FR2593657A2 - Optico-mechanical scanning device - Google Patents

Abstract

In this optico-mechanical scanning device, the frame scanning is obtained using a plane mirror which rolls on a conical one of the focal points of which is at the center of the pupil, exiting the objective and the other focus substantially at the top of a field mirror bending the analysis beam towards the line scanning means. The field mirror is driven by a movement synchronous with the movement of the raster mirror, such that there is constantly optical conjugation of the center of said pupil with a fixed point on the axis of rotation of the line scanning means. Application: infrared vision of objects. (CF DRAWING IN BOPI)

Description

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  The present invention is a third addition to that which is the subject of the patent application No. 75 03 923,

  lodged on 7 February 1975 in the name of the plaintiff and

  first and second certificates of addition to this patent,

  respectively Nos 76 37 685 and 76 37 686, filed simultaneously

on December 14, 1976.

  It constitutes an improvement of the optical scanning device of a field of view and of visualization of said field described in said first and second patent applications.

  certificate of addition. It concerns the frame part of this

  in connection with the movement of the field mirror.

  According to these patent applications and certificates of

  an optical scanning device of a field of view divided into different zones and of visualization of said field of view is described.

  field, device according to which said scanning is carried out

  two perpendicular directions, namely, according to a

  tion x a so-called line scan and, according to another

  direction y, a scan called frame or image scan, available

  operating said scans according to beams from different

  zones of the field and ensuring the convergence of

  on an element sensitive to the radiation contained in the

  beams, generally comprising in the following order,

  the direction of the path of the median incident beam from the field

  of vision, a lens, weft scanning means according to

  rection y, a system for folding the beams delimited by the opening of the objective towards means of line scanning of the

  image field of the objective according to the direction x and the sen-

  sible, said line scanning means, the sensitive element, possibly

  other elements related to those previously

  cited for the direct visualization of the image of the

  lysed, said device being remarkable in that: the objective has its optical axis included in a plane P containing the direction y and perpendicular to x, in that said objective is interchangeable and that its focal surface is curved and such that its center of curvature is located in the center of the exit pupil of the objective, - the frame scanning means are constituted by a plane mirror rotating reciprocating about an axis parallel to

  the direction x, placed in a convergent bundle behind the objective

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  next to the image of the field in said objective, - the line scanning means are constitlués on the one hand a drum in uniform rotation about a fixed axis YY 'contained in

  said plane P and carrying a large number of reflecting plane faces.

  regularly distributed around the drum, and,

  on the other hand, a symmetrical image

  port to said plane P forming an image of the sensing element at a fixed point A 'of the axis YY' of rotation of the drum, said drum being placed in a convergent beam in the path of said transport system on the image side of the sensitive element, symmetrical with said point A 'with respect to each face of the drum when said face

  is perpendicular to the plane P being in the vicinity of the symmetrical D

  of the focal point of the objective with respect to the weft mirror in a position parallel to YY ', the optical system for folding the beams consists of a so-called concave mirror of the field admitting the plane P as plane of symmetry and whose vertex is placed in the vicinity of D on the axis ZZ 'passing through D and perpendicular to YY', said mirror being determined so that it combines the center O of the exit pupil of the objective with a fixed point 0 ' of the axis TY ', said point 0' being symmetrical with respect to ZZ 'of the point of intersection of the optical axis of the objective with the axis YY', said field mirror, to possibly ensure the nullity dead time of scanning between two consecutive lines, having at most a width in the x direction slightly smaller than the length of the analyzed line itself equal to the distance between the images of the detector in two consecutive faces of the rotating drum, said mirror being animated or not with a movement t of small amplitude in phase with the movement of the weft scanning means, said small movement comprising on the one hand an alternative translation along the axis ZZ 'in the vicinity of D and an alternating rotation about an axis parallel to the direction x symmetrical with respect to ZZ ', the amplitude of said translation being such that it corrects the

  defocusing introduced by the frame scanning means, the

  the amplitude of said rotation being such that it ensures the fixity at 0 'of the conjugate by the field mirror of the center O of the exit pupil of the objective during the alternative rotation of the means

raster scan.

  In this device we manage to avoid, during

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  from the frame scan, the defocusing of the analysis beam to the

  point D, as well as to ensure the crossing under

  constant dence of line scanning elements by rays

  means of the beams, irrespective of the direction of the field

  lysed, skillfully combining and synchronizing movements

  alternating rotation of the frame and rotation mirror and trans-

lation of the field mirror.

