel, electro-ocular, test mark projector and heat image receiver; Figure 2 is a diagram showing the automatic harmonising process Figure 3a and Figure 3b are diagrammatic views of the test mark projector with an optical adjustment unit and an integrated electro-ocular; and Figure 4 is a view similar to Figure 1 of another embodiment.

Referring to Figures 1 to 3b, a night display unit 4 with a heat image channel 9 (in other words a heat image unit) is mounted on a locating system 1 having a day display channel 2 and an infra-red goniometer 3. The heat image now serves for aiming at night, the heat image scene depicted on the electro-ocular 6 being imaged into the day display channel 2 of the existing daytime locating system 1. A difficulty occurs in that there. is no spatial relationship of any kind between the heat image shown on the electro-ocular 6 and the image field of the heat image objective 5 which is to be scanned by infra-red detectors.

According to Figure 1, the night display unit 4 is mounted on the day locating system I by support means (not shown). By reason of the design of the support means, a rough adjustment of heat image axis 9 and goniometer axis 10 is achieved, the latter being already fully aligned with the axis of the day display channel 2. In order to align the attached night display unit 4 in relation to the day locating system 1, the two flaps 11 are closed. A test spot is projected into the image plane of the infra-red goniometer 3 by the test mark projector 7 via the deflecting mirror 8, the spectral divider 12 and the beam dividing prism 13. If there is a deviation of the test spot from the goniometer axis 10, the co-ordinate evaluating electronic unit 14 provides cartesian deviation signals which, through a plug connection 15 and a conductor 16, are used for controlling a positioning motor 17 which in turn, through a mechanism 18, rotates two optical rotating wedges 19 until the test spot lies on the goniometer axis and the deviation voltage becomes zero. Via the wedges 19, the different beams from the test mark projector 7 for night display unit 4 and goniometer 3 are simultaneously deflected in the same direction and by the same angle. Via the spectral divider 22, which allows the test mark projector beam in the goniometer wavelength range to pass and reflects the beam in the heat image range, and also via the deflecting prism 23 and the heat image optical system 5, the test spot is projected onto the detector 24 and processed by the electronic camera system 25 and is indicated on the electro-ocular 6.

This imaged test spot represents the point of intersection of the goniometer axis 10 and the heat image plane. The screen image of the electro-ocular 6 is displaced in the same direction as the other test marks by the wedges 19 and can be observed via the day display channel 2 and the pentagonal ridge prism 26 in the eyepiece 27. A fixed day sight mark or reticule 28 appears in the eyepiece image plane and marks the point of coincidence of the goniometer axis 10 with the day vision channel 2.

After automatic adjustment of the test spot to coincide with the goniometer axis 10, there is initially no definite connection between the heat image in the image plane of the objective 5 and the electronically generated picture on the electro-ocular 6.

The common linking element is the imagedin test mark which, in the aligned condition, constitutes the goniometer axis 10. The heat image of the electro-ocular 6 is depicted in the image plane of the ocular 27 together with the day reticule. After alignment, the heat test point will not in general coincide with the point of intersection of the reticule and may be displaced via the electronic camera unit and in the x- and y-directions until such time as the test mark spot appears at the point of intersection of the reticule. Only then is there complete harmony between day channel 2, night channel 9 and goniometer channel 10, so that the test mark projector 7 can be switched off once the rotating wedge position is interlocked in respect of the adjustable deflecting mirror.

For aiming and firing at night, the flaps 11 are opened. The light radiated by the tracer composition of a rocket for example enters the goniometer 3 via the window 29 and the spectral divider 12 with about 90nun transmission and 10% reflection. The window 30 is transparent to heat rays entering the night display unit 4. According to requirement, before every shot or after every change of position, it is possible to check the automatic axial alignment by closing the flaps 11 and switching on the test mark projector 7, the deviation voltage of the goniometer being checked and used for fine adjustment. If during checking the heat test point appears at the point of intersection of the reticule, then there is optimum harmonisation in the system.

Deviations must again be compensated by image displacement.

As already mentioned, instead of a heat test spot it is also possible to produce a heat reticule identical to the day reticule in the test mark projector 7, which must then be made to coincide with the latter. This test mark has the advantage that even tilting of the night display unit in respect of the day locating system can be indicated and overcome, although such tilting plays only a subsidiary part in the vicinity of the aiming line.

Fig. 2 once again shows the harmonising process but in a simple diagrammatic form.

