Device for detecting irregularities in a moving sheet material
AssigneeAgfa-Gevaert
InventorWalter P. Van Beeck
Life of this patent
Estimating the term…
Abstract
Device and method for the optical inspection of speck-like and streaklike defects in a moving web. A source of radiation illuminates a transverse zone of the web, a series of photocells measures the radiation after transmission through, or reflection from the web, and a grating arrangement modulates the radiation received by the photocells, thereby to modulate the output signal of each cell by an A.C. component.
Claims11
A device for detecting speck-and streaklike irregularities in a moving sheet material, comprising
- a source for directing electromagnetic energy across at least a portion of the width of the material,
- a row of stationarily mounted radiation responsive photocells, each having a common predetermined length of field parallel to said row, that are substantially uniformly spaced transversely across the path of the sheet material to receive radiation from said source after modulation of said radiation by the moving sheet material,
- a grating arrangement disposed in the path of the radiation to said photocells and serving to intercept and transmit radiation from linear periodically alternating areas in a direction parallel with the photocell row, and
- means for displacing said grating arrangement to reverse the areas of transmission and interception, the linear periodicity of the grating being equal to 1/X times said field length of a photocell, wherein X is an integer at least equal to 5.
A method of testing sheet material to detect the presence or location of speck- and streaklike irregularities therein affecting radiation transmitting or reflecting properties thereof, comprising the steps of advancing the sheet material in its own plane across a projected path of radiation which intersects the plane of the sheet material at a zone extending in at least one direction in said plane, periodically alternately intercepting radiation transmitted through or reflected from alternating different portions of each of a number of like incremental sub-zones extending in succession along said zone of intersection, detecting the resulting transmitted or reflected modulated radiation by a plurality of photocells each of which has a detection field having a dimension measured parallel to said zone direction equal to a whole number multiple of one of said incremental sub-zones, and deriving AC modulated signals from the output of said cells.
Dependencies are inferred from the claim text.