Concentrator fresnel lens with varying draft angle

Abstract

The present invention relates to a Fresnel lens and a respective mold, the lens comprising a plurality of draft facets, wherein the draft angle of the draft facets has at least two different angular values for two different draft facets, in particular, wherein the draft angle is bigger for a draft facet closer to the edge of the lens or, respectively, of the mold, than for a draft facet closer to the center of the lens or, respectively, of the mold.

The invention claimed is: 
     
       1. A mold for a Fresnel lens comprising
 a mold plate having a surface including a plurality of alternating sloped facets and draft facets arranged concentrically about a center location, each slope facet oriented at a respective slope angle with respect to a plane parallel to the mold plate, each draft facet oriented at a respective draft angle relative to a line perpendicular to the mold plate, the draft angles of the draft facets of the mold having at least two different values for two different draft facets, 
 wherein the draft facets of a first region of the mold have a first common draft angle common to all of the draft facets of the first region, the draft facets of a second region of the mold have a second common draft angle common to all of the draft facets of the second region, and the draft facets of a third region of the mold have a third common draft angle common to all of the draft facets of the third region, the first common draft angle being smaller than the second common draft angle, and the third common draft angle being larger than the second common draft angle, and 
 further wherein at least two draft facets of the first region are at different radial distances from the center location, at least two draft facets of the second region are at different radial distances from the center location, and 
 wherein the first region is a center region extending from the center location to a first radius corresponding to the a last facet having a complete circumference, the second region extends from the first radius to a second radius greater than the first radius, and the third region extends from the second radius to a third radius greater than the second radius, and wherein the first common draft angle is constant within the first region, the second common draft angles is constant within the second region, and the third common draft angle is constant within the third region. 
 
     
     
       2. The mold according to  claim 1 , wherein the mold plate is non-circular. 
     
     
       3. A Fresnel lens comprising
 a substrate having a surface including a plurality of alternating sloped facets and draft facets arranged concentrically about a center location, each slope facet oriented at a respective slope angle with respect to a plane parallel to the substrate, each draft facet oriented at a respective draft angle relative to a line perpendicular to the substrate, the draft angles of the draft facets having at least two different values for two different draft facets, 
 wherein the draft facets of a first region of the Fresnel lens have a first common draft angle common to all of the draft facets of the first region, the draft facets of a second region of the Fresnel lens have a second common draft angle common to all of the draft facets of the second region, and the draft facets of a third region of the Fresnel lens have a third common draft angle common to all of the draft facets of the third region, the first common draft angle being smaller than the second common draft angle, and the third common draft angle being larger than the second common draft angle, and 
 further wherein at least two draft facets of the first region are at different radial distances from the center location, at least two draft facets of the second region are at different radial distances from the center location, and 
 wherein the first region is a center region extending from the center location to a first radius corresponding to the a last facet having a complete circumference, the second region extends from the first radius to a second radius greater than the first radius, and the third region extends from the second radius to a third radius greater than the second radius, and wherein the first common draft angle is constant within the first region, the second common draft angle is constant within the second region, and the third common draft angle is constant within the third region. 
 
     
     
       4. The lens according to  claim 3 , wherein the Fresnel lens is a fixed height lens or a fixed pitch lens. 
     
     
       5. The lens according to  claim 3 , wherein the substrate is non-circular. 
     
     
       6. A method of manufacturing a Fresnel lens or a mold for a Fresnel lens, comprising
 forming a substrate or a mold plate having a surface including a plurality of alternating sloped facets and draft facets arranged concentrically about a center location, each slope facet oriented at a respective slope angle with respect to a plane parallel to the substrate or the mold plate, each draft facet oriented at a respective draft angle relative to a line perpendicular to the substrate or the mold plate, the draft angles of the draft facets having at least two different values for two different draft facets, 
 wherein the draft facets of a first region of the lens or the mold have a first common draft angle common to all of the draft facets of the first region, the draft facets of a second region of the lens or the mold have a second common draft angle common to all of the draft facets of the second region, and the draft facets of a third region of the lens or the mold have a third common draft angle common to all of the draft facets of the third region, the first common draft angle being smaller than the second common draft angle, and the third common draft angle being larger than the second common draft angle, and 
 further wherein at least two draft facets of the first region are at different radial distances from the center location, at least two draft facets of the second region are at different radial distances from the center location, and 
 wherein the first region is a center region extending from the center location to a first radius corresponding to the last facet having a complete circumference, the second region extends from the first radius to a second radius greater than the first radius, and the third region extends from the second radius to a third radius greater than the second radius, and wherein the first common draft angles are constant within the first region, the second common draft angles are constant within the second region, and the third common draft angles are constant within the third region. 
 
