AN IMPROVED IMAGE SCANNING UNIT

Abstract: An improved scanning device adapted to direct an image through a nodding mirror (1) to a collecting mirror (5) scanned in turn by a rotating scanner (8) in which the collecting mirror is a half spherical mirror (5) and the correcting elements are mirrors (6, 7) carried on a scanner (8) having its axis of rotation (9) normal to the optical axis (14) of the collecting mirror (5) and intersecting same whereby to direct the image generally along the optical axis (14) of the collecting mirror (5) to a fixed mirror (10) and thence to a detector (11).

Description: "AN IMPROVED IMAGE SCANNING UNIT" The present invention relates to a scanning unit of the general type used for instance in infrared scanners in which a nodding mirror directs the incoming 5. rays onto a mirror which in turn directs the rays onto a spherical mirror from which the rays are directed to correcting devices such as mirrors or lenses which rotate about an axis and which in turn direct the rays after correction to a detector, 10. these devices operating on the principle that the rotating scanner which has a series or groups of correcting lenses around its axis of rotation direct the corrected image to the detector, the rotating scanner producing a series of line images spaced 15. apart progressively by the nodding mirror to result in a display of the visual image reaching the device. Such devices are already known, see for instance an earlier application by NEAL KEITH JONES, Australian Patent No. 516,790 dated 11th April 1978, which 20. relates to a scanning system using a Schmidt optical system including a spherical primary focusing mirror and a series of correcting lenses mounted on a rotating member to direct an image to a detector, or the specifi¬ cation of United States Letters Patent No. 3,817,593, 25. which again relates to a similar system but using a half spherical mirror as part of a Schmidt optical system, the other part of which is a tilted correcting plate resulting in off-axis scanning with unsymmetrical aberrations across the field and using a series 30. of roof reflectors which, as part of their functions, is to provide a nodding movement perpendicular to the scan. OMPI &7 The object of the present invention is to provide a simplified and compact form of these earlier devices. A further object is to achieve an arrangement in which the aberrations which are to be corrected 5. are uniform across the field and can be removed by the rotating elements. A further object is to allow a straight line scan in object space in association with a nodding mirror. 10. The invention relates to an improved scanning device which collects an image through a mirror nodding in a first plane and directs it to a focussing collecting mirror scanned in turn by a rotating scanner unit having pairs of optical elements moving in a second 15. plane at right angles to the first plane and wherein the focusing mirror is a half spherical mirror and the rotating optical elements are aspheric correcting mirrors, characterised in that the collecting mirror is a half spherical mirror and the correcting mirrors 20. are carried on a scanner having its axis of rotation normal to the optical axis of the collecting mirror and intersecting same to move the correcting mirrors about the half spherical collecting mirror centre of curvature whereby to scan a straight line in object 25. space, the focusing collecting mirror aberrations being uniform across the field and corrected symmetrically by the rotating optical correcting mirrors. Thus present invention uses a nodding mirror to direct the rays onto a spherical receiving mirror 30. which is a half mirror to allow efficient use of OMPI the mirror area provided and to allow the correcting mirrors of the rotating scanning system to be advantage¬ ously positioned in relation to the half spherical collecting mirrσr to give a compact assembly which 5. allows on-axis scanning of a straight line in object space. In its preferred form the invention comprises a half spherical collecting mirror associated with a nodding mirror positioned adjacent the collecting 10. mirror and to one side of the optical axis of the half spherical collecting mirror, characterised by a fixed receiving mirror on the optical axis of the half spherical collecting mirror positioned on the same side of the half spherical collecting mirror as the 15. nodding mirror and parallel to the planar edge of the collecting mirror, a detector positioned to receive the image projected by the half spherical collecting mirror to the fixed mirror, and a series of aspheric correcting mirrors mounted on a scanner arranged to rotate about an 20. axis normal to the optical axis and intersecting same whereby the image is moved across the half spherical collecting mirror in a first plane by the nodding mirror and the half spherical collecting mirror is scanned by the correcting mirrors in a second plane at right 25. angles to the first scan. The aspheric correcting mirrors are pairs of half spherical mirrors with one mirror of each pair on one side of the optical axis of the half spherical collecting mirror and the other mirror on the opposite 30. side of the optical axis with the planar edges adjacent the optical axis and parallel to the planar edge of the half spherical collecting mirror. The fixed mirror is disposed within the circle of rotation of the aspheric correcting mirrors so that the correcting mirrors