Patent GB-1193887-A (GB)
Title: Printing Mechanism
IPC: B41J33/56
Filed: 1968-03-13
Abstract: 1,193,887. Ink-ribbon mechanism. INTERNATIONAL BUSINESS MACHINES CORP. 13 March, 1968 [15 March, 1967], No. 12155/68. Heading B6F. Varying successive throws of vibrator mechanism.-In a feed mechanism for single pass ink ribbons of the total release type, such as carbon, or of the plastic type, in which the ink ribbon is lifted to the printing position for each print operation, is advanced longitudinally in increments, and is lifted by varying amounts for each successive longitudinal advance, means are selectively operable to interrupt the operation of the ribbon feed so that the ribbon is advanced at intervals of a preselected number of print operations, and the amount of ribbon left for each successive print operation between those at which the ribbon is advanced is varied slightly to a combined extent, between ribbon advance operations, which is less than the extent of the variation of ribbon lift at each successive ribbon advance operation. In practice, said means is rendered inoperative for a carbon ribbon and operative for a plastic ribbon. The ribbon 20 is lifted by guides 62, 63, Fig. 4, connected to arms 64, 65 which are pivotable about a rod 67 by a cam follower 77 pivoted at 78 and co-operating with a cam 79 on the drive shaft 42, which is rotated once for each print operation. The cam follower 77 acts on the arm 64 through a pin 75 slidably received in a slot 76 of the cam follower 77, so that the position of the pin 75 in the slot 76 governs the extent to which the ribbon is lifted by the cam 79. The pin 75 is connected through a link 73 to a cam follower 71, Fig. 5, which co-operates with a cam surface on the periphery of a ratchet wheel 36 controlling the advance of the ribbon 20, to change the position of the pin 75 for each ribbon advance. The ribbon is advanced by a feed roller (27), Figs. 1, 6 (not shown), co-operating with a pressure roller (26), the feed roller being rotated by a pawl 46 which is reciprocated by a cam 43 on the shaft 42 acting on a follower 44 and which rotates the ratchet wheel 36 stepwise. The reciprocation of the pawl 46 may be prevented by a lever 51, Fig. 2, for a preselected number of print operations, the operation of both the ribbon advance and ribbon lift variation mechanisms being thereby interrupted. While the lever 51 prevents such reciprocation by engagement with a pin 54, the extent of ribbon lift is varied slightly by changing the pivot point of the arm 64 by means of an eccentric 106, Fig. 4. The eccentric is rotated for each print operation by a pawl (104), Fig. 3 (not shown), reciprocated by engagement with the cam 79 and effecting stepwise rotation of a ratchet wheel (105) formed integral with the eccentric. The lever 51 is held against the pin 54 by a spring 90 for a preselected number of print operations after which it is pivoted about a pin 52 by a cam 91 acting on a projection (93, Fig. 1) of the lever 51. The cam 91 is rotated by a fraction of the angle between the lobes 95 formed thereon by a pawl 96, Fig. 2, engaging a ratchet wheel 94 and reciprocated by engagement with the cam 79, Fig. 4. The lever 51 may also be removed from engagement with the pin 54 by a mode change lever 55 so that the ribbon is advanced and the lift varied for each print operation for use with carbon ribbons. The eccentric 106 is not rotated in this mode of operation. Tension arrangements.-Since plastic ribbons are less strong than carbon ribbons, the tension applied to the ribbon in the plastic ribbon mode of operation is made less than that applied in the carbon ribbon mode. A roller 111, Fig. 2, tensions the ribbon due to the action of a spring 116, which is less taut in the plastic ribbon mode as shown than in the carbon ribbon mode wherein a pin on the underside of the mode change lever 55 engages a shoulder 58, owing to a corresponding change in position of a lever 109 to which the spring 116 is connected. Stencilling arrangements.-A "stencil" lever (35, Fig. 1) stops rotation of the feed roller (27) by preventing reciprocation of the pawl 46 and also suppresses ribbon lift by disengaging the cam follower 71 from the ratchet wheel periphery, thus moving the pin 75 to a position whereby rotation of the cam follower 77 does not transmit motion to the arm 64. Ribbon loading arrangements.-A load/unload lever (131, Fig. 1) co-operates with a lug 135, Fig. 4, to lift the ribbon guides 62, 63 above the printing position, and also separates the pressure roller (26) from the feed roller (27) to facilitate loading and unloading ribbons. The ink ribbon feed mechanism may be mounted on a movable type carriage incorporating a spherical type head 14, Fig. 4, or may be fixed to a typewriter base, the platen then being movable.