Abstract:
A beam shaping apparatus including an optical lens is provided. The optical lens includes a diverging surface and a cylindrical surface. The diverging surface expands the input laser beam into a uniform line in one plane. The cylindrical surface converges the laser beam in another plane. Therefore, the output laser line has the desired width and the uniform density along its length.

Description:
FIELD OF INVENTION 
   The present invention relates to an apparatus, a module, and an optical lens for a line scanning technology to provide a uniformly projected beam line. 
   BACKGROUND OF THE INVENTION 
   In the spectral machine vision technology, the line scanning is provided to overcome the deficiencies of the point-scanning and the global-scanning technologies. Typically, in order to provide the line scanning capability, beam-shaping of a Gaussian laser beam into a beam line results in a Gaussian intensity distribution along the length of the projected line. U.S. Pat. No. 4,826,299 to Powell describes a single optical element which projects a laser line having uniform intensity along its length, as shown in  FIG. 1 . However, Powell lens  10  is designed to expand a circular beam, for example, a He—Ne laser, in a single direction to form a line. Such lens has been found to be very inefficient when used with a laser diode having an elliptical configuration, for example. In addition, Powell lens  10  is difficult to control the desired width of the projected line. 
   U.S. Pat. No. 5,283,694 discloses an anamorphic asphere lens that receives the non-circular beam as an input, and redistributes the non-circular input in two directions as rays which form a line of uniform width and intensity along its length and also form the line with well defined ends. However, it is quite complicated to manufacture the anamorphic asphere lens of U.S. Pat. No. 5,283,694, and the width of the beam line cannot be smaller than the diameter of the input beam. 
   U.S. Pat. No. 6,069,748 discloses a single lens element that controls the divergence of a diverging laser and creates a laser line at a target surface. The single element has a first surface of a toroidal shape. The first surface is concave about a center of curvature in at least one cross section and, in this cross section the laser diode is located at the center of curvature. However, the laser diode needs to be aligned with the center of curvature, and it is difficult to achieve the desired width of the laser line. 
   U.S. Pat. No. 6,688,758 also provides an apparatus and method for generating line patterns of laser. Wherein a diffractive optical element is positioned downstream of the anamorphic system for receiving and diffusing the first laser beam of the anamorphic system into a plurality of second laser beams. The plurality of second laser beams overlap one another at least partially so as to project a second linear pattern on the far field of altered intensity with respect to the first linear pattern. However, the additional diffractive optical element increases the cost, and it is difficult to achieve the desired width of the laser line. 
   Although the related art described above are useful for beam shaping, they may be improved. In particular, there is a need to achieve the desired width of the uniform laser line for the line scanning technology in a simple way. It will be advantageous that if an apparatus, a module, or an optical lens can divert the output uniform laser line in a desired direction. 
   SUMMARY OF THE INVENTION 
   The main aspect of the present invention is to provide an apparatus, a module, and an optical lens for the line scanning technology to provide a uniformly projected line. 
   Another aspect of the present invention is to provide an apparatus, a module, and an optical lens for the line scanning technology to provide a projected line with the desired width. 
   Still another aspect of the present invention is to provide an apparatus, a module, and an optical lens for the line scanning to provide a projected line output in the desired direction in a simple way. 
   In one embodiment, disclosed is a beam shaping apparatus including an optical lens and a source generating a laser beam. The optical lens includes a first surface and a second surface. The first surface, oriented toward the source to receive the laser beam, has an apex and being shaped to conform to a curve defined in a (x,y,z) Cartesian coordinate system by the following equation 
             z   =       cy   2       1   +       (     1   -       (     1   +   Q     )     ⁢     c   2     ⁢     y   2                   ,         
where y and z are independent of x, c is the curvature at said apex and Q is the conic constant less than (−1). The second surface, receiving the laser beam from the first surface, has a cylindrical shape and having an axial direction perpendicular to x direction.
 
