Method and system for detecting localized birefringence defects in a dynamic global birefringence field
US5757978A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 18, 1996 |
| Grant date | May 26, 1998 |
| Priority date | — |
| Expiry date | Jul 18, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B11/10582
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A method and system are provided for reliably detecting localized birefringence defects of an object such as an optical media substrate in a dynamic local birefringence field created during cooling of the optical media substrate at an inspection station. A birefringence digital filter filters out high frequency defect data while eliminating background birefringence data in a digital image created by a camera adapted to respond to the birefringence of the optical media substrate under control of a computer. Resulting filtered high frequency defect data is then processed to determine the localized birefringence defects in real-time. In one embodiment, the birefringence digital filter includes an addressable storage device such as a PROM which stores a lookup table which is able to produce filtered data in real-time at a data rate in excess of 8 million pixels per second. In another embodiment, a finite impulse response (FIR) filter, including registered multiplier-adders may be used to calculate or obtain filtered data at a higher rate (i.e. 10 million pixels per second). The filtered data may be post processed to accomplish gain and offset correction as well as to impose nonlinear c…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.