Patent GB-666194-A (GB)
Title: Improvements in web roll accelerating apparatus
IPC: B65H19/16
Filed: 1949-07-07
Abstract: 666,194. Control of D.C. motors. WOOD NEWSPAPER MACHINERY CORPORATION. July 7, 1949. [Jan. 21, 1949] No. 17998/49. Class 38 (iii). [Also in Groups XVI and XXXV] In a web roll accelerating apparatus wherein a voltage derived from a first tachometer generator driven at a speed proportional to the running web is compared with that derived from a second tachometer generator driven at a speed proportional to the angular velocity of a fresh roll to be joined to the running web to control the motor driving the fresh roll, the voltage of the second tachometer generator is reduced in proportion to the diameter of the fresh roll so that the fresh roll and running web have the same linear speed at the instant of joining. A resistor is also provided for connection in series with the motor armature and series field should the speed of the running web fall appreciably below the speed of the fresh roll so as to brake the driving motor. Fresh roll diameter detecting mechanism (Fig. 1). A spider 11 on a shaft 12<SP>1</SP> carries the running roll R and fresh roll F the spider and shaft being rotated by a motor 19. Axial adjustment of the spider and shaft and associated mechanism may be provided for, and the splice mechanism including brushes 36 and knives 37 operates as described in Specification 436,610. The diameter detecting mechanism includes a pivoted arm 73 carrying a ratchet 75<SP>1</SP> and roller 75. The ratcher 75<SP>1</SP> is engaged by a spring biased pawl 76 pivotally connected to a fixed frame 77 by a shaft 29 and connected by an arm 78 to a lever 79 the lower end of which carries a roller 80 disposed in the path of projections 81 fixed on the housing 69 of the spider spindle 22. Thus as the spider rotates the fresh roll to its accelerating position shown the projection 81 engages the roller 80 and releases the pawl 76 from ratchet 75<SP>1</SP> allowing roller 75 to drop on the surface on the roll, and as projection 81 passes roller 80 the pawl is re-engaged with the ratchet thereby fixing the arm 73 in the position required. A rack 83 fixed to move with the arm 73 operates a gear 84 during movement of the roller 75 which in turn through further gearing, Fig. 5 (not shown), sets a potentiometer 89 (Fig. 10) in the fresh roll speed generator circuit at the required value in dependence on the roll diameter. Control circuit (Fig. 10). To initiate the changeover to the fresh roll, power switches 104, 106 are closed which energize the valve heaters and a time delay relay TR, which, after allowing time for the heating of the valves closes its contact 112 and energizes relay FLR. The brush lowering switch 128 is then closed energizing a motor 41 to lower the brush arm 38 and thereby close contacts 132 to energize a main relay 17 thereby completing a circuit to the fresh roll driving motor 42. The motor 42 drives a generator 49 which delivers a voltage, modified by the setting of the potentiometer 89 to a valve V for comparison with a voltage derived from a generator 91 driven by the running web. The current flow through the valve V determines that through a 'valve D in turn controlling the winding 141 of a saturable core reactor SC connected in a bridge circuit controlling a pair of thyratrons 100, 101 which supply the motor 42. The speed of motor 42 is thus controlled in dependence upon the difference of voltages supplied by generators 49, 91. If during splicing the running web slows down below that of. the fresh roll speed, a relay R drops to energize a second relay DBR which inserts a braking resistor 116 in parallel with the motor 42 and series field EF. After splicing, a brush raising switch 127 is depressed to energize motor 41 to raise the brush arm 38 and open contact 132 thereby de-energizing the main relay M and motor 42. Contacts 118 of the relav M are made at this time to energize relay DBR to apply braking by means of the resistor 116. Known clutch mechanism is provided for connecting and disconnecting the motor 42 to the fresh roll at the appropriate times. During acceleration of the motor 42 the armature current is limited by the action of a rectifier valve FF providing a D.C. voltage proportional to armature current across potentiometer IVR. This voltage is applied through a valve DD which is biased to cut-off for all safe armature current values. If the armature current becomes excessive the valve DD conducts and draws the grid of valve D negative to phase back the firing point of the thyratrons to reduce the armature current.