Patent GB-710501-A (GB)
Title: Apparatus to maintain the top of a pile of sheets in sheet feeding apparatus at a sensibly constant height
Inventor: BATTEY ALFRED PIERSSENE
IPC: B65H1/18
Filed: 1951-04-03
Abstract: 710,501. Feeding sheets. CRABTREE & SONS, Ltd., R. W. Sept. 19, 1951 [April 3, 1951], No. 7722/51. Class 100 (1) Pile height detectors.- In a sheet feeding mechanism of the kind in which a pile-height detector exercises a vacuum control over the pile raising mechanism and in which pneumatic suckers are used to separate the sheets, the suckers having vacuum applied intermittently, the vacuum first causing the sucker to move down on to the top sheet and, when the sheet is taken, causing it to move up carrying the sheet with it, the pile raising mechanism being adapted to maintain the top sheet of the pile within reach of the pneumatic suckers, the pile height detector comprises a vertically sliding piston carrying a sheet detecting abutment, the piston being repeatedly moved by application of vacuum in phase with that applied to the pneumatic suckers to bring the abutment into contact with the top of the pile. Fig. 1 shows the pile support 1, sheet separating suckers 6 and sheet lifting and forwarding suckers 9. The pile support 1 is carried on chains 3 depending from a shaft 4 which is turned to raise the support by a worm gear 39 operated by a ratchet wheel 38. The top sheet is fed from the pile by the following operations of the sheet taking means:- the suckers 6 descend into contact with the top sheet (the vacuum being applied during the descent) and rise again with the sheet; a blast of air from nozzle 8 assists the separation. As suckers 6 rise suckers 9 descend and take the front end of the sheet and swing forward to advance it between feed rollers. The vacuum is shut off from sucker 6 as it rises thus releasing the sheet to the control of suckers 9 which are likewise made inoperative when the sheet is transferred to the feed rollers. The pile-height detector, adjustably mounted on a bracket 35, is shown in section in Fig. 2 and comprises a fixed cylinder 14 and a sliding piston 13 carrying a detector rod 12, an end 22 on which abuts the top of the pile 2. The detector rod 12 is urged upwardly by a spring 21 and is bored to make a passage 15 communicating through opening 16 with chamber 17 below the piston and at the upper end with chamber 19 joined by a pipe 20 with the vacuum supply to the suckers 6 so that as vacuum is applied to the suckers vacuum is also applied to the chamber 17 causing the piston 13 to be drawn down against spring 21, thus lowering the detector end 22 against the top of the pile. The detector rises again when the vacuum is shut off from the suckers 6. The guide 23, for the upper end of the rod 12 is formed with passageways 24 joining ports 28 with a bore 25 connecting with a pipe 26, Fig. 1. Corresponding bores 29 in the rod 12 are adapted to register with bores 28 when the pile top reaches a predetermined low level causing application of the vacuum from chamber 19 and pipe 20 to pipe 26 which controls the pile lifting mechanism. A continuously oscillating lever 36, Fig. 1, driven from a crank 44 carries a pawl 37 normally held out of reach of the ratchet wheel 38 by a lever 40, the position of which is controlled by a trigger 41 governed by a piston responsive to the vacuum in pipe 26. When vacuum is applied the pawl is allowed to engage the teeth of the ratchet wheel and the support is lifted until the vacuum is shut off by the detector. In case of failure of the pile raising mechanism controlled by the means described, a lower limit to the movement of the detector rod 12 is provided by a spring-loaded ball 33 adapted to snap into a groove 34 in piston 13 to retain it in this lower position. The ports 28, 29 pass out of register again before the detector assumes this position. The pile support 1 must, in such case, be raised by some other means As shown in Fig. 6 the suckers 6 and detector rod 12 are arranged so that a sheet, when lifted, is bent about the detector thus facilitating its separation from the pile.