Patent GB-632424-A (GB)
Title: Improvements in or relating to an apparatus for controlling the flow of current through an electronic circuit for the photoelectric inspection of articles
IPC: H01J40/00
Filed: 1945-07-03
Abstract: 632,424. Photo-electric inspection of articles. HURLEY, S. C. July 3, 1945, No. 16880. Convention date, July 20, 1944. [Class 40 (iii)] [Also in Group XL (c)] In apparatus for inspection by photo - electric camming, the shadow of an article traversing an inspection zone is projected on a plurality of photo-electric devices, arranged in predetermined positions relative to the shadow projected by a standard article, and respectively controlling the bias on independent control grids determining the current in a single electronic circuit operating current-responsive indicating means. In Fig. 9, phototubes, 1, 2, 18, 19 arranged so that a passing article of correct size correctly positioned, darkens phototubes 1, 18, leaving 2, 19 lightened (Fig. 10), are connected with resistances 3, 4 in two bridge circuits, balanced when both the photo-cells in each bridge are lightened or darkened, and respectively unbalanced by the passage of the article to increase the negative bias on the associated control grids of amplifying tubes, 6, 16, and drive the grids 29, 30 of the normally cut-off, preferably gas-filled, control tube 17 positive with respect to cathode. The control tube current operates relay 31 to energize an operative control circuit 109. Oversize or undersize articles respectively darken or lighten all four phototubes, maintaining the balance of both bridges and the negative bias on both control tube grids. A misplaced article obscures phototubes 1, 2 or 18, 19, and the bridges similarly remain balanced, maintaining the control tube cut-off bias. After each inspection, switch 32 is opened to de-ionize the control tube, and is closed before the next article passes. Fig. 12 shows a modification in which correct positioning of an article lightens photo-tube 43 and darkens photo-tube 42, unbalancing the bridge comprising the photo-tubes 42, 43 and resistances 45, 46, to drive positively the normally negatively biassed grid 54 of control tube 55, and grid 73 of control tube 74. Improper positioning, which darkens or lightens both phototubes, applies zero voltage to the control tube grids, while lightening of tube 42 and darkening of tube 43 applies a further negative bias. Photo-tubes 40, 41 are bridge-connected with resistances 45, 46, 63<1> and 68 so that grids 63, 80 of the control tubes are driven positively when the photo-tubes are darkened and vice versa. An undersize correctly positioned article lightens both photo-tubes 40, 41 and negatively biasses grids 63, 80. An article of proper size darkens photo-tube 41 and lightens 40, driving grid 63 positive to ionize control tube 55, and operate indicator 32. An oversize article darkens photo-tube 40, driving grid 80 positive and ionizing control tube 74 to operate relay 84 to disable indicator 132 and operate indicator 133. The control tubes are deionized after each inspection by manual or automatic operation of switch 32. Additional standing negative bias from rectifiers 65, 82 may be added if the bias developed by the illuminated photo-tubes is insufficient to cut off the control tubes. The invention is applicable to sorting papers 35 distinguished by the presence or absence of codemarks 36, 37, 38, 39 (Fig. 13). In a further modification (Fig. 14, not shown), articles are optically inspected and sorted by compressed air under control of a photo-electric system as described. Applications to distance and angle measurement, inspection of articles for shape, alignment, or position, and the alignment of moving webs, are referred to.