In line thickness measurement

Abstract

This invention relates to an apparatus and method for measuring the thickness of mold components and/or lenses during a manufacturing process. In particular, the present invention uses fiber optic interferometry to measure the center thickness of ophthalmic lenses created by a double-sided molding process.

1 . A method for determining the thickness of a sample having at least one boundary which reflects light said method comprising the steps of: 
 providing one or more interferometers supplied with a coherent light source and a non-coherent light source;    positioning the contact lens such that said non-coherent light source is incident upon the sample; and    obtaining measurements of the contact lens thickness as generated by interference fringes created by said interferometer, wherein said method occurs on a manufacturing line and wherein said sample is a contact lens or contact lens mold.    
   
   
       2 . The method of  claim 1 , further comprising analyzing said interference fringes.  
   
   
       3 . The method of  claim 1  further comprising the step of positioning the sample above said non-coherent light source.  
   
   
       4 . The method of  claim 1  further comprising the step of positioning the sample below said coherent light source.  
   
   
       5 . The method of  claim 1 , wherein said one or more interferometers comprise one or more fiber-optic interferometers.  
   
   
       6 . The method of  claim 2 , wherein said analyzing step further comprises calculating distance using optical path and group index.  
   
   
       7 . The method of  claim 1 , wherein said positioning step further comprises placing a probe within about 5 degrees normal to the surface to be measured.  
   
   
       8 . The method of  claim 1 , wherein the distance between the sensor and the sample is substantially constant.  
   
   
       9 . The method of  claim 1 , further comprising aligning said sensor over the center of the lens lens mold prior to said positioning step.  
   
   
       10 . The method of  claim 1 , wherein said interference fringes are generated by light reflecting off of the boundaries between: 
 a medium and the lower surface of a female mold;    the upper surface of the female mold and the lens material within the assembled mold;    the lens material within the assembled mold and the lower surface of a male mold; and    the upper surface of the male mold and said medium.    
   
   
       11 . The method of  claim 10 , wherein said medium is air.  
   
   
       12 . The method of  claim 10 , wherein the medium is saline.  
   
   
       13 . The method of  claim 1 , wherein said positioning step further comprises aligning the interferometer probe with the center of said sample.  
   
   
       14 . The method of  claim 1 , wherein said obtaining step further comprises converting an optical path distance to material thickness.  
   
   
       15 . The method of  claim 14 , wherein said converting the optical path distance comprises: 
 measuring the optical path distance; and    dividing said optical path distance by the group index of the material.    
   
   
       16 . An apparatus for determining the thickness of a contact lens having at least one boundary which reflects light comprising: one or more movement stages connected to a lens measurement system; a means for calculation in electronic communication with, and a lens measurement system that contains a housing that holds a sample lens, wherein the lens measurement system is connected to said movement stages via a support post; and wherein said lens measurement system further comprises a light source and a fiberoptic interferometer.  
   
   
       17 . The apparatus of  claim 16 , further comprising a means for aligning said fiber optic interferometer with said sample lens.  
   
   
       18 . The apparatus of  claim 16 , wherein said means for calculation further comprises a computer that, in conjunction with said interferometer, is capable of determining the group index of a material.