GB939489A - Photo-electric scanning device - Google Patents

Abstract

939,489. Photo-electric flow detectors. E. SICK. July 28, 1960 [July 31, 1959], No. 26386/60. Class 40 (3). In an arrangement for detecting flaws or defects in surfaces providing diffuse reflection by scanning the surface line by line with a focused beam of rays oscillating in one plane, the scanning beam is directed to a concave mirror curved in such a way that the sharp focusing of the beam is equalized over the width of the surface which is being examined, and that the focal point of the beam of rays is imaged on a radiation detector device. As shown diagrammatically in Fig. 1, a beam from a source 1 is focused by a lens 2 on a slit 3 and passes via a half-silvered mirror 8 to a rotating mirror drum 4 and to a concave cylindrical parabolic mirror 5 so that with the aid of a cylindrical lens 7 a small scanning spot is sharply focused over the whole width of the surface 6 to be scanned for flaws. The light reflected from the surface passes back via the elements 4, 5, 7 to the half-silvered mirror from which it is reflected to a slit 10 behind which is a photoelectric device 9. In a modification, Fig. 2 (not shown), the reflected beam passes to the photoelectric cell via a small mirror located near the slit 3 and in a further modification, Figs. 3, 4 (not shown), the variably reflected beam is arranged to pass beneath the mirror 5 and is directed to the photo-electric cell by means of a second concave mirror, or to a number of photocells associated with an equal number of concave parabolic mirrors. The different effects of wrinkles of the surface as opposed to superficial spots are illustrated in connection with Figs. 8, 9 (not shown). A scanning assembly, Figs. 10 and 11, comprises a light source 22 providing a beam reflected by a mirror 23 to an objective lens 24 and to a rotating mirror drum 25 from which the scanning beam passes via inclined mirrors 26, 27 to a mirror 28 and thence across a cylindrical parabolic mirror 29 to provide a detecting beam equally focused and reduced to point size by a cylindrical lens 31 across the width of the sheet 30. The diffusely reflected beams 32, 33 due to surface spots and wrinkles pass in the reverse path through the optical system, and the beam passing through the upper and lower parts of the slit is reflected by mirrors 34, 35 or 34, 37 to respective photoelectric devices 36, 38, which are preferably photo-multipliers. In a modification of Fig. 2, Fig. 12 (not shown), the light diffusely reflected from the sheet is deviated by an optical wedge to a different path in relation to the mirror 5 and in which it impinges on a separate rotating mirror drum passing the reflected beam via a slit in a diaphragm to a photo-electric device.