Infrared-optical aiming and guiding device

In the combination of a daylight aiming device, a night aiming device and a guiding device for tracer missiles emitting infrared beams of a narrow spectral band both the night aiming device and the guiding device work on infrared beams of the same spectral region. This region includes the narrow spectral band of the beams emitted by the missile. Partially transmitting mirror means are arranged along the optical axis of the night aiming device for filtering the missile beams of the narrow spectral band out of the beam bundle and reflecting them to the guiding device, which conducts flight path control signals to the missile. The remaining beams of the spectral region are transmitted to the aiming device. An infrared/visible-light image converter is part of the aiming device. The visible light rays emitted by the converter are reflected into the ocular lens of the aiming device for viewing by the operator.

BACKGROUND OF THE INVENTION 
The invention relates to an aiming device in combination with a device for 
guiding tracer missiles to the target, especially anti-tank missiles. 
More particularly the invention relates to a combination of such an aiming 
and guiding device which uses the infrared beams of the spectral region. 
In the combination the guiding device usually comprises first a goniometer 
for measuring the difference between the flight path of the missile and 
the line of sight of the aiming device and, secondly, a controlling device 
for transmitting control signals to the missile. The magnitude or 
intensity of the signals is derived from the measurement of the 
goniometer. 
For fighting tanks, preferably semi-automatic weapon systems of the 
`line-of-sight-guiding-type` are used today. In this system, after firing 
the missile, the latter is caused to `jump` on the line of sight of the 
aiming device by signals transmitted by the controlling device which 
operates in combination with the aiming device. For such a guiding action 
it is a condition that the line of sight of the aiming device and the 
zero-line of the goniometer are identical or, at least, extend in 
parallel. 
In such devices the goniometers use almost exclusively beams of a wave 
length of 0.002-0.005 millimeters (=2-5 .mu.m) which equals approximately 
0.00008-0.0002 inches. In infrared technology this wave length region is 
known as the `1st window` as compared, for example, to the 3rd window 
which consists of beams having a wave length of approximately 8-14 .mu.m 
(=0.00032-0.00056 inches). The aiming device is usually a monocular 
telescope having cross lines. This constitutes a daylight aiming device. 
For the use at night a supplementary aiming device is required which either 
works with infrared beams of the 1st window or of the 3rd window. Using 
beams of the 3rd window requires considerably more provisions especially 
with regard to the detector than would be needed if beams of the 1st 
window were applied. However, if beams of the 3rd window are used an image 
of the target is obtained that comprises considerably more information 
details than an image made up of beams of the 1st window. 
Therefore, in spite of the more difficult working conditions mostly a night 
aiming device is used which works with beams of the 3rd window. 
For the guiding device image details are not required. 
Therefore the guiding devices usually work with infrared beams of the 1st 
window because this is easier to accomplish and less costly. 
It is, however, a disadvantage of such a combined aiming and guiding device 
of which the aiming device works in the 3rd window and the guiding device 
works in the 1st window that in hazy weather in spite of poor visibility 
in the target area the aiming device still works satisfactory in the 10 
.mu.m band while the guiding device in the 2 .mu.m band cannot see the 
missile, even at a short distance from the place of its firing. The 
guiding device can then no longer receive beams from the missile and 
conduct control signals to the missile and the missile may get lost. 
It is therefore an object of the present invention to provide an infrared 
optical aiming and guiding device which overcomes this disadvantage. 
This object could easily be attained if an aiming device and a guiding 
device would be combined that both use infrared beams of the same window. 
In such a combination the two devices will `see` the same objects, i.e. 
both will have the same range of vision. It can then no longer occur that 
the aiming device recognizes more details than the guiding device. 
However, there arises the following difficulty: If the beams emitted by the 
missile and the beams used by the aiming device and the guiding device are 
of the same wavelength region then the missile light will blind the aiming 
device to an extent that makes proper aiming very difficult, if not 
completely impossible. 