traverse between the half circular collecting mirror and the fixed mirror to scan the half 5. circular collecting mirror. While the invention can be somewhat varied in the layout of the components the illustration accompanying this specification shows a preferred arrangement of the device but the construction need 10. not necessarily closely follow the form shown. FIG. 1 is a somewhat schematic longitudinal sectional elevation of a unit constructed according to this invention, and FIG. 2 shows the basic components of the system 15. indicating the position of the optical axis of the half spherical collecting mirror and the rotational axis of the scanner carrying the pairs of correcting mirrors. The nodding mirror 1 is supported in any convenient 20. manner in a housing 2 and is provided with a cam 3 to oscillate it about an axis 4 to cause a vertical scan of the area under surveillance, and this mirror 1 directs the light rays to the half spherical collect¬ ing mirror 5 which is fixed in position in relation 25. to the nodding mirror 1 and is arranged to direct the rays from it to the rotating aspheric correcting mirrors 6 and 7 of the rotating scanner 8 which rotates about the axis 9, only two pairs of correcting mirrors being shown in the drawings. A fixed mirror 10 directs the rays to the detector 11 which may be of any usual or approved form and may be connected to a visual display or to a mini- processor or the like for image storage or analysing 5. purposes. The illustrations shows the compact nature of the device which is arranged in a fold-back pattern with the nodding mirror 1, the half spherical mirror 5, and the detector 11 being arranged in close proximity 10. in a generally stacked formation, allowing the aspheri- cal compensating mirrors 6 and 7 of the scanner 8 to be readily positioned about the optical axis 14. A driving motor 16 rotates the scanner 8 which carries the set of aspheric correcting mirrors 6 and 7. 15. Because of the particular arrangement it is possible to use mirrors for each of the light directing members so that it is unnecessary to use apertured lenses or the like. The image is deflected by the nodding mirror 1, directly to the half spherical 20. collecting mirror 5, thence to the rotating correcting mirror 6, then to the correcting mirror 7, and thence to the fixed mirror 18 and to the detector 11. Because the multiple assemblies of the pairs of correcting mirrors 6 and 7 of the scanner 8 are 25. arranged about the axis 9 these mirrors scan the image projected to the half mirror 5. The axis 4 about which the nodding mirror 1 moves is parallel to the planar edge 15 of the collect¬ ing mirror 5 and the axis 9 about which the scanner unit 8 rotates is normal to the plane of the planar edge 15 of the collecting mirror 5 as well as normal to the optical axis of the half spherical collecting mirror 5. From the foregoing it will be realised although 5. the general principle of the device is similar to earlier known devices of this type, a very much improved assembly results from the use of a half spherical collecting mirror 5 which allows all compo¬ nents to be mirrors, including the aspheric correcting 10. mirrors 6 and 7 on the rotating scanner 8 but no obstruction of one mirror by any other occurs in this arrangement. In operation a relatively horizontal field of view is directed by the nodding mirror 1 to the 15. half-circular collector mirror 5, but the field of view is progressively scanned vertically as the mirror 1 nods. The image is then directed by the half spherical collecting mirror 5 generally along the optical axis of 20. the collecting mirror 5 and is directed by the mirror 6 of each set of correcting mirrors to the associated correcting mirror 7 which projects the image to the fixed mirror 10 and thence to the detector 11. As the series of correcting mirrors 6 and 7 on 25. the scanner rotate about the axis of rotation 9 of the scanner 8 a transverse scan of the image projected from the collecting mirror 5 occurs and, as the aspheric correcting mirrors 6 and 7 are arranged about the OMPI optical axis of the collecting mirror 5, enables the collecting mirror aberrations to be uniform across the field and corrected symetrically by the rotating aspheric correcting mirrors. 5. In the illustration an electronics bay is desig¬ nated 21 and an output to a display is designated 22. An encoder is designated 23 and a window of the housing 1 is designated 24. - j REX OMPI

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An improved scanning device adapted to collect an image through a mirror nodding in a first plane and directed to a collecting mirror scanned in turn by a rotating scanner unit having optical elements 5. moving in a second plane at right angles to the first said plane, characterised in that the collecting mirror (5) is a spherical mirror arranged to be used as a half spherical mirror and the correcting elements are mirrors (6,7) carried on a scanner (8) having its 10. axis of rotation (9) normal to the optical axis (14) of the collecting mirror (5) and intersecting same to move the aspheric correcting mirrors (6,7) about the collecting mirror (5) centre of curvature whereby to scan a straight line in object space and whereby the 15. collecting mirror (5) aberrations are uniform across the field and are corrected symmetrically by the rotating aspheric correcting mirrors (6,7). 