GB622827A - Improvements in web printing machines - Google Patents

Abstract

622,827. Automatic control systems. HOE & CO., Ltd., R. April 15, 1946, No. 11523. Convention date, April 16, 1945. [Class 38 (iv)] [Also in Group XL (b)] In multi-colour web printing machine the dimensions of the web are corrected. longitudinally and transversely, to improve registry, as it passes through the printing units. This avoids lack of registry arising from stretching or shrinking of the web through variation. of moisture content during printing. In the fourcolour offset printing press shown in Fig. 1 the first colour unit 17 prints spaced register marks 58 on the web W which are scanned at the point 86 by a photo-electric cell 83. This cell influences a triode valve 101, Fig. 4, which, at each passage of a mark 58, tends to fire a gas discharge tube 102. The two parallel anode circuits are, however, normally broken at rotating contact discs 88, 89 driven from the plate roller 49, Fig. 1, of printing unit 17. The discs are so geared that this condition is maintained as long as a mark 58 is being printed at the same instant as a mark is at the scanning point 86. If, however, the web is ahead of its correct position at the point 86, an anode circuit for gas tube 102, Fig. 4, is completed through contact 94 when the photo-electric cell 83 is energized, and, if the web is behind its correct position, the anode circuit is completed through contact 93. In either case the appropriate relay 103, 107 is energized to actuate its contacts 104, 106 or 108, 109 and motor,controllers 42, 54 are thereby operated, the former to control motor 41, Fig. 1, and so increase or decrease the web tension by jockey roller 23 which in turn controls the tensioning motor 34, and the latter to control motor 53 which increases or decreases the pressure on a slipping clutch drive 51 and thus varies the pull on the web. The subsequent printing units also have known scanning means 61, 62 which control the rotational setting of the plate rollers through motors 71 and epicyclic differential gearing. In this case the passage of a mark 58 past these scanning devices must coincide with the energization of a cell 68 by a shutter 64 attached to the roller, the setting of which is adjusted to give correct registry in printing. The transverse dimension and positioning of the web is determined by marginal datum marks 116, 117, Fig. 5, also printed by the first unit 17. These are scanned by two light cells 122, 123 or 126, 127 which, through a control circuit 131, adjust the axial setting of the plate roller 49 or influence tensioning rollers 133, 134 to stretch or release the web. The electrical circuit is shown in Fig. 10 which diagrammatically represents marks 116, 117 scanned by cells 122, 123 and 126, 127 respectively. Movement of a mark 116 to one side influences the anode current of the appropriate valve 206, 207, the former being in parallel with tensioning solenoid 177 and the latter in series with it, so as to increase or decrease the current in tensioning solenoid 177. Similar functions are carried out at the opposite edge of the web and in each case an increase in current, resulting from a mark being too near the middle of the web, causes oblique guide rollers 133, 134, Fig. 5, to grip the edge of the web more tightly and stretch it outwards. If the web is too wide at the scanning point, the grip of the rollers is decreased. If the web moves bodily to one side, the increase in anode current of one valve in each pair 206, 207, Fig. 10, and 216, 217 operates the two corresponding anode relays 208, 209, 218, 219 which operate relays 234 or 236 in control unit 132 (see also Fig. 5). This actuates a motor 136 which drives a screw 138 and shifts the plate roller 49 in the appropriate direction. to follow the web, the movement of which is, at the same time, also -corrected by the guide rollers. Interlocking relays 205, 215, Fig. 10, when energized, prevent the closing of contacts 221, 211 respectively by relays 218, 208. This ensures that all four contacts 211, 212, 221, 222 are not closed at the same time when the four cells view the unprinted web between marks. When the whole web shifts to one side the reduction in current through one relay 205, 215 renders it ineffective and allows the appropriate circuit to be completed to control gear 132. An application of the invention to an intaglio press is described with reference to Figs. 11 and 12 (not shown). In this machine, the general application is the same as the foregoing, but the web is dried after each printing operation and to counteract the resultant shrinkage the spreader rollers apply progressively increasing pressure to maintain the original width.