Abstract:
The collimated test object according to the invention is used for projecting to infinity a set of marks, the positions of which are very accurately known so as to be able to verify the alignment et/or the distortion of optical equipment such as sensors or collimated screens. This test object comprises a plurality of microcollimated sets each comprising a light source, an elementary test object comprising a mark illuminated by said source as well as a collimation lens for projecting said mark to infinity. 
     With this solution, one gets free of aberration problems to which are subject convention test objects of large dimensions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a test object used for projecting to infinity a set of marks which may for example form a grid of points, of crosses or other patterns and the positions of which are very accurately known in order to verify alignment and/or distortion of optical equipment such as for example sensors, collimated screens, . . . . 
         [0003]    2. Description of the Prior Art 
         [0004]    Traditionally, a collimated test object is made from a plate comprising the set of desired marks and a device for projecting to infinity these marks, comprising a combination of lenses. 
         [0005]    This combination of lenses, often very complex, is designed so as to achieve not only collimation but also correction of chromatic and geometrical aberrations which are all the more apparent since the dimensions of the test object located behind the lenses are large. 
         [0006]    Generally, this combination of lenses is specifically designed for each particular purpose and has a very high manufacturing cost. 
       OBJECT OF THE INVENTION 
       [0007]    The object of the invention is therefore more particularly to suppress these drawbacks. 
       SUMMARY OF THE INVENTION 
       [0008]    For this purpose, instead of using a test object comprising a plurality of light marks and a collimation device common to all the marks of this test object and which consequently comprises a complex and costly combination of lenses for suppressing aberrations, it proposes a test object comprising a plurality of microcollimated sets each comprising a light source, an elementary test object comprising a mark illuminated by said source as well as collimation means for projecting said mark to infinity. 
         [0009]    Considering the fact that in each of the microcollimated sets, the mark which has very small dimensions is centered on the optical axis of the collimation means, the aberration problems mentioned earlier are disposed of and it becomes possible to use collimation means consisting in a simple collimation lens, easy to mount and therefore not very costly. 
         [0010]    Thus, unlike the prejudices of one skilled in the art who would naturally tend to use a single optical assembly for reducing costs, this solution proves to be less costly and further provides larger flexibility in use. 
         [0011]    Moreover, the axes of the collimated assemblies may be oriented depending on the field required for forming the overall collimated image of the test object. This orientation may be obtained statically, for example by machining the support of the test object or dynamically by for example using micromechanisms, magnetic or electromagnetic, acousto-optical systems, etc. 
     
    
     
       BRIEF DSCRIPTION OF THE DRAWINGS 
         [0012]    Embodiments of the invention will be described hereafter, as non-limiting examples, with reference to the appended drawings wherein: 
           [0013]      FIG. 1  is a front view of a test object according to the invention comprising a plurality of microcollimated sets; 
           [0014]      FIG. 2  is a sectional view of a microcollimated set used in the test object illustrated in  FIG. 1 ; 
           [0015]      FIGS. 3 and 4  show an alternative embodiment of a microcollimated set equipped with a device for adjusting the elementary test object,  FIG. 3  being a schematic perspective view,  FIG. 4  being a partial axial sectional view; 
           [0016]      FIGS. 5-8  are schematic illustrations of the extreme positions of an elementary test object. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    In the example illustrated in  FIGS. 1 and 2 , the test object according to the invention consists of a supporting plate  1  provided with a plurality of through-perforations  2  of a small diameter (a few millimetres) in each of which a collimated assembly is positioned, comprising a light source  3 , an elementary test object  4  forming a light mark  5  illuminated by the source  3  and a collimation lens  6  for projecting said mark  5  to infinity. 
         [0018]    In this example, the perforations  2  and, consequently, the microcollimated marks are positioned so as to form a &lt;&lt;radiating&gt;&gt; pattern from a central mark. The position of these marks is determined and known accurately. 
         [0019]    The perforations  2  of the supporting plate housing the collimated assemblies each have a cylindrical shape stepped with several bore levels comprising:
       a first tapped cylindrical section T 1  which extends from the rear face  7  of the plate  1  and has a length here substantially equal to three quarters of the thickness of the plate  1 ,   a second section T 2  with smooth cylindrical surface which has a diameter less than that of the first section T 1 ,   a third section T 3  of a small length, with a diameter less than that of the second section T 2 : this third section T 3  appears as an annular ring, forming a bore shrinkage,   a fourth section T 4  of a frustro-conical shape, flaring right up to the front face  8  of the plate  1 .       
 
