GB762837A - Web positioning device - Google Patents

Abstract

762,837. Automatic control systems for moving webs. GOODYEAR TIRE & RUBBER CO. Dec. 7, 1954 [June 29, 1954], No. 35385/54. Class 38 (4). [Also in Group XL (b)] In a system for automatically centring a moving web on a required line of travel a pair of photo-cells independently follow the irregular edges of the web, and an electrical signal representing the sense of the relative displacement of the cells from the required line of travel, and hence the sense of the deviation of the centre of the web from that line, initiates the necessary lateral displacement of the web to reduce the deviation to zero. The photo-cells 13, 14, Fig. 1, have associated light sources 3, 6, energized from a supply 8, and identical bridge circuit 15, 16 respectively. The latter are energized from a D.C. source B and comprise tapped potentiometers 19, 28 and pairs of triodes 17, 18 and 24, 25 respectively, the output of cells 13, 14 being applied respectively to the grids of valves 18, 24. The web is initially centred on the required line of travel, and the cells are aligned with the web edges and hence equidistant from the required line. The potentiometers 19, 28 are then adjusted to balance the bridges, the balance being indicated on ammeters 23, 29. Subsequent lateral movements of the web edges result in changes in the cell outputs with consequent out-of-balance outputs from the bridges, these being applied over choppers 31, 34 and phase-sensitive amplifiers 36, 37 to energize the reversible two-phase motors 38, 39 in a sense as to move the cells back into alignment with the web edges. Rotation of the motors 38, 39 also causes adjust. ment of tappings on potentiometers 42, 43, the latter being energized over a rectifier 46 and variable resistors 44, 45, 47 from the supply 8. The resulting current in winding 48 of a relay MP, having a direction depending on the sense of the relative displacement of the cells from the required line of travel, causes closing of one or other of relay contacts MP1, MP2. One or other of relay windings 51, 52 are thus energized over a rectifier 53 and resistors 54, 55 to close one of contacts 63, 64, and thus energize a reversible two-phase motor 61 over a changeover switch 65. Rotation of motor 61 causes an alteration in the angle of a teeter-roll in a correct sense as to restore the centre of the web to the required line of travel. With switch 65 in the MANUAL position, motor 61 may be controlled by a switch 66 for an initial setting of the web. Rectifiers 58, 59, connected across relay windings 51, 52, respectively, prevent arcing across contacts MP1, MP2. Each photocell unit, Fig. 2, comprises a cell housing 67, a light source housing 68, adjustable lenses 69, 70 for beam focusing, lead screws 74, 75 driven from a motor assembly 78 through gearing as shown, and a potentiometer 80 adjustable by motor 78. Units 78, 80 correspond to the motors 38, 39 and potentiometers 42, 43 of Fig. 1 respectively.