2. An improved scanning device according to Claim 1 characterised in that the pairs of aspheric correcting mirrors are arranged with one mirror (6) of each pair on one side of the said optical axis (14) and the other 5. mirror (7) of the pair on the opposite side of the said optical axis (14) whereby the said aspheric correcting mirrors (6,7) receive and project the image generally along the optical axis (14) of the said collecting mirror (5) . 3. An improved scanning device according to Claim 2 characterised in that the aspheric correcting mirrors (6,7) are generally half spherical with their planar edges adjacent to the said optical axis and parallel to 5. the planar edge (15) of the half spherical collecting mirror (5) . OMPI 4. An improved scanning device according to Claim 1 characterised in that the axis of the nodding mirror (1) is parallel to the planar edge (15) of the said half spherical collecting mirror (5) and 5. is provided with means (3) whereby to nod the said mirror (1) about the said axis, further characterised in that the said fixed mirror (10) is on the said optical axis (14) of the half spherical collecting mirror (5) and positioned to mirror on the same 10. side of the half spherical mirror (5) as the said nodding mirror (1) further characterised in that the series of aspheric correcting mirrors (6,7) are mounted on the said scanner (8) in pairs about the said optical axis (14) of the said half spherical 15. collecting mirror (5), the said fixed mirror (10) being disposed within the circle of rotation of the said correcting mirrors (6,7) whereby the aspheric correcting mirrors (6,7) traverse between the said half circular collecting mirror (5) and the said 20. fixed mirror (10) to effect a transverse scan of the half circular collecting mirror (5). 5. An improved scanning device adapted to collect an image through a mirror nodding in a first plane and directed to a collecting mirror scanned in turn by a rotating scanner unit having optical elements 5. moving in a second plane at right angles to the first said plane to direct the image to a detector, characterised by a spherical collecting mirror (5) supported by a housing (2) and adapted to have half of its spherical surface in use, a nodding mirror 10. (1) disposed above the said half of the said spherical mirror (5) arranged to nod in a first plane and supported by the said housing (2) to project an image on to the said used half of the said spherical mirror (5), pairs of aspheric correcting mirrors (6,7) carried on a scanner (8) supported in bearings by the said housing (2) and having its axis of rotation normal to the optical axis (14) of the collecting 5. mirror and intersecting same to move the correcting mirrors (6,7) about the primary mirror centre of curvature whereby to scan a straight line in object space, whereby the collecting mirror (6,7) aberrations are uniform across the field and are corrected symmetri- 10. cally by the rotating pairs of aspheric correcting mirrors (6,7), one said aspheric correcting mirror (6) of each pair being disposed on that side of the said optical axis (14) opposite to the said collecting mirror (5) and adjacent said axis and 15. the other mirror (7) of the pair being disposed on the opposite side of the said optical axis (14) beyond the said nodding mirror (1) whereby the said mirrors (6,7) receive and project the image generally along the optical axis (14) of the said collecting 20. mirror (5) to a detector (11) also supported by the said housing (2). 6. An improved scanning device according to Claim 5 further characterised in that the said spherical collector mirror (5) is a generally half spherical mirror with its planar edge (15) parallel to the nodding 5. axis (4) of the said nodding mirror (1). 7. An improved scanning device according to Claim 5 or 6 further characterised by a fixed mirror (10) carried by the said housing (2) to direct the image from the said aspheric correcting mirrors (6,7) ς to the said detector. OMPI 8. A method of scanning an image which comprises (a) directing the image by means of a nodding mirror (1) on to generally a half of a spherical collecting mirror (5) with the nodding mirror (1) 5. disposed on a first side of a plane passing through the optical axis (14) of the said collecting mirror (5) whereby to project the image generally in the ' direction of the optical axis (14), (b) receiving the said image on a first mirror (6) 10. of pairs of correcting mirrors (6,7) rotating about an axis (9) normal to the said optical axis (14), said first correcting mirror (6) being disposed adjacent to the said plane and on a second side thereof generally opposite to the said nodding 15. mirror (1) , (c) receiving the said image on a second correcting mirror (7) of the said pair (6,7) disposed adjacent to the said plane on the first side of the said plane and receiving the said image from the said 20. second correcting, mirror (7) on a detector (11). 9. A method according to claim 8 comprising directing the said image from the said second correcting mirror (7) to the said detector by means of a fixed mirror (10) generally on the said optical axis (14). 10. An improved scanning device constructed and operating substantially as described and illustrated in the accompanying drawings.

Inventors: MCQUISTAN GAVIN WILLIAM, MCQUISTAN, GAVIN, WILLIAM
Applicants: COMMW OF AUSTRALIA, THE COMMONWEALTH OF AUSTRALIA CARE OF THE SECRETAR
Application year: 1984
Main classification: G02B27
IPC codes: G01J5, G02B26, G02B27