Patent US3840303A successfully refreshed from Google Patents.
US3840303A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Device for detection of blemishes in the surface of symmetrical planar objects
Assignee: Ferranti International PLC
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Filing: 1973-07-18
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Granted: 1974-10-08
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Expires: 1993-07-18
Abstract
Abstract In a detector of blemishes in the surface of a planar object, or web, which is symmetrical about an axis in the plane of the object, a beam of radiation from a laser in a scanning station is focussed onto the surface and caused to scan transversely to the axis while the object is caused to move past the scanning station parallel to the axis of symmetry. The axis is arranged to be located such that the beam crosses it at a predetermined time into the scan, at which time a datum signal is generated. During each scan, when the beam crosses a leading edge of the object onto the surface, an edge signal is generated. The time between the edge signal and the datum signal is half the time taken for the beam to traverse the surface so that the traverse time can be calculated and used to turn off the detector before the trailing edge is crossed by the beam.
Inventors
- 👤 G Clarke
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 20:12
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/84; G01N21/88; G01N21/89
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
235 words
A detector of blemishes in a surface, the surface in which the blemishes are to be detected, or a projection of the surface, being disposed about an axis of symmetry in a viewing plane, comprising a scanning station, arranged to be movable relative to the surface in a plane parallel to said viewing plane and in a direction parallel to said axis of symmetry, the scanning station including a source of a beam of electromagnetic radiation, a lens system for focussing the beam onto the surface, scanning means for causing the beam to scan over the surface transversely to said axis of symmetry, and means for receiving radiation diffusely reflected from the surface and for producing a blemish signal in response to a change in intensity of the received radiation; means for generating an edge signal when the beam crosses the edge of the surface onto the surface, means for generating a datum signal at a predetermined point in each scan, the locus of the predetermined points being arranged to lie along said axis of symmetry; means for determining the interval between the generation of the edge signal and the datum signal, and hence the time taken for the beam to traverse the whole width of the surface; gating means operable for a predetermined fraction of said traverse time; and blemish counting means responsive to operation of the gating means to count said blemish signals.
Claim 2
Dependent Claim
235 words
A detector of blemishes in a surface, the surface in which the blemishes are to be detected, or a projection of the surface, being disposed about an axis of symmetry in a viewing plane, comprising a scanning station, arranged to be movable relative to the surface in a plane parallel to said viewing plane and in a direction parallel to said axis of symmetry, the scanning station including a source of a beam of electromagnetic radiation, a lens system for focussing the beam onto the surface, scanning means for causing the beam to scan over the surface transversely to said axis of symmetry, and means for receiving radiation diffusely reflected from the surface and for producing a blemish signal in response to a change in intensity of the received radiation; means for generating an edge signal when the beam crosses the edge of the surface onto the surface, means for generating a datum signal at a predetermined point in each scan, the locus of the predetermined points being arranged to lie along said axis of symmetry; means for determining the interval between the generation of the edge signal and the datum signal, and hence the time taken for the beam to traverse the whole width of the surface; gating means operable for a predetermined fraction of said traverse time; and blemish counting means responsive to operation of the gating means to count said blemish signals.
Claim 3
Dependent Claim
95 words
A detector of blemishes as claimed in claim 1 in which the means for determining the time taken for the beam to traverse the surface comprises a dual-slope integrator operable in each scan to produce, in response to an edge signal, an output signal which increases in magnitude in one sense from a zero level and, in response to a subsequent datum signal, to an output signal which decreases in magnitude in said one sense towards zero, said traverse time being the period for which the magnitude of the output signal is greater than zero.
Claim 4
Dependent Claim
44 words
A detector of blemishes as claimed in claim 2 in which the gating means comprises a comparator having a preset reference level and arranged to produce a gating signal when the magnitude of the integrator output signal is in excess of said reference level.
Claim 5
Dependent Claim
89 words
A detector of blemishes as claimed in claim 1 in which the means for determining the time taken for the beam to traverse the surface comprises a reversible counter operable in each scan, in response to an edge signal, to count in one direction at a predetermined rate from a zero state and, in response to a subsequent datum signal, to count in the other direction at said predetermined rate, said traverse time being the period of time for which the state of the count is greater than zero.
Claim 6
Dependent Claim
42 words
A detector of blemishes as claimed in claim 4 in which the gating means comprises a generator operable to produce an output gating signal when the state of the count is in excess of a preset minimum, greater than said zero state.
Claim 7
Dependent Claim
21 words
A detector of blemishes as claimed in claim 1 in which the source of the beam of radiation is a laser.
Claim 8
Dependent Claim
68 words
A detector of blemishes as claimed in claim 1 further arranged to verify the symmetry of the surface about said axis wherein there is also provided meAns for generating a further edge signal when the beam crosses the trailing edge of the surface off the surface, and verification means operable to detect whether the beam crosses the trailing edge coincidentally with the end of the calculated traverse time.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-10-07 | 1978-04-08 | 1978-10-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-10-07 | 1982-04-08 | 1982-10-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-10-07 | 1986-04-08 | 1986-10-08 | $7700.00 | Window Closed / Lapsed |