         [0024]    The collimation lens  6  of a partly cylindrical shape, with a diameter substantially equal to that of the second section T 2  and with a lens slightly longer than the latter, is positioned inside the perforation  2 . 
         [0025]    This lens  6  is engaged into the second section T 2  so as to come axially into abutment onto the bore shoulder of the third section T 3 . 
         [0026]    Maintaining the lens  6  in position in the second section T 2  is ensured by means of a cylindrical bushing  9  with an outer threaded surface which will screw into the tapped thread of the first section T 1  until it bears upon the lens  6  in order to maintain it applied against the shoulder of the section T 3 . 
         [0027]    The cylindrical inner surface of the bushing on the side opposite to its supporting surface on the lens, has a bore stepping  10  forming a cylindrical bore section T 5  with a larger diameter, in which the elementary test object  4  illuminated by the light source  3  is positioned. The elementary test object  4  consists in a flat disk provided at its centre with a perforation forming the light mark  5 . 
         [0028]    In this example, the light source  4  has been schematically illustrated by a block, it being understood that the invention is not limited to a particular light source. 
         [0029]    The elementary test object  4  is centered here on the optical axis of the lens  6  and its front face is placed in the object focal plane of said lens  6 . 
         [0030]    Consequently at the output of the lens  6 , a parallel light beam is obtained. The image of the light mark  5  is projected to infinity. 
         [0031]    By means of these arrangements, the test object according to the invention behaves in a similar way to conventional test objects using an optical assembly common to the light marks of the test object. However, the beams emitted by the microcollimated sets are not subject to aberration phenomena as this is the case in conventional test objects. 
         [0032]    The field required for forming the collimated global image produced by the test object illustrated in  FIG. 1  is obtained by tilting by a predetermined angle, the optical axis of the microcollimated assemblies. This tilt may be obtained statically during machining of the perforations  2  or dynamically by using micromechanical, magnetic or other assemblies for example. 
         [0033]      FIGS. 3-8  illustrate the principle of a centering and/or play compensating device of the elementary test object  4  in a spacer bushing  9 ′ of the type of bushing  9  illustrated in  FIG. 2 . 
         [0034]    In this example, the spacer bushing  9 ′ is provided on the side of the elementary test object  4 ′ with two axial perforations positioned at about 45° from each other, which open into the cylindrical bore section T′ 5 . 
         [0035]    Moreover, on this same side, the spacer bushing  9 ′ may be closed by adjustment tooling comprising a lid-shaped body  15  which will be screwed onto the end of the spacer bushing  9 ′. This body  15  comprises two tapped perforations  16 ,  17 , respectively located in the axis of the axial perforations  13 ,  14 , a central perforation  18  intended to receive (or to be illuminated by) a light source and an axial cavity  19  formed in the border of the lid opposite to both tapped perforations  16 ,  17 . 
         [0036]    As earlier, the elementary test object  4 ′ has a diameter less than the diameter of the bore section T′ 5  of the bushing  9 ′ and is positioned axially in abutment against the bore shoulder E′. 
         [0037]    It is retained vertically on two supporting cones  20 ,  21  which extend, two adjustment screws  22 ,  23  coaxially which will respectively be screwed into the tapped perforations  16 ,  17 . 
         [0038]    By means of these arrangements, the displacement of the elementary test object  4 ′ in a radial plane of the spacer bushing  9 ′ is obtained by a wedge effect by turning the screws  22 ,  23  so as to generate axial displacements of the conical ends of said screws  22 ,  23 . 
         [0039]    Control of the position of the optical axis of each microcollimator (materialized by the position of the elementary test object  4 ′) is carried out by means of a theodolite, the illumination of the microtest object  4 ′ being then ensured by means of the light source associated with the adjustment tooling. 
         [0040]    When the elementary test object  4 ′ is placed properly, a point of adhesive  25  is injected through the axial cavity  19 . 
         [0041]      FIGS. 5-8  show different positions of the microtest object versus the screwing level of the screws. 
         [0042]    Thus,  FIG. 5  corresponds to a position in which the screws  22 ,  23  are in the unscrewed condition. In  FIG. 6 , the screw  22  is in the screwed condition, whereas the screw  23  is in the unscrewed condition.  FIG. 7  corresponds to a position in which both screws  22 ,  23  are in the screwed condition. In  FIG. 8 , the screw  23  is in the screwed condition whereas the screw  22  is in the unscrewed condition. 
         [0043]    As indicated earlier, the solution proposed by the present invention has many advantages. In particular:
       The overall size of the microcollimated test object is not limited. The overall size may range well beyond what may be contemplated with a lens combination.   The shape of the collimator is not limited. The making of concave or convex collimators may be contemplated for encompassing detectors with very large fields (example: a projection dome for large field cameras).   The dynamics of marks. It is possible to independently control each mark and thereby produce a dynamic collimated test object.   Easy production of a visible, infrared, near infrared or combined collimated test object.   The manufacturing cost is much less than for a collimator with a lens combination.