Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1990-07-12
1992-01-28
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356430, G01V 904
Patent
active
050846280
ABSTRACT:
Holes, tears and missing portions in a sheet, such as a banknote, are detected. The sheet is irradiated with radiation so that the radiation passes through the sheet with a relatively low degree of attenuation in areas where holes, tears and missing portions do not exist and with a relatively high degree of attenuation in areas where holes, tears and missing portions exist. The attenuated radiation is retroreflective back through the sheet and is then received by appropriate photodetectors. Since the sheet is relatively opaque and the radiation passes through the same points in the sheet twice, the contrast between the received radiation having passed through the holes, tears and missing portions and the received radiation passing through the relatively opaque sheet is very high making it simple to differentiate between those areas and thereby to positively detect holes, tears and missing portions in the sheet.
REFERENCES:
patent: 3588513 (1971-06-01), Hiroo
patent: 3594087 (1971-07-01), Victor
patent: 3859538 (1975-01-01), Mannonen
patent: 4368982 (1983-01-01), Van Arnam et al.
patent: 4380396 (1983-04-01), Arndt et al.
patent: 4709145 (1987-11-01), Spillman, Jr.
Burge Anthony R.
Potter Michael
De La Rue Systems Ltd.
Le Que T.
Nelms David C.
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