GB795480A - Apparatus and method for classifying sheets according to length - Google Patents

Abstract

795,480. Photo-electric control systems. UNITED STATES STEEL CORPORATION. Sept. 13, 1955 [May 11, 1955], No. 26228/55. Class 40 (3). Sheets longer or shorter than an acceptable length are detected by gauging apparatus which as described is photo-electric and which registers over or undersized sheets on a timer so that such sheets are diverted when they reach a deflector spaced along the conveyer. As shown, metal strip is unwound from an uncoiler 10, passes through a roller leveller 12, and is cut into strips by a flying shear 13, the strips then passing over a conveyer 14 where they are gauged and into one of prime or reject boxes 17, 18 according to the position of deflector 15. The gauge comprises a plate 20 (Fig. 2) in which are three apertures 21, 22, 23. Apertures 22, 21 are spaced in the direction of movement of the plate to be gauged and their leading edges are accurately machined. Aperture 23 is further spaced and has its trailing edge machined. Photo-cells 28, 29 receive light from a source 24 through apertures 21, 22 respectively, while a further cell 20 receives light from a source 26 through aperture 23. The distance between the machined edges of slits 21, 23 represents the maximum permissible sheet length and the distance between slots 22, 23 the minimum. In operation, as the trailing edge of the sheet uncovers cell 28, amplifier 31 produces a positive signal which causes a " flip-flop " to generate a negative signal which continues until the trailing edge uncovers cell 29 which then generates a positive pulse and the negative flip-flop output pulse terminates. If the positive pulse produced when the trailing edge of the sheet passes slot 23 occurs within the period of negative flip-flop output pulse a clipper amplifier 35 carrying both the pulses is maintained non-conductive; if outside, the clipper amplifier conducts and acts through pulse lengthener 37 to record on a timer 36 driven at a speed proportional to that of the moving strip the fact that a defective sheet has been rejected. At the correct time deflector 15 operates to deflect the imperfect sheet. The machined edges of apertures 21, 22, 23 may be adjustable. Specifications 673,140 and 784,142 are referred to.