Abstract:
System for inspecting a surface, the system including a light source, a first transparent mirror, and a detector, wherein the light source projects a first light beam on the first transparent mirror, the first transparent mirror reflects the first light beam towards the surface in a direction normal to the surface, and wherein the detector detects a second light beam reflected from the surface, in a normal direction, through the first transparent mirror.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to light detection systems in general, and to methods and systems for inspecting reflective surfaces and objects, in particular.  
         BACKGROUND OF THE INVENTION  
         [0002]    Systems for detecting surface anomalies are known in the art. These systems detect changes in surface properties of continues strips of reflective surfaces, and defects in objects moving on a conveyor system. Such surface properties include printed matter in a press, detection of lacquer quality and thickness thereof on printed matter, cold seal of packages, color of metals and the like. Defects include burrs and corrosion on metals, defects in sharp edges of knives and the like.  
           [0003]    It will be appreciated by those skilled in the art that the detection reflective of any detail of a reflective material is problematic due to the high intensity of light, which is reflected from the reflective material towards the detector.  
           [0004]    Reference is now made to FIG. 1, which is a schematic illustration of a detection system, known in the art. The system includes a light source  10  and a camera  12 . The light source produces a plurality of light rays  20 ,  22  and  24  which are directed at an inspected surface  14 , which has a reflective semi-transparent layer  16 . The surface  14  incorporates two particles  18 A and  18 B. The term “particle” herein after refers to foreign particles with respect to reflective semi-transparent layer  16 , such as dust, debris, solid matter, and the like. Light ray  20  is reflected from particle  18 B, as a light ray  20 ′ about an axis of symmetry  30 , normal to surface of particle  18 B. Light ray  22  is reflected from reflective semi-transparent layer  16 , as a light ray  22 ′ about an axis of symmetry  32 , normal to reflective semi-transparent layer  16 . Light ray  24  is reflected from particle  18 A, as a light ray  24 ′ about an axis of symmetry  34 , normal to surface of particle  18 A. Detector  12  detects light rays  20 ′,  22 ′ and  24 ′.  
           [0005]    A light ray  26  striking the reflective semi-transparent layer  16  away from particles  18 A or  18 B, is reflected sideways as a light ray  26 ′ from reflective semi-transparent layer  16 , and is not detected by camera  12 . It is noted that the light intensity of ray  22 ′ is significantly greater than of rays  20 ′ and  24 ′. The image, which is detected by camera  12 , is affected by the intensity of the most powerful rays, detected thereby. Hence, the details, which are embedded in weaker rays, are likely to disappear in that image.  
           [0006]    U.S. Pat. No. 4,291,990 to Takasu, is directed to an apparatus for measuring the distribution of irregularities on a mirror surface. The mirror surface may be a silicon wafer. The mirror surface to be inspected illuminated by means of a light source. Light surfaces reflected from the mirror surface are projected onto a screen by means of a half-mirror.  
           [0007]    U.S. Pat. No. 5,331,397 to Yamanaka, et al. is directed to an inner lead bonding inspecting method and inspection apparatus. The pellet is to be inspected using the apparatus and is illuminated by means of a light source that is reflected onto pellet by means of half mirror. Reflections from the surface being inspected, are then transmitted through the same half mirror as indicated by beam and is picked up by the image pick-up device. The pick-up device may be a monochromatic ITV camera. The image signal from the image pick-up device is then transmitted to the measurement device and stored in an image memory for use by a measurement device. The images seen by the pick-up device may also be displayed on a monitor.  
           [0008]    U.S. Pat. No. 5,497,234 to Haga is directed to an inspection apparatus for detecting marks formed on a sample surface. The system includes an illuminating device for a light source, which is projected onto the sample to be inspected by means of a beam splitter. The image from the sample is then reflected through collimator lens and back through the beam splitter and into camera tube.  
           [0009]    U.S. Pat. No. 5,523,846 to Haga is directed to an apparatus for detecting marks formed on a sample surface. The light source is projected onto a sample surface through a half mirror. The light reflected from the surface is then returned to the half mirror through camera lens and projected onto a CCD.  