Of great importance is the fact that electroocular 6 and test mark projector 7 form one mechanically stable unit. The potentiometers 32 and 33 allow manual adjustment of the heat image in respect of the eyepiece image plane.

The rigid connection between test mark projector 7 and electro-ocular 6 is shown diagrammatically in Fig. 3, as part of the system for introducing the heat image and the test mark into the day locating system 1.

The test mark projector 7 consists of a wide band collimator 34, in the focal plane of which there is a test mark in the form of a diaphragm 35 which is illuminated from the back by a source of light 36, this light source 36 emitting a beam in all the relevant wavelength ranges from the visible range to the heat radiation range of around 10 Mm wavelength. The size of the two rotating wedges 19 is such that both the rays from the electro-ocular 6 which are deflected via the prism 37 and which the lens 38 converts into a parallel beam of rays, and also the rays from the test mark projector 7, are refracted to the same degree. By reason of the spectral divider layer 22 in the prism system 39, the test mark beam 20 for the heat image unit is reflected upwardly while the shorter wavelength rays 21 from the electro-ocular 6 are combined with the projector rays 44 for the goniometer in the prism 40 at the spectral divider layer 41 and, via the pentagonal prism 42 with the ray divider layer 12, introduced into the day locating system. During operation, a diaphragm 43, which can be pivoted in the direction of the double-headed arrow 45, fades out the test mark beam of the range finder and vision channels or switches off the light source 36.

Referring now to Figure 4, a night display unit 4 with a heat image channel 9, in other words a heat image instrument, is mounted on the locating system 1 with its day display channel 2 and the infra-red goniometer 3.

The heat image unit is used for aiming operations at night, the heat image scene shown on its image reproduction unit 6 being reflected into the day display channel 2 of the day locating system 1.

Referring to Fig. 4, the night display unit 4 is mounted on the daytime locating system 1 by means of a support. By reason of the design of the support, explained above, rough alignment of the goniometer axis 10 and the heat image axis 9 is achieved, the goniometer axis being already fully aligned with the axis of the day display channel 2. For aligning the mounted night display unit 4 with respect to the day locating system 1, the flaps 11 which are pivotable in the direction of the doubleheaded arrows shown in the drawing and associated with the two outwardly directed windows 29 and 30 are closed. The test mark projector 7, via the deflector mirror 8, the pivotably mounted spectral divider 12 and the beam divider prism 13, produces a test spot (generated for example in the 2.2 pin wavelength range) in the image plane of the infra-red goniometer 3. If there is a deviation of the test spot from the goniometer axis 10, the electronic coordinates evaluator 14 delivers cartesian deviation signals which, via the plug-in connection 15 and the line 16, are converted in the memory unit 47 to proportional voltages these being stored until a fresh alignment process is begun.

When alignment is required the screen image, including the test spot image, of the image reproduction unit 6, which in this case is constructed as an electro-ocular, is displaced according to the said voltages. If, for example by reason of external influences, there is any change in the relationship between the axial alignment unit 50 and the heat image axis 9, then the scene reproduced is corrected. In such a case, the quadrant receiver 18' may be mounted, in a manner not shown in the drawings, directly in the image plane 19' of the day display channel 2, or on the image screen of an image reproduction tube which is rigidly connected to the image plane 19' of the cross hairs 28, or-as a third possibility-in axis 10 delivering via the electronic evaluator 14 cartesian deviation signals which are likewise, via the plug-in connection 15, the line 16 and the storage unit 47, used for following-up the screen image on the electro-ocular 6, the screen image being displaced until such time as the converted test spot lies on the goniometer axis 10 and the deviation voltage is "nil".

A further method of correcting the screen image when there is a change within the optical axis of the heat image installation, is manual adjustment via potentiometers 32 and 33. Once this correction, necessitated by reason of a deviation between the harmonising unit 50 and the heat image axis 9 has been carried out, the new position of the reproduced scene is stored and as such becomes a starting position for subsequent harmonising processes.

Through the spectral divider 22 which allows through the test mark projector beam in the range finder wavelength range and reflects it in the heat image range and through the deflector prism 23 and the image-forming lens 5 for the heat image scene, the test spot produced by the test mark projector 7 is displayed on the detector 24 and processed via the electronic camera unit 25 and is also indicated on the image reproduction unit 6.

