Abstract:
An optical lens array featuring low cost and simple manufacture. The lens array has two lens sections separated by spacers, with a stop on the front surface. An optional wraparound frame protects the lens array from external light. The spacers and stop, as well as the optional frame, are made of black polymer to block unwanted scattered or external light. The lens sections, stop, spacers, and frame can all be made by injection-molding. Notches, locating holes, posts, and ears serve to orient and align the parts, and to prevent incorrect assembly.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to optics. More specifically, the present invention discloses an array of lenses for high-resolution imaging of a surface. 
   2. Description of the Prior Art 
   Traditionally, the lens for a one to one imaging optical scanner is a rod lens array. Please refer to  FIG. 1 , a perspective drawing of a prior-art rod lens array  100 . The rod lens array  100  is constructed from a plurality of fiber optic rod lenses  110 . Each individual fiber optic rod lens  110  is cut from a fiber optic glass strand, and its ends must be polished. The plurality of fiber optic rod lenses  110  are then arranged side by side, in a row or multiple rows with their optical axes in parallel, in a frame  120  and held in place by an adhesive layer  130 . The fiber optic rod lenses  110  are typically made from GRIN (graduated index) fibers, with the refractive index of the glass carefully controlled during manufacture to have a graduated refractive index that decreases radially from the central axis to the edge. 
   However, this type of lens is expensive to manufacture. GRIN type fiber optic glass strands are expensive in and of themselves; cutting and polishing the strands to precise lengths to form fiber optic rod lenses  110 , assembling them so that their axes are precisely parallel in the frame  120 , and gluing the fiber optic rod lenses  110  are all precision steps for which entire technologies have had to be developed in order to satisfy requirements. 
   In addition, a major disadvantage of this type of lens is that because of the number of lenses and the difficulty in orienting them, it is not practical to shape the ends of the lenses so that they can magnify the surface that they are imaging; flat ends are used. In order to increase the imaging resolution, it is necessary to use larger numbers of smaller-diameter rod lenses  110 , limiting the maximum resolution and driving up the costs as the desired resolution increases. Furthermore, suppliers for the necessary GRIN fiber optic strands are limited, and thus the base materials themselves are expensive. 
   Therefore there is need for an improved lens array for which materials are substantially cheaper and which is simpler to manufacture, and which can have increased resolution without substantially increasing costs. 
   SUMMARY OF THE INVENTION 
   To achieve these and other advantages and in order to overcome the disadvantages of the conventional method in accordance with the purpose of the invention as embodied and broadly described herein, the present invention provides a lens array where pluralities of lens faces are molded into surfaces of polymer bars, thus simplifying manufacturing, using inexpensive materials, and aligning the lenses without requiring significant manufacturing infrastructure. 
   The present invention further provides a lens array where the lens faces are configurable at the time of design to support increased resolution. 
