GB1304788A - - Google Patents

Abstract

1304788 Selective printing SIEMENS AG 21 April 1971 [21 April 1970] 10338/71 Heading B6F Variable line spacing.-A platen roller (1, Fig. 1) has a gear-wheel 2 fastened to the drive shaft thereof. The gear-wheel is driven by one or other of two internally-toothed prongs 3v (for forward drive) 3r (for reverse drive) of a feed fork 3. The fork 3 is reciprocated by a cam 5 which pivots a single arm lever 8 carrying a bell-crank lever 14 on a pivot 13. One arm of the bell-crank lever has a plurality of notches 14a, 14b, 14c defining single, one and a half and double spacing respectively. A connecting rod 15 pivoted to the drive fork 3 has a pin biassed into engagement with one of the notches by a spring 16. When an electromagnet 11 attracts its armature 10 against the bias of spring 9, the lever 8 is allowed to pivot about 7 as the cam 5 rotates. This provides a feed stroke of the fork 3 via bell-crank lever 14 and connecting rod 15. When the magnet is energized, an extension (20, Figs. 1 and 3) of the armature 10 allows a lever (22) to pivot about as a second cam (6) rotates. This has the effect of allowing an additional lever (24) pivoted at (25) to lever (22) to pivot under the influence of a spring (23), so that a rod (24a) attached to the lever (24) moves the drive fork 3 upwards, since the rod (24a) is engaged in a slot 26 in the fork 3. For reverse feed, an electromagnet (27) is energized to attract its armature (29) which engages a pin (28) fastened to the lever (24) between the pivot (25) and rod (24a). This has the effect of reversing the motion of rod (24a) as cam (6) rotates, so that drive fork 3 is moved downwards for its feed stroke. To accomodate occasional half-spacing, a control magnet 31 is provided, whose armature 32 is normally held in a position situated outside the range of movement of the bell-crank lever 14. However, when magnet 31 is energized, a roller 14d carried by lever 14 comes into contact with the rounded end of armature 32. Instead of lever 14 pivoting when lever 8 is pivoted by cam 5 it undergoes a parallel displacement along a small circular arc, corresponding to that of pivot pin 13. The connecting rod 15 therefore only moves the drive fork 3 a distance equivalent to a half-space.