     
     
       7. The method of  claim 6 , further comprising:
 forming the substrate or the mold plate to have a non-circular shape. 
 
     
     
       8. The mold according to  claim 2 , wherein the mold plate is square or rectangular. 
     
     
       9. The mold according to  claim 2 , wherein the common draft angle of the draft facets of the first region is 3.5°±1.5°. 
     
     
       10. The lens according to  claim 5 , wherein the substrate is square or rectangular. 
     
     
       11. The lens according to  claim 3 , wherein the common draft angle of the draft facets of the first region is 3.5°±1.5°. 
     
     
       12. A lens plate comprising
 a substrate including a plurality of Fresnel lenses arranged next to one another and each configured to focus sunlight impinging on the a Fresnel lens onto a region smaller than the Fresnel lens, each Fresnel lens of the plurality of Fresnel lenses comprising a portion of the substrate and including a surface in a region of the substrate having a plurality of alternating sloped facets and draft facets arranged concentrically about a center location, each slope facet oriented at a respective slope angle with respect to a plane parallel to the substrate, each draft facet oriented at a respective draft angle relative to a line perpendicular to the substrate, the draft angles of the draft facets having at least two different values for two different draft facets, 
 wherein the draft facets of a first region of the mold Fresnel lens have a first common draft angle or angles common to all of the draft facets of the first region, the draft facets of a second region of the mold Fresnel lens have a second common draft angle or angles common to all of the draft facets of the second region, and the draft facets of a third region of the mold Fresnel lens have a third common draft angle or angles common to all of the draft facets of the second region, the first common draft angle or angles being smaller than the second common draft angle or angles and the third common draft angle or angles being larger than the second common draft angle or angles, and 
 further wherein at least two draft facets of the first region are at different radial distances from the center location, at least two draft facets of the second region are at different radial distances from the center location, and 
 wherein the first region is a center region extending from the center location to a first radius corresponding to the a last facet having a complete circumference h and the second region extends from the first radius to a second radius greater than the first radius, and the third region extends from the second radius to a third radius greater than the second radius, and wherein the first common draft angles are constant within the first region, the second common draft angle or angles are constant within the second region, and the third common draft angle or angles are constant within the third region. 
 
     
     
       13. The lens plate of  claim 12 , wherein each of the Fresnel lenses is square or rectangular. 
     
     
       14. A Fresnel lens, comprising:
 a series of alternating slope facets and draft facets positioned in concentric circles within a periphery of a noncircular substrate;   wherein the draft facets of a first region of the Fresnel lens have a first common draft angle common to all of the draft facets of the first region, the draft facets of a second region of the Fresnel lens have a second common draft angle common to all of the draft facets of the second region, and the draft facets of a third region of the Fresnel lens have a third common draft angle common to all of the draft facets of the third region, wherein the first common draft angles are constant within the first region, the second common draft angle is constant within the second region, and the third common draft angle is constant within the third region, and wherein the first common draft angle is smaller than the second common draft angle, and the third common draft angle is larger than the second common draft angle;   wherein a draft angle of each draft facet comprising a complete circumference within the periphery of the noncircular substrate is equal to each draft angle of each draft facet comprising a complete circumference within the periphery of the noncircular substrate; and   wherein another draft angle of each other draft facet comprising an incomplete circumference within the periphery of the noncircular substrate is different from each draft angle of each draft facet comprising a complete circumference within the periphery of the noncircular substrate.    
     
     
       15. The Fresnel lens of claim 14, wherein each other draft angle of each other draft facet comprising an incomplete circumference within the periphery of the noncircular substrate is greater than each draft angle of each draft facet comprising a complete circumference within the periphery of the noncircular substrate.  
     
     
       16. The Fresnel lens of claim 14, wherein each other draft angle of each other draft facet comprising an incomplete circumference within the periphery of the noncircular substrate increases with increasing distance from a geometric center of the Fresnel lens.  
     
     
       17. The Fresnel lens of claim 14, wherein each other draft angle of each other draft facet comprising an incomplete circumference in a fourth region proximate to a geometric center of the substrate is different from each other draft angle of each other draft facet comprising an incomplete circumference in a fifth region distal from a geometric center of the noncircular substrate.  
     
     
       18. The Fresnel lens of claim 17, wherein each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region is less than each other draft angle of each other draft facet comprising an incomplete circumference in the fifth region.  
     