           [0010]    U.S. Pat. No. 5,369,492 to Sugawara is directed to a bonding wire inspection apparatus. The sample is illuminated by a light source, which is deflected through half-mirror onto sample. The reflected light beam is then passed through half-mirror and is picked up by camera.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the present invention to provide a method and a system for inspecting reflective surfaces and objects, which overcomes the disadvantages of the prior art.  
           [0012]    In accordance with the present invention there is thus provided, a system for inspecting a surface. The system includes a light source, a first transparent mirror and a detector. The light source projects a first light beam on the first transparent mirror, and the first transparent mirror reflects the first light beam towards the surface in a direction normal to the surface. Furthermore, the detector detects a second light beam reflected from the surface, in a normal direction, through the first transparent mirror.  
           [0013]    The system further includes an image processor, connected to the detector, for processing at least one image detected by the detector, and a controller connected to the light source. The controller controls properties of the light source, such as the size of aperture, illumination intensity, radiation wavelength, illumination duration, intervals of illumination, and the like.  
           [0014]    The system further includes a controller connected to the detector, whereby the controller controls the size of the aperture of the detector. The detector is either a charge coupled device (CCD), or a television camera, and the surface is either stationary or moving.  
           [0015]    The system furthermore includes an optical condenser, located between the light source and the first transparent mirror. The system further includes a first screen located in sequence with the optical condenser and the first transparent mirror, along an axis, wherein the axis is determined by the light source and the first transparent mirror.  
           [0016]    The system further includes a second transparent mirror, and a concave mirror. The second transparent mirror is located in sequence with the surface and the first transparent mirror, on an axis normal to the surface, wherein the axis is determined by the first transparent mirror. The concave mirror is located along an axis determined by the detector and the second transparent mirror. The second transparent mirror reflects the second light beam towards the concave mirror, and the detector detects a light beam reflected from the concave mirror through the second transparent mirror.  
           [0017]    The system can further includes a second screen located in sequence with the first transparent mirror and the second transparent mirror, on an axis normal to the surface.  
           [0018]    In accordance with another aspect of the present invention, there is thus provided a method for inspecting a surface. The method includes the steps of projecting a first light beam by a light source on a first transparent mirror, reflecting at least a portion of the first light beam by the first transparent mirror, in a direction normal to the surface, and detecting a second light beam reflected by the surface in a normal direction, through the first transparent mirror.  
           [0019]    The method further includes the steps of collimating the first light beam, absorbing a passing portion of the first light beam, passing through the first transparent mirror, and reflecting at least a portion of the second light beam by a second transparent mirror, towards a concave mirror. The method can furthermore includes the steps of absorbing a passing portion of the second light beam, passing through the second transparent mirror, and detecting a light beam reflected by the concave mirror through the second transparent mirror.  
           [0020]    In accordance with a further aspect of the present invention, there is thus provided a system for inspecting a surface. The system includes a detector, a light source, a transparent mirror, a mirror, and an optical condenser. The light source is located in sequence with the surface and the detector. The mirror is located in sequence with the surface and the transparent mirror.  
           [0021]    The mirror reflects a first light beam received from the light source, towards the surface through the transparent mirror, in a direction normal to the surface. The transparent mirror reflects light towards the detector, wherein the light is initially reflected from the surface.  
           [0022]    The transparent mirror reflects a second light beam, received from the light source, towards the surface, and the surface receives also a third light beam from the light source. The optical condenser is located between the mirror and the transparent mirror, wherein the optical condenser collimates a reflection of the first light beam, from the mirror towards the surface. The system further includes an image processor, and a controller. The image processor is connected to the detector, for processing at least one image detected by the detector. The controller is also connected to the light source. The controller controls properties of the light source, such as the size of aperture, illumination intensity, radiation wavelength, illumination duration, intervals of illumination, and the like.  
           [0023]    The system can further include a controller connected to the detector, for controlling size of the aperture of the detector. The detector is either a charge coupled device (CCD), or a television camera, and the surface is either stationary or moving. It is noted that the same controller can be adapted to control both the detector and the light source.  
