The present invention relates to a reloadable ribbon cassette system.  More particularly, the invention relates to a ribbon cassette of the type which includes reloadable ribbon spools, in which a supply spool for unwinding the ribbon and a take-up spool for winding the ribbon up are rotatably mounted on bearing pins in the cassette, which includes a foldable cover provided with an opening, with the free end of the ribbon of the full supply spool being provided with a fastening element for threading the ribbon around reversal points in the cassette and for fastening to the core of the take-up spool. 
U.S. Pat.  No.  3,731,781 discloses a removable cassette for a carbon ribbon to be used in a printer having a rotatable drive element for ribbon advance, with the cassette being composed of a housing accommodating a ribbon supply spool and a take-up spool.  A pivotal feed roller equipped with a sprocket wheel cooperates with a take-up spool disposed on a stationary axis to wind up the carbon ribbon.  For exchanging the cassette, the feed roller and the sprocket wheel must first be put out of engagement with the take-up spool.  This exchange process requires a plurality of manipulations since, after insertion of the new cassette in the receptacle of the machine, the feed roller must be brought back into engagement with the take-up spool. 
U.S. Pat.  No.  4,010,839 discloses a ribbon cassette for a typewriter or office machine of a similar construction in which the feed roller and its sprocket wheel are also disposed in the cassette.  The feed roller remains in constant engagement with the carbon ribbon on the take-up spool.  In this way it is possible to exchange ribbon cassettes with only one hand.  This prior art ribbon cassette is very expensive since the members for driving the carbon ribbon contained in the ribbon cassette are discarded together with the ribbon when it is used up.  Since, moreover, the feed roller is always in engagement with the take-up spool and the drive elements are mounted in the bottom portion and in the cover, which is fixed to the bottom portion, it is not possible to exchange the supply and take-up spools. 
Additionally, U.S. Pat.  No.  4,780,010, issued Oct. 25th, 1988, discloses a ribbon cassette for office machines in which the supply and take-up spools are arranged to be exchangeable.  This makes it possible to exchange only the ribbon spools if the ribbon is used up.  The drawback of this cassette is that the ribbon can be threaded incorrectly within the cassette and interfere with the ribbon drive.