GB2144880A

GB2144880A - A method and device for axis harmonisation of optical instruments which are connected to one another

Info

Publication number: GB2144880A
Application number: GB08420191A
Authority: GB
Inventors: Dr Siegfried Roth
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1983-08-11
Filing date: 1984-08-08
Publication date: 1985-03-13
Also published as: GB2144880B; GB8420191D0; GB8420273D0; DE3328974C1; FR2550631A1

Abstract

In the case of optical instruments 1, 2 which are connected to one another, for example in a housing 3, axis harmonisation is effected by autocollimation by way of a common reflection device, for example by way of a flat reflecting surface 5 which masks the optical entry systems, e.g. lenses 1.5 and 2.5 of all the instruments 1, 2 and reflects luminous marks 1.3 and 2.3 in the individual optical instruments 1, 2. <IMAGE>

Description

SPECIFICATION A method and device for axis harmonisation of optical instruments which are connected to one another This invention relates to a method and a device for axis harmonisation of optical instruments which are connected to one another.

In the case where optical devices are connected to one another, for example in a common housing, and the directions of the respective optical axes relative to one another have to be known, for example where an exact parallel alignment of all the axes is required, in the past a so-called test mark projector was usually used (German Offenlegungsschrift No. 26 31 814 or German Auslegeschrift No. 29 41 627). With the aid of such a test mark projector, a test mark is mirrored into the beam path of the optical devices and the displacement of this test mark from the optical axis of each device is ascertained.

The use of a test mark projector requires a high degree of precision and moreover worsens the performance of the optical devices through the additional mounting of optical elements of the mirroring-in of the test mark.

Further, because of the use of a test mark projector the volume and the mass of the entire device is increased.

The object of the invention is, therefore, to provide a method for axis harmonisation of optical instruments which are connected to one another without the use of a separate test mark projector.

This object is achieved in accordance with the invention by a method wherein the directions of the optical axes of the optical instruments are determined by auto-collimation by way of at least partially reflecting flat surfaces whose position relative to one another is known.

This method is accomplished by a device, which is a further aspect of the invention, wherein each optical instrument has within an image plane at least one mark which radiates in the spectral region of the optical instrument, and in that arranged in front of the entry apertures of the optical instruments is a reflection device for autcollimation which has at least in the region of the entry apertures at least partially reflecting surfaces whose position relative to one another is known.

The autocollimation, provided for in accordance with the invention, is accomplished in that in an optical device a mark located on a plane surface is observably reflected on itself.

To carry out the method, therefore, in each optical device one mark is provided, which radiates in the spectral region of the optical device and is arranged within an image plane of the device. In front of the entry apertures of the optical devices a reflection device having one or more plane surfaces of known position relative to one another, is either fixedly installed or arranged so as to be forwardly-tiltable for the purpose of the autocollimation. Since the autocollimation procedure is sufficiently sensitive to ascertain small changes in direction or inclination, axis harmonisation can be carried out without using a test mark projector.

The invention will be described further, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a schematic view of a first embodiment of a device in accordance with the invention for axis harmonisation of two optical instruments by means of a swingable reflection device; Figure 2 is a partial schematic view of a second embodiment of the device of the invention having a fixedly-instailed reflection device and mirrors for axis harmonisation; and Figure 3 is a partial schematic view of a third embodiment of the device of the invention having a plane front lens and a triple prism for purposes of autocollimation.

In the first embodiment of the device of the invention, as shown in Fig. 1, a thermal image instrument 1 and an optical (visible light) instrument 2 are accommodated together in a housing 3. The optical axes 1.1 and 2.1 of the respective instruments have to be aligned exactly parallel, so that the image centre, appearing on the the detector 1.4, of the thermal image instrument 1 coincides with the image centre observed by way of the eye 4.

For autocollimation respective marks 1.3 and 2.3 are arranged in the thermal image instrument 1 and in the optical (visible light) instrument 2 in the image planes 1.6 and 2.6 respectively of the entry optical systems, e.g.

lenses 1.5 or 2.5 respectively. The mark 1.3 of the thermal image instrument can consist, for example, of a metallic coating which is deposited by evaporation on a plate which is transparent in the infra-red range of the spectrum. The metallic mark then radiates either in a spectral region corresponding to the temperature of the plate, or, in the case of a heated graticule, at the operating temperature. The mark 2.3 of the optical (visible light) instrument can be made observable, for example, by known illumination (not shown in more detail) or by a fluorescing coating.

