Patent GB-1412207-A (GB)
Title: Web handling apparatus
IPC: B65H19/16
Filed: 1973-03-20
Abstract: 1412207 Control of tension BUTLER AUTOMATIC Inc 20 March 1973 [20 March 1972] 13418/73 Heading G3R In handling apparatus {providing a web to a printing press 24 consuming same at a constant velocity Vp}, the braking force on roll 10 of running web, provided by disc brake 72 is controlled to be proportional to instantaneous roll radius, so that the web tension is maintained substantially constant. Web sufficient for splicing without printing interruption } is stored in festoons between mutually offset rollers 42, 44, any change in the height of dancer 46 engendering, via a signal from potentiometer 66 which is processed to provide a signal having a PD characteristic the latter being multiplied with a signal representing instantaneous roll radius, the change in the drag provided by brake 72, keeping dancer height constant, or a function increasing or decreasing with decreasing radius of roll 10. The instantaneous roll radius, calculated in units (92, 96), Fig. 2 (not shown), effectively as the ratio of the angular velocities, detected by tachos, 38 of guide roller 16, and 32 of roll 10, is fed to multiplier (122) where it is combined with the signal, derived with a PD characteristic as a function of dancer height, differential amplifier (150) receiving the output of potentiometer 66 on one input, the other coupled to a dancer height setting circuit (152), its output being combined with the differentiated dancer height from differentiator (162) and amplifier (164), and a tension pre-set signal from variable resistor (176). The multiplied output from unit (122), via driver (124) and transducer (126) controls the drag of disc brake 72. The weight of the dancer 46 is communicated via pulleys 54, 56 to a piston-cylinder 58, 62, possibly via differential pulleys to reduce piston stroke relative to dancer height range, solenoid valve 63 normally controlling feed and bleed of air ensuring that the effort on piston-rod 58 balances the dancer weight. Control of splicing When the radius of running roll 10 reaches a predetermined minimum pre-set in unit (102 Fig. 2), and detected in comparator (98) switches (172) and (184) are operated, to replace the dancer height derived tension command by the output of ramp generator (186) producing deceleration of roll 10. When the web velocity reaches a predetermined value, which may be zero, as detected by threshold set, and comparator units (108, 110) splice and acceleration relay (114) initiate the acceleration, by eddy current unit 82, of ready roll 26, the leading edge of its web being spliced in unit 14 to the web from 10 whence the latter is cut, dancer 46 meanwhile moving down, being heavily velocity damped for a time set in unit (191) increasing the gain of attenuator (166) to avoid bottoming. When dancer velocity has decreased to between given upward and downward limits detected by units (192, 194), indicating that web speedfrom roll 26 is within the range 0.7-0.9 Vp, relay (202) causes de-energization of eddy current unit (82). By adjusting the setting of potentiometer 152 in response to the output of divider 96, web storage can be decreased as roll radius decreases. Fast stop signal 155 changes the gain of attenuator 155, in a manner equivalent to a sudden increase in dancer height, causing a corresponding increase in brake force. Broken web Should dancer velocity exceed a predetermined maximum, detected by comparing a pre-set value from unit (206) with the amplified output of differentiator (162) a broken web relay (210) causes braking of the running roll, or control of the air supply to cylinder (62) to slow the dancer before it strikes a limit stop.