Patent GB-761232-A (GB)
Title: A method of, and apparatus for, feeding a web in step-by-step fashion
IPC: B31B19/10
Filed: 1952-10-13
Abstract: 761,232. Making bags. KELLER, T. W. Oct. 13, 1952 [April 9, 1952], No. 25551/52. Class 94(2). [Also in Groups XVI and XL(b)] During the feeding of a web in step-by-step fashion past a station at which a bag making operation is performed on the web when at rest the feed of the web is effected by intermittently driven rolls and the drive to the rolls is disconnected and a frictional braking force applied to the rolls prior to, during and after the drive disconnection. The invention is described with reference to the manufacture of bags by sealing the ends of a flattened tube of thermoplastic material which is then severed. As shown, the web to be severed is fed from either of two supply rolls 34 over let-off mechanism 40 which is of known type. Two webs one from each roll may pass through the apparatus side by side. The web passes over a table 44 through a first feed roll stand 48, a heat sealer 50 which seals the flattened sides of the tube together by heating them under pressure through a second feed roll stand 52 and a cutter 54 where the individual bags are severed and on to a receiving shoot 56. Feed rolls, heat sealer, and cutter are all operated by a main motor 60 and control of the feed is accomplished by a photo-electric device 264 responsive to a repetitive pattern on the material which disconnects the drive to the feed rolls and brakes them thus preventing overrunning of the rolls and consequent stretching of the material when the pattern is in the correct position relative to the cutter. Sealing and severing takes place when the web is at rest. Feed rolls and heat sealing mechanism, Figs. 5 and 6. The main motor 60 drives a main shaft 70 through a chain and sprocket drive and shaft 70 carries an adjustable throw crank 78 which oscillates a toothed rack 80. The rack drives through a sprocket 90 and a one-way clutch 92 feed roll driving shaft 86. This shaft is split, the two halves being coupled by an electromagnetic clutch C the output side of the shaft carrying an electromagnetic brake disc 260, both brake and clutch being, if desired, under the control of the photo-electric mechanism. The first pair of feed rolls 96 are driven through a chain 104 and a sprocket on the end of the lower roll shaft. The two rollers which are rubber faced are geared to each other to rotate in opposite directions. The pressure between the rolls is screw adjusted. The second feed rolls in stand 52 are driven by a chain and sprocket mechanism from the shaft of the lower feed rolls in stand 48. The final drive is by means of a belt over a variable speed pulley the effective diameter of which may be adjusted by means of a hand wheel. This enables the two sets of rolls to be driven at slightly different speeds thereby allowing for stretch of the thermoplastic material. The heat sealing mechanism is operated by a cam 134 on a shaft 132 driven by a chain 138 from a sprocket on the main drive shaft 70 the cam operates through pivoted follower 166 bar 172 and bell crank lever 182 to move the lower jaw 150 of a pair of jaws 148, 180 upwardly until the thermoplastic material is compressed between them. Each jaw is provided with a heating element 154 held in place by a block 156 and travel of the lower jaw is limited by stops adjustable by screws 164. A further cam (not shown) on shaft 132 reciprocates a horizontal bar to pull downwards a pivoted blade 190 which is urged into engagement with a fixed blade 188 by a spring 186 thereby severing the completed web. Shaft 132 also carries four cams operating four switches (not shown) for purposes to be described. Photo-electric control and circuits (Figs. 9 and 10). The photo-electric cell unit is mounted at the side of the machine and is adjustable along its length by means of a lead screw 284. The photo-electric cell is mounted in a head 266 above the strip and a light source and appropriate lens system in a head 276 below the strip. The heads are carried on rods 268 which are adjustable transversely of the strip in a bracket 270. The photo-cell may be arranged to respond to any part of a repetitive pattern. When the machine is under the control of the photo-electric switches RS, AS, PS and BS, Fig. 10, are closed switch CS remaining open. Operation is then as follows, the cam-operated switches being shown in the position they occupy at the start of the web advancing stroke of the rack 80. After 134 degrees rotation of the crank driving the web-advancing rack, camoperated switch 134 closes thus forming part of a locking circuit of photo-electric relay PR. One degree later switch OCS opens a lock-out circuit which, when closed prevents energization of relay PR. The lock-out circuit forms a safeguard against actuation of relay PR by the response of the photo-electric cell to the previous pattern. When the pattern is detected by the cell photo-electric relay PR pulls up completing the circuit of a further relay CR which removes the supply from the clutch C stopping the drive, and transferring it to the brake B which then stops the roll feed drive. After the web has been braked to a halt the return stroke of the rack driving crank commences while the web remains at rest and during this period the heatsealing and severing operations are carried out, 43 degrees before the end of this period camoperated switch ICS interrupts the locking circuit of photo-electric relay PR thus deenergizing relay CR, re-engaging clutch C and removing brake B. A little later cam-operated switch CCS closes the lock-out circuit preventing operation of the photo-electric relay by the trailing end of the repeated pattern. The brake magnet may be energized before the de-energization of the clutch to allow for the time taken by its field to build up a cam operated switch being provided for this purpose. This switch energizes a relay BR which energizes the brake B through a rheostat RV which may be set as desired. Where unprinted bags are made on the machine, switches RS, CS and BS only are closed. In the arrangement cam-operated switch CCS replaces photo-electric relay PR, and de-energizes the clutch and energizes the brake after 157 degrees of rotation of the crank. It is possible to omit cam controlled switch CCS relying on braking relay BR to prevent rolls overrunning.