Method and apparatus for grinding and polishing free-form ophthalmic surfaces

Abstract

A system for polishing and grinding optical surfaces is provides by employing a pad surface that is controllably moved over an affected surface in accordance with control procedures to facilitate a desired surface contour. The system does not require multiple hard master shapes for each desired surface contour but rather is using a limited set of polishing and grinding pad to provide a plurality of conventional and non-conventional surface contours.

1 . An apparatus for grinding or polishing an ophthalmic surface, comprising: 
 a surface shaping pad;    a rotational pad driver coupled to said pad for maintaining said pad in constant contact pressure with an affected surface and for rotating said pad about a first rotational axis; and    a position drive means coupled to said pad driver to controllably move said pad relative to the surface being ground or polished along a substantially spiraling contour path, said contour path centered at the center of said surface, said contour path having parallel spiral arcs, said parallel spiral arcs spaced at a constant distance apart along any given radius of said spiraling contour path, said contour path extending between the contour perimeter and the contour center, such that a removal profile is produced along said contour path having circular symmetry with peak removal at the center of pad movement and minimal removal at the extremes of pad movement.    
   
   
       2 . The apparatus of  claim 1  wherein the pad driver includes a pad support for supporting said pad on one end thereof, said pad support being adjustable in a direction generally perpendicular to a surface being ground or polished to maintain constant pressure contact between said pad and said surface.  
   
   
       3 . The apparatus of  claim 2  wherein said pad support comprises: 
 a plano pad support;    a set of five spherical concave pad supports, each said pad support having a different curvature ranging from −2 diopters to  31  10 diopters, in increments of −2 diopters; and    a set of five spherical convex pad supports, each said pad support having a different curvature ranging from 2 diopters to 10 diopters, in increments of 2 diopters.    
   
   
       4 . The apparatus of  claim 1  wherein said pad driver includes a spring preloaded reciprocating means to provide a constant pressure between said pad and the affected surface and to dynamically absorb any unexpected small deviations of said surface, said small deviations due to any small mechanical mounting misalignments of said surface.  
   
   
       5 . The apparatus of  claim 1  wherein said rotational pad driver includes means to continuously produce location signals indicating the incremental motion of said rotating pad and additionally including speed control means responsive to said location signals to control the speed of said rotational pad driver.  
   
   
       6 . The apparatus of  claim 1  wherein said position drive means includes a pivoting drive with a pivoting axis to pivot said pad driver about said pivoting axis for maintaining said pad driver orthogonal to the surface being ground or polished.  
   
   
       7 . The apparatus of  claim 6  wherein said position drive means includes a reciprocating drive to reciprocate said pad driver relative to said contour path, such that said pivoting axis is maintained mechanically aligned to the point of contact between said pad and said surface.  
   
   
       8 . The apparatus of  claim 1  wherein said position drive means is operative to dynamically adjust the speed of movement of said pad driver along said contour path as a function of the position of said pad driver relative to the surface being ground or polished.  
   
   
       9 . An apparatus for grinding or polishing an ophthalmic surface, comprising: 
 one grinding pad or one polishing pad;    a blocking device coupled to the backside of the surface being ground or polished;    a rotational chuck holder drive means for holding and rotating said blocking device;    a rotational pad driver coupled to said grinding pad or said polishing pad for moving each said pad in a manner which will produce a removal profile having circular symmetry with peak removal at the center of pad movement and minimal removal at the extremes of pad movement;    a chuck position drive coupled to said chuck holder drive means for rotating said chuck holder drive means at a controllable velocity about an angular direction;    a pad position drive coupled to said pad driver for moving said pad driver at a controllable velocity over a radial direction; and    control means for actuating said chuck position drive and said pad position drive at a predetermined velocity in each of said angular direction and said radial direction so that the relative path followed by said pad driver with respect to said chuck holder drive means is a spiraling contour path, said contour path centered at the center of the surface being ground or polished, said contour path having parallel spiral arcs, said parallel spiral arcs spaced at a constant distance apart along any given radius of said spiraling contour path, said contour path extending between the contour perimeter and the contour center of said surface.    
   
   
       10 . The apparatus of  claim 9  wherein said grinding pad or said polishing pad includes a polishing surface and said pad driver includes means to dispose said polishing surface in constant pressure contact with a surface to be ground or polished.  
   
   
       11 . The apparatus of  claim 10  wherein said pad disposing means includes means to position said polishing surface in contact with and substantially parallel to the surface being ground or polished.  
   
   
       12  The apparatus of  claim 9  wherein said constant distance is less than 5% of the minimum dimension of said grinding pad or said polishing pad.  
   
