Measuring surface flatness using shadow moire technology and phase-stepping image processing
US5969819A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 3, 1998 |
| Grant date | Oct 19, 1999 |
| Priority date | — |
| Expiry date | Jun 3, 2018 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01R31/309
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A two-dimensional array of phase values is calculated from digitized phase-shifted shadow moire fringe patterns that are indicative of the flatness of the surface of an object. The light intensity "I.sub.1 " of a pixel in a first of such shadow moire fringe patterns is approximated by I.sub.0 +Acos.o slashed., the light intensity "I.sub.2 " of the pixel in a second of such shadow moire fringe patterns is approximated by I.sub.0 +Acos[.o slashed.+(.pi./2)], the light intensity "I.sub.3 " of the pixel in a third of such shadow moire fringe patterns is approximated by I.sub.0 +Acos[.o slashed.+.pi.], and the light intensity "I.sub.4 " of the pixel in a fourth of such shadow moire fringe patterns is approximated by Acos[.o slashed.+(3.pi.)/2)]. The phase values ".o slashed." are equal to arctan((I.sub.2 -I.sub.4)/(I.sub.1 -I.sub.3), and a first two-dimensional array of phase values are calculated. A plurality of two-dimensional arrays of image values are calculated from a first two-dimensional array of phase values, and the two-dimensional arrays of image values are filtered. A second two-dimensional array of phase values is calculated from the filtered two-dimensional arrays of image …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.