OPTICAL RASTER SCAN GENERATOR

• US 3,764,192 A
• Filed: 05/28/1971
• Issued: 10/09/1973
• Est. Priority Date: 05/28/1971
• Status: Expired due to Term

• Current Assignee: Bryce A. Wheeler
• Original Assignee: Bryce A. Wheeler
• Inventors: Wheeler, Bryce A.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/152,466
• Time in Patent Office: 865 Days
• Field of Search: 350/6,7,285 178/7.6 250/234,235,236
• US Class Current: 359/206.1
• CPC Class Codes: H04N 3/09 for electromagnetic radiation in the invisible region, e.g. infrared

Abstract

Optical apparatus for scanning a field of view in a raster pattern including a motor-driven spinning mirror structure having a plurality of substantially optically flat mirrors positioned substantially uniformly about the axis of spin of the structure with the surfaces of the mirrors normal to a radial direction from the axis of spin; an oscillating, substantially planar, mirror positioned to intercept reflected light from a portion of the aforementioned spinning mirror structure, said oscillation being about an axis which is parallel to a plane which is perpendicular to the axis of spin of the spinning mirror structure, the spinning mirror structure producing the line sweeps of the raster scan and the oscillating mirror indexing the line sweeps over the raster scan to cause the line sweeps to be substantially uniformly spaced, said axis of oscillation being located so that light impinging from a fixed source or pupil onto said oscillating mirror will for any position in the oscillation of said mirror be reflected through a common fixed area constituting a virtual aperture or pupil, said pupil being the origin point for said elevation scan and the axis of said spinning mirror being located so as to place the center of each face of said mirror successively at said virtual pupil whereby both said elevation and azimuth scans appear to originate from said fixed area virtual pupil thereby precluding astigmatic distortion when said scan is optically coupled to a magnifying system having its optical axis passing through said fixed area.

Claims

1. Apparatus for producing a non-astigmatic raster scan for an infrared detector suitable for use with an afocal magnifying system, said apparatus being characterized by:

a rotatable mirror structure mounted for rotation about a spin axis relative to said frame, including a plurality of radially directed axes defined on and rotating with said structure perpendicular to said spin axis, said axes being substantially uniformly spaced about said spin axis, a plurality of mirror surfaces on said mirror structure, each said mirror surface being perpendicular to a different one of said radial axes;

means forming a mirror surface, mounted for oscillation relative to said frame about an oscillation axis parallel to a plane which is perpendicular to said spin axis;

said oscillating mirror being positioned in a light path which periodically includes each of said rotating mirror surfaces, said oscillation axis orthogonally passing through a point on a locus of oscillation centers, said locus lying in the plane of the central rays incident on and reflected from said oscillating mirror and making an angle Beta with said reflected ray which is equal to the angle of incidence ( Beta ) of said central ray on said oscillating mirror when said mirror is in its nominal central position so that the orthogonally directed scans produced by said rotatable mirror and said oscillating mirror both appear to originate from substantially the same spot on a surface of said rotatable mirror.

2. In combination:

means defining a first optical axis;

means forming an angularly oscillating mirror surface intercepting said optical axis, said oscillating mirror, when at a preselected nominal position in its swing, defining a second optical axis in the direction of reflection of said first optical axis, the angle of incidence of said first optical axis upon said mirror surface and the angle of reflection of said second optical axis, when said mirror surface is in its nominal position, defining an angle Beta . a rotatable mirror structure having a shape substantially as a polygonal cylinder, the sides thereof forming mirror surfaces, said second optical axis being positioned when said first-mentioned mirror surface is in its nominal position, in a plane substantially parallel to the top and bottom of said mirror structure, a third optical axis defined in said plane, said third axis being coincident with the reflection of said second optical axis from one of said mirror surfaces of said mirror structure when said mirror structure is in a predetermined nominal angular Position relative to said second optical axis so that rotation of said mirror structure causes said third optical axis to sweep in a line, and oscillation of said oscillating mirror produces line-to-line indexing of said line sweeps by said third optical axis, both the sweep of said third optical axis and the indexing of said sweep appearing to originate from a common virtual pupil on said mirror surface from which said second optical axis is reflected to form said third optical axis.

