Mechanism for detecting end of ink ribbon in a ribbon cassette

Claim 1

A mechanism for detecting the end of an ink ribbon supplied from an enclosed cassette to a print mechanism, the cassette and the print mechanism being supported for travel on a frame of a printer and the ink ribbon being fed from a supply spool in the cassette and returned to a take-up spool therein, the take-up spool having an axis of rotation, the cassette having a wall adjacent to at least the take-up spool, the mechanism further comprising: an opening in the wall of the cassette adjacent to the take-up spool; a detector member in the cassette, the detector member including a movable surface contacting the outside layer of the ink ribbon on the take-up spool, the detector member being supported in the cassette for radial motion relative to the take-up spool and axial motion along an axis substantially parallel to the axis of rotation of the take-up spool, the detector member moving to project along said axis substantially parallel to the axis of rotation of the take-up spool through the opening in the cassette wall when the ink ribbon on the take-up spool has reached a predetermined level thereon; and resilient means for maintaining the detector member in contact with the ink ribbon on the take-up spool as the level changes, the resilient means urging the detector against the cassette wall and also urging the detector member to project through the opening in the cassette wall when the ink ribbon on the take-up spool has reached the predetermined level thereon.