APPARATUS FOR DETECTING RUNNING OF INK RIBBON

PURPOSE:To achieve cost reduction and to enhance reliability by allowing the outer peripheral surface of a sensor roller to slightly protrude from that of a guide toward an ink ribbon. CONSTITUTION:Two sensor rollers 3 and the guide roller 5 positioned between said sensor rollers 3 are respectively mounted to the support shaft 7 of a ribbon guide 1 in a rotatable manner. At least one permanent magnet 2 is embedded in each of the sensor rollers 3 and, when the sensor rollers 3 are rotated along with the running of an ink ribbon 8, the contacts of respective lead switches 4 are opened or closed. The radius R of each sensor roller 3 and the radius (r) of the guide roller 5 are set so as to become R>r. Therefore, the lengths L, l of the ink ribbon 8 passing along the outer periphery of each sensor roller 3 and that of the guide roller 5 between the inlet end P and outlet end Q of the ribbon guide 1 become L>l and the tension T at both end parts of the ink ribbon 8 passing the sensor rollers 3 between the inlet and outlet ends P, Q and the tension(t) at the central part of the ink ribbon 8 passing the guide roller 5 become T>t.