  In such systems, there is always an interest in

  limit the oscillating weight of the frame mirror, so its dimensions

  the mirror as close as possible to the focus of the lens. This is the result that is sought in the

  German Patent No. 2,011,883. This patent describes a device

  of scanning a field in a single direction using a plane mirror tilting the beam transmitted by a lens, said

  beam being constantly focused in one fixed point.

  This result is obtained by giving the plane mirror a motion such that it is constantly tangent to an elliptic curve, one of which

  households is placed in the main plane of the objective and the

  be at said fixed point, the focal length f of the lens being,

  according to this patent, equal to the sum of the half axes a and b of the

  lipse, which means that a = b. It follows that the ellipse, from the point of view of pure theory, is in fact a circle and that, according to this patent, the point of focus is located in the main plane of the objective. Such an arrangement, even when approximated, leaves only a small distance between objective and point of focus. It would thus be difficult to place at the focal point the top of the field mirror of the optico-mechanical scanning device, according to the main patent application, to which the present addition is attached. Moreover, the average radii of the analysis beams after their convergence at the fixed point have variable orientations as a function of the analyzed field direction. It follows that the device according to the patent

  German version 2.011.883 can not, on its own, fulfill the

  weft scanning according to said main patent. Another

  feature of the device according to the German patent comes from the fact that the mirror rolls on a substantially circular ellipse in the vicinity of its minor axis, at a distance practically half of

  the focal length of the lens. The width of the beam

  cepté and the surface of the mirror thus remain relatively large,

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  said mirror being therefore of significant weight and bulk.

  The present invention designs the optico-mechanical scanning device of the main patent and its first and second certificate of addition with a new version of frame scanning means not having the same disadvantages as

  those of the prior art cited. These means essentially comprise

  a plane mirror whose movement is designed in relation to

  that of the field mirror so as to simultaneously

  beam at a fixed point located substantially at the top

  concave field mirror, and reflection of the mean radius of the

  in a stable direction whatever the direction of the

field analyzed.

  The invention also makes rolling and tipping

  the frame mirror on a curve so that it is consistent

  in a position fairly close to the focus of the objec-

  tif and such that the beam is focused at a fixed point independent of the analyzed field direction. The mirror of

  The field is animated by a single rotation

  the mirror of the frame mirror and as it reflects the average radius of the beam analyzed by the frame mirror according to a

fixed radius.

  According to a preferred embodiment of the invention,

  laying in the case where the focal surface of the lens is spherical and concavity turned towards the objective, the curve enveloped by

  the frame mirror is an ellipse of exentricity that can be no-

  different from the unit and one of which is located in the center of the exit pupil of the objective and whose other focus is the fixed point of focus of the beam and is located substantially at the top of the mirror of field and confused with the image of the detector given by the line scanning means reached in the middle of a line. The field mirror oscillates around an axis passing through this focal point in synchronism with

  frame mirror, so as to reflect the average radius of the

  in a fixed direction and thus ensure the optical conjugation of the center of the exit pupil with a fixed point of

  the axis of rotation of the line scanning system.

  A simplified variant of the invention,

  when the amplitude of the raster scan is limited, it consists in choosing, for the rolling curve of the weft mirror, the circle

  tangent to this ellipse at the point of contact of the corresponding mirror.

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  dailt To the direction -.diane of the field analyzes and centered in the center

  curvature of the e] llipse at said point of contact. A slight d.6fo-

  calibration is thus introduced on both sides of the center of the field. It is reduced by shifting the axis of rotation of the field mirror by a very small distance from the focus of the ellipse.

  According to the invention, the rolling curve of the

  frame can be, depending on the curvature of the sur-

  focal face of the lens, a conic different from an ellipse.

  This is how this curve is a parabola for a surface

  focal plane and an exit pupil of the objective rejected

  finished, and a hyperbola for a convex focal surface with respect to the incident light and an exit pupil located behind the

focal area.

  The invention will be better understood using the

  following description of some of the ways in which

  vention accompanied by drawings which represent: - Fig. 1 - A sectional representation of an embodiment of the opticomechanical scanning device subject of the

  It is the first and second certificates of addition.

  At E-g. 2 - A sectional representation of the scanning means

  in conjunction with the field mirror according to the present invention.

  tion. - Fig. 3 - A representation of a particular embodiment

of these means.

  - Fig. 4 - A curve relating to the preceding embodiment indicating the defocus correction, as a function of the angle

of field, eefectuce.

