Process and apparatus for sensing defects on a smooth surface

Claim 1

A process for sensing the effective magnitude and/or number and/or spatial distribution of individual depression and/or protrusion defects on a high-precision smooth surface of an article which may have said defects randomly distributed and relatively spatially-distant each from the other and which additionally may have relatively spatially-distant rough spots comprising adjacent randomly-distributed defects, comprising: a. producing two coherent optical radiation beams of the same intensity, one of said beams having a different frequency from said other beam, the frequency difference Δf being within the radio frequency range; b. converging said beams to form an interference zone comprising a fringe pattern within the zone of convergence, said fringe pattern continuously moving laterally at a rate equal to Δf; c. adjusting the cross-sectional area of the fringe pattern in the x-y plane so that it is substantially smaller than said surface and no larger than an area which includes about an average predetermined spatial incidence of about one defect per pattern area on said surface; d. adjusting the fringe period λ s of the pattern to a width which is substantially wider than the effective cross-sectional dimension of a predetermined, maximum-size defect as indicated by backscatter signal magnitude; e. positioning at least the portion of said article bearing said smooth surface within the fringe pattern in such manner that said surface lies substantially in a plane defined by the x and y axes of the fringe pattern and the angle of incidence of the bisector of the pair of converging beams forming the fringe pattern is at an angle relative to said surface at the point of incidence such as to provide an angle of specular reflection, whereby substantially all specularly-reflected radiation bypasses a receiver of the backscattered optical radiation; f. continuously spatially displacing the interference zone and/or said smooth surface relative to each other while maintaining the relative orientation of said surface and said fringe pattern substantially as defined in (e) supra; g. continuing said relative displacement in such manner that substantially the entire predetermined area of said surface or sufficient area to determine the presence of unacceptable defects is scanned by said fringe pattern; and h. as said relative displacement continues, continuously sensing the AC and DC signal components of the backscattered radiation, wherein, at any given instantaneous moment of scan: 1. in the case comprising sensing of a single defect within the cross-sectional area of the fringe pattern: aa. substantially zero AC and DC signals indicate smooth, defect-free surface; bb. a substantially zero AC signal and a substantially non-zero DC signal indicate an effective defect width substantially at least as wide as λ s ; cc. substantially non-zero AC and DC signals wherein the AC/DC ratio is substantially equal to 1 indicate the presence of a defect, the effective width of which is substantially proportional to the AC and DC signal amplitudes and substantially less than the width of λ s ; dd. substantially non-zero AC and DC signals wherein the AC/DC ratio is substantially less than 1 indicate a defect, the effective width of which is approaching λ s ; and ee. the amplitude of said non-zero AC signal and/or the ratio of said AC/DC signal indicate the effective cross-sectional width of said defect; and 2.

Claim 59

A system for sensing the effective magnitude and/or number and/or spatial distribution of individual defects on a high-precision smooth surface of an article which may have said defects randomly distributed and relatively spatially-distant each from the other and which additionally may have relatively spatially-distant rough spots comprising adjacent, randomly-distributed defects comprising: a. means for producing a pair of coherent optical radiation beams of substantially the same size and intensity, one of said beams having a different frequency from said other beam, the difference in frequency being within the radio frequency range; b. means for converging said beams to form a laterally-moving fringe pattern; c. means for adjusting the cross-sectional area of the fringe pattern so that it is substantially smaller than said smooth surface and no larger than an area which includes about an average predetermined spatial incidence of about one defect per pattern area on said surface; d. means for adjusting the fringe period of the pattern to a width that is substantially wider than the effective cross-sectional dimension of a predetermined, maximum size defect as indicated by backscatter signal magnitude; e. means for positioning at least the portion of said article bearing said smooth surface within the fringe pattern in such manner that said surface lies substantially in a plane defined by the x and y axes of the fringe pattern and the angle of incidence of the bisector of the pair of converging beams forming the fringe pattern is at an angle relative to said surface at the point of incidence such as to provide an angle of specular reflection, whereby substantially all specularly-reflected radiation bypasses means for receiving the backscattered optical radiation; f. means for continuously spatially displacing the interference zone and/or said smooth surface relative to each other while maintaining the relative orientation of said fringe pattern substantially as defined in (e) supra; g. means for continuing said relative displacement in such manner that substantially the entire predetermined area of said surface can be scanned by said fringe pattern; h. means for continuously sensing the backscatter radiation from said surface; i. means for continuously determining the amplitude of the AC signal; j. means for continuously recording and/or displaying information as to the magnitude of the AC signal; k. means for continuously recording and/or displaying information as to the number of said defects on said smooth surface; and l. means for continuously recording and/or displaying information as to the position of each defect on said surface.

Claim 60

A system for sensing the effective magnitude and/or number and/or spatial distribution of individual defects on a high-precision smooth surface of an article which may have said defects randomly distributed and relatively spatially-distant each from the other and which additionally may have relatively spatially-distant rough spots comprising adjacent, randomly-distributed defects comprising: a. means for producing a pair of coherent optical radiation beams of substantially the same size and intensity, one of said beams having a different frequency from said other beam, the difference in frequency being within the radio frequency range; b. means for converging said beams to form a laterally-moving fringe pattern; c. means for adjusting the cross-sectional area of the fringe pattern so that it is substantially smaller than said smooth surface and no larger than an area which includes about an average predetermined spatial incidence of about one defect per pattern area on said surface; d. means for adjusting the fringe period of the pattern to a width that is substantially wider than the effective cross-sectional dimension of a predetermined, maximum size defect as indicated by backscatter signal magnitude; e. means for positioning at least the portion of said article bearing said smooth surface within the fringe pattern in such manner that said surface lies substantially in a plane defined by the x and y axes of the fringe pattern and the angle of incidence of the bisector of the pair of converging beams forming the fringe pattern is at an angle relative to said surface at the point of incidence such as to provide an angle of specular reflection, whereby substantially all specularly-reflected radiation bypasses means for receiving the backscattered optical radiation; f. means for continuously spatially displacing the interference zone and/or said smooth surface relative to each other while maintaining the relative orientation of said fringe pattern substantially as defined in (e) supra; g. means for continuing said relative displacement in such manner that substantially the entire predetermined area of said surface can be scanned by said fringe pattern; h. means for continuously sensing the backscatter radiation from said surface; i. means for continuously determining the amplitude of the AC signal; j. means for continuously recording and/or displaying information as to the magnitude of the AC signal; k. means for continuously recording and/or displaying information as to the number of said defects on said smooth surface; and l. means for continuously recording and/or displaying information as to the position of each defect on said surface.