Finger imaging apparatus using curved platen
US4783167A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 5, 1987 |
| Grant date | Nov 8, 1988 |
| Priority date | — |
| Expiry date | May 5, 2007 |
Classification
- Technology area (CPC A)Human Necessities
- CPC primaryA61B5/1172
- WIPO fieldMedical technology
- WIPO sectorInstruments
Abstract
A curved cylindrical segment platen has a concave touching surface. An interrogating slit light beam is scanned around the platen to scan a finger held against the touching surface. An optical imaging system images the zone illuminated onto an array of photo-transducers to provide a signal representing the fingerprint. The optical system is rotated around the platen. The axis of the interrogating light beam is substantially normal to the touching surface. The axis of the imaging system is off normal by about 56 degrees, an amount which is greater than a critical angle equal to the maximum angle of refraction in the platen. This critical angle is approximately 41 degrees. The axis of the imaging system is also off normal to the non-touching surface by an angle that is less than this critical angle of 41 degrees and thus less than the angle of total internal reflection. As a consequence, the image at the photo-transducers provides a completely dark valley zone and a sharply contrasting light image ridge zone. In a second embodiment, a thick flat platen has a flat touching surface and an opposed parallel flat surface through which an illuminating light beam is applied to scan across a…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.