Method And System For Real-Time In-Process Measurement Of Coating Thickness

Abstract

The present disclosure is generally directed to methods and systems for measuring the thickness of coatings or thin films on various substrates. For example, one disclosed method includes the steps of providing and directing light waves of varying wavelengths toward a moving substrate comprising a coating, linearly polarizing the light waves, converting the linearly polarized light waves to circularly polarized light waves, analyzing elliptically polarized light waves reflected by the moving substrate, capturing analyzed light waves, generating light wave data based on the captured light waves, and determining a thickness of the coating based on the light wave data.

We claim: 
     
         1 . A system comprising:
 a processor;   a moving substrate comprising a coating applied by a coating applicator;   a light source in communication with the processor, the light source configured to provide and direct light waves of varying wavelengths toward the moving substrate;   a polarizer positioned between the light source and the moving substrate;   a wave plate positioned between the polarizer and the moving substrate;   an analyzer positioned to receive light waves reflected by the moving substrate;   a detector, in communication with the processor, positioned to capture light waves reflected by the analyzer and configured to generate light wave data based on the captured light waves; and   a memory in communication with the processor,
 wherein the memory comprises computer program code executable by the processor to determine a thickness of the coating based on the light wave data, and 
 wherein the memory further comprises computer program code executable by the processor to, in response to a determination that the thickness of the coating is outside a predetermined range, generate a signal instructing the coating applicator to adjust the rate of application of the coating onto the moving substrate. 
   
     
     
         2 . The system of  claim 1 , wherein the coating is less than 0.2 microns thick. 
     
     
         3 . The system of  claim 1 , wherein the coating is a lubricious coating. 
     
     
         4 . The system of  claim 1 , wherein the coating is a liquid coating. 
     
     
         5 . The system of  claim 1 , wherein the wave plate is a rotating quarter-wave plate. 
     
     
         6 . The system of  claim 1 , wherein the analyzer is a rotating analyzer in communication with the processor. 
     
     
         7 . The system of  claim 1 , wherein the computer program code executable by the processor to determine the thickness of the coating based on the light wave data comprises computer program code executable by the processor to determine phase shift and polarization state changes of captured light waves compared to the provided light waves based on the light wave data. 
     
     
         8 . The system of  claim 1 , wherein the computer program code executable by the processor to determine the thickness of the coating based on the light wave data comprises computer program code executable by the processor to apply the Levenberg-Marquardt algorithm to match the light wave data with a theoretical model. 
     
     
         9 . The system of  claim 1 , wherein a position and an orientation of the analyzer are adjustable and a position and an orientation of the detector are adjustable. 
     
     
         10 . The system of  claim 9 , wherein the memory further comprises computer program code executable by the processor to:
 detect a disturbance in the movement of the moving substrate based on the light wave data; and   adjust the position or the orientation of the analyzer or adjust the position or the orientation of the detector based on the detected disturbance.   
     
     
         11 . The system of  claim 9 , wherein the memory further comprises computer program code executable by the processor to:
 detect a disturbance in the movement of the moving substrate based on the light wave data; and   adjust the position or the orientation of the analyzer and adjust the position or the orientation of the detector based on the detected disturbance.   
     
     
         12 . The system of  claim 1 , wherein the memory further comprises computer program code executable by the processor to adjust the intensity of the provided light waves based on the light wave data. 
     
     
         13 . The system of  claim 1 , wherein the signal instructs the coating applicator to decrease the rate of application of the coating onto the moving substrate. 
     
     
         14 . The system of  claim 1 , wherein the signal instructs the coating applicator to increase the rate of application of the coating onto the moving substrate.