   These and other objectives of the present invention will become obvious to those of ordinary skill in the art after reading the following detailed description of preferred embodiments. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  is a perspective drawing of a prior art rod lens array; 
       FIG. 2  is an exploded perspective drawing of a lens array of the present invention; 
       FIG. 3   a  is a drawing of a surface of a stop for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 3   b  is a drawing of a surface of a spacer for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 3   c  is a drawing of a surface of a spacer for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 4   a  is a drawing of a first surface of a first lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 4   b  is a drawing of a second surface of a first lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 4   c  is a drawing of a cross-section of a first lens section for a lens array of the present invention along the long axis; 
       FIG. 5  is a drawing of a cross-section of a first lens section for a lens array of the present invention across a width of the first lens section; 
       FIG. 6   a  is a drawing of a second surface of a first lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 6   b  is a drawing of an end of a second surface of a first lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 6   c  is a drawing of a cross-section of a first end of a first lens section for a lens array of the present invention along the long axis; 
       FIG. 6   d  is a drawing of a cross-section of a second end of a first lens section for a lens array of the present invention along the long axis; 
       FIG. 7   a  is a drawing of a first surface of a second lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 7   b  is a drawing of a second surface of a second lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 7   c  is a drawing of a cross-section of a second lens section for a lens array of the present invention along the long axis; 
       FIG. 8   a  is a drawing of a first surface of a second lens section for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 8   b  is a drawing of a cross-section of an end of a second lens section for a lens array of the present invention along the long axis; 
       FIG. 9  is a drawing of a cross-section of a second lens section for a lens array of the present invention across a width of the second lens section; 
       FIG. 10   a  is a detail drawing of a first end of a surface of a stop for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 10   b  is a detail drawing of a second end of a surface of a stop for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 10   c  is a detail drawing of an end of a surface of a spacer for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 10   d  is a detail drawing of an end of a surface of a spacer for a lens array of the present invention with the view in line with the optical axis; 
       FIG. 11   a  is a perspective drawing of a lens array of the present invention; 
       FIG. 11   b  is a drawing of a lens array of the present invention mounted to a printed circuit board, with the view in line with the optical axis; 
       FIG. 11   c  is a cross-section drawing of a lens array of the present invention mounted to a printed circuit board, along the long axis; 
       FIG. 12   a  is a top view of a lens array of the present invention in a frame mounted to a printed circuit board; 
       FIG. 12   b  is a cross-section drawing of a lens array of the present invention in relation to a printed circuit board, along the long axis; and 
       FIG. 12   c  is a cross-section drawing of a lens array of the present invention in relation to a printed circuit board, across the width of the lens array and printed circuit board. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
   Please refer to  FIG. 2 , which shows an exploded perspective drawing of a lens array of the present invention. The lens array  200  of this embodiment consists of a stop  240 , a first lens section  210 , three spacers  221 , 222 , 223 , and a second lens section  230 . Each component is discussed in further detail below. The number of spacers may vary between embodiments depending on design considerations. Only one spacer is required, but two or more may be used; the example embodiment uses three spacers. A frame (not shown) may optionally enclose the perimeter of the assembled lens array  200 , providing support, mounting, and protection, and blocking external light. 
   Please refer momentarily to  FIG. 6   b , which is a cross-section drawing of a lens array of the present invention in relation to a printed circuit board. This figure will be discussed in greater detail later; until then, note the distance  201  between the optical axes of two adjacent lens surfaces, referred to hereafter as the inter-axis distance  201 . 
   Please refer to  FIG. 3   a , which is a drawing of a surface of a stop for a lens array of the present invention with the view in line with the optical axis, in combination with  FIG. 10   a  and  FIG. 10   b , which are detail drawings of the same part as marked in  FIG. 3   a  by A and B respectively. The stop  240  has a plurality of holes  241  organized such that the centers of the holes form a line down the center of the spacer. The first plurality of holes  241  are spaced apart equally by the inter-axis distance. The first plurality of holes  241  are circular, oval, cylindrical, or conical. Along the edges of the stop  240 , a plurality of notches  242  is positioned to mate with a plurality of ears  211   e  of the first surface  211  of the first lens section  210 . A locating hole  243  near one end of the stop  240  is sized and positioned to fit around the phasing post  351  of the first lens array. 
   Please refer to  FIG. 3   b , which is a drawing of a surface of a spacer for a lens array of the present invention with the view in line with the optical axis, in combination with  FIG. 10   c , which is a detail of one end of the part as marked in  FIG. 3   b  by C. The third spacer  223  is substantially identical to the first spacer  221  and is not shown separately here. The first and third spacers  221 , 223  have a plurality of holes  410  organized such that the centers of the holes form a line down the center of the spacer. The holes  410  are spaced apart equally by one inter-axis distance  201 . The holes  410  may be tapered right conic frustums or they may be cylindrical. Along the sides of the spacer  220 , a plurality of notches  420  is positioned to mate with the ears  211   e  of the lens arrays. A locating hole  430  near one end of the first and third spacers  221 , 223  is sized and positioned to fit around the phasing post  350  of the second lens array. The locating hole  430  and the plurality of notches  420  serve to locate and hold the first and third spacers  221 , 223  in alignment with the first and/or second lens sections  210 , 230  so that the centers of the holes  410  are centered on the lens axes. The minimum diameter of the holes  410  is the outer diameter of the lens faces molded into the surface against which the spacer is disposed. 