Both marks 1.3 and 2.3 are on the one hand observable directly either on the detector 1.4 or with the eye 4; on the other hand there arises in the image places 1.6 or 2.6 respectively a further image of the marks produced by reflection of radiation emitted from the marks off a plane reflection layer present in front of the lenses 1.5 or 2.5 respectively. This image, too, appears on the detector 1.4, or is visible with the eye 4. In the event that the optical axes 1.1 and 2.1 are exactly parallel, in both instruments the displacement of the marks which have arisen through reflection from the directly observed marks is the same both with respect to spacing and the angular position. If in the ideal case the reflection plane 5 is perpendicular to the optical axes 1.1 and 2.1, then in both instruments the images of the directly observed and the reflected marks fall upon one another.

When it is necessary to change the alignment of one or more of the optical axes to bring about harmonisation, the instruments 1 or 2 respectively the instruments 1 or 2 respectively can be rotated as a whole by means of adjusting members (not shown) inside the housing 3. Another possibility as shown in Fig. 1 consists of arranging optical elements causing beam deflection, for example a pair of rotating wedges 1.2 or a tiltable plane plant 2.2, in the beam path of the respective instruments.

To produce a reflection layer which is as flat as possible and is arranged in the same position in front of both instruments, the housing 3 has a flat front disc 3.1 which masks both lenses 1.5 and 2.5 and in front of which a covering 6 can be swung. The covering 6 consists of a stiff plate 6.1 and a housing-side soft-elastic coating 6.2, for example foam material. The reflection layer 5, for example a metal foil, is applied to this coating 6.2.

When the covering 6 is swung forward the reflection layer 5 is pressed against the flat front disc 3.1, uniform pressure being assured by virtue of the soft-elastic coating 6.2.

Another way of producing a flat reflection layer is by providing the front disc with a weakly reflecting surface on which the radiation emitted from the marks 1.3 and 2.3 is reflected.

The second embodiment of the device of the invention, as shown in Fig. 2 differs in two fundemental ways from the embodiment of Fig. 1. Firstly the optical elements for the beam deflection inside the instruments consist of tiltable mirrors 1.7 and 2.7 respectively, which are arranged either between the mark 1.3 and the lens 1.5 or in front of the lens 2.5. The individual instruments accommodated in the housing 3 can be of the same type as those in Fig. 1.

The second difference compared to the embodiment of Fig. 1 is that the reflection device 7 for autocollimation does not consist of a single reflecting plane surface, but of a frame 7.1 which is resistant to bending and in which separate parallel front discs 7.2 and 7.3 are provided, one for each instrument 1, 2. This has the advantage that the material of the front discs 7.2, 7.3 can be selected as appropriate for spectral regions of the individual optical instruments. The front discs 7.2 and 7.3 each have a coating 7.4, 7.5 on the side facing the respective lens 1.5, 2.5. The coatings 7.4 and 7.5 respectively are virtually transparent for the spectral region in which the respective optical instrument works and only weakly reflect the radiation of the mark 1.3 or 2.3 respectively, so that the image of the reflected mark is still perceptible for a detector or for the eye respectively.

In the third embodiment of the device, as shown in Fig. 3, two optical instruments 1 and 2 are again accommodated in a common housing 3, as in the previous embodiment.

For the purposes of axis harmonisation, each instrument again has, in the image plane of the respective lens a luminous mark 1.3, 2.3 respectively. For the purpose of autocollimation the front lens of the entry optical system 1.5 has a plane front surface 1.5.1 from which the image of the mark 1.3 is weakly reflected. On the other hand, arranged between the instruments 1 and 2 is a rotatable or swingable triple prism 8. by means of which the image of the mark 2.3 of the instrument 2 is similarly directed onto the plane surface 1.5.1 of the front lens 1.5 and is reflected back from there. Autocollimation of both instruments 1 and 2 is thus effected by way of the reflecting plane surface 1.5.1.

The triple prism 8 is sO arranged that it can be swung out of the beam path of the instruments 1 and 2 of the latter. For correction of the optical axes tiltable flat plates 2.2. are provided.

If opto-electronic detectors are used in the individual optical instruments, the optical elements for beam deflection or adjusting members for shifting of the individual instrument can be dispensed with since the displacement error of the marks for autocollimation is detected in an electronic manner and is used for correction of the optical axis, for example by shifting the electronically produced image.

Furthermore, axis harmonisation can also be achieved in that the marks themselves are shifted perpendicularly to the beam path of the optical instrument until the images of the directly observed and the reflected mark are either in register or in all the instruments have the same displacement values.

