GB1600191A

GB1600191A - Electrooptical range finders

Info

Publication number: GB1600191A
Application number: GB12377/78A
Authority: GB
Original assignee: Siemens Corp
Current assignee: Siemens Corp
Priority date: 1977-03-31
Filing date: 1978-03-30
Publication date: 1981-10-14
Also published as: NO145490C; DE2714412B2; SE7803542L; FR2386052A1; FR2386052B1; NO781094L; BE865577A; CH628994A5; LU79330A1; DE2714412A1; NO145490B; NL7803484A; IT1093954B; IT7821758A0; DE2714412C3

Abstract

To integrate a laser rangefinder (5, 7) operating in the IR range into a binocular telescope operating in the visible spectral range, the rangefinder is largely coaxially inserted into the beam path of a telescope branch, the optical sight and laser receiver (7) axes always being identical independently of the position of the inserted frequency-selective beam combination cubes (9, 11) and the laser transmitter beam being inserted in parallel but slightly off-centre. The target marker (18) is inserted into one telescope branch by means of a triple prism (10) which is provided at the beam combination cube (9) arranged in the telescope branch. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRO-OPTICAL RANGE FINDERS (71) We, SIEMENS AKTIENGESELLS CHAFT, a German Company of Berlin and Munich, German Federal Republic, 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 electro-optical range finders of the type combining an optical telescope or binocular viewing system together with a transmitter of electro-magnetic radiation within that part of the spectrum obeying optical laws, in particular a laser, and a receiver for said radiation. As in the case of many range finder systems, the optical viewing system may be a binocular device to facilitate the range-finding function.Irrespective of the relevant functioning principle, apparatus of this type, used for guidance range-finding or locating purposes, generally has a serviceability that is dependent upon whether such systems have adequate practicable adjustment facilities, with the requisite high degree of accuracy, and it will be assumed that the known means for such adjustment is provided, adequate to ensure that any axial error angle between the transmitting, receiving and the viewing optical systems is of a degree permissible for laser range finders over large distances, e.g. not more than +0.1 mrad.

One object of the present invention to provide an improved construction for such viewing or sighting systems in which the adjustment facilities provided to ensure a high degree of accuracy and a good directional stability need only be effected with respect to an advantageous configuration of optical axes, such that mechanical and thermal environmental influences have substantially no adverse effects.

The invention consists in an electro-optical range finder in which an optical viewing system is incorporated with a transmitter of electro-magnetic radiation within that part of the spectrum obeying optical laws, and an opto-electrical receiver for detecting reflected energy from said transmitted radiation, said receiver having an optical axis coupled via a first beam-splitter into the or an axis of said optical viewing system in such manner that said viewing system optical axis and the optical axis of any received reflected energy are coaxial, said transmitter supplying an output beam normal to the receiver optical axis, which beam is deflected to a direction parallel to that axis and coupled by said first beam splitter on a path substantially co-axial to said viewing system optical axis, a second beam splitter being provided on said receiver optical axis to inject light from a source via a target graticule into the optical axis of the receiver and thence into the viewing system optical axis to be directed to the viewing system eyepiece from a corner reflector prism mounted on said first beam splitter on the receiver optical axis on that side of said beam splitter remote from the receiver.

In a preferred embodiment constructed in accordance with the invention, the projected graticule and the opto-electrical receiver are substantially coaxially coupled into the beam path of one arm of a binocular sighting system, whilst the transmitted beam of radiation that is coupled in via the first beamsplitter does not run precisely coaxially but is slightly off-centre, in order to ensure that it does not significantly impair the optics of the sighting device. Since all the optical axes are arranged to be spatially combined, and the one arm of the binocular sighting device is advantageously linked to the receiver axis in such manner that the latter must always be identical with the sighting axis, any adjustment of the optical axes can be safely effected with a high degree of accuracy and directional stability.Furthermore, in a device constructed in accordance with the invention the target graticule is arranged in this one arm of the binocular arrangement, so that the target graticule and receiver field stop can be arranged close to one another, and the target graticule is relayed back via a corner reflector which is highly compatible with prismatic beam-splitters.

The construction proposed in accordance with the invention allows an additional module to be integrated into an existing optical device or fire control system in a particularly advantageous manner. In this way, for example, a laser range finder operating in the near IR range can have one of its two substantially parallel aligned beam axes aligned with the axis of a telescope operating in the visible spectral range, thus providing an accurate alignment of the optical axes.

