Laser scanner flaw detection system using baseline follower signal processing

Claim 2

A flaw detection system for detecting flaws on a surface of material comprising a. a laser for emitting a laser beam of radiation, b. means for successively scanning said laser beam across a surface of material being examined, c. detector means receiving radiation from said material producing a detector signal in response to the intensity of the radiation applied thereto, d. baseline extractor means having said detector signal applied thereto for providing a baseline signal therefrom, e. differential circuit means having said detector signal and said baseline signal applied thereto for producing a difference signal between said detector signal and said baseline signal, f. threshold means for providing a threshold signal, and g. discriminator means having said difference signal and said threshold signal applied thereto for producing a flaw output signal when said difference signal exceeds said threshold signal.

Claim 3

The structure set forth in claim 1 wherein said baseline signal is applied to said threshold means for scaling said threshold signal in accordance with said baseline signal.

Claim 4

The structure set forth in claim 2 including a hold circuit coupled between the output of said discriminator means and said baseline extractor means for maintaining the level of said baseline signal during the occurrence of a flaw output signal from said discriminator means.

Claim 5

The structure set forth in claim 1 including a clamping means having said detector signal applied thereto, blanking means for preventing said laser beam from appearing on said material during an inactive scanning interval, and means for activating said clamping means during the blanking interval of said blanking means for clamping said detector signal to a predetermined level to compensate said detector signal for the effects of ambient lighting conditions.

Claim 6

The structure set forth in claim 1 wherein said baseline extractor means comprises a comparator having said detector signal applied to one input terminal thereon, and a variable resistor and a capacitor forming an RC circuit coupled to the output of said comparator, the feedback path from said RC circuit coupled to another input terminal of said comparator for providing said baseline signal which is the moving average of said detector signal.

Claim 7

The structure set forth in claim 3 wherein said hold circuit comprises an analog switch.

Claim 8

The structure set forth in claim 5 including a hold circuit comprising an analog switch coupled between the output of said discriminator and said RC circuit which is activated by a flaw output signal from said discriminator for maintaining the level of said baseline signal on said capacitor during the occurrence of a flaw output signal.

Claim 9

A flaw detection system for detecting flaws on a surface of material, comprising a. a laser for emitting a laser beam of radiation, b. means for successively scanning said laser beam across a surface of material being examined, c. detector means receiving radiation from said material producing a detector signal in response to the intensity of the radiation applied thereto, d. means for preventing said laser beam from appearing on said material during a non-active scanning interval, e. means for providing a clamping pulse during a portion of said non-active scanning interval, f. clamping means having said detector signal applied thereto, g. means for coupling said clamping pulse to said clamping means for clamping said detector signal at a predetermined level thereby removing from said detector signal the effects of ambient radiation on said detector signal, h. discriminator means, i. threshold means for providing a threshold level signal, and j. means for coupling said threshold level signal and said clamped detector signal to said discriminator for providing flaw output signal indicative of a flaw on the surface of the material being examined when said clamped detector signal exceeds said threshold level signal.

Claim 10

A flaw detection system for detecting flaws on a surface of material, comprising a. a laser for emitting a laser beam of radiation, b. means for successively scanning said laser beam across a surface of material being examined, c. detector means receiving radiation from said material producing a detector signal in response to the intensity of the radiation applied thereto, d. means for preventing said laser beam from appearing on said material during a non-active scanning interval, e. means for providing a clamping pulse during a portion of said non-active scanning interval, f. clamping means having said detector signal applied thereto, g. means for coupling said clamping pulse to said clamping means for clamping said detector signal at a predetermined level thereby removing from said detector signal the effects of ambient radiation on said detector signal, h. discriminator means, i. threshold means for providing a threshold level signal, and j. means for coupling said threshold level signal and said clamped detector signal to said discriminator for providing flaw output signal indicative of a flaw on the surface of the material being examined when said clamped detector signal exceeds said threshold level signal.

Claim 11

A flaw detection system for detecting flaws on a surface of material comprising a. a laser for emitting a laser beam of radiation, b. means for successively scanning said laser beam across a surface of material being examined, c. detector means receiving radiation from said material producing a detector signal in response to the intensity of the radiation applied thereto, d. baseline extractor means having said detector signal applied thereto for providing a baseline signal therefrom, e. threshold means having said baseline signal applied thereto for providing a threshold signal which is scaled in accordance with said baseline signal, and f. discriminator means having said detector signal and said threshold signal applied thereto for producing a flaw output signal when said detector signal exceeds said threshold signal.

Claim 12

A flaw detection system for detecting flaws on a surface of material comprising a. a laser for emitting a laser beam of radiation, b. means for successively scanning said laser beam across a surface of material being examined, c. detector means receiving radiation from said material producing a detector signal in response to the intensity of the radiation applied thereto, d. baseline extractor means having said detector signal applied thereto for providing a baseline signal therefrom, e. threshold means having said baseline signal applied thereto for providing a threshold signal which is scaled in accordance with said baseline signal, and f. discriminator means having said detector signal and said threshold signal applied thereto for producing a flaw output signal when said detector signal exceeds said threshold signal.

Claim 13

The structure set forth in claim 9 including a hold circuit coupled between the output of said discriminator means and said baseline extractor means for maintaining the level of said baseline signal during the occurrence of a flaw output signal from said discriminator means.

Claim 14

The structure set forth in claim 9 including a clamping means having said detector signal applied thereto, blanking means for preventing said laser beam from appearing on said material during an inactive scanning interval, a means for activating said clamping means during the blanking interval of said blanking means for clamping said detector signal to a predetermined level to compensate said detector signal for the effects of ambient lighting conditions.

Claim 15

The structure set forth in claim 9 wherein said baseline extractor means comprises a comparator having said detector signal applied to one input terminal thereon, and a vaRiable resistor and a capacitor forming an RC circuit coupled to the output of said comparator, the feedback path from said RC circuit coupled to another input terminal of said comparator for providing said baseline signal which is the moving average of said detector signal.

Claim 16

The structure set forth in claim 9 including a hold circuit comprising an analog switch coupled between the output of said discriminator and said RC circuit is activated by a flaw output signal from said discriminator for maintaining the level of said baseline signal on said capacitor during the occurrence of a flaw output signal.