Defect detection system
US4030835A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 28, 1976 |
| Grant date | Jun 21, 1977 |
| Priority date | — |
| Expiry date | May 28, 1996 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/00375
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Defect detection apparatus, for optically inspecting a spiral groove of a video disc record, directs a coherent light beam at the grooved surface of the disc. The incident beam, focused at a point beyond the disc surface, illuminates the grooved surface with a light spot that spans a plurality of convolutions of the groove. Relative motion is established between the disc surface and the incident beam in a manner causing the illuminating spot to rapidly scan the groove surfaces in a coarse spiral pattern. The structure of the illuminated groove convolutions, absent any defects, serves as a diffraction grating for diffracting the light into an undeviated zero diffraction order cone of light that converges at a first location in a plane spaced from the disc surface and into deviated higher diffraction order cones of light that converge at additional locations in said plane separated from the first location. A photodetector is positioned to be in registry with the first location and spaced from said additional locations. A blocking means is placed over a central region of the photodetector to normally intercept the zero diffraction order light, thereby preventing the conversion of ligh…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.