Patent GB-907587-A (GB)
Title: Apparatus for detecting the non-feed of sheets to a machine
Inventor: KING CARL GUSTAVE
IPC: B41F33/00
Filed: 1959-03-17
Abstract: 907,587. Feeding-sheets. ROTAPRINT Ltd. March 2, 1960 [March 17, 1959], No. 9238/59. Classes 100 (1) and 100 (2). Apparatus for detecting the non-feed of sheets in a machine of the kind wherein in use a sheet is picked up by a suction member and is passed between two rotatable members, comprises a device actuated by variations in the air pressure in the suction member so as to effect separation of the rotatable members if the suction member fails to pass a sheet to the two rotatable members. As shown the rotatable members comprise the blanket cylinder 1 and the impression cylinder 2 of an offset printing press, both of which are driven, the impression cylinder shaft 15 having eccentric end portions 16 journalled in the machine frame. Sheets are fed singly from a pile P by suction members 3 either directly between the cylinders 1, 2 or between feed rollers 42 which forward the sheets to the cylinders 1, 2. The suction members 3 are connected by a conduit 4 and a manifold 5 to a vacuum pump. A conduit 6 connects the manifold 5 with a cylinder 8 in which a piston 7 is slidable, the piston being biased to the right, Fig. 1, by a spring 9 and carrying a piston rod 10. The piston rod 10 carries a stop 11 against which a pivoted lever 12 is held by a spring 13. A lever 17 is secured to the impression cylinder shaft 15, movement of the lever causing rotation of the shaft about the eccentric portions 16 so that the impression cylinder is raised or lowered into or out of contact with the printing cylinder. One end of a toggle device 18, 19 is pivoted to the lever 17, the other end being pivoted at 20 to the machine frame. The centre pivot of the toggle device carries a pawl 21 to one end of which is secured a spring 22. The spring 22 biases the toggle device towards the straight-line position shown wherein the part 19 thereof engages a stop 23. The pawl 21 is formed with a slot 24 in which a pin 34 carried by a member 35 is slidable. The member 35 is pivotally mounted on a bell-crank lever 39 and is slightly hooked at the end 36 opposite to the pin 34. The bell-crank lever is biased towards the position shown by a spring 40. An arm 27 pivoted at 28 carries a cam-follower 29 which is held in engagement with a cam 31 mounted on the impression cylinder by a spring 30. The end of the arm 27 adjacent to the cam follower is engageable with a hooked part 25 of the pawl 21. The impression cylinder has a cut-away portion 41 and vertical movement of the impression cylinder is effected only when the portion 41 is opposite to the blanket cylinder 1. If there is no sheet on the suction members 3 the parts 7, 12 remain in the Fig. 1 position; as the portion 41 comes opposite to the blanket cylinder the cam follower 29 engages a reduceddiameter part 33 of the cam 31 which allows the toggle device 18, 19 to assume the straight-line position and allows the end of the arm 27 to engage behind the hooked part 25 of the pawl 21. When the larger diameter portion 32 of the cam urges the cam follower and arm 27 to the right the pawl 21 is also carried to the right so that the toggle device moves the lever 17 and the impression cylinder is lowered. Movement of the pawl 21 to the right causes the pin 34 to ride up the slot 24 so that the member 35 is rotated slightly in a clockwise direction until the hooked end 36 thereof lies below the level of the lower end of the lever 12. If the sucker members 3 now pick up a sheet in order to feed it between the cylinders 1, 2 at their next cycle the piston 7 is sucked towards the closed end of the cylinder 8 and the lever 12 is moved to the Fig. 3 position where it overlies the end 36 of the member 35. As the portion 41 comes opposite to the blanket cylinder again the arm 27 moves to the left, the toggle device assumes the straight-line position and the impression cylinder is raised, but as the member 35 is restrained against anti-clockwise rotation the pawl 21 is cammed upwards by the interengagement of the pin 34 and slot 24 to the Fig. 3 position. Thus when the arm 27 is again moved to the right it passes beneath the hooked part 25 of the pawl and engages an adjacent inclined part 36 thereof, the toggle device remaining in the straight line position. The engagement between the arm 27 and the part 26 of the pawl causes the latter to lift slightly so that the hooked end 36 of the member 35 is moved downwards a short distance out of engagement with the lever 12. When the leading edge of the sheet has been fed into the nip of the cylinders 1, 2 or of the rollers 42 the suction to the members 3 is cut off whereby the lever 12 returns to the Fig. 1 position until the next sheet is picked up by the members 3. If the members 3 drop the sheet before it can be fed between the cylinders 1, 2 the lever 12 is swung from the Fig. 3 to the Fig. 1 position before the cam follower 29 engages the large diameter portion 32 of the cam 31. This allows the pawl 21 to return to the Fig. 1 position so that the arm 27, as it travels to the right, engages the hooked part 25 of the pawl and lowers the impression cylinder. A valve may be fitted in the conduit 6 which valve is opened by the suction members as they rise after picking up a sheet whereby the lever 12 cannot be operated until the suction members have risen.