Print ribbon cassette including ribbon tensioning means

Claim 1

A print ribbon cassette removably mountable on a printing office machine, comprising: a cassette body including a bottom member; a feed spool mounted for rotation in said cassette body and having a ribbon wound thereon; a take-up spool mounted for rotation in said cassette body for winding the ribbon thereon; ribbon guide means provided on said cassette body for guiding the ribbon to be fed from said feed spool to said take-up spool; and ribbon locking means for permitting rotation of said feed spool to feed the ribbon therefrom during use of the ribbon and for preventing inadvertent rotation of said feed spool during disuse of the ribbon; said ribbon locking means including a flange mounted for coaxial and integrally rotatable relationship with said feed spool and having peripheral serrations formed thereon; a lock member mounted for pivotal motion on said cassette body and having a tip end for engagement with said peripheral serrations of said flange, a ribbon lock control member movable in response to a tensile force of the ribbon fed out from said feed spool between an operative position in which said ribbon lock control member engages with a portion adjacent said tip end of said lock member to press said lock member into engagement with said flange and an inoperative position in which said ribbon lock control member disengages from said lock member to allow said lock member to be disengaged from said flange, and a spring member for urging said ribbon lock control member to said operative position; said bottom member having a support rib provided thereon and said ribbon lock control member having a groove formed on a bottom face thereof and fitted with said support rib to allow said ribbon lock control member to move back and forth along said support rib, said ribbon lock control member having a ribbon guide face formed at a forward end thereof, said ribbon lock control member having at the opposite rearward end thereof a receiving portion for receiving said spring member thereon.