GB973108A - Improvements in or relating to duplicators - Google Patents

Abstract

973,108. Printing apparatus. GESTETNER Ltd. June 17, 1963 [June 26, 1962], No. 24532/62. Heading B6C. Each copy sheet fed to a stencil duplicator passes over a detector which comprises a pneumatically operated piston continuously reciprocating into and away from the path of the sheet, the drive to the piston deriving from a cam rotating in synchronism with the duplicator driving mechanism. Should the piston fail to detect a sheet, pressure air moves a further piston which, through a lever arrangement, disconnects the mechanism provided for moving the pressure roller of the duplicator towards the printing cylinder thereof. In the described embodiment a detector piston 48, Fig. 1, reciprocates through a hole 54 in a paper fence such reciprocation arising from a continuous series of alternate pressure and suction pulses transmitted to the cylinder 45 associated with the piston 98 through a pipe 44. These pulses derive from coacting cam 22 and ball follower 32, Fig. 2, the former of which is secured to a cylinder of the stencil and the latter of which is attached to a piston 34 reciprocable in a cylinder 35 inward of the piston relative -to-the cylinder being against a spring 36. If a copy sheet is not in position relative to the paper fence the piston 48 moves therethrough thereby uncovering an outlet 46 in the cylinder 45 such that the pressure pulse from the piston 34 which is driving the piston 48 is communicated to a cylinder 55 the associated piston 56 of which is then moved to prevent the pressure roller 57 of the duplicator swinging into contact with the stencil on the duplicator cylinder. Such prevention is effected by causing the piston 56 to remove a lever 59 from the path of a reciprocating drive peg 60. The latter, which is reciprocated by means synchronized with the feeding of the sheets, pivots the frame 58, which mounts the pressure roller 57, through abutting the lever 59 pivotally mounted on the frame. A catch 66 is provided to engage and hold the lever 59 away from the path of the peg 60 during the stroke of the latter which is coincident. with the detection by the piston 48 of an absent copy sheet. The catch 66 is so shaped that the ensuing return movement of the peg 60 releases it thus allowing the lever to resume its normal operative position in abutting relation with the peg. A manually operable spring-loaded lever. 72 is provided such that the pressure roller may be enabled to swing into contact with the duplicator cylinder when required, e.g. when wishing to press a backing sheet against a stencil, even though no paper is passing through the duplicator. The lever 72 carries a pin 74 which is movable to a blocking position, Fig. 5, to hold the piston 56 down against the action of air pressure. The pin 74 is held in blocking position by a catch 76, a trip pawl 77 of which is located in the path of an abutment on the roller frame 58. As the pressure roller returns from the cylinder the abutment on the frame 58 engages the pawl 77 thereby shifting the catch 76 to allow the spring-bias of the lever 72 to return it to its non-blocking position.