           [0024]    In accordance with another aspect of the present invention, there is thus provided a system for inspecting a surface. The system includes a light source, a detector, a transparent mirror, and a concave mirror located in sequence with the detector and the transparent mirror. The light source projects a light beam towards the surface, and the transparent mirror reflects a portion of light towards the concave mirror, wherein the light is reflected from the surface. The concave mirror directs the portion of light towards the detector through the transparent mirror, and the detector detects the portion of light. The system further includes a screen located in sequence with the transparent mirror and the surface, on an axis normal to the surface.  
           [0025]    In accordance with a further aspect of the present invention, there is thus provided a method for inspecting a surface. The method includes the steps of reflecting a first light beam, towards the surface, through a transparent mirror, and reflecting light, which is reflected from the surface, by the transparent mirror towards a detector. The method further includes the steps of detecting the light by the detector, reflecting a second light beam by the transparent mirror towards the surface, and projecting a third light beam towards the surface, wherein the first light beam, the second light beam, and the third light beam are produced by a single light source. The method can further include the step of collimating a reflection of the first light beam.  
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0026]    The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with drawings in which:  
         [0027]    [0027]FIG. 1 is a schematic illustration of a detection system, known in the art;  
         [0028]    [0028]FIG. 2A is a schematic illustration of a moving sample, having a transparent coating and a detection system, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0029]    [0029]FIGS. 2B and 2C are schematic illustrations of the moving sample and the detection system of FIG. 2A, at different positions;  
         [0030]    [0030]FIG. 3A is an illustration of another reflective moving sample and the detection system of FIG. 2A;  
         [0031]    [0031]FIG. 3B is an illustration of a moving sample partly reflective and partly diffusive, and the detection system of FIG. 2A;  
         [0032]    [0032]FIG. 4 is a schematic illustration of a partly reflective partly diffusive sample and a detection system, constructed and operative in accordance with another preferred embodiment of the present invention;  
         [0033]    [0033]FIG. 5 is a schematic illustration of a reflective sample and a detection system, constructed and operative in accordance with a further preferred embodiment of the present invention; and  
         [0034]    [0034]FIG. 6 is a schematic illustration of a reflective sample and a detection system, constructed and operative in accordance with another preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    The detailed description of the invention is generally applicable to optical devices for detection of surface anomalies. In particular, the description is concerned with detection of changes in surface properties of continuous strips of reflective materials, and defects in objects moving on a conveyor system. Such surface properties include printed matter in a press, detection of lacquer quality and thickness thereof on printed matter, cold seal of packages, and color of metals. Defects include burrs and corrosion on metals, and defects in sharp edges of knives. The device according to the present invention can differentiate among colors on a reflective surface.  
         [0036]    The present invention overcomes the disadvantages of the prior art by providing a system in which the final illuminating beam and the detection line of sight are located on the same axis, perpendicular to the scanned work-piece.  
         [0037]    Reference is now made to FIGS. 2A, 2B and  2 C. FIG. 2A is a schematic illustration of a moving sample, generally referenced  150 , having a transparent coating and a detection system, generally referenced  100 , constructed and operative in accordance with a preferred embodiment of the present invention. FIGS. 2B and 2C are schematic illustrations of the moving sample  150  and the detection system  100  of FIG. 2A, at different positions.  
         [0038]    Detection system  100  includes a light source  102 , a transparent mirror  108 , a detector  104 , and an image processor  106 . Light source  102  can be an incandescent, halogen, fluorescent, mercury vapor, metal halide, high pressure sodium, low pressure sodium lamp, a light emitting diode, laser, a semiconductor device, and the like. Furthermore, light source  102  can create coherent or incoherent beams of light in any frequency within and including the infrared and ultraviolet frequencies.  