The image on the image reproduction unit 6 is displaced according to the electrical deviation signals produced by the goniometer 3, and can be observed through the day display channel 2 and the pentagonal ridge prism 26 in the eyepiece 27. Rigidly mounted in the eyepiece image plane are the cross hairs 28, also referred to as the daytime reticule, the point of intersection of which marks the point of intersection of the goniometer axis 10 with the day display channel 2. After the automatic follow-up of the screen image of the image reproduction unit 6 according to the cartesian deviation voltages of the goniometer 3, the now-visible heat test spot is shown in the image plane of the eyepiece 27 and the cross hairs 28. The visible heat test spot will after harmonisation be at the centre of the cross hairs and thus on the goniometer axis 10. Thus there is complete harmony (self-testing arrangement) established between day display channel 2, night display channel 9 and goniometer channel 10 and the fact is indicated, so that the test mark projector 7 can be switched off. For aiming and shooting, the flaps 11 are opened; infra-red tracer composition radiation from a rocket, for example, reaches the goniometer 3 via the window 29, and heat radiation enters the night display unit 4 through the window 30. According to requirement, axial alignment can be checked prior to each shot or after every change of position, by closing the flaps 11, switching on the test mark projector 7 and checking the position of the visible heat test spot in relation to the cross hairs. If there is a deviation of the heat test spot from the centre of the cross hairs, then a fresh axial harmonising process may be actuated. By pivoting in the filter 49, the goniometer test spot can be faded out and the visible heat test spot shown for constant checking of the state of harmony even during the aiming process, and in fact without influencing the controlling of any flying object.

WHAT WE CLAIM IS: 1. Apparatus comprising two or more separate optical instruments mechanically connectable to and detachable from each other and operating in different wavelength ranges, a first one of the instruments having an angle sensing device to provide an electrical signal at its output indicative of the angular deviation of rays incident thereon from the optical axis of the device, and a second instrument having a test mark projector and an image reproduction unit optically coupled to the first instrument, the output of the angle sensing device being connectable to means for displacing the image of the image reproduction unit formed in the first instrument so that an output signal caused by deviation of rays from the test mark projector from the axis of the device gives rise to an adjustment in the position of the said image to compensate for mechanical misalignment of the first and second instruments with respect to each other.

2. Apparatus according to claim 1 wherein the first instrument constitutes a locating system having a visual display channel including a viewing eyepiece, and an infrared goniometer, both the display channel and the goniometer sharing a common objective; and wherein the second instrument constitutes a night display unit which is operable to receive heat rays via a second objective and which is detachably mounted on the first instrument to project a heat image, converted to a visible wavelength by the image reproduction unit, into the first instrument via the said common objective.

3. Apparatus according to claim 2 wherein the second instrument includes a triple speculum prism for directing visible radiation from the image reproduction unit to the objective of the first instrument.

4. Apparatus according to claim 2 or claim 3 wherein the first instrument has a viewing eyepiece which is operable to form an image either from visible rays received at the common objective directly from an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. axis 10 delivering via the electronic evaluator 14 cartesian deviation signals which are likewise, via the plug-in connection 15, the line 16 and the storage unit 47, used for following-up the screen image on the electro-ocular 6, the screen image being displaced until such time as the converted test spot lies on the goniometer axis 10 and the deviation voltage is "nil". A further method of correcting the screen image when there is a change within the optical axis of the heat image installation, is manual adjustment via potentiometers 32 and 33. Once this correction, necessitated by reason of a deviation between the harmonising unit 50 and the heat image axis 9 has been carried out, the new position of the reproduced scene is stored and as such becomes a starting position for subsequent harmonising processes. Through the spectral divider 22 which allows through the test mark projector beam in the range finder wavelength range and reflects it in the heat image range and through the deflector prism 23 and the image-forming lens 5 for the heat image scene, the test spot produced by the test mark projector 7 is displayed on the detector 24 and processed via the electronic camera unit 25 and is also indicated on the image reproduction unit 6. The image on the image reproduction unit 6 is displaced according to the electrical deviation signals produced by the goniometer 3, and can be observed through the day display channel 2 and the pentagonal ridge prism 26 in the eyepiece 27. Rigidly mounted in the eyepiece image plane are the cross hairs 28, also referred to as the daytime reticule, the point of intersection of which marks the point of intersection of the goniometer axis 10 with the day display channel 2. After the automatic follow-up of the screen image of the image reproduction unit 6 according to the cartesian deviation voltages of the goniometer 3, the now-visible heat test spot is shown in the image plane of the eyepiece 27 and the cross hairs 28. The visible heat test spot will after harmonisation be at the centre of the cross hairs and thus on the goniometer axis 10. Thus there is complete harmony (self-testing arrangement) established between day display channel 2, night display channel 9 and goniometer channel 10 and the fact is indicated, so that the test mark projector 7 can be switched off. For aiming and shooting, the flaps 11 are opened; infra-red tracer composition radiation from a rocket, for example, reaches the goniometer 3 via the window 29, and heat radiation enters the night display unit 4 through the window 30. According to requirement, axial alignment can be checked prior to each shot or after every change of position, by closing the flaps 11, switching on the test mark projector 7 and checking the position of the visible heat test spot in relation to the cross hairs. If there is a deviation of the heat test spot from the centre of the cross hairs, then a fresh axial harmonising process may be actuated. By pivoting in the filter 49, the goniometer test spot can be faded out and the visible heat test spot shown for constant checking of the state of harmony even during the aiming process, and in fact without influencing the controlling of any flying object. WHAT WE CLAIM IS:

1. Apparatus comprising two or more separate optical instruments mechanically connectable to and detachable from each other and operating in different wavelength ranges, a first one of the instruments having an angle sensing device to provide an electrical signal at its output indicative of the angular deviation of rays incident thereon from the optical axis of the device, and a second instrument having a test mark projector and an image reproduction unit optically coupled to the first instrument, the output of the angle sensing device being connectable to means for displacing the image of the image reproduction unit formed in the first instrument so that an output signal caused by deviation of rays from the test mark projector from the axis of the device gives rise to an adjustment in the position of the said image to compensate for mechanical misalignment of the first and second instruments with respect to each other.

observed scene, or from visible rays received at the common objective from the image reproduction unit.

5. Apparatus according to any of claims 2 to 4, wherein the goniometer has an output which is connectable to a guided missile control system.

6. Apparatus according to any of claims 2 to 5 wherein the test mark projector is operable to project an infra-red beam which is received by the goniometer and, via the image reproduction unit, in the eyepiece as a test mark in the form of a circular spot.

7. Apparatus according to any of claims 2 to 5 wherein the test mark projector includes an illuminated diaphragm and wherein the test mark is a circular spot for the goniometer spectral range and a line or reticule for the other optical channels, its dimensions and form coinciding with those of a fixed line or a line produced by the test mark projector in one or more of the other opto-electronic channels, the test spot of the goniometer channel being represented in the centre of the line mark.

8. Apparatus according to any of claims 2 to 7, wherein the test mark projector is arranged to project a test mark into a heat radiation receiver in the second instrument, the receiver being connected to the image reproduction unit so that a visible test mark is projected into the optical day display channel which is equipped with a fixed or adjustable line mark, and wherein mechanical or electrical devices are provided by means of which the image on the image reproduction unit is displaceable and rotatable to cause the image of the test mark produced in the day display channel to coincide with a defined position with respect to the reticule of the said channel.

9. Apparatus according to any of claims 2 to 8 wherein, after automatic axial alignment of the two instruments, pivoting of a diaphragm into the path of rays from the test mark projector causes the test mark in the aligned optical channels to disappear so that the apparatus is free for observation and aiming.

10. Apparatus according to claim 9 wherein the state of alignment of the combined instruments can be checked by manual or automatic pivoting of the diaphragm, and by observing the position of the test mark in respect of a fixed line mark.

11. Apparatus according to any preceding claim wherein the projected beam from the test mark projector is displaceable in response to the output signal of the angle sensing device to produce a "zero" deviation output signal, the test mark projector beam thereby forming a reference axis for the optical instruments having sighting axes which are to be aligned.

12. Apparatus according to claim 11 wherein the means for displacing the image of the image reproduction unit and the beam of the test mark projector comprises a pair of rotatable wedge prisms situated in the second instrument.

13. Apparatus according to claim 12 wherein the prisms are motor-driven via an electrical bridge circuit.

14. Apparatus according to claim 11 wherein the means for displacing the image of the image reproduction unit and the beam of the test mark projector comprises a plane mirror which is independently pivotable about perpendicular axes.

15. Apparatus according to claim 12 or claim 13 wherein the image reproduction unit and the test mark projector are rigidly coupled together, and wherein the wedge prism are of sufficient size that during automatic alignment of the two instuments, radiation from the test mark projector is refracted by the same angle as radiation from the image reproduction unit.

16. Apparatus according to claim I or claim 2 wherein the image reproduction unit includes a screen upon which, in use of the device, a visible image is produced, the position of the image on the screen being adjustable in accordance with the output signal of the angle sensing device.

