GB373189A - Improvements in and relating to printing presses - Google Patents

Abstract

373,189. Feeding webs. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and WHITELEY, A. L., 11, Stanley Road, Rugby. Feb. 13, 1931, No. 4614. [Class 100 (i).] Apparatus for automatically maintaining within pre-determined limits the relative positions of webs of material such as paper fed to a printing-press or other machine comprises a light-sensitive cell 1 co-operating with holes or marks at definite intervals on the web to pass electric impulses to a relay which is actuated thereby to effect forward or backward displacement of the web, together with means operative after a pre-determined time delay for returning the relay to normal condition and for terminating the operation of displacing the web, and a contact-making device actuated in accordance with the rate of feed of another web and having contacts in the relay supply circuit arranged to prevent impulses from reaching the relay unless the web is out of register. Alternatively, two relays may control accelerating and retarding mechanism for the web-feeding apparatus. The cell 1 is connected as shown, Fig. 1, to the grid of a thermionic valve so that the variation in potential of the grid due to the marks &c. on the web causes a current to flow in the thermionic valve 5. This impulse is communicated to one or other of the valves 21, 22 of the three-electrode vapour discharge type by conducting strips 17, 18 on the contactmaking device 20. The strips 17, 18 co-operate with fixed contacts 15, 16 respectively and the drum 20 rotates synchronously with the collating - cylinder or other suitable part of the main press. If the inset web lags behind, the impulse in the valve 5 is generated when the strip 17 is in contact with the contact 15 and is communicated to the grid of the valve '21, thereby raising its potential and starting the arc to complete the anode circuit through the normally-closed switch 31. This energizes the coil 29 which operates the apparatus which raises the speed of the inset web or effects its forward displacement. The current through the valve 21 may be stopped by momentarily opening the switch 31, by means of a time-lag relay of the pendulum or dashpot type, or by means such as described below. Should the inset web lead, the strip 18 engages the contacts 16 to energize the valve 22 and coil 30, the latter serving to operate the mechanism for retarding the feed. The contact-making device may be replaced by a cam-operated switch, comprising two cams, rotating on a common shaft in timed relation with the main press, which impart movement to two pivoted arms to close contacts in the secondary circuit of the transformer 12. The mechanism for varying the rate of feed may comprise a pilot motor which is driven in an appropriate direction according to which of the coils 29, 30 is energized ; the pilot motor controls a compensating roll for displacing the web backwards or forwards and a variable speed gear, consisting of cone pulleys connected by a belt. An additional hand compensating roll is provided, and chain drives are used to facilitate adjustment &c. Alternative methods of breaking the arc of the valves 21, 22 comprise : (1) A rotary drum 45, Fig. 2, driven by the pilot motor and having a small conducting plate 43 thereon which closes the plate circuit of the valve 21, or 22 to start the motor. Upon rotation of the drum the plate 43 moves away from the fixed contacts 41 in the circuit of the valve, so that this circuit is broken but the valve is short-circuited through fixed contacts 55 which engage a conducting strip 53 on the periphery of the drum. The motor therefore continues to rotate until the break in the strip 53 comes under the contacts 55 and in this position the contacts 41 again engage the plate 43, so that the valve is ready to receive a fresh impulse. The control is duplicated for the valve 22 and switches are arranged in the circuits of the valves, so that when one valve is operating, the switch in the circuit of the other valve is open. (2) A second similar valve 65 is connected as shown in Fig. 3 to the first valve 21. The valve 65 is normally conducting, but when an impulse arrives at the grid of the valve 21, due to the passage of a perforation &c. on the web past the photo-electric cell as described above, the arc starts in the valve 21, resulting in a fall of potential of the plate of the valve 65, which accordingly ceases to conduct. After a time, however, the potential of the condenser 69 and therefore of the grid 68 reaches a sufficient valve to start the arc again in the valve 65, and the resulting fall of plate potential of the valve 21 causes the arc in this valve to fail. (3) The second valve 65 of Fig. 3 is replaced by a fixed contact periodically engaging one of a number of contacts situated on the periphery of a drum driven by the pilot motor and having a low potential. When the two contacts engage the plate potential of the valve 21 falls and the current through the valve is interrupted until the next impulse reaches the grid. The photo-electric device may be connected to two thermionic valves 5, Fig. 1, each controlling its appropriate amplifying circuit and valve, whereby a greater degree of decoupling is made possible. Two photoelectric cells may be used, spaced apart upon the web, each coupled to its appropriate amplifying valve circuit. The output circuit of each such amplifying device is connected to the control circuit of the appropriate relay through contacts such as 15, and one serves to operate a control circuit for accelerating the web while the other operates a retarding control-circuit.