         [0039]    Transparent mirror  108  is a mirror that reflects part of the light beam falling on it, and transmits part. Transparent mirror  108  faces light source  102  in an inclined position. Detector  104  is an optic detector such as a Charge Coupled Device (CCD), a photoemissive tube, and the like. Detector  104  is located behind transparent mirror  108 , such that line of sight of detector  104  is perpendicular to the beam emanating from light source  102 . Image processor  106  is an electronic unit that converts video signal to electric current. Detector  104  inputs a video signal to image processor  106 .  
         [0040]    Moving sample  150  is positioned below detector system  100 , and moves in a direction designated by arrow  130 . Moving sample  150  includes a transparent and reflective coating  152 . Moving sample  150  includes foreign particles  154 A, and  154 B. Foreign particle  154 A is located below coating  152 , and foreign particle  154 B is located above coating  152 . Both foreign particles  154 A and  154 B are located to the right of detection system  100 , and foreign particle  154 B is to the right of foreign particle  154 A. Detection system  100  detects foreign particles  154 A and  154 B at specific positions of moving sample  150 , with respect to detection system  100 .  
         [0041]    Light source  102  directs diverging beams of light  120 A,  122 A, and  124 A, to transparent mirror  108 . Transparent mirror  108  reflects beams  120 A,  122 A, and  124 A, as beams  120 B,  122 B,  124 B, respectively, and directs them to sample  150 . Coating  152  reflects diverging beams  122 B, and  124 B, sideways, as beams  122 C, and  124 C, respectively, and therefore beams  122 C, and  124 C, do not reach the transparent mirror  108 . Normal light beam  120 B, penetrates coating  152 , and reaches the moving sample  150 . Moving sample  150  reflects normal light beam  120 B, perpendicularly in the original path of light beam  120 B. Normal light beam reflected from moving sample  150 , passes through transparent mirror  108 , and reaches detector  104  as light beam  120 C. Detector  104  detects light beam  120 C, and generates a video signal, which is then processed by image processor  106 .  
         [0042]    It is noted that foreign particles  154 A, and  154 B, are located to the right of normal light beam  120 B. Therefore, normal light beam  120 B, does not reach foreign particles  154 A, and  154 B, and detector  104  does not detect foreign particles  154 A and  154 B. Likewise, image processor  106  reports that moving sample  150  is free from foreign particles. If foreign particle  154 B is located at a horizontal position similar to foreign particle  154 A, likewise it is not detected by detector  104 . Light rays  122 C, and  124 C are again reflected sideways, and do not reach detector  104 .  
         [0043]    With reference to FIG. 2B, moving sample  150  is in an advanced position with respect to its position in FIG. 2A. Moving sample  150  is in such state that foreign particle  154 A is partly located under normal light beam  120 B. Therefore, foreign particle  154 A reflects the normal light beam  120 B, sideways, as light beam  120 C, which does not reach detector  104 . In this case too, as in FIG. 2A, the image processor  106  reports that moving sample  150  is free from foreign particles.  
         [0044]    With reference to FIG. 2C, the moving sample  150  is in a further advanced position with respect to its position in FIG. 2B. Moving sample  150  is in such state that foreign particle  154 A is directly located under normal light beam  120 B. Foreign particle  154 A reflects normal light beam  120 B, perpendicularly in the original path of light beam  120 B. Normal light beam reflected from foreign particle  154 A, passes through transparent mirror  108 , and reaches detector  104  as light beam  120 C. Detector  104  detects light beam  120 C, image processor  106  senses a change in the incoming signal, and reports that foreign particle  154 A is present. If foreign particle  154 B is located at a horizontal position similar to particle  154 A, likewise it is detected by detector  104 .  
         [0045]    Reference is now made to FIG. 3A, which is an illustration of a reflective moving sample, generally referenced  160  and the detection system  100  of FIG. 2A. Sample  160  is a substantially reflective matter, such as aluminum foil, moving under detection system  100 , in a direction, normal to detection system  100 . A stripe of cold seal  164  is located on top of sample  162 , normal to direction of movement of sample  160 . Moving sample  160  is in such position with respect to detection system  100 , that the cold seal  164  is located directly below normal light beam  120 B. Cold seal  164  reflects normal light beam  120 B, perpendicularly in the original path of light beam  120 B. Normal light beam reflected from cold seal  164 , passes through transparent mirror  108 , and reaches detector  104  as light beam  120 C. Detector  104  detects light beam  120 C, and image processor  106  reports that cold seal  164  is present.  