     
       19. The Fresnel lens of claim 17, wherein each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region is equal to each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region and wherein each other draft angle of each other draft facet comprising an incomplete circumference in the fifth region is equal to each other draft angle of each other draft facet comprising an incomplete circumference in the fifth region.  
     
     
       20. A mold for making an array of Fresnel lenses, comprising:
 an array of noncircular cavities, each cavity shaped to form a respective Fresnel lens, each cavity comprising:
 a series of alternating slope facets and draft facets positioned in concentric circles within a periphery of the respective cavity; 
 wherein the draft facets of a first region of the mold have a first common draft angle common to all of the draft facets of the first region, the draft facets of a second region of the mold have a second common draft angle common to all of the draft facets of the second region, and the draft facets of a third region of the mold have a third common draft angle common to all of the draft facets of the third region, wherein the first common draft angle is constant within the first region, the second common draft angle is constant within the second region, and the third common draft angle is constant within the third region, and wherein the first common draft angle is smaller than the second common draft angle, and the third common draft angle is larger than the second common draft angle; 
 wherein a draft angle of each draft facet comprising a complete circumference within the periphery of the respective cavity is equal to each draft angle of each draft facet comprising a complete circumference within the periphery of the respective cavity; and 
 wherein another draft angle of each other draft facet comprising an incomplete circumference within the periphery of the respective cavity is different from each draft angle of each draft facet comprising a complete circumference within the periphery of the respective cavity.  
   
     
     
       21. The mold of claim 20, wherein each other draft angle of each other draft facet comprising an incomplete circumference within the periphery of the respective cavity is greater than each draft angle of each draft facet comprising a complete circumference within the periphery of the respective cavity.  
     
     
       22. The mold of claim 20, wherein each other draft angle of each other draft facet comprising an incomplete circumference within the periphery of the respective cavity increases with increasing distance from a geometric center of the Fresnel lens.  
     
     
       23. The mold of claim 20, wherein each other draft angle of each other draft facet comprising an incomplete circumference in a fourth region proximate to a geometric center of the respective cavity is different from each other draft angle of each other draft facet comprising an incomplete circumference in a fifth region distal from a geometric center of the respective cavity.  
     
     
       24. The mold of claim 23, wherein each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region is less than each other draft angle of each other draft facet comprising an incomplete circumference in the fifth region.  
     
     
       25. The mold of claim 23, wherein each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region is equal to each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region and wherein each other draft angle of each other draft facet comprising an incomplete circumference in the second region is equal to each other draft angle of each other draft facet comprising an incomplete circumference in the fifth region.  
     
     
       26. A method of making a Fresnel lens, comprising:
 forming a series of alternating slope facets and draft facets positioned in concentric circles within a periphery of a noncircular substrate;   wherein forming the series of alternating slope facets and draft facets comprises forming the draft facets of a first region of the Fresnel lens to have a first common draft angle common to all of the draft facets of the first region, the draft facets of a second region of the Fresnel lens to have a second common draft angle common to all of the draft facets of the second region, and the draft facets of a third region of the Fresnel lens to have a third common draft angle common to all of the draft facets of the third region, wherein the first common draft angle is constant within the first region, the second common draft angle is constant within the second region, and the third common draft angle is constant within the third region, and wherein the first common draft angle is smaller than the second common draft angle, and the third common draft angle is larger than the second common draft angle;   orienting a draft angle of each draft facet comprising a complete circumference within the periphery of the substrate to be equal to each draft angle of each draft facet comprising a complete circumference within the periphery of the substrate; and   orienting another draft angle of each other draft facet comprising an incomplete circumference within the periphery of the substrate to be different from each draft angle of each draft facet comprising a complete circumference within the periphery of the substrate.    
     
     
       27. The method of claim 26, further comprising orienting each other draft angle of each other draft facet comprising an incomplete circumference within the periphery of the substrate to be greater than each draft angle of each draft facet comprising a complete circumference within the periphery of the substrate.  
     
     
       28. The method of claim 26, further comprising orienting each other draft angle of each other draft facet comprising an incomplete circumference within the periphery of the substrate to increase with increasing distance from a geometric center of the Fresnel lens.  
     
     
       29. The method of claim 26, further comprising orienting each other draft angle of each other draft facet comprising an incomplete circumference in a fourth region proximate to a geometric center of the substrate to be different from each other draft angle of each other draft facet comprising an incomplete circumference in a fifth region distal from a geometric center of the substrate.  
     
     
       30. The method of claim 29, further comprising orienting each other draft angle of each other draft facet comprising an incomplete circumference in the fourth region to be less than each other draft angle of each other draft facet comprising an incomplete circumference in the fifth region.