3. Means for producing a nonastigmatic optical raster scan comprising:

a frame having at least five axes defined thereon, the second said axis intercepting the first said axis and turned from said first axis through an angle (180* - 2 Beta ) degrees, the third said axis intercepting said second axis at a distance A csc2 Beta from the interception of said first and second axes and turned from said second axis through an angle Beta , said first, second and third axes being coplanar, said fourth axis being perpendicular to said second axis and parallel to the plane of said first three axes, said fifth axis intercepting said second axis a distance A from said interception of said first and second axes, said second and fifth axes defining a plane perpendicular to the plane of said first three axes and said fifth axis being turned from said second axis through an angle delta ;

a rotatable mirror structure rotatable about said fourth axis, including a plurality of radial directions defined thereon perpendicular to said fourth axis, having a plurality of mirror surfaces thereon, each perpendicular to a different said radial direction, said mirror surfaces being positioned to intercept said second axis consecutively when said structure is rotated;

an oscillating mirror structure having limited rotation about an axis centered on and perpendicular to said third axis and parallel to the plane of said second and fifth axes, said oscillating mirror structure having a mirror surface thereon intercepting said first and second axes.

4. Apparatus as recited in claim 3 and further comprising means for spinning said mirror structure about said fourth axis and for oscillating said oscillating mirror structure in a predetermined synchronism.

5. Apparatus as recited in claim 4 in which rotation of said mirror structure produces an optical sweep about said fifth axis through a usable angle 2 Alpha , whereby radiation delivered in a bundle substantially along said second axis to said mirror surfaces of said rotatable mirror structure is projected and swept through at least an angle 2 Alpha from said fifth axis about an axis parallel with said fourth axis and radiation delivered, at least within an angular region 2 Alpha of said fifth axis, to said mirror surfaces of said rotatable mirror structure is scanned and delivered substantially along said second axis to said oscillating mirror structure.

6. Apparatus as recited in claim 5 wherein Alpha is substantially 30*.

7. Apparatus as recited in claim 4 wherein the oscillation of said oscillating mirror structure is through an angle gamma whereby radiation delivered substantially along said first axis to said oscillating mirror is projected and swept at least through an angle 2 gamma , and radiation received through at least an angle 2 gamma about an axis passing through the intersection of said second and fifth axes and perpendicular to the plane of said first and second axes at least through an angle 2 gamma is delivered and projected substantially along said first axis.

8. Apparatus as recited in claim 4 and further comprising means for producing a pencil of beams substantially along said first axis.

9. Apparatus as recited in claim 8 in which said means comprises a substantially point source of light, a collimating lens, and an optical stop between said source and said lens.

10. Apparatus as recited in claim 4 and further comprising means for sensing a pencil of Radiation received along said first axis from said oscillating mirror.

11. Apparatus as recited in claim 10 in which said means for sensing comprises a radiation sensor, a focusing lens for focusing incoming radiation on said sensor, and on optical stop between said lens and said sensor.

12. Apparatus as recited in claim 4 wherein said means for spinning said mirror structure and for oscillating said oscillating mirror structure comprises:

a motor, said mirror structure being connected to the shaft of said motor to rotate therewith;

a pinion gear connected to said shaft to rotate therewith;

a spur gear meshing with said pinion gear and adapted to rotate about a shaft whose axis is perpendicular to the shaft of said pinion gear;

a cam, connected to rotate with said spur gear, said cam having a predetermined contour for oscillating said oscillating mirror structure in a predetermined program;

a cam follower following said cam and connected to said oscillating mirror structure to cause said oscillating mirror structure to oscillate with the oscillation of said cam follower.

13. Apparatus as recited in claim 12 in which said pinion gear and said spur gear are helical gears.

14. Apparatus as recited in claim 12 wherein said cam is a substantially linear cam over at least a portion of the periphery thereof.

15. Apparatus as recited in claim 11 and further comprising means for sensing the rotation of said cam.

16. Apparatus as recited in claim 3 wherein Beta is substantially 45*.

17. Apparatus as recited in claim 3 wherein delta is substantially 65*.

18. Apparatus as recited in claim 3 and further comprising pickoff means for sensing the transition between consecutive mirror surfaces of said mirror structure.

19. Means for producing a nonastigmatic optical raster scan comprising:

a first mirror mounted for constrained oscillation about an elevation axis and positioned to reflect an optical pupil to a single fixed position virtual pupil in any position within its constrained oscillation;

a multifaceted mirror wheel rotatable about an azimuth axis and positioned so that the multiple faces of said wheel will sequentially be positioned at said fixed position of said virtual pupil during the rotation of said wheel; and

means for synchronously moving said mirrors and for mounting said first and second mirrors to position said elevation axis about which said first mirror oscillates parallel to a plane which is perpendicular to said azimuthal axis about which said mirror wheel rotates.