Patent GB-593193-A (GB)
Title: Improvements in and relating to escapement mechanism
IPC: B41J19/32
Filed: 1945-01-09
Abstract: 593,193. Escapement mechanism. JENNINGS, H. W. K. (Sweeney, J. L.). Jan. 9, 1945, No. 767. [Class 80(iv)] [Also in Group XVI]' Escapement mechanism comprises a disc mounted on a shaft, and a pair of clutches, one fixed and the other movable about the shaft axis, arranged to cooperate independently with the disc, the extent of movement of the movable clutch being infinitely variable within predetermined maximum and minimum limits to enable the shaft to be released for corresponding infinitely adjustable movements. As employed for effecting variable letter-spacing movement of a typewriter carriage, a rack 42, Fig. 1, on the carriage 12 engages a pinion 43 on a shaft 44 carrying the control disc 50. Each typelever 14 is formed with a cam surface 27 which, as the type 15 nears the platen 11 engages a universal bail 26 fixed to a plate 28 so as to move the latter rearwardly against the action of a spring 39. A yoke 34 pivoted at 83 supports the rear end 33 of the plate. Movement of the plate actuates the clutches as described below. The fixed clutch comprises balls 51, Fig. 8, supported between inclined faces on a fixed member 52 and the disc, the balls being seated in holes in a yoke 54 carried by a lever 55 pulled downwardly by a spring 57 so as to cause the balls to grip the disc 50 and prevent its rotation and therefore stop movement of the carriage. A link 59 pivoted at 33 to the plate 28 and supported by a link 61 carries a cone-ended screw 58 which normally engages a roller 60 on the yoke 54 to raise the latter and free the clutch. As the plate 28 moves rearwardly, the screw 58 moves from beneath the roller 60 and allows the clutch to lock the disc 50 against rotation. The movable clutch consists of balls 72, Figs. 6 and 7, mounted between inclined faces 73 on a stirrup 70, 71 pivoted on the shaft 44 and movable between stops 90, 92, a spring 103, Fig. 5, (not shown) tending to hold the stirrup against the stop 92. As shown, the stop 90 is fixed and the stop 92 is carried by a pivoted member 93 adjustable by a screwed spindle 98. Pivoted at 75 on the stirrup 70 is an inner stirrup 74, having apertures to accommodate the balls 72 and urged by a spring 76 in a direction to cause the balls to bind on the disc 50. As the plate 28 moves rearwardly, an arm 82 thereon engages a spring strip 80 so as to move two balls 78 towards the disc 50. The inner ball is seated in an aperture in the stirrup 74 and rises on an inclined surface 79 on the disc hub to move the stirrup and release the clutch. When the cam 27 begins to act on the bail 26, the fixed clutch 51 locks the disc 50 and the movable clutch 72 is released as described above, the latter moving under spring action against the adjustable stop 92. After printing has taken place and the type lever 14 moves away from the platen, the plate 28 moves forwardly so that the clutch 51 is released and the clutch 72 allowed to operate. The carriage-control spring which is sufficiently strong to overcome the effect of the spring attached to the stirrup 70, then turns the disc 50 carrying the stirrup 70 with it until the latter engages the stop 90. This constitutes one letter-spacing movement and completes one cycle of operations. The extent of the spacing thus is determined by the adjustment of the stop 92.