         [0046]    Reference is further made to FIG. 3B, which is an illustration of a moving sample partly reflective and partly diffusive, generally referenced  168  and the detection system  100  of FIG. 2A. Moving sample  168  includes a non-reflective diffusive section  166 . Normal light ray  120 B striking the surface of diffusive section  166 , is diffusively reflected as light rays  120 D, and therefore light rays  120 D do not reach detector  104 . As described with reference to FIG. 3A, light rays  122 C and  124 C are reflected sideways, and do not reach detector  104  neither. Therefore, detection system  100  can differentiate between a reflective section of moving sample  168  (for instance cold seal  164  as described with reference to FIG. 3A), and a diffusive section  166 .  
         [0047]    If surface of section  166  is reflective, but less reflective than cold seal  164 , part of the light rays  120 D reflected from surface of section  166  reach detector  104 , whereas as described with reference to FIG. 3A, light ray  120 B is perpendicularly reflected from (reflective) cold seal  164 , and light ray  120 B is entirely detected by detector  104 . For example, if surface of cold seal  164  is 90% reflective, and surface of section  166  is 80% reflective, then, respectively 90% and 80% of light ray  120 B is reflected from cold seal  164  and section  166 , and respectively 90% and 80% of light ray  120 C reach detector  104 . Therefore, the intensity of light ray  120 B reflected from surface of section  166 , and reaching detector  104 , is less than the intensity of light ray  120 B reflected from cold seal  164 . The detector  104  generates video signals, which are different for light rays of different intensities, detected thereby. Thus, detection system  100  of FIG. 3B can differentiate surfaces of different reflectivities. Similarly, detection system  100  of FIG. 3A can detect cold seal  164 , because the reflectivity of cold seal  164  and surface  162  of moving sample  160  are different.  
         [0048]    Reference is now made to FIG. 4, which is a schematic illustration of a partly reflective partly diffusive sample, generally referenced  250  and a detection system, generally referenced  200 , constructed and operative in accordance with another preferred embodiment of the present invention. Detection system  200  includes a light source  202 , a detector  204 , an image processor  208 , a controller  212 , a mirror  216 , a condenser  218 , and a transparent mirror  220 .  
         [0049]    Light source  202 , is an ordinary or a flashing light bulb, or a chromatic or monochromatic light bulb, or a halogen lamp and the like, having constant or variable intensity. Detector  204  is an optic detector such as a Charge Coupled Device (CCD), a television camera, and the like. Image processor  208  is an electronic unit that converts video signal to electric current. Controller  212  controls the operating parameters of light source  202 , such as intensity, wavelength, duration, and frequency of illumination, according to signals received from image processor  208 . Mirror  216  is a flat mirror that reflects light beams. Condenser  218  consists of two Fresnel lenses, and it condenses light beams. Transparent mirror  220  is a mirror that reflects part of the light beam falling on it, and transmits part.  
         [0050]    Mirror  216  is positioned to the left and slightly above light source  202 , and at an angle to the horizon, in order to reflect the light beams it receives from light source  202 , to condenser  218 . Condenser  218  is positioned horizontally below mirror  216 . Sample  250  is below the detection system  200 . Transparent mirror  220  is located below condenser  218 , at an angle to the horizon, in order to direct light beams reflected from sample  250 , to detector  204 . Detector  204  is positioned to the right of transparent mirror  220 , and above sample  250 . Image processor  208  is connected between detector  204 , and controller  212 . Light source  202  in turn is connected to controller  212 .  