In a particularly preferred embodiment, the beam-splitters are each formed by a respective pair of prisms, which have the property that the optical axes of sighting device and receiver are always identical, regardless of the spatial location of the beamsplitter. That is to say that these optical axes are identical even when the beam dividing reflectipn plane of the first beam splitter has to have its position changed, for example for adjustment of the angle which this reflection plane forms with the optical axis of the receiver or of the sighting device.

To enable the transmitted beam to be input coupled into the sighting device, the first beam divider element expediently consists of two 90 prisms, of which the prism remote from the receiver is longer than that adjacent the receiver. Here it has proved particularly advantageous for the longer prism to exceed the shorter by the diameter of the transmitter outlet pupil but not more than double the length of the shorter prism.

It is also expedient if the beam splitters have mutually inverse transmission characteristics, so that the first beam-splitter reflects radiation entering from the exterior and having a wavelength in the infra-red range, and transmits the visible range, whilst the second beam splitter transmits light in the infra-red range and reflects the visible range.

An advantageous further development consists in that the transmitted beam is observed with an opto-electronic image converter in such manner that the transmitted beam imaged of the remote field and the target mark are simultaneously fed to a second eyepiece of a binocular sighting device.

The invention will now be described with reference to the drawings, in which: Figure 1 is a schematic illustration of one exemplary embodiment constructed in accordance with the invention; and Figure 2 is an explanatory graph.

In the embodiment schematically illustrated in Figure 1, a binocular viewing system (sighting) has eye-pieces 1 and 2, coupled via respective objective lenses 3 and 4 to respective viewing fields. In a viewing device of this kind, for example a telescope or a binocular viewing system forms the sighting device into which a laser range finder is integrated. The viewing system possesses two eye-pieces 1 and 2, and two objectives, 3 and 4, the sighting beam path in the two viewing arms being entered in the drawing as unbroken lines. The viewing system also includes an electro-magnetic radiation transmitter 5 with a transmitting optical system 6 and a receiver 7 with a receiving optical system 22. Means for beam division and deflection are constituted by a first beam-splitter 9, a second beam-splitter 11, a deflecting prism 12, and a third-beamsplitter 13.The first beam-splitter 9 precedes a receiver objective 8 and a viewing objective 3 and consists of two 90 prisms which are combined to form a beam-splitter prism assembly which is arranged in the optical axis of the sighting or viewing system path and is aligned to the optical axis of the receiver, which is substantially normal thereto. Here the first beam-splitter 9 consists of two 90 prisms 9a and 9b, of which the prism 9a remote from the receiver 7 exceeds the length of the prism 9b that is adjacent to the receiver 7 by at least the diameter of the outlet pupils 6a of an optical system 6 provided for the transmitter, and has a maximum length of double that of the shorter prism.The beam-splitter 9 carries on that side 14 of the longer prism 9a remote from the receiver 7 with a corner reflector prism 10 which is aligned with the optical axis of the receiver 7 and has transmission characteristics which cause radiation in the infra-red range entering from the exterior to be reflected and deflected as a received beam to the laser receiver 7, whereas it is transmissive to visible light entering from the exterior so that this radiation reaches the eyepiece 1.

The second beam-splitter 11, which is assigned to the receiver 7, and is arranged on the optical axis thereof, forms an independently utilisable and interchangeable module together with the receiver objective 8, and, in the same way as the first beam-splitter 9, consists of two combined 90 prisms in this case of equal length, but as can be seen from Figure 2, this second beam-splitter possesses a transmission characteristic which is inverse to that of the first beam-splitter 9. i.e. it is transmissive to light in the infra-red range and reflects light in the visible range.

In order to produce mutually inverse transmission characteristics for the two beam-splitters 9 and 11, a respective dichroic filter is arranged in the region of the common connection surface between the two prisms which form each relevant beam-splitter, and on the reflector surface of the longer prism 9a, the frequency-selective properties of said filter being contrived accordingly.The second beam-splitter 11 is provided with a field stop 16 on the side 15 adjacent the receiver 7, and on a side face 17 adjacent an illumination source 19 a graticule 18 is provided, so that the target graticule projection is realised by focussing the target graticule via the target mark illumination means 19, the second beam-splitter 11, (which reflects the target mark into the optical axis of the receiver) the receiver objective 8, and the first beam splitter 9, (from the corner reflector prism 10 of. which the target graticule is is reflected back) and, following reflection in the first beam-splitter 9 and passage through the objective 3, passes via a third beam-splitter 13 into the eyepiece 1 of the viewing system sighting device. The sighting beam received at any instant across the third beam into the eyepiece 1.The third beam-splitter 13 can also be designed with a double prism 20, so that any reflection of the laser-transmitted beam is fed to an opto-electronic image converter 21 in such manner that the transmitted beam reflected from the image field, together with the target graticule projections simultaneously reflected, are fed to a second eyepiece 2. Here the beam dividing plane of the prism 20 is contrived to be such that it is permeable to the infra-red range of the transmitted beam, and to part of the target mark projection beam.