  In Figure 1 is found in a section through its plane P of symmetry the overall structure of the device

  subject to the main patent and the first and second

  tificat of addition. Under the number It is indicated a fixed objective whose optical axis is 12 and the focus F. The objective 11l is

  shown in this figure as made using lenses.

  It is known from the main patent that this objective can just as easily be made from mirrors. The optical axis 12 intersects the axis YY 'at point E. The axis YY' is the axis of rotation of a system comprising a drive device 13 and a drum

  13 'laterally bearing a large number of reflective faces.

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  As mentioned in the main patent, this drum may have

  several forms. It is supposed here prismatic, its faces

  bending being regularly regenerated around the axis YY '.

  One of its faces is represented in 17 in a position per-

  pendicular to the plane P. The plane mirror 14 said frame mirror is movable about an axis perpendicular to the sheet and passing

  In fact, according to the invention, this axis does not need to

  This arrangement shown in Figure 1 is only preferential in the case ol the device, as

  indicated in the main patent, is provided with additional means

  to view the field directly with the help of

  electroluminescent diodes. Said mirror 14 reflects everything

  from an area of the field and, passing through the objective 11,

  towards the mirror 16 where it forms an image of

  on this last mirror. In Figure 1, the beam

  particular indicated is that which has a mean radius

  melted with the optical axis 12, the image being formed at the point D on the axis ZZ 'perpendicular to YY', corresponding to the center of the field. -The mirror 14 says frame, ensures the scan

  of the field in the y direction perpendicular to the axis 12 and

held in the plane of the figure.

  The device comprises a concave mirror forming detector 19 placed in A an image at A '. It is constituted by

  example of the set of two paraboloid portions respectively

  18 and 18 'of revolution around the YY axis and whose

  reflective surfaces are facing. The summits of these para-

  Bolotdes are respectively S and S 'and the foci A and A'. They are located on YY '. A 'is symmetrical of D with respect to the face

3o 17 of the drum.

  The system constituted by the rotating drum 13 ', the mirrors 18, 18' and the detector 19 makes it possible, during the rotation of the drum, to analyze, line by line, in the direction x perpendicular to the plane of the sheet, of the image

  of the field given by the objective 11 and the frame mirror 14 in the vicinity

  This system constitutes the line or analysis analysis system x. The mirror 16 symmetrical with respect to the plane (ZZ ',

  YY ') and whose summit is in the vicinity of D, ensures the conju-

  optical gestation of the center of the exit pupil 0 of the objective

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  11 with the fixed point 0 'of the axis YY', symmetrical of E with respect to

  port at ZZ ', so as to ensure convergence on the detector

  19 of any beam resting on the exit pupil of the ob-

  jectif 11. This mirror 16 in that it defines the field analyzed is what is called field mirror. In Figure 2, the device is shown only partially in section by its plane P of symmetry. The objective is found under the number 11 with its optical axis 12, its focal point F. The curve 21 represents the section of the focal surface of this objective by the plane P. In order to make the difference with the prior art more apparent, the exit pupil is assumed not to be confused with the main plane of the lens. This pupil is represented under number 22, while the main plane is assumed to be 11. The center of this pupil is the point O. In this example the focal area seen from O is concave spherical. Its center

  Curvature is O Curve 21 is a circle. We also find

  in this figure the axis YY 'of rotation of the means of

  League layout, the point D coincides with the image of the detector given by the line scanning means when said scanning is in the middle of a line. O ', on the axis YY', is an optical conjugate fixed point of the point O by the frame mirror and the field mirror whose position and motion are subsequently explained. Under the

  number 23 is represented an ellipse whose foci are respected

  0 and D and whose major axis is equal to OF, radius of curvature at F of the focal surface 21. The weft mirror whose reflecting surface is opposite to D moves while remaining constantly tangent to this ellipse, point of contact of the mirror

  with said ellipse being the point of intersection of this

  lipses with the average radius of the analyzed beam. In Figure 2 we

  represented two of these bundles: the median beam 15

  in F and for which the weft mirror is in the

  position T, the point of contact with the ellipse being E intersect

  12 with the ellipse, the end beam 24 converges to FI1 on the curve 21 and for which the frame mirror is in the position T1, the point of contact with the ellipse being Ej

  intersection of radius 25 with the ellipse. The points F2 and E2 remain

  respectively on 21 and 23 are the analogous points to F1 and E1 for the symmetric extreme analysis beam of 24 per report

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  At the qtique axis. When the weft mirror rolls alternately on the ellipse 23 of E1 E2 and E2 to E it focuses the analyzed beam at the point D regardless of its position on the ellipse. It is thus possible to scan the field in the weft direction without any defocusing at point D. At this point is placed the vertex of the concave field mirror 16 which is rotated about an axis perpendicular to P and passing through synchronous D of the frame mirror movement and such as the radius

  the analyzed beam, such as for example 12 or 25, or ref16-

  chi according to the fixed radius DO '. Preferably to reduce the

  of the weft mirror and lighten its weight, the arc E1 E2 of the ellipse used is located near the point D and away from the

small axis of the ellipse.

