Anti-reversal backcheck for printer ribbon cartridge takeup spool

Abstract

In a typewriter ribbon cartridge, it is necessary to maintain tension on the span of ribbon extending outside the cartridge to prevent tangling and to insure high print quality during machine operation. One technique for insuring that adequate tension is maintained is disclosed herein as an anti-backup back check device. Connected to the takeup spool of the ribbon cartridge is a disc member supporting thereon a pair of thin flexible resilient arms with outwardly oriented pointed ends. These ends formed in the shape of points engage ratchet teeth formed around the interior surface of a cylinder. The cylinder is formed as a part of the ribbon cartridge and, thus, is permanently positioned and fixed with respect to it. As the takeup spool disc and arms are rotated by the ribbon feed mechanism, the arms will flex and permit a rotation of the disc and takeup spool with a minimal drag force. Upon reversal, the points on the ends of the arms engage the ratchet teeth and the arms become compression columns resisting the rotation of the disc and spool. The center of the disc and the takeup spool are free floating within reasonable physical constraints. The teeth of the arms are positioned such that they are one-half tooth pitch out of phase to insure that one tooth is always in engagement with a tip of one of the two pawls.