To enable a laser range finder to be integrated into a binocular telescope both the receiver 7 and the transmitter 5 are input coupled by means of the first beam-splitter co-axially into one arm of the viewing system. The transmitted beam, which is initially directed at right angles to the optical axis of the receiver 7, and is entered in dashdotted lines, is deflected by the 90 deflecting prism 12, which is arranged off-centre relative to the optical axis of the receiver 7, between the receiver objective 8 and the second beam-splitter 11, on a path in parallel with the optical axis of the receiver 7, and is reflected by the first beam splitter 9, i.e. by that region of the longer prism 9a which projects beyond the shorter prism 9b, to follow a path substantially in parallel yet offcentre to the axis of the sighting beam.On the other hand, the received beam, which is to be fed to the receiver 7, and which is entered in by broken lines, is coaxially input coupled into the viewing arm so that the receiver axis is identical to the sighting axis.

This safely ensures that a stable adjustment of the three optical axes prevails at all times, e.g. that the transmitted beam. received beam and projected sighting beam all have a common axis following the beam-splitter 9, thus allowing not only for integration of the laser range finder into the viewing system, but also for elimination of any mechanical or thermal environmental influences. Due to the advantageous properties of the beamsplitter prisms 9 and 11, irrespective of the spatial location of the beam splitter 9, the optical axes of the sighting device and of the receiver are always identical, i.e. regardless of the angle formed by the beam-splitting plane of the prism assembly 9 with the optical axis of the receiver and of the sighting device.

WHAT WE CLAIM IS: 1. An electro-optical range-finder in which an optical viewing system is incorporated with a transmitter of electro-magnetic radiation within that part of the spectrum obeying optical-laws, and an opto-electrical receiver for detecting reflected energy from said transmitted radiation, said receiver having an optical axis coupled via a first beamsplitter into the or an axis of said optical viewing system in such manner that said viewing system optical axis and the optical axis of any received reflected energy are coaxial, said transmitter supplying an output beam normal to the receiver optical axis, which beam is deflected to a direction parallel to that axis and coupled by said first beam-splitter on a path substantially co-axial to said viewing system optical axis, a second beam-splitter being provided on said receiver optical axis to inject light from a source via a target graticule into the optical axis of the receiver and thence into the viewing system optical axis to be directed to the viewing system eyepiece from a corner reflector prism mounted on said beam-splitter on the receiver optical axis on that side of said beamsplitter remote from the receiver.

2. A range finder as claimed in Claim 1, in which said optical viewing system is a binocular system with said first beam-splitter in one path thereof.

3. A range finder as claimed in Claim 1 or Claim 2, in which said transmitter is a laser.

4. A range finder as claimed in Claim 3, in which said laser is an infra-red laser.

5. A range finder as claimed in any preceding Claim, in which said first beamsplitter and said second beam-splitter are formed by respective pairs of prisms.

6. A range finder as claimed in Claim 5, in which said first beam-splitter comprises two 90 prisms, that prism remote from said receiver being longer than that prism adjacent the receiver.

7. A range finder as claimed in Claim 6, in which said longer prism exceeds the shorter by at least the diameter of the transmitter outlet pupil but is not more than double the length of the shorter prism.

