Patent GB-770969-A (GB)
Title: Improvements in or relating to web tension control systems
Inventor: JR WILLIAM BAUMRUCKER
IPC: B65H23/08
Filed: 1955-04-29
Abstract: 770,969. Automatic tension control systems. RESEARCH CORPORATION. April 29, 1955, No. 12482/55. Class 38 (4). [Also in Group XVI] A web tension control including a web roll and drive therefor, comprises braking means between the web roll and a processing apparatus, the braking means controlling web tension between the braking means and processing apparatus, a loop-forming device disposed between the web roll and braking means which compensates for sudden small variations in web tension and to maintain a braking action on the web, and means associated with the loopforming device actuated by variations in tension in the web to vary the speed of the web roll drive to maintain the tension within predetermined limits. As shown, a roll 10, Fig. 1, supplying web to a printing machine, is driven by at least one driving belt 14 driven by a pulley 16 and engaging an idler pulley 20 pressed towards the roll 10 to maintain contact therewith upon reduction of roll diameter. The pulley 16 is coaxial with and driven by a pulley 22 driven through a belt 24 by a stepped pulley 26 on a shaft 28, preferably driven by a motor, not shown, which drives the machine being fed. A bell-crank lever 34 has a roller 42 engaging the belt 24, the position of the bell-crank lever being controlled by a piston-rod 112 and piston 110 slidable in a cylinder 104. Actuation of the bell-crank lever 34 causes the roller 42 to vary the tension in the belt 24, thus causing the belt to move to a larger or smaller diameter portion of the stepped pulley 26. Closure of a switch 58<SP>1</SP> or 60, as a result of tension variations in the web energizes a solenoid 100 which controls a control valve 102 connected to the cylinder 104 by conduits 106 and 108. The switches 60 and 58<SP>1</SP> are positioned on either side of the web as it passes over a U-shaped coverplate 50 having a trough 48 connected to a vacuum conduit 54. Fluctuations in the web tension, e.g. those caused by an out-of-round roll 10, are compensated for by a loop in the web over the cover-plate 50. After passage around guide rollers 62, 64 the web is fed by rollers 66 driven by a variable speed motor 68, whereby the rollers 66 can be adjusted to run at a lower speed than the web in the printing machine, thereby tensioning the web. In place of the rollers 66, the web may be tensioned by air jets 96 (Fig. 5, not shown), directed on to a plate over which the web passes. Alternatively, the web passes over a suction box having a slotted cover, e.g. formed with chevron-shaped slots such that the web is tensioned Àlongitudinally in proportion to the suction applied and is also smoothed laterally. In a modification of the web tension control effected by the belt 14, the switches 58<SP>1</SP> and 60, Fig. 6, control a selector switch 128 which energizes a reversible electric motor 126 driving a lead screw 120 through reduction gearing 124. Rotation of the lead screw 120 rocks the bell-crank lever 34 pivotally connected to a nut 122. Actuation of the bell-crank lever varies the tension in the belt 24, thus causing it to shift to a larger or smaller diameter portion of a stepped driving pulley 26, Fig. 1, a third switch 130, Fig. 6, mid-way between the switches 58<SP>1</SP> and 60 may de-energize the motor 126. In a modification, the loop may be formed by air blast and the switches 581 and 60 may be replaced by photoelectric cells for sensing variations in the length of loop.