         [0051]    Light source  202  directs diverging light beams  230 A, and  232 A, to mirror  216 , for inspection of a reflective section of sample  250 . Mirror  216  reflects light beams  230 A, and  232 A, as light beams  230 B, and  232 B, respectively, to condenser  218 . Condenser  218  condenses light beams  230 B, and  232 B, to light beams  230 C, and  232 C, respectively. Light beams  230 C, and  232 C, pass through transparent mirror  220 , and strike the sample  250  as light beams  230 D, and  232 D, respectively. Sample  250  reflects light beams  230 D, and  232 D, as light beams  230 E, and  232 E, respectively, and strike transparent mirror  220 . Transparent mirror  220  reflects light beams  230 E, and  232 E, as light beams  230 F, and  232 F, respectively. Light beams  230 F, and  232 F, in turn enter detector  204 .  
         [0052]    Detector  204  detects light beams  230 F, and  232 F, and outputs video signal  206 . Image processor  208  converts video signal  206  to electric signals  209 , and  210 . Signal  209  is input to a display unit (not shown), that displays the image detected by detector  204 . Controller  212  controls functional parameters of light source  202 , such as intensity, wavelength, duration, and frequency of illumination through a signal  214  to light source  202 . Furthermore, image processor  208  can supply feedback signal  210  to controller  212 .  
         [0053]    Light source  202  directs diverging light beams  234 A, and  236 A, for inspection of a diffusive section of sample  250 . Transparent mirror  220  reflects light beam  234 A, as light beam  234 B. Sample  250  diffusively reflects light beam  234 B as light beam  234 C. Transparent mirror  220  reflects light beam  234 C, as light beam  234 D, and detector  204  detects light beam  234 D. Sample  250  diffusively reflects light beam  236 A, as light beam  236 B. Transparent mirror  220  reflects light beam  236 B, as light beam  236 C, and detector  204  detects light beam  236 C. light beams  230 A,  232 A,  234 A, and  236 A are in phase. Therefore, detector  204  can simultaneously  
         [0054]    Detection system  200  can determine quality of color prints having transparent and reflective coatings, as well as quality of reflective colors. Detection system  200  further determines thickness of reflective coatings, such as lacquer. This is due to the fact that intensity of light beams reflected off a transparent coating, and reaching a detector, is a function of thickness of the coating. Detection system  200 , further yet determines quality of metallic articles having a reflective surface, such as knife-edges, corrosion, and burrs on a machined mechanical part. Furthermore, detection system  200 , determines changes in surface properties, such as an unreflective cold seal on a reflective substance, and changes in color on a reflective metal surface.  
         [0055]    The present invention also provides means for controlling the resolution of an image of sample  250  detected by detector  204 . The resolution of the image is controlled by varying either the diameter of an aperture (not shown) of light source  202 , through which the light rays exit light source  202 , or the diameter of an aperture (not shown) of detector  204  through which light rays enter detector  204 . The aperture may be of the type employed in still image cameras, and the diameter of the aperture may be changed by methods known in the art, such as by an electric motor, and the like. The smaller the aperture of light source  202  or detector  204 , the greater the resolution and brightness of an image of sample  250  detected by detector  204 . It is noted that detection system  200  may be employed for detecting stationary samples.  
         [0056]    It may be appreciated by those skilled in the art, that one advantage of detection system  200  is that while employing a strobing light source, no synchronization between light beams  230 A and  234 A, or between  232 A and  236 A is needed. Furthermore, light beams  230 A and  232 A have the same spectrum as light beams  234 A and  236 A, since they originate from a single light source.  
         [0057]    Reference is now made to FIG. 5, which is a schematic illustration of a detection system, generally referenced  300 , and a reflective sample, generally referenced  340 , constructed and operative in accordance with another preferred embodiment of the present invention. Detector system  300  includes a light source  326 , a detector  332 , an image processor  330 , and a controller  328 , as described in connection with FIG. 4. Detection system  300 , further includes a Fresnel condenser  302 , a transparent mirror  304 , a black screen  306 , a transparent mirror  308 , a concave mirror  310 , and a black screen  312 .  
         [0058]    Fresnel condenser  302 , converts diverging light beams, to parallel light beams. Transparent mirror  304  is a mirror that reflects part of the light beam falling on it, and transmits part. Transparent mirror  308 , is identical to transparent mirror  304 . Screen  306 , is a substantially flat screen of flat black color, which absorbs the incident light. Screen  312 , is identical to screen  306 . Concave mirror  310 , focuses the incoming parallel light beams at its focal point.  
