Patent GB-774910-A (GB)
Title: Back spacing mechanism for typewriters or like machines
IPC: B41J25/04
Filed: 1954-06-29
Abstract: 774,910. Typewriters &c. ROYAL McBEE CORPORATION. [formerly ROYAL TYPEWRITER CO., Inc.]. June 29, 1954 [Aug. 20, 1953], No. 19081/54. Addition to 750,051. Class 100(4) A power-operated typewriter or like machine is provided with back spacing means operable by a single key either to effect a single back spacing or to effect repeated back spacing by power means. A known construction of typewriter has a main frame A, a carriage B with a platen C and an escapement mechanism D, Fig. 3,. which has a wheel 12 actuated by a rocker plate 17 having fixed and limber dogs 18, 19 and is coupled by a ratchet device to a pinion 11. The back spacing mechanism, Fig. 3, is actuated on the upward movement of a thrust link 31 which through a lever 33 and arm 35 moves a thrust bar 36 to the right so that a pin 38 on it moves from the inclined end of a slot 39 of a bracket 40 to allow a tooth 41 to enter the escapement rack 6. Movement of the thrust bar 36 through its lever arm 36b rocks a rack 'lock 47 to prevent upward movement of the bail 7 and moves an escapement wheel stop 45 to prevent reverse rotation of the escapement wheel 12. Continued movement of the thrust bar 36 after engagement of its tooth 41 in the rack 6 moves the carriage one letter space backwards. The upward thrust of the link 31 is effected in different ways for a single or multiple operation of the back spacing mechanism by movement of a back spacing key F, Fig. 1. A quick depression of the key F causes its upward projection 77 to rock a lever 79 so that an attached flipper 83 pushes down an actuator 53 to bring a trigger 72 into contact with an abutment 62 thus releasing a pawl 69 which by a spring 71 is engaged with a snatch roll 52. The snatch roll 52 then drives the pawl 69 and actuator 53 as a unit to rock a lever 55 which through a link 95 straightens a toggle 104, 105 to elevate the link 31 to effect a single back spacing. Alternatively a mechanism H as described and claimed in the parent Specification is used to effect repeated step by step back spacing the key F acting through a pad 164, a lever 166, a link 170. a bell crank 174 to move a cam follower arm 139 into the path of the lobes 127, 128 of a constantly rotating cam 126. A lobe 127 or 128 acting on the follower. 146 of the arm 139 moves a link 148, lever 151, shaft 152, arm 156, and link 158 which has a pin and slot connection 160, 159 with the trigger 72 which thus releases the pawl 69 to engage the snatch roll 52 for a back spacing action as above described. While the key F is kept depressed back spacing will be caused as each lobe 127, 128 engages the follower 146 although the trigger 72 restores after each engagement of the pawl and snatch roll and the cam follower 139 is restored between each lobe by a spring 162. The flicking of the key F will thus cause a single back spacing at all times through the first means described even if the cam follower is positioned between the lobes and all the repeat operation parts have restored when this occurs. The driving connections G between the actuator 53 and the thrust link 31 are provided with cushioning devices. The pull link 95 is in two relatively slidable parts connected by a spring 101, and the toggle movement stop member is preferably of resilient material to give additional cushioning. The driving impulse given by the snatch roll 52 can be varied by limiting the amount of the engagement of the pawl 69 either by adjusting the movement of the engagemerit of a pawl stop 93 with an actuator stop 92 by bending the latter or in machines where actuator pawls are provided for a number of power operated instrumentalities a common adjustable knock off bar 94 may be provided.