Construction for mounting an ink ribbon cassette in a heat transferable line printer

A line printer comprising:

• upper and lower units pivotably connected with each other through a pivot shaft, the upper unit having therein a platen extending parallel with the pivot shaft, the lower unit having therein a thermal print head extending under and along the platen of the upper unit and a pair of spool shafts fixed at one end thereof to the inside of a back side portion of the lower unit and extending below the thermal print head and parallel to the pivot shaft;
• a symmetrical ink ribbon cassette removably mounted in the lower unit and carrying an ink ribbon passing between the platen and the thermal print head, the ink ribbon cassette comprising a casing having front and back sides and having a symmetrical shape to enable mounting of the casing in the lower unit in either a frontward position in which the casing front side lies adjacent the front side of the lower unit or a backward position in which the casing back side lies adjacent the front side of the lower unit, a pair of guide rollers extending parallel with each other on an upper side of the casing for guiding the ink ribbon therebetween;
• first and second spools disposed within the casing and detachably coaxially receiving therein the respective spool shafts of the lower unit for reversibly transporting the ink ribbon therebetween, and a cylindrical hub gear fixedly disposed on and around each of the opposite ends of the respective spools and projecting outwardly through a corresponding opening formed in one of the front and back sides of the casing;
• power transmitting means carried by the lower unit and having a driving gear selectively engageable with one of the two cylindrical hub gears of the first and second spools, depending on whether the casing is mounted in the frontward or backward position, for driving the selected spool to wind the ink ribbon through engagement between the driving gear and the cylindrical hub gear;
• back-tension applying means carried by the lower unit and having a back-tension gear selectively engageable with one of the two cylindrical hub gears other than the ones engageable with the driving gear of the power transmitting means, depending on whether the casing is mounted in the frontward or backward position, for preventing slipping rotation of the spool being used for feeding the ink ribbon to the other spool;
• locking means for releasably locking the ink ribbon cassette in an operating position thereof in cooperation with the pair of spool shafts within the upper and lower units, the locking means comprising a pair of shoulders formed outside the respective guide rollers on the upper side of the casing, a pair of rods fixedly disposed within the upper unit so as to extend along and engage with the respective shoulders, a plate spring disposed on the bottom of the lower unit for urging the casing against the rods to thereby engage the shoulders with the rods, the rods being immovably positioned relative to the lower unit, and a flange formed on an end of each rod so that the flange engages with one of the opposite ends of the shoulders to thereby hold the ink ribbon cassette in position with respect to the axial directions of the spool shafts;
• first gear-adjusting means coacting with the power transmitting means for resiliently absorbing impact between the teeth of the cylindrical hub gear and the driving gear, which impact is caused when the ink ribbon cassette is loaded into the lower unit with these gear teeth being mutually aligned, and for subsequently adjusting these gears to suitably mesh with each other;
• and
• second gear-adjusting means coating with the back-tension applying means for resiliently absorbing impact between the teeth of the cylindrical hub gear and the back-tension gear, which impact is caused when the ink ribbon cassette is loaded into the lower unit with these gear teeth being mutually aligned, and for subsequently adjusting these gears to suitably mesh with each other;
• whereby the ink ribbon cassette is releasably simply locked in the same operating position regardless of whether the ink ribbon cassette is mounted in the lower unit in the frontward or backward position.