Thermal printer

A thermal printer comprising:

• a printing head for printing on paper;
• a platen having a shaft opposed to the printing head by a small gap for urging the paper against the printing head;
• a bearing for rotatably holding the platen shaft and having an engagement portion for holding the platen in place, the engagement portion having a symmetrical, non-circular shape with respect to a central axis of the platen shaft;
• a movable platen frame for selectively moving the bearing between a first position at which the platen is closely spaced from the printing head to perform printing and a second position at which the platen is spaced further apart from the printing head than in the first position;
• a frame having an engagement groove engageable with the engagement portion of the bearing when the platen is moved into the first position to perform printing, the engagement groove having a shape corresponding to the engagement portion of the bearing;
• and a lock arm for retaining a part of the bearing and fixing the bearing in engagement with the engagement groove, the lock arm having a platen release mechanism for allowing the platen to be locked and unlocked from the first position.