Patent GB-1060756-A (GB)
Title: Escapement mechanisms for typewriters
IPC: B41J19/58
Filed: 1964-05-29
Abstract: 1,060,756. Typewriters. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 29, 1964 [June 26, 1963], No. 22276/64. Heading B6F. An escapement mechanism for a paper carriage or type carriage of a typewriter comprises an escapement rack 11 biased to move in characterspacing direction, an escapement pawl 22 movable longitudinally of the rack and also pivotally into and out of engagement with the rack, a spring 20 biasing the pawl for such movements, and stop means for limiting the longitudinal movement of the pawl 22 in both directions, the stop means being settable so that either normal character spacing may occur or a reduced spacing e.g. half the normal spacing may be introduced. The pawl 22 has a slot 18 engaging a pivot pin 19, and associated with the pawl is a pawl-actuating lever 25 having a slot 26 engaging the pin 19, and a half-space lever 27 pivoted on the pin. For normal spacing the parts are positioned as shown, Fig. 1, with the lever 25 held in its rightward position by the engagement of a lug 28 thereon with a surface 29 on the lever 27 against the action of a spring 31 attached to the lever 25. The lug 28 lies under the end 30 of the pawl 22. Stops 37, 36 are provided respectively on the pawl 22 and lever 25. Actuation of a space or character key causes anti-clockwise movement of lever 25 thus releasing pawl 22 from the rack 11 and allowing the pawl to move leftwards until stop 37 engages stop 36, and allowing the rack 11 to move rightwardly. The pawl 22 is then engaged with the next tooth of the rack by the action of springs 20, 31, and moves rightwardly with the rack 11 until the left-hand end of slot 18 engages pin 19 whereupon the rack 11 also is brought to rest. The slot 18, pin 19, and stops 36, 37 thus determine the normal spacing movement. For half spacing, a key 45 is depressed and, through a bell-crank lever 43 held in either of two positions by an over-centre spring 54, turns the lever 27 anticlockwise. A shoulder 58 on the lever engages a projection 59 on the pawl 22 to release the pawl and allow it to move leftwardly, the projection 59 moving beyond the shoulder 58. At the same time, the lever 25 and therefore the stop 36 moves leftwardly because the lug 28 is now engaging a cam surface 60 on the lever 27. The pawl 22 re-engages the next tooth of the rack, its leftward movement having been limited by the engagement of stops 36, 37. On the subsequent rightward movement of the pawl 22 with the rack 11, the projection 59 on the pawl engages a surface 62 on the shoulder 58 to stop further movement so that the carriage has moved a half space only. In this position with the key 45 depressed, operation of the space or character keys causes normal spacing to take place. If the key 45 is subsequently raised by the operator, another half-space movement is obtained. The key 45 can be restored to its normal raised position when carriage return, tabulation or margin release is initiated; by providing an extension 65 on the bell crank lever 43 which is pulled downwardly when the carriage return, &c., mechanism is operated.