   
       13 . The apparatus of  claim 1  wherein said constant distance is less than 5% of the minimum dimension of said surface shaping pad.  
   
   
       14 . A method for grinding an ophthalmic surface, comprising the steps of: 
 rotating a grinding pad having a maximum dimension of less than 25% of the minimum dimension of the surface to be ground with a pad driver;    maintaining said rotating grinding pad in constant pressure contact with the surface being ground;    moving said pad driver across a contour path so that the center of pad movement follows said contour path to produce a surface removal, being said removal maximum substantially at the center of pad movement and minimum at the extremes of pad movement; and    directing the pad driver along said contour path over the surface to be ground, being said contour path a spiraling contour path centered at the center of said surface, said contour path having parallel spiral arcs, said parallel spiral arcs spaced at a constant distance apart along any given radius of said spiraling contour path, said constant distance being less than 5% of the minimum dimension of said grinding pad; said contour path extending between the contour perimeter and the contour center of said surface.    
   
   
       15 . The method of  claim 14  further including the control of the speed of rotation of said grinding pad and also including the control of the speed of movement along the contour path of said pad driver so that surface removal can be controlled as a function of both said speed of rotation and said speed of movement.  
   
   
       16 . The method of  claim 14  additionally including the use of: 
 one plano pad support;    one set of five spherical concave pad supports, each said pad support having a different curvature ranging from −2 diopters to −10 diopters, in constant increments of −2 diopters; and    one set of five spherical convex pad supports, each said pad support having a different curvature ranging from 2 diopters to 10 diopters, in constant increments of 2 diopters.    
   
   
       17 . The method of  claim 16  wherein each of different said pad supports is used in combination with: 
 an emery media based on aluminum oxide, said media having an average particle size of 9 to 20 microns;    a flexible media like neoprene rubber sheet attached to said pad supports, said media having a thickness of typically 3 mm and said media having a typical hardness 30 Shore “A” based on the Durometer scale; and    a multi perforated zinc pad with a thickness of 0.5 mm attached to said flexible media, wherein perforations of said zinc pad allow an even distribution of said emery media.    
   
   
       18 . A method for polishing an ophthalmic surface, comprising the steps of: 
 rotating a polishing pad having a maximum dimension of less than 25% of the minimum dimension of the surface to be polished with a pad driver;    maintaining said rotating polishing pad in constant pressure contact with the surface being polished;    moving said pad driver across a contour path so that the center of pad movement follows said contour path to produce a surface removal, being said removal maximum substantially at the center of pad movement and minimum at the extremes of pad movement; and    directing the pad driver along said contour path over the surface to be polished, being said contour path a spiraling contour path centered at the center of said surface, said contour path having parallel spiral arcs, said parallel spiral arcs spaced at a constant distance apart along any given radius of said spiraling contour path, said constant distance being less than 5% of the minimum dimension of said polishing pad; said contour path extending between the contour perimeter and the contour center of said surface.    
   
   
       19 . The method of  claim 18  further comprising controlling the speed of rotation of said polishing pad and also including controlling the speed of movement along the contour path of said pad driver so that surface removal can be controlled as a function of both said speed of rotation and said speed of movement.  
   
   
       20 . The method of  claim 18  additionally including the use of: 
 one plano pad support;    one set of five spherical concave pad supports, each said pad support having a different curvature ranging from −2 diopters to −10 diopters, in constant increments of −2 diopters; and    one set of five spherical convex pad supports, each said pad support having a different curvature ranging from 2 diopters to 10 diopters, in constant increments of 2 diopters.    
   
   
       21 . The method of  claim 20  applied to glass surfaces wherein each of different said pad supports is used in combination with: 
 a polishing media based on cerium oxide, said media having an average particle size of 1.2 microns and said media having a density of 6 to 8 degree Baumé;    a flexible media like neoprene rubber sheet attached to said pad supports, said media having a thickness of typically 3 mm and said media having a typical hardness 40 Shore “A” based on the Durometer scale; and    an urethane pad with a typical thickness of 1.5 mm attached to said flexible media.    
   
   
       22 . The method of  claim 20  applied to plastic surfaces wherein each of different said pad supports is used in combination with: 
 a polishing media based on aluminum oxide, said media having an average particle size of 1 to 2 microns and said media having a density of 25 to 35 degree Baumé;    a flexible media like neoprene rubber sheet attached to said pad supports, said media having a thickness of typically 3 mm and said media having a typical hardness 40 Shore “A” from the Durometer scale; and    a napped poromeric structure pad with a typical thickness of 1.5 mm attached to said flexible media, wherein said poromeric structure creates a pumping action under the compression of said pad, said pumping action enhancing the flow of said polishing media.