     FIG. 3   c  is also a drawing of a surface of a spacer for a lens array of the present invention with the view in line with the optical axis, in combination with  FIG. 10   d , which is a detail of the same part, noted in  FIG. 3   c  by D. The spacer  222  is similar to the first spacer  221  and third spacer  223  except that the diameter of the plurality of holes  411  are smaller. The plurality of holes  411  are spaced apart equally by one inter-axis distance  201 . The notches  421  are the same size as the notches  420  of the spacers  221 , 223 . 
   Please refer to  FIG. 4   a , which is a drawing of a first surface of a first lens section for a lens array of the present invention with the view in line with the optical axis. Two section lines A-A and B-B are marked for use in  FIG. 4   c  and  FIG. 5  respectively.  FIG. 4   a  shows the first surface  211  of the first lens section  210 . The first surface  211  has a channel  211   c  down the center of the lens, and a first plurality of lens surfaces  213  are formed with their optical axes in line, spaced apart equally by one inter-axis distance  201 . The line of the centers of the first plurality of lens surfaces  213  in this example embodiment is along the center line of the channel  211   c . A plurality of ears  211   e  is formed along the edges  211   a ,  211   b  of the first lens surface  211  of the first lens section  210 , such that the ears  211   e  are sized and spaced to mate with the notches  242  of the stop  240 . The width of the first lens section  210  is substantially the same as the width of the stop  240 . A first post  211   p  is located at one end of the first lens section  210 , sized and positioned to mate with the locating hole  243  of the stop  240 . A surface of the stop  240  fits snugly against the faces of the edges  211   a ,  211   b  with notches  242  mating to ears  211   e  so that the plurality of holes  241  of the stop  240  are lined up with their centers on the optical axes of the first plurality of lens surfaces  213 . The locating hole  243  and the plurality of notches  242  serve to locate and hold the stop  240  in alignment with the first lens section  210  so that the centers of the holes  241  are substantially on the optical axes of the first plurality of lens surfaces  213 . 
   Please refer to  FIG. 4   b , which is a drawing of a second surface of a first lens section for a lens array of the present invention with the view in line with the optical axis, in combination with  FIG. 6   a  and  FIG. 6   b , which are detail drawings of the same part as marked by C and D in  FIG. 4   a , respectively. These figures show the second surface  212  of the first lens section  210 . The second surface  212  has a channel  212   c  down the center of the lens, and a second plurality of lens surfaces  214  are formed with their optical axes in line, spaced apart equally by one inter-axis distance  201 . The line of the centers of the first plurality of lens surfaces  213  in this example embodiment is along the center line of the channel  212   c . A plurality of ears  212   e  is formed along the edges  212   a ,  212   b  of the first lens surface  212  of the first lens section  210 , such that the ears  212   e  are sized and spaced to mate with the notches  420  of the first spacer  221 . The width of the first lens section  210  is substantially the same as the width of the first spacer  221 . A first hole  212   h  is located and sized to mate with a second post  231   p  (see  FIG. 7   a ,  FIG. 7   c , and  FIG. 8   b ) of the second lens section  230  (see  FIG. 7   a ,  FIG. 7   b ,  FIG. 7   c ,  FIG. 8   a ,  FIG. 8   b , and  FIG. 9 ). A surface of the first spacer  221  fits snugly against the faces of the edges  212   a , 212   b  with notches  420  mating to ears  212   e  so that the plurality of holes  410  are lined up with their centers on the optical axes of the second plurality of lens surfaces  214 . 
