Printer ribbon supply mechanism with end of ribbon detect expedient which reduces ribbon drag

摘要

In a conventional ribbon supply spool structure which comprises a supply of ribbon wound on a hub rotatable about and axially movable with respect to a hub receiving member on which the hub is seated and which is coaxial with respect to the hub, an improved end of ribbon detection device is provided by the combination of deflectable spring means within the spool hub which exert a force when deflected having a first force component acting against but restrained by wound ribbon on the hub and a second component acting along the hub axis. A spring tensioned member exerts a force along the hub axis which opposes the component of force of the deflectable spring along the hub axis. In this manner, the deflectable spring and the spring tensioned member are maintained in static equilibrium at a selected point along said axis so long as the deflectable spring is restrained by a predetermined minimum of ribbon remaining wound on the hub. This predetermimned minimum of ribbon remaining wound is indicative of the end of ribbon. In the preferred embodiment this is in effect the point where the ribbon becomes substantially unwound.