A ribbon cartridge includes a pair of housings having apertures, a pair of ribbon spools rotatably supported in the housings, and a ribbon wound on the spools. A portion of the ribbon is exposed to the outside of the housings through the apertures when the ribbon is fed from one spool to the other. Each...http://www.google.de/patents/US4074799?utm_source=gb-gplus-sharePatent US4074799 - Ribbon cartridge having slack preventing means