8. A range finder as claimed in any preceding Claim, in which said second beamsplitter is arranged on the optical axis of the receiver and that face adjacent the receiver is

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. filter being contrived accordingly. The second beam-splitter 11 is provided with a field stop 16 on the side 15 adjacent the receiver 7, and on a side face 17 adjacent an illumination source 19 a graticule 18 is provided, so that the target graticule projection is realised by focussing the target graticule via the target mark illumination means 19, the second beam-splitter 11, (which reflects the target mark into the optical axis of the receiver) the receiver objective 8, and the first beam splitter 9, (from the corner reflector prism 10 of. which the target graticule is is reflected back) and, following reflection in the first beam-splitter 9 and passage through the objective 3, passes via a third beam-splitter 13 into the eyepiece 1 of the viewing system sighting device.The sighting beam received at any instant across the third beam into the eyepiece 1. The third beam-splitter 13 can also be designed with a double prism 20, so that any reflection of the laser-transmitted beam is fed to an opto-electronic image converter 21 in such manner that the transmitted beam reflected from the image field, together with the target graticule projections simultaneously reflected, are fed to a second eyepiece 2. Here the beam dividing plane of the prism 20 is contrived to be such that it is permeable to the infra-red range of the transmitted beam, and to part of the target mark projection beam. To enable a laser range finder to be integrated into a binocular telescope both the receiver 7 and the transmitter 5 are input coupled by means of the first beam-splitter co-axially into one arm of the viewing system. The transmitted beam, which is initially directed at right angles to the optical axis of the receiver 7, and is entered in dashdotted lines, is deflected by the 90 deflecting prism 12, which is arranged off-centre relative to the optical axis of the receiver 7, between the receiver objective 8 and the second beam-splitter 11, on a path in parallel with the optical axis of the receiver 7, and is reflected by the first beam splitter 9, i.e. by that region of the longer prism 9a which projects beyond the shorter prism 9b, to follow a path substantially in parallel yet offcentre to the axis of the sighting beam.On the other hand, the received beam, which is to be fed to the receiver 7, and which is entered in by broken lines, is coaxially input coupled into the viewing arm so that the receiver axis is identical to the sighting axis. This safely ensures that a stable adjustment of the three optical axes prevails at all times, e.g. that the transmitted beam. received beam and projected sighting beam all have a common axis following the beam-splitter 9, thus allowing not only for integration of the laser range finder into the viewing system, but also for elimination of any mechanical or thermal environmental influences. Due to the advantageous properties of the beamsplitter prisms 9 and 11, irrespective of the spatial location of the beam splitter 9, the optical axes of the sighting device and of the receiver are always identical, i.e. regardless of the angle formed by the beam-splitting plane of the prism assembly 9 with the optical axis of the receiver and of the sighting device. WHAT WE CLAIM IS:

1. An electro-optical range-finder in which an optical viewing system is incorporated with a transmitter of electro-magnetic radiation within that part of the spectrum obeying optical-laws, and an opto-electrical receiver for detecting reflected energy from said transmitted radiation, said receiver having an optical axis coupled via a first beamsplitter into the or an axis of said optical viewing system in such manner that said viewing system optical axis and the optical axis of any received reflected energy are coaxial, said transmitter supplying an output beam normal to the receiver optical axis, which beam is deflected to a direction parallel to that axis and coupled by said first beam-splitter on a path substantially co-axial to said viewing system optical axis, a second beam-splitter being provided on said receiver optical axis to inject light from a source via a target graticule into the optical axis of the receiver and thence into the viewing system optical axis to be directed to the viewing system eyepiece from a corner reflector prism mounted on said beam-splitter on the receiver optical axis on that side of said beamsplitter remote from the receiver.

provided with a field stop, said target graticule is provided on one side face of the beamsplitter, adjacent said light source.

9. A range finder as claimed in any preceding Claim, in which said first beamsplitter lies in the output path from an objective lens of said receiver and from an objective lens of said viewing device.

10. A range finder as claimed in any preceding Claim, in which said beam-splitters have mutually inverse transmission characteristics, said first beam-splitter reflecting that radiation entering from the exterior that has a wavelength in the infra-red range, and transmitting that light having a wavelength in the visible range, and the second beamsplitter transmitting radiation having a wavelength in the infra-red range and reflecting light in the visible spectrum.

Il. A range finder as claimed in any preceding Claim, in which deflection of the transmitted beam on to a path parallel to the optical axis of the receiver is effected by a deflecting prism arranged between the receiver objective and the second beam-splitter at a position off-centre to the optical axis of the receiver.

12. A range finder as claimed in any preceding Claim, in which the incoming light path and the projection of the target graticule are reflected by means of a third beamsplitter into an eyepiece of the viewing system.

13. A range-finder as claimed in Claim 12, in which the transmitted beam reflected from the remote field and the projected target graticule are also reflected via said third beam-splitter to an opto-electronic image converter, and thence to a further eyepiece forming part of the other arm of a binocular viewing system.

14. A range finder substantially as described with reference to Figure 1.