Determination of CD and/or MD variations from scanning measurements of a sheet of material
First Claim
1. A process for determining CD variations from scanning measurements made of a sheet of material comprising:
- scanning at least one sensor over a moving sheet of material to be measured at a first scanning speed to generate first scan measurements, the at least one sensor moving transversely relative to the moving sheet of material, the first scan measurements including mixed CD-MD variations of the sheet of material;
transforming said first scan measurements into a first spatial power spectrum with respect to a first spatial frequency;
detecting first spatial dominant spectral components of said first spatial power spectrum;
scanning at least one sensor over said moving sheet of material to be measured at a second scanning speed to generate second scan measurements, the at least one sensor moving transversely relative to the moving sheet of material, the second scan measurements including mixed CD-MD variations of the sheet of material;
transforming said second scan measurements into a second spatial power spectrum with respect to a second spatial frequency;
detecting second spatial dominant spectral components of said second spatial power spectrum; and
identifying CD spectral components of the scanning measurements by determining at least one of said first spatial dominant spectral components that are at the same spatial frequency as at least one of said second spatial dominant spectral components, the CD spectral components representing the CD variations separated from the mixed CD-MD variations of the sheet of material, the CD variations including a plurality of values over a CD range of the sheet of material.
2 Assignments
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Accused Products
Abstract
CD variations and/or MD variations in scan measurements are determined from spectral components of power spectra of scan measurements taken using two or more scanning speeds. Dominant spectral components having the same spatial frequencies identify CD variations and dominant spectral components having the same temporal frequencies identify MD variations. Dominant spectral components are extracted from a noisy power spectrum (PS) by sorting all spectral components into an ordered PS. A first polynomial representing background noise of the ordered PS is used to set a first threshold. Spectral components of the ordered PS that exceed the first threshold are removed to form a noise PS. A second polynomial representing the noise PS is used to set a second threshold. Spectral components of the PS that exceed the second threshold are identified as dominant spectral components of the PS.
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Citations
11 Claims
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1. A process for determining CD variations from scanning measurements made of a sheet of material comprising:
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scanning at least one sensor over a moving sheet of material to be measured at a first scanning speed to generate first scan measurements, the at least one sensor moving transversely relative to the moving sheet of material, the first scan measurements including mixed CD-MD variations of the sheet of material; transforming said first scan measurements into a first spatial power spectrum with respect to a first spatial frequency; detecting first spatial dominant spectral components of said first spatial power spectrum; scanning at least one sensor over said moving sheet of material to be measured at a second scanning speed to generate second scan measurements, the at least one sensor moving transversely relative to the moving sheet of material, the second scan measurements including mixed CD-MD variations of the sheet of material; transforming said second scan measurements into a second spatial power spectrum with respect to a second spatial frequency; detecting second spatial dominant spectral components of said second spatial power spectrum; and identifying CD spectral components of the scanning measurements by determining at least one of said first spatial dominant spectral components that are at the same spatial frequency as at least one of said second spatial dominant spectral components, the CD spectral components representing the CD variations separated from the mixed CD-MD variations of the sheet of material, the CD variations including a plurality of values over a CD range of the sheet of material. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A process for determining MD variations from scanning measurements made of a sheet of material comprising:
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scanning at least one sensor over a moving sheet of material to be measured at a first scanning speed to generate first scan measurements, the at least one sensor moving transversely relative to the moving sheet of material, the first scan measurements including mixed CD-MD variations of the sheet of material; transforming said first scan measurements into a first temporal power spectrum with respect to a first temporal frequency; detecting first temporal dominant spectral components of said first temporal power spectrum; scanning at least one sensor over said sheet of material to be measured at a second scanning speed to generate second scan measurements, the at least one sensor moving transversely relative to the moving sheet of material, the second scan measurements including mixed CD-MD variations of the sheet of material; transforming said second scan measurements into a second temporal power spectrum with respect to a second temporal scanning frequency; detecting second dominant spectral components of said second temporal power spectrum; and identifying MD spectral components of said scanning measurements by determining at least one of said first temporal dominant spectral components that is at the same temporal frequency as at least one of said second temporal dominant spectral components, the MD spectral components representing the MD variations separated from the mixed CD-MD variations of the sheet of material, the MD variations including a plurality of values over an MD range of the sheet of material. - View Dependent Claims (9, 10, 11)
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Specification