   Please refer to  FIG. 4   c , which is a drawing of a cross-section of a first lens section for a lens array of the present invention along the long axis, in combination with  FIG. 6   c  and  FIG. 6   d , which are detail drawings of the same part for the details marked in  FIG. 4   c  by E and F respectively. The cross-section view also shows the distal portion of the lens in the background. The cross-section cuts across the first plurality of lens surfaces  213  and the second plurality of lens surfaces  214 , as well as the first post  211   p  and first hole  212   h . The second edges  211   b ,  212   b  and ears  211   e ,  212   e  are visible in the background, behind the channels  211   c ,  212   c . In  FIG. 6   c , a first post  211   p  for positioning a stop  240  is located on the first surface  211 . Several first lens surfaces of the first plurality of lens surfaces  213  are located in the channel  211   c . Several second lens surfaces of the second plurality of lens surfaces  214  are located in the channel  212   c . In  FIG. 6   d , the first hole  212   h  is located in the second surface  212 . The plurality of optical axes of the first plurality of lens surfaces  213  are inline with the plurality of optical axes of the second plurality of lens surfaces  214 . Please note that the optical axes of the second plurality of lens surfaces  214  are aligned with the optical axes of the first plurality of lens surfaces  213  and that the number of lens surfaces in the first plurality of lens surfaces  213  is the same as the number of lens surfaces in the second plurality of lens surfaces  214 . 
   Please refer to  FIG. 5 , which is a cross-section drawing of a first lens section for a lens array of the present invention across a width of the first lens section. This cross-section cuts along the optical axes of a pair of lens surfaces consisting of one of the first plurality of lens surfaces  213  in channel  211   c  and one of a lens surface of the second plurality of lens surfaces  214  in channel  212   c , two ears of the plurality of ears  211   e , and two ears of the plurality of ears  212   e . Visible in the background is the first post  211   p . Edges  211   a  and  211   b , against which the stop  240  (not shown) will be placed when assembled, are shown. Edges  212   a  and  212   b , against which the first spacer  221  will be placed when assembled, are also shown. 
   Please refer to  FIG. 7   a , which is a drawing of a third surface of a second lens section for a lens array of the present invention with the view in line with the optical axis, in combination with  FIG. 8   a , which is a detail of the same part for the region marked in  FIG. 7   a  by C. Two section lines A-A and B-B are marked for use in  FIG. 7   c  and  FIG. 9  respectively.  FIG. 7   a  shows the third surface  211  of the second lens section  230 . The third surface  231  has a channel  231   c  down the center of the lens, and a third plurality of second lens surfaces  233  are formed with their optical axes in line, spaced apart equally by one inter-axis distance  201 . The line of the centers of the third plurality of lens surfaces  233  in this example embodiment is along the center line of the channel  231   c . A plurality of ears  231   e  is formed along the edges  231   a ,  231   b  of the second lens surface  231  of the second lens section  230 , such that the ears  231   e  are sized and spaced to mate with the notches  410  of the first spacer  221 , the notches  411  of the second spacer  222 , and the notches  410  of the third spacer  223 . In this embodiment, the ears  231   e  are substantially longer than the ears  212   e  on the first lens section  210 , and mate with the notches on all three spacers, compared with the first lens section  210  only mating with the notches on the first spacer  221 , but this is implementation-dependent and may vary in practice. The width of the second lens section  230  is substantially the same as the width of the first spacer  221 , second spacer  222 , and third spacer  223 . A second post  231   p  is located at one end of the second lens section  230 , sized and positioned to mate with the locating hole  430  of the first spacer  221 , the locating hole  431  of the second spacer  222 , the locating hole  430  of the third spacer  223 , and the first hole  212   h  of the first lens section  210 . This second post  231   p  is stepped down in diameter since the locating holes  430 , 431 , 430  are larger in diameter than the first hole  212   h  (see further discussion for  FIG. 8   b ). A surface of the third spacer  223  fits snugly against the faces of the edges  231   a , 231   b  with notches  420  mating to ears  231   e  so that the plurality of holes  410  are lined up with their centers on the optical axes of the third plurality of lens surfaces  233 . 