         [0059]    The interconnections of the light source  326 , the detector  332 , the image processor  330 , and the controller  328 , are identical to those described in connection with FIG. 4. Sample  340  is located below detection system  300 . Fresnel condenser  302  is positioned vertically to the right of light source  326 . Transparent mirror  304 , is positioned to the right of Fresnel condenser  302 , generally at 45 degrees to the vertical and in a negative slope, in order to reflect the parallel light beams coming from the Fresnel condenser  302 , vertically onto sample  340 . Screen  306  is positioned vertically to the right of transparent mirror  304 , in order to absorb the light beams coming from transparent mirror  304 , and prevent their reflection. Transparent mirror  308 , is positioned directly above transparent mirror  304 , generally at 45 degrees to the vertical and in a positive slope, in order to reflect the parallel light beams reflected from sample  340 , vertically onto the concave mirror  310 . Concave mirror  310 , is positioned vertically to the right of transparent mirror  308 , with its concave side pointing towards transparent mirror  308 , in order to focus the parallel light beams reflected from transparent mirror  308 , at the lens of detector  332 . Detector  332  is positioned to the left of transparent mirror  308 , in order to receive the converging light beams, reflected from concave mirror  310 . Screen  312  is positioned horizontally above transparent mirror  308 , in order to absorb the light beams reflected from sample  340 , and passing through transparent mirrors  304 , and  308 , and prevent their reflection.  
         [0060]    Light source  326 , directs diverging light beams  320 A,  322 A, and  324 A, to Fresnel condenser  302 . Fresnel condenser  302  converts light beams  320 A,  322 A, and  324 A, to parallel and horizontal light beams  320 B,  322 B, and  324 B, respectively. Transparent mirror  304 , reflects light beams  320 B,  322 B, and  324 B, to parallel and vertical light beams  320 C,  322 C, and  324 C, respectively, on to sample  340 . Sample  340 , reflects light beams  320 C,  322 C, and  324 C, vertically in their original path. Part of light beams  320 B,  322 B, and  324 B, pass through transparent mirror  304 , exit as light beams  320 D,  322 D, and  324 D, and are absorbed by the screen  306 .  
         [0061]    Light beams  320 C,  322 C, and  324 C, reflected from sample  340 , pass through transparent mirror  304 , and exit as light beams  320 E,  322 E, and  324 E, respectively. Transparent mirror  308 , reflects light beams  320 E,  322 E, and  324 E, to parallel and horizontal light beams  320 F,  322 F, and  324 F, respectively, on to concave mirror  310 . Part of light beams  320 E,  322 E, and  324 E, pass through transparent mirror  308 , exit as light beams  320 G,  322 G, and  324 G, and are absorbed by screen  312 . Concave mirror  310 , reflects the parallel and horizontal light beams  320 F,  322 F, and  324 F, as converging light beams  320 H,  322 H, and  324 H, respectively, onto detector  332 .  
         [0062]    Reference is further made to FIG. 6, which is a schematic illustration of a detection system, generally referenced  400 , and a reflective sample, generally referenced  418 , constructed and operative in accordance with another preferred embodiment of the present invention. Detection system  400  is substantially similar to system  300  of FIG. 5, except that light source  326  and the Fresnel condenser  302 , are replaced by a light source  402  and a reflector  404 .  
         [0063]    System  400  includes a transparent mirror  406 , a concave mirror  408 , a black screen  410 , a detector  412 , an image processor  414 , and a controller  416 , which are substantially similar to the respective components described in connection with FIG. 5. Light beams exit the reflector, strike sample  418 , at substantially right angles thereto, and are reflected therefrom at substantially right angles. The light beams reflected from sample  418 , follow a path substantially similar to that depicted in FIG. 5, and are detected by detector  412 . It is noted that concave mirror  408  produces an image of light source  402  on detector  412 .  
         [0064]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. Rather the scope of the present invention is defined only by the claims, which follow.