Patent GB-1262116-A (GB)
Title: Inserter and splicer with register control for a preprinted web
Inventor: LEWIS CLARENCE A JR
IPC: B65H23/188
Filed: 1969-04-21
Abstract: 1,262,116. Feeding webs. J. BOBST ET FILS S.A. 21 April, 1969, No. 20280/69. Heading B8R. [Also in Division G3] In a system in which registration of a preprinted web is automatically controlled by means which scan the web and correct errors by adjusting the web tension, the tension is continuously measured and any increase above a higher limit or decrease below a lower limit is prevented. Registration errors are detected by comparison between a preprint scanner 74 and a "phase micrometer" 76 on a print roll 30 and correction is effected by a continuously running servo motor 70 which, by a differential 54, adds or subtracts to the speed of a common drive shaft 50 to drive steel and rubber draw rolls 18, 20. The drive from differential to rolls 18, 20 is by selsyns 58, 62. Web tension is detected by four bridge connected strain gauges in the bearings of a roller 22. The servo motor speed is controlled by the registration error plus the integral of error, and preferably also the rate of change of error which is effective only when a large error occurs at the change over to a new web roll 12. A voltage proportional to tension is derived from the strain gauges and is compared in operational amplifiers with upper and lower limit voltages from separate potentiometers. The amplifier outputs are shorted to ground by breakdown diodes until the respective limits are exceeded, whereupon their polarity changes and they are algebraically added to the servo controlling voltage so that further correction in the limited direction is prevented. The servo motor is energized from a frequency doubled supply via "forward" and "reverse" poled thyristors (Fig. 2, not shown). Either thyristor is triggered by transistor circuits according to the polarity of the combination of the control signal and armature voltage feedback, but the "reverse" polarity thyristor is for braking only, not actual reversal. The feedback voltage is modified by a cadmium sulphide resistor which is illuminated by alamp dependent upon the web speed, measured by a tachogenerator; the arrangement is linear and is such that a given error produces a greater change in servomotor speed the greater the web speed. To maintain registration when changing the web roll, a retroreflective marker is added to the end of the new roll at the appropriate angular position and is scanned photo-electrically. The new roll is brought up to speed and the glued beginning is attached to the existing web by pressure from a brush which is actuated electromagnetically when an AND gate detects simultaneous signals from the new roll scanner, the existing web scanner and an operator actuated button. The exhausted web is then automatically cut. When this operation occurs a switch interrupts the normal registration error signal, so that the tension drops to the lower limit, for a predetermined time, sufficient for the join to clear the machine. The output of the strain gauges is indicated on an ammeter 158 calibrated in tension (lbs per inch width) and a second scale indicates by how much the print roller should be "shaved" to bring the tension to an optimum value.