Selectable dual ratchet feed for a printer platen

#It is many times desirable to be able to shift conveniently between alternate line feed rates when typing. With means of some types, it appears much neater on the page when a 51/3 lines per inch line feed rate is utilized while other types appear to be more ascetically related when a six lines per inch feed rate is used.

#Heretofore intricate systems involving gear trains and idler gears parallel shafts, and mechanisms to engage and disengage the platen from drive feed ratchets have been used. Many of these devices are cumbersome, complex and expensive to manufacture as well as being potential sources of mechanical malfunction.

#Other devices require multiple feed pawls, each individually driven in accordance with the selected feed rate and still other prior art patents illustrate varying drive ratios controlled through planetary gear change.

#FIG. 1 is an exploded perspective view of the ratchet drive assembly.

#FIG. 2 is a partial sectional view of the ratchet drive assembly.

#Referring to FIGS. 1 and 2, a platen 10 is provided with a frustro-conical shaped surface 12 interiorally thereof as is conventional. This frustro-conically shaped surface is engaged by the platen variable 14 which is spring biased by spring 16. In the platen variable 14 are two apertures 18 which engage and receive shafts 20. Shafts 20 are carried by a hub 22. Hub 22 is mounted on an sleeve 24 such that the sleeve and hub move together. Slipped over sleeve 24 is retaining bracket 26 which in FIG. 1 is shown separated. This bracket serves to retain the parts which are contained between its ends and thus restrict lateral movement thereof.

#Rotationally positioned on sleeve 24 is a ratchet 28. Ratchet 28 may be formed independently by itself or with a spacer ring shown as 30. Also freely positioned on shaft 24 is a ratchet 32. The teeth configuration of ratchets 28 and 32 may be formed so as to give any desired line feed increments. However the most common increments are 51/3 lines per inch and six lines per inch. On the interiors of the ratchet wheels 28 and 32 are formed frustro-conical recesses which have ridges or serations running in planes which have the axis of shaft 24 lying thereon. These recesses can be seen at 34 and 36 of FIG. 2 and 36 of FIG. 1.

#Rigidly keyed by way of key 38 or other suitable attaching means to sleeve 24 through hole 40 is drive member 42. Drive member 42 is double frustroconical member shaped to mate with recessed frustro-conical surfaces 34 and 36. The serations on drive cone 42 are such that they will positively engage the serated surfaces of complimentary shape in the recesses 34 and 36. Sleeve 34 is hollow so that it may flip over platen shaft 44. Platen shaft 44 is configured with detent grooves 46 to engage detent ball 48 against the force of detent spring 50. Bracket 26 may be anchored to the typewriter or used for any other convenient purpose.