   Please refer to  FIG. 7   b , which is a drawing of a second surface of a second lens section for a lens array of the present invention with the view in line with the optical axis.  FIG. 7   b  shows the second surface  232  of the second lens section  230 . The second surface  232  has a channel  232   c  down the center of the lens, and a fourth plurality of lens surfaces  234  are formed with their optical axes in line, spaced apart equally by one inter-axis distance  201 . The line of the centers of the third plurality of lens surfaces  233  in this example embodiment is along the center line of the channel  232   c . The edges to the sides  232   a ,  232   b  help protect the fourth plurality of lens surfaces  234  from handling damage during manufacture. 
   Please refer to  FIG. 7   c , which is a drawing of a cross-section of a second lens section for a lens array of the present invention along the long axis, in combination with  FIG. 8   b , which is a detail of the same part as marked in drawing  7   c  by D. The cross-section view also shows the distal portion of the lens in the background. The cross-section cuts across the third plurality of lens surfaces  233  and the fourth plurality of lens surfaces  234 , as well as the second post  231   p , which has a section of a first diameter  231   p   1  and a section of a second diameter  231   p   2 . The section  231   p   1  is larger in diameter than the section  231   p   2 ; the section  231   p   1  is designed to mate with the locating holes  430 , 431 , 430  in the first spacer  221 , second spacer  222 , and third spacer  223  respectively. The section  231   p   2  is designed to mate with the first hole  212   h  of the first lens section  210 . The second edges  231   b ,  232   b  and ears  231   e  are visible in the background, behind the channels  231   c ,  232   c . Please note that the optical axes of the third plurality of lens surfaces  233  are aligned with the optical axes of the fourth plurality of lens surfaces  234  and that the number of lens surfaces in the third plurality of lens surfaces  233  is the same as the number of lens surfaces in the fourth plurality of lens surfaces  234 . 
   Please refer to  FIG. 11   a , a perspective drawing of a lens array of the present invention, in combination with  FIG. 12   b  and  FIG. 12   c , cross sections of a lens array of the present invention. The lens array  200  is assembled with a frame  250  (not shown) so that it is held at a fixed distance from a sensor  260  which is mounted on a printed-circuit board (PCB)  270 . The stop  240  is positioned against the first surface  211  of the first lens section  210 . The first spacer  221  is positioned with one face against the second surface  212  of the first lens section  210 , with its notches  420  aligned with and held in place by the ears  212   e , which extend only partially through the depth of the plurality of notches  420  of the first spacer  221 ; one face of the second spacer  222  is positioned against the other face of the first spacer  221 ; and then one face of the third spacer  223  is positioned against the other face of the second spacer  222 ; finally, the other face of the third spacer  223  is positioned against the third surface  231  of the second lens section  230 . The second post  231   p  of the second lens section  230  fits its larger-diameter segment  231   p   1  through the locating holes  430 , 431 , 430  of the first spacer  221 , second spacer  222 , and third spacer  223  respectively; and the longer ears  231   e  of the second lens section  230  fit through the notches  420 , 421 , 420  of the first spacer  221 , second spacer  222 , and third spacer  223  respectively. The smaller-diameter segment  231   p   2  of the second post  231   p  fits into the first hole  212   h  of the second surface  212  of the first lens section  210 . The ears  231   e  of the second lens section  230  abut the ears of the first lens section  210 . The ears, posts, holes, and notches combine to hold the stop  240 , the three spacers  221 , 222 , 223 , and the two lens sections  210 , 230  in alignment. 