Also in the case of embodiments similar to those shown in Figs. 2 and 3 it is advantageous, during axis harmonisation, to mask or to darken the entry apertures of the individual instruments, in order to improve the contrast conditions for observation of the marks.

Furthermore it is possible, by comparison of the position of the images of the directly observed and of the reflected mark, to define the optical centre and thus the direction of the optical axis and to place a further mark there.

Claims

1. A method for axis harmonisation of optical instruments which are connected to one another, characterised in that the direc tions of the optical axes of the optical instruments are determined by autocollimation by way of at least partially reflecting flat surfaces whose position relative to one another is known.

2. A method as claimed in claim 1, characterised in that the autocollimation is effected by way of at least partially reflecting flat surfaces which lie in one plane.

3. A method as claimed in claim 1 or 2, characterised in that the axis harmonisation of at least two optical instruments is effected by autocollimation by way of a common flat surface.

4. A method as claimed in-claim 1, 2 or 3, characterised in that a change in direction of the optical axis of at least one optical instrument is effected by mechanical variation of the position of the optical instrument as a function of the result of autocollimation.

5. A method as claimed in any preceding claim, characterised in that the direction of the optical axis of at least one optical instrument is varied by means of at least one optical element disposed in the beam path of the optical instrument as a function of the result of autocollimation.

6. A method as claimed in any preceding claim, characterised in that the change in direction of the optical axis of at least one optical instrument by shifting a mark, arranged in a focal plane, perpendicularly to the beam path as a function of the result of autocollimation.

7. A method as claimed in any preceding claim, characterised in that inside at least one optical instrument by comparison of the position of the images of the directly contemplated and reflected mark a further marle is set which defines the direction of the optical axis.

8. A device for carrying out the method as claimed in any of claims 1 to 7, characterised in that each optical instrument has within a focal plane at least one mark which radiates in the spectral region of the optical instrument, and in that arranged in front of the entry apertures of the optical instruments is a reflection device for autocollimation which has at least in the region of the entry apertures at least partially reflecting surfaces whose position relative to one another is known.

9. A device as claimed in claim 8, characterised in that the reflection device has a flat and at least partially reflecting surface which covers all the entry apertures.

10. A device as claimed in claim 8 or 9, characterised in that the reflection device is a disc common to all the optical instruments.

11. A device as claimed in claim 8 or 9, characterised in that the reflection device has a frame which is resistant to bending carrying individual front discs which are parallel to one another and are associated with the spectral regions of the respective optical instruments.

1 2. A device as claimed in claim 8, characterised in that the front surface of the entry lens of at least one optical instrument is flat and has a degree of reflection which is adequate for autocollimation or in that arranged in front of the entry optical system of an optical instrument Is an at least partially reflecting flat surface, in that all the optical instruments have in a focal plane a mark and in that arranged in front of the optical instruments is at least one triple prism for autocollimation by way of the plane front surface of the entry lens or by way of the reflecting plane surface of at least one optical instrument.

1 3. A device as claimed in any of claims 9 to 11, characterised in that at least one surface of the front disc is coated in such a way that the marks are sufficiently reflected for autocollimation.

14. A device as claimed in any of claims 8 to 13, characterised in that the entry apertures of the optical instruments can be darkened by at least one covering.

1 5. A device as claimed in claim 14, characterised by a covering which jointly masks the entry apertures of the optical instruments and the inside of which is flat and has a reflection layer.

16. A device as claimed in claim 15, characterised in that the reflection layer is arranged on an elastic substrate of the covering and is pressed by operation of the covering against a front disc masking the optical instruments or against flat front surfaces of the entry lenses of the optical instruments.

1 7. A device as claimed in any of claims 8 to 16, characterised in that arranged in the beam path of at least one optical instrument is at least one optical element for beam deflection.

18. A device as claimed in claim 1 7, characterised in that the optical element is a tiltable mirror.

1 9. A device as claimed in claim 17, characterised in that the optical element is a tiltable flat plate.

20. A device as claimed in claim 17, characterised in that the optical element is a pair of rotatable wedges.

21. A device as claimed in any of claims 1 to 20, characterised in that the mark is displaceable perpendicularly to the beam path of the optical device.

22. A device as claimed in any of claims 10 to 21, characterised in that at least one optical instrument has adjusting members for the positional change.

23. A method for axis harmonisation of optical instruments which are connected to one another substantially as hereinbefore described with reference to the accompanying drawings.

24. A device for carrying out the method as claimed in any of claims 1 to 8 substantially as hereinbefore described with reference to and as illustrated in Fig. 1, or Fig. 2, or Fig. 3 of the accompanying drawing.