  In practice, the movement of the mirror is

  for example, by two elec-

  liptic identical to 23 placed in planes parallel to the plane P, located on either side of said plane so that the sections of said paths project orthogonally to P following 23, mechanical pressure means ensuring the non-slip contact

mirror on said paths.

  A particular embodiment of the invention relates to the case where the field analyzed is not very large. In this case, the F1F2 arc is not even very large, the centers of curvature C1 C2 C of the ellipse respectively at the points E1 E2 E are very close together. We can then assimilate the elliptical arc El E2 to a circle of center C and radius E C. In this case, we can roll the frame mirror on this circle, a simple way to achieve such a movement consisting in bonding said mirror to an arm articulated around C and of constant length. Such a movement causes a slight defocus. This defocusing 1 with respect to D, is indicated in FIG. 4 as a function of

  the angle> <of the direction analyzed with the optical axis of the ob-

  jective, by the curve 41. In this figure 1 and <are assigned a sign. They are void for point F, said to be positive for the

  direction corresponding to point F2 and so-called negative for the

  rection corresponding to point F1. These defocalisatiors are

  males for the points F1 and F2, (points A and B of the curve 41).

  According to the invention, the importance of this defocusing is reduced by moving slightly and adequately in the plane P the center of rotation of the field mirror with respect to the point D. FIG. 3 shows the displacement effected.

  in order to simultaneously cancel the defocus for the

  analyzed field rection corresponding respectively to F, F and F2. In this figure we find the focal curve 21, the focus F and the image F1 of the field in the extreme direction of analysis making the angle of value X M with the optical axis 12 on

  which is represented by the point E of FIG.

  the center O of the exit pupil and its conjugate O 'on

  the YY axis. The frame mirror is represented in its position T1.

  This mirror envelops the circle 31 of radius E C. The image of F1 in

  the frame mirror in position T1 is F1 ', the defocusing introduced

  duit is therefore D F'1. To cancel this defocus, the axis of the field mirror is moved parallel to the plane P at the point I which is the intersection of the outer bisector of the angle E D O '

  and the mediator of the segment D F'1 said axis remaining perpendicular

  in the P plane. During frame scan the field mirror

  oscillates around this point I on either side of D I of the po-

  32 is set at position 33 respectively corresponding to field image point I and F2 in the lens. In this way the maximum focal points are almost divided by two, the residual differences being those measured between

  crrihe 41 and the line A B of FIG.

  It goes without saying that the invention also extends to the case where the focal surface of the lens is convex spherical with respect to the incident light and the exit pupil located behind the focal surface, or, in case, where the exit pupil is rejected to infinity and the focal plane surface. According to the invention the mirror rolls on a portion of hyperbola or parabola. In the case of hyperbole the foci of this one are still the center of the exit pupil of the objective and the point D. In the case

  of the parable its focus is at the point D and its parallel axis

  to the optical axis of the lens.

  It goes without saying that in these latter cases it is possible to use circles tangent to said parabola and hyperbola at the point of constact of the frame mirror corresponding to the median direction of the field and having the same radius of curvature.

  that said parabola and hyperbole. Also part of the

  the measures taken to reduce the defocusing as well

  introduced, measures similar to those taken for a

lens wedge, concave.

  It goes without saying that part of the invention is

  any application and industrial use of the raster scan system in connection with the motion of the field mirror

described above.