   Referring now to  FIG. 11   b , a top view of the lens array of the present invention assembled with a PCB, in combination with  FIG. 12   a , a detail view of the same assembly, as marked on  FIG. 11   b  by B. A cross-section used in  FIG. 11   c  and  FIG. 12   b  is marked with the section line A-A. The lens array  200  is assembled inside a frame  250  which secures the lens to the PCB  270 . The stop  240  is fitted against the first surface, and the first plurality of lens surfaces  213  of the first surface  211  of the first lens section  210  is visible through the plurality of holes  241  in the stop. 
   The lens surfaces of the first plurality of lens surfaces  213  have identical diameters and optical radii. The lens surfaces of the second plurality of lens surfaces  214  have identical diameters and optical radii. The lens surfaces of the third plurality of lens surfaces  233  have identical diameters and optical radii. The lens surfaces of the fourth plurality of lens surfaces  234  have identical diameters and optical radii. The four pluralities of lens surfaces  213 , 214 , 233 , 234  are identical in number and in the center-to-center spacing of the lens faces. The four pluralities of holes  410 , 411 , 410 , 241  from the first spacer  221 , second spacer  222 , third spacer  223 , and stop  240  also are identical both in number and in the center-to-center spacing of the holes to the four pluralities of lens surfaces. As shown in  FIG. 12   b , the optical axes of the four pluralities of lens surfaces, and the centers of the four pluralities of holes, are all aligned, thus forming a single plurality of lens units. Each quad of four lens faces, one from each of the four pluralities above, positioned on the same optical axis forms a lens unit with a lens axis. One embodiment for imaging A4 sized paper at 300 dpi has 330 lens units. Note that there is no restriction on the configuration of the lens units; although this example embodiment shows an array in a single line, two or more lines of lens units can be used, organized in a square grid, or a rectangular grid, or hexagonally. 
   Please refer to  FIG. 11   c , a cross-section view of the lens array of the present invention assembled with a PCB, in combination with  FIG. 12   b , a detail view of the same assembly, as marked on  FIG. 11   c  by C. A line at the top of  FIG. 12   b  represents the object plane  280 , which corresponds to a surface to be imaged. The stop  240  is proximal to the object plane  280 , along with the first plurality of lens surfaces  213 . The plurality of lens surfaces gathers and focuses light reflected from the surface so that the light travels in a divergent beam through the first lens section to the second plurality of lens surfaces  214 . The light is generated by an external source. The first spacer  221 , second spacer  222 , and third spacer  223  block and absorb scattered light, while the pluralities of holes  420 , 421 , 420  allow desired, focused light to reach the third plurality of lens surfaces  233 . The light then transits the second lens section and exits through the fourth plurality of lens surfaces  234 , which focuses the light onto the sensor  260  mounted on the PCB  270 . 
   In the preferred embodiment, the first lens section and second lens section are preferably made of a refractive, substantially transparent polymer. The spacer(s), stop, and frame are preferably made of an opaque polymer, preferably black, to absorb and/or block undesirable scattered or external light. One or more spacers can be used; using fewer spacers reduces manufacturing costs. Use of a frame is optional. 
   The dots per inch (DPI) resolution of the lens array is adjustable at design time by changing the optical radii, conic constant, or aspherical coefficients of the four lens groups. In contrast with the prior art rod lenses, the lens array can be designed to magnify the surface being imaged. The lens surface is defined by the formula: 
                 z   =         cy   2       1   +       1   -       (     1   +   k     )     ⁢     c   2     ⁢     y   2               +       A   2     ⁢     y   2       +       A   4     ⁢     y   4       +       A   6     ⁢     y   6     ⁢     A   8     ⁢     y   8       +       A   10     ⁢     y   10                 (     eq   ⁢           ⁢   1     )               
for each of the two lens sections.
 
   The lens array thus provides a substantial improvement over the prior art by reducing manufacturing complexity and materials costs. Furthermore, the lens array makes it substantially less difficult to increase the resolution of a device using the lens array compared to the prior art. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the invention and its equivalent.