Method and apparatus for phase evaluation of pattern images used in optical measurement
US5361312A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Apr 8, 1993 |
| Grant date | Nov 1, 1994 |
| Priority date | — |
| Expiry date | Apr 8, 2013 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01J2009/0249
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The invention relates to measuring a phase-modulated signal 5. The signal is measured along at least five different steps (P1-P5) corresponding to preselected phase angles of the carrier wave 4. From the associated sets of measured values, at least three sets of measured values are formulated in a manner that from each of the sets a phase value [.phi..sub.i =arctan (Z.sub.i /N.sub.i) where i is equal to or greater than 3] can be calculated. The same correct phase value is computed based upon these three sets for a signal with the frequency of the carrier wave. The essence of the invention is finding that linear combinations of a.sub.i Z.sub.i and a.sub.i N.sub.i can be used for the computation of an accurate phase measurement where the factors a.sub.i are selected so that the phase error, as a function of the preselected phase steps, has at least three zero positions among the measured phase steps (P1-P5). As a result, the systemic errors that normally accompany phase measuring are significantly reduced. The invention is particularly suitable for the evaluation of bar pattern images and multiple-bar pattern images.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.