1986-01-14
1987-11-24
Arnold, Bruce Y.
350487, G02B 2610
Patent
active
047084200
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Infrared detection systems which operate over the 2 to 20 .mu.m wavelength region, and which are required to have an optical resolution of 1 mrad or less, conventionally employ either a germanium refracting objective or a catadioptric objective such as a Schmidt system. The optical system is used in conjunction with a single infrared detector or array of detectors, associated signal processing electronics, and a suitable target indicator device or display.
In order to detect targets over a substantial field of view, the small instantaneous field of view defined by the focal length of the optical system and the size of individual detectors may be optically scanned through the total search field of view. This may be achieved, for example, by means of rotating optical components which generate a line-by-line rectangular raster scan.
Alternatively, a large number of detectors may be employed without scanning, i.e. a staring focal plan array system. This technique suffers from various limitations arising from the finite spacing between adjacent detectors.
A disadvantage of refractive and catadioptric system is their high unit cost. Furthermore, optomechanical scanning techniques which employ motor-driven components moving at high speed to generate the desired search field, add to system complexity and overall cost.
SUMMARY OF THE INVENTION
The object of the present invention is the construction of a low cost optical system which incorporates a novel scanning technique to fill the gaps in optical coverage between adjacent sensors of a focal plane array of infrared detectors.
In accordance with the invention, the optical system is of the Cassegrain type, both the primary and secondary mirrors being constructed of a metal such as aluminum. The secondary mirror is caused to vibrate by means of a piezoelectric drive unit, the angular displacement of this mirror being of sufficient amplitude to scan the optical image by the desired amount at the focal plane.
Piezoelectric drive means for mirror oscillation have been proposed heretofore, see the specification of U.S. Pat. No. 4,436,364, and Offenlegungsschrift DE3035314, both by Lauer and Pfefferle, the first relating to a device comprising a pair of coplanar but oppositely actuated piezoceramic strips coupled to a mirror disposed between facing ends, the second relating to a single piezoceramic strip extending to a mirror anchored on a second flexible strip normal to the first strip to give a modular motion, in each case the mirror being carried by the piezoceramic strip or strips.
The invention comprises a focal plane scanning device arranged to move a mirror in an optical scanning device such as an infrared scanner wherein the mirror is mounted to be angularly displaced by means of a piezoelectric assembly comprising at least a piezoelectric member connected to the said mirror by means of a first flexure member to support the said mirror on a support bracket to allow the mirror to be tilted about a selected axis relative to the said support bracket and at least a piezoelectric drive element carried on the said support and connected to the said mirror, characterised by a pair of piezoceramic drive elements (4-5) arranged generally parallel to the plane of the said mirror (1) each connected at one end to the said support bracket (2) and extending in opposite direction past a first flexure member (3) which supports the said mirror (1), and by flexure members (8-9) one on the other end of each of said piezoceramic drive elements (4-5) connecting that piezoceramic member to the said mirror (1) remote from the said first flexure member (3), whereby a balanced movement of the said mirror (1) about the said first flexure member (3) results when said piezoceramic members (4-5) are oppositely energised.
BRIEF DESCRIPTION OF THE DRAWINGS
To enable the invention to be fully understood an embodiment thereof will be described with reference to the drawings in which
FIG. 1 shows schematically a general arrangement of a preferred embodiment of th
REFERENCES:
patent: 1438974 (1922-12-01), Wente
patent: 3544201 (1970-12-01), Fowler et al.
patent: 4436364 (1984-03-01), Lauer et al.
Arnold Bruce Y.
Ben Loha
The Commonwealth of Australia
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