   Also disclosed is a line scanning module for a machine vision system. The line scanning module includes an optical lens and a source generating a laser beam. The optical lens includes a first surface and a second surface. The second surface has a positively cylindrical shape for receiving the uniformed laser beam transmitted from the first surface. Then the second surface converges the laser beam in a plane intersecting the (y,z) plane. 
   Still disclosed is an optical lens including a first surface, a second surface, and a third surface. The third surface diverts a transmitted laser beam from the first surface to the second surface or from the second surface to the first surface. 
   It is understandable to those skilled in the art that the first surface, the second surface, and the third surface of the optical lens of the present invention should preferably have matching optical properties. 
   The foregoing and other features of the invention will be apparent from the following more particular description of embodiment of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not intended to be limited by the figures of the accompanying drawing, in which like notations indicate similar elements. 
       FIG. 1  is an illustration of a Powell lens  10  according to the prior art; 
       FIG. 2   a  is a perspective view of the optical lens  200  according to an embodiment of the present invention; 
       FIG. 2   b  is a (x,z) plane view of the optical lens  200  in  FIG. 2   a;    
       FIG. 2   c  is a (y,z) plane view of the optical lens  200  in  FIG. 2   a;    
       FIG. 2   d  is a (y,z) plane view of the optical lens  200  according to another embodiment of the present invention; 
       FIG. 3   a  illustrates the length profile achieved by optical lens  200 . 
       FIG. 3   b  illustrates the width profile achieved by optical lens  200 . 
       FIG. 4  explains the definition of uniformity. 
       FIG. 5  is a perspective view of the optical lens  500  according to an embodiment of the present invention; and 
       FIG. 6  illustrates an optical lens  600  for a machine vision inspection system according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   As follows, the invention has been described with reference to specific embodiments. However, it will be appreciated that various modifications and changes can be made without departing from the scope of the present invention. The specification and figures are to be regarded in an illustrative manner, rather than a restrictive one, and all such modifications are intended to be included within the scope of present invention. Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. 
     FIG. 2   a  illustrates the optical lens  200  in (x, y, z) Cartesian coordinate system, while  FIG. 2   b  illustrates the optical lens  200  in (x,z) plane and  FIG. 2   c  illustrates the optical lens  200  in (y,z) plane. The optical lens  200  has a first surface  202  and a second surface  204 . Note that the optical lens  200  can be a single optical element or a combination of separate elements. Preferably, the material of the optical lens  200  is BK7 when the wavelength of the input laser beam is approximately 632 nm. 
   The shape of the first surface  202  spreads the energy out more at the center, but at the same time contains the energy at the edges thus producing a beam line of more uniform intensity. The shape of the first surface  202  has a small radius of curvature and a large negative conic constant. This results in the center and most intense portion of the laser beam seeing a rapidly changing surface and therefore undergoing greater divergence than that found with the less intense portion at the other periphery of the beam. As shown in  FIG. 2   c , the first surface  202  is two-dimensional in the (y,z) plane of (x, y, z) Cartesian coordinate system and can be described by the following equation: 
             z   =       cy   2       1   +       (     1   -       (     1   +   Q     )     ⁢     c   2     ⁢     y   2                   ,         
where c is the curvature at the apex, Q is the conic constant and the first surface  202  is defined in an (x, y, z) Cartesian coordinate system. Preferably, the value of Q lies between (−4.5) and (−1.6), depending on the target position and the desired divergence angle in the (y,z) plane or the desired length of the projected line. Those skilled in the art can fully recognize the functions of the first surface  202  of the present invention with reference to the U.S. Pat. No. 4,826,299.
 
   The second surface  204  is a portion of a cylindrical shape and has its axial direction (shown as DA in  FIGS. 2   b  and  2   c ) perpendicular to x direction. The axial direction DA is also defined as perpendicular to any normal of the second surface  204 . As shown in  FIG. 2B , the second surface  204  is defined as positively cylindrical. If a laser beam is transmitted from the first surface  202  and towards the second surface  204 , the positively cylindrical shape converges the transmitted laser beam. The curvature of the second surface  204  depends on the target position and the desired width of the projected line, or the desired convergence angle in the (x,z) plane. By adjusting the curvature of the second surface  204 , the width of the projected line is varied and is possible to be smaller than the diameter of the input laser beam. Also as shown in  FIG. 2   c , the first surface  202  and the second surface  204  are furthest from each other at the apex  203 . However, in another embodiment, the first surface  212  and the second surface  204  are closest from each other at the apex  213 , as shown in  FIG. 2   d.    
   An example to meet the 532 nm laser and diameter is 2.3 mm, the radius of curvature of first surface  202  is modified to 1.2 mm and conic constant is −4.0 to achieve 50.0 mm length at z=80.0 mm shown in  FIG. 3   a . The length profile can achieve the uniformity that is above 80% where the definition of uniformity is the minimum power divided by the maximum power within the desired range of beam profile, as shown in  FIG. 4 . Explicitly, uniformity can be expressed as 
   
     
       
         
           U 
           = 
           
             
               
                 P 
                 min 
               
               
                 P 
                 max 
               
             
             . 
           
         
       
     
   
   The radius of curvature of second surface  204  is −27.8 to design an illuminated area that is with 0.5 mm width at z=80.0 mm which is smaller than incident beam diameter as shown in  FIG. 3   b . To meet the specifications, the radius of curvature of first surface  202  can be −1.2. When the incident wavelengths have to be different, the radius of curvature and conic constant can be adjusted to achieve the desired specifications. 
   Referring to  FIG. 5  of another embodiment, the optical lens  500  has a first surface  502 , a second surface  504 , and a third surface  506 . Note that the optical lens  500  can be a single optical element or a combination of separate elements. The third surface  506  diverts a transmitted laser beam from the first surface  502  to the second surface  504 , or from the second surface  504  to the first surface  502 . In one embodiment, the input laser beam firstly strikes the first surface  502 , and the first surface  502  uniforms the input laser beam in the (y,z) plane and directs it to the third surface  506 . The third surface  506  can be, but is not limited to, a reflective flat plane for diverting the uniformed laser beam to the second surface  504 . Then the second surface  504  converges the diverted beam in a plane which intersects the (y, z) plane. Therefore, the desired length, width, and output angle of the projected line are well controlled by the optical lens  500 , even though the input laser beam is not a circular beam. 
   It should be noted that, in addition to diverting the laser beam, the third surface  506  can have shapes other than the flat plane to, for example, converge or diverge the laser beam. And the known optical elements, such as filters, polarizers, thin films, etc., additionally attached on the third surface  506  are also covered by the scope of the present invention. Furthermore, the diverting angle of the third surface  506  depends on the target position. Referring to the optical lens  600  in  FIG. 6 , in practice, the laser source  610  is set up horizontally and the input laser beam is incident horizontally to the optical lens  600 , and the diverting angle may be 30 or 40 degrees corresponding to the targets  620  (e.g., wafers to be inspected) which are also moving horizontally. 
   Those skilled in the art should appreciate the present invention may be implemented as an optical lens, a beam shaping apparatus, or, in particular, a line scanning module for a machine vision system where the length and the width of the projected line need to be well defined. While this invention has been described with reference to the illustrative embodiments, these descriptions should not be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent upon reference to these descriptions. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as falling within the true scope of the invention and its legal equivalents.