17. Apparatus according to claim 1 or claim 2 wherein the image reproduction unit is adjustably mounted in the second instrument, the position of the unit being variable in accordance with the output signal of the angle-sensing unit to displace the position of the image of the image reproduction unit formed in the first instrument.

18. Apparatus according to any of claims 1, 2, 16 or 17, wherein the test mark projector is rigidly mounted in the second instrument.

19. Apparatus according to any of claims 16 to 18 including a memory unit for storing deviation valucs derived from output signals of the angle sensing device.

20. A method of aligning two or more optical instruments in the apparatus of any preceding claim, wherein alignment is carried out by switching on the test mark projector to produce deviation signals at the output of the angle sensing device, and, in response to said signals, automatically shifting the image produced in an image reproduction unit to compensate for the mechanical misalignment of the instruments.

21. A method of operating apparatus according to claim 1 or claim 2, including the steps of: (i) receiving heat radiation from a viewed scene together with heat radiation from the test mark projector; (ii) depicting heat images of the scene and of a test mark produced by the test mark projector in the image reproduction unit; (iii) directing radiation from the image reproduction unit via an objective of the first instrument into an eyepiece of the first instrument to produce a visible image of the scene and of the test mark; (iv) directing radiation in the wavelength range of the angle sensing device into the angle sensing device from the second instrument via the same objective to produce a second test mark image; (v) sensing the deviation of the second test mark image from the axis of the angle sensing device and producing an output signal corresponding to the deviation; (vi) feeding the output signal to a memory device via an electronic coordinates evaluator.

22. A method according to claim 20, wherein a heat test mark is converted into an equi-positional test mark radiating in the spectral range of the angle sensing device, and is fed into the angle sensing device to produce the electrical deviation signals, and wherein, by means of the corresponding deviation voltages, the image produced in the image reproduction unit is displaced until such time as the heat test mark lies on the axis at "zero" deviation.

23. A method according to claim 22, wherein conversion of the test mark occurs by means of a layer provided in an image tube in the image reproduction unit, the said layer being caused to radiate in the spectral range of the angle sensing device, and radiation from the said layer being fed to the angle sensing device via reflecting and beam-dividing optical elements, transmission of the ascertained deviation being effected via an electrical connection between an electronic coordinates evaluation unit and an electronic memory.

24. Apparatus according to any of claims 1 to 19 including a beam deflecting optical element for directing radiation from the second instrument to the optical intake of the first instrument, the beam deflecting element being pivotable to cut-off the said radiation.

25. Apparatus according to any of claims 1 to 19 including a pivotable filter for changing the intensity of radiation forming a test mark image.

26. Apparatus according to any of claims 1 to 19 wherein, in the direction of the rays passing through it, the image reproduction unit comprises an image reproducing matrix, a deflecting prism and a projection lens.

27. Apparatus according to claim 26 wherein the image reproducing matrix comprises at least a light emitting diode, a plasma, liquid crystals or an optical display unit for reproducing the heat image.

28. Apparatus according to any of claims 1 to 19, and 24 to 27, wherein the image reproduction unit and the test mark projector are coupled in aligned relationship and are grouped together into an aligning unit.

29. Apparatus according to any of claims I to 19, wherein a heat test mark image produced in the image reproduction unit is adjustable following alignment by the angle sensing device deviation signals.

30. Apparatus according to claim 29 wherein the heat test mark is adjustable by mechanical and/or electrical means in a heat image receiver.

31. Apparatus according to claim 29 wherein the image of the image reproduction unit, including the heat test mark, is adjustable with respect to cross hairs provided in a viewing channel of the first instrument by means of a quadrant receiver which is rigidly mounted in the centre of the image plane of the viewing channel and which is dperable to generate deviation voltages for adjustment of the heat image position.

32. Apparatus according to claim 31 wherein the quadrant receiver is mounted rigidly in the image plane.

33. Apparatus according to claim 31 wherein the quadrant receiver is rigidly mounted on the image screen of a second image reproduction tube rigidly mounted in the image plane of the viewing channel reticule.

34. Apparatus according to claim 31 wherein the quadrant receiver is rigidly mounted in an image plane reflected on a beam divider prism.

35. Apparatus comprising two or more interconnectable optical instruments, the apparatus being constructed and arranged substantially as herein described and shown in the accompanying drawings.

36. A method of aligning interconnectable optical instruments, the method being substantially as herein described with reference to the drawings.