GB504818A - Improvements in or relating to the feeding of sheets - Google Patents

Abstract

504,818. Photo - electric control of sheet - delivery apparatus ; valve relays. WATERLOW & SONS, Ltd., and HOLNESS, R. F. G. July 30, 1937, No. 21136. [Classes 40 (iii) and 40 (v)] In feeding sheets, especially in colour printing machines, the sheets are registered to lay marks thereon in such a manner that any error in registration due to humidity or other cause is distributed about a predetermined point on the sheet, the registration of the sheet being controlled automatically by photo-elec. tric devices influenced by the lay marks. As shown, each sheet, Fig. 1/has three opaque lay marks 2, 3, 4, in two lines. intersecting at the centre point 4 of the sheet. The automatic devices ensure the centralization of the point 5 of each sheet and distributes errors of registration about this point. One such sheet 1 is fed at a time from a stack 6, Fig. 2, to a laying-on board 21 and carried on by tapes 36, 37 toward grippers 7 on an impression cylinder.8. When the laymarks 2, 3 pass between light sources 9, 10 and photo-sensitive devices 12, 13, electromagnetically controlled grippers 17, 18 respectively grip the sheet over a transverse lay-bar 20, swivelling means being provided to allow the necessary rotations of the sheet about the axes of these grippers. Then a cam 41 allows the lay-bar 20 to be moved transversely of the machine by a spring 20a until the lay mark 4 comes between a light source 11 and a photo-sensitive device 14, whereupon the lay bar 20 is locked by an electromagnetic brake 20b, 'and the sheet is fed to the grippers 7. The electromagnetic brake 20b may be replaced by a brake, Figs. 4 and 5 (not shown), comprising a pair of spring-urged gripping balls controlled by a spring urged lever adapted to be operated by an electromagnet. The photo-sensitive devices 12, 13, 14, control the various electromagnets by means of amplifiers and relays 12a, 13a, 14a, together with additional relays 22, 23, 24, and switches 25, 26, 27, the connections of which are indicated in Fig. 3 (not shown). The switches 25, 26, 27 are on a spindle 28 driven by a sprocket 28a and chain 29 from a sprocket 30 on a shaft of the sheet feeding device. The sheet may receive a preliminary registration along two edges by mechanism known per se comprising front lays 51, 52, which stop the leading edge while a spring gripper 53a pulls the sheet against a side lay 54, after which the front lays 51; 52 are lifted. The photosensitive device may be an emissive type of cell or a conductive type such as the selenium cell described in Specification 284,942. A suitable amplifier shown in Fig. 6 comprises the photo-sensitive cell 12, 13 or 14, a threeelectrode valve 66, and a gas discharge relay tube 31, 32, or 33. D.C. is supplied through a choke 79 and decoupling and biassing resistances with suitable condensers ; and the photocell is coupled to the valve 65 by resistancecapacity and the valve 65 to the relay tube by a transformer 66 and a resistance 67 to limit grid current.