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Claims (3)

CLAIMS:   1. An optical scanning device for a field of vision divided into different zones and for visualizing said field, the device according to which said scanning is carried out in two perpendicular directions, namely, in one direction x a scan called line scanning and following another direction y a scan called frame scan or image, device operating said scans according to beams from different areas   of the field and ensuring the convergence of said beams on a   radiation-sensitive content of said beams,   positive generally comprising in the order, in the direction of the path of the median incident beam from the field of view, an objective, weft scanning means in the y direction, a system for folding the beams delimited by the opening of the objective towards line scanning means of the image field of the objective in the direction x and the sensitive element, said line scanning means, the sensitive element, possibly other elements related to those mentioned above for viewing direct from the image of the analyzed field, the means of said device being as follows: the objective has its optical axis included in a plane P containing the direction y and perpendicular to x, its focal surface being spherical and such that its center of curvature is located in the center of the exit pupil of the objective, - the frame scanning means are constituted by a plane mirror, said frame, rotating reciprocating about a p axis arallel to the x direction, placed in a converging beam behind the objective near the image of the field in this objective, - the line baying means consist, on the one hand, of a drum in uniform rotation around a fixed axis YY 'contained in   said plane P and carrying a large number of reflecting plane faces.   and distributed on the periphery of said drum, and, on the other hand, an image transport system symmetrical with respect to said plane P forming an image of the sensitive element.   a fixed point A 'of the drum rotation axis YYt', said drum   bour being placed in convergent bundle in the path of said system.   conveying the image of the sensitive element, the symmetry   said point A 'with respect to each face of the drum when said face is perpendicular to the plane P being a point D of a 12 2593657   ax-ZZ 'perpendicular to YY, the optical system for folding the beams consists of a so-called crncave said field mirror admitting the plane P as a plane of symmetry and whose vertex is placed substantially at the point D, said mirror being determined from in such a way that it combines in connection with the frame mirror the center O of the exit pupil of the objective with a fixed point O 'of the axis YY', said mirror of   field to ensure the nullity of the dead time of   lay between two consecutive lines having at most one width   in the direction x slightly less than the length of the line   lysed itself equal to the distance between the images of the detector in two consecutive faces of the rotating drum, said mirror being animated with a small amplitude movement in phase with the movement of the weft scanning means, characterized in that the focal surface of the objective is concave with respect to the incident light, the weft mirror rotates reciprocally while remaining tangent to an ellipse portion located in the long axis plane P equal to the radius of curvature of the focal surface of the objective, and one of which is occupied by the center of the exit pupil of the objective and the other by the point-D, and   in that the movement of the field mirror is a movement of rotation   alternating rotation about an axis passing through D parallel to x, said rotation being synchronous with the movement of the weft mirror and such that the average radius of the beam is reflected in the fixed direction DO ', 2. Device according to claim 1, characterized in that the portion of ellipse used is located mainly on the half of the ellipse, bounded by its minor axis, and which is the closest to D,   3- Device according to claim 1 or 2, characterized   in that the envelope curve of the mirror is a circle very close to the preceding ellipse, said circle being the circle tangent to the ellipse at the point of contact corresponding to the center of the   analyzed field and whose center and radius of curvature are   the center and radius of curvature of the ellipse at said point of contact, the slight defocus introduced being reduced by a slight translation parallel to the plane P of the axis of rotation of the field mirror, Device according to claim 3 characterized 4. 13 2593657   in that the axis of rotation of the field mirror is displaced parallel to the plane P at the point of intersection of the outer bisector of the angle EDO 'and the mediator of the line segment D FI, where E is the point of contact of the frame mirror with its corresponding envelope circle-in the middle of the analyzed field and FI the image of the field given by the objective and the frame mirror for one of the extreme field directions analyzed, 5. Device-like device according to one   Claims 1 to 2 characterized in that the pupil of   the end of the lens being infinite and its focal surface plane,   the weft mirror rolls on a parabola portion of parallel axis   correlates with the optical axis of the objective and focal point occupied by the point D, 6. Device similar to the device according to one   Claims 1 to 2, characterized in that the focal area   of the objective being convex and the exit pupil of the objective downstream from the focal surface, the frame mirror rolls on a portion of hyperbole whose foci are occupied respectively by the center of the exit pupil of the objective and by point D,   Device according to one of claims 5 and 6   in that the envelope curve of the frame mirror is   a circle very close to a parabola or a hyperbole   being tangent to the said parabola or hyperbola at the point of con-   tact of the mirror with its envelope and whose center and radius of curvature are respectively the center and radius of curvature of the parabola or hyperbola at said point of contact, the slight defocusing introduced being reduced by a slight translation parallel to the plane P of the axis of rotation of the field mirror as indicated in claim 4,   8. Device according to one of claims 1 to 7   characterized in that it is provided on both sides of the plane P and   parallel to this plane, tracks of identical section   tick to the conical curve wrapped by the frame mirror and on each of which rolls said mirror,   9. Device according to one of claims 3, 4,   7, characterized in that the weft mirror is integrally bonded to an arm of constant length, articulated about an axis passing by the center of the envelope circle.