It is, therefore, the particular object of the invention to provide a 
combined infrared optical aiming and guiding device that both work in the 
same spectral region but wherein in spite thereof the aiming device is not 
blinded by the missile. 
SUMMARY OF THE INVENTION 
This particular object of the invention is attained by providing a combined 
aiming and missile guiding device which uses a goniometer and a night 
aiming device that both work in the same spectral region (infrared beam 
window) and which comprises filter means that prevent the infrared beams 
emitted by the missile from impinging on the aiming device and blinding 
the latter. Thus, according to the invention the combination includes in 
the beam path of the night aiming and the guiding device a reflecting 
means which is exactly adjusted to the wavelength of the missile light and 
thus cuts the missile beams out of the general beam bundle and reflects 
them to the goniometer, while the remaining beams are left to travel to 
the aiming device. 
In a preferred embodiment of the invention both the night aiming device and 
the guiding device work in the wavelength region between 8-14 .mu.m (3rd 
window) and a laser in the 10 .mu.m region is used as the missile light. 
The reflecting means is then adjusted accurately to this small 10 .mu.m 
band. Preferably a CO.sub.2 -laser may be used which emits beams having a 
wavelength of 10.6 .mu.m.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, in FIG. 1 the objective lens of the daylight 
aiming device is designated by the reference numeral 1. This daylight 
aiming device works with visible light. In combination with an ocular 3 it 
constitutes a normal aiming telescope. 
The objective lens of the night aiming device is designated by the numeral 
4. It is arranged with its optical axis extending parallel to the axis of 
the objective lens 1. In the image-side beam path of the objective lens 4 
there is arranged a first partially reflective (and consequently partially 
transmitting) mirror 5 which reflects the beams of the 10.6 .mu.m 
wavelength band but transmits all other beams of the 8-14 .mu.m spetral 
region (3rd window). The reflected beams travel to the guiding device 
(goniometer) 6 which measures the difference between the missile path and 
the line of sight of the aiming device and issues control signals to the 
missile to bring the latter back on the line of sight, if such difference 
should exist. 
The transmitted beams impinge on a second partially reflective mirror 7 
which reflects a portion of the complete band width (8-14 .mu.m) to an 
image converter 8. The image converter transforms the infrared-light image 
into a visible-light image. From the converter 8 the visible light beams 
emerge in the direction of the reflective mirror 7. They pass through the 
latter to a third partially reflective mirror 9 arranged in the beam path 
of the daylight aiming device. The mirror 9 reflects a portion of the 
beams into an ocular 3 and into the observers eye 10. 
The device functions as follows: 
For aiming during daytime the objective lens 1 is used in combination with 
the ocular 3. For guiding the missile the objective lens 4 of the night 
aiming device is used both during daytime and at night in combination with 
the mirror 5 and the guiding device 6. 
In case of dim light conditions and at night the objective lens 4 of the 
night aiming device is used for aiming as well as for missile guiding. By 
the partially reflective mirror 5 the beams of the 10.6 .mu.m wavelength 
are reflected to the guiding device 6 where they are used for measurement 
and missile control. All the other beams transmit via mirror 5 to the 
image converter 8. The visisble light image provided by the converter is 
then viewed by the observer via the ocular 3. 
FIG. 2 shows diagrammatically the intensity of the beams impinging on the 
image converter 8 in dependence on their wavelength. The diagram shows 
that at a wavelength of 10.6 .mu.m there is a drastic gap in the beam 
intensity. This results from the 10.6 .mu.m wavelength being filtered out 
of the beam bundle and reflcted to the guiding device by the mirror 5. 
From this description it will be well understood that the stated object of 
the invention is fully attained: both devices, the aiming device and the 
guiding device work in the same spectral region but still the aiming 
device is not blinded by the beams emitted by the missile because 
precisely these beams are filtered out of the beam path prior to reaching 
the aiming device.