US Patent 7857533 Method of judgement of ink ribbon jamming

Magnetic force lines 51 are generated in the direction from a first limited portion 52 of an inside peripheral face 50a of a ribbon-delivering cylindrical core 50 toward an opposing second limited portion 54. A first magnet is fixed at the first limited portion: a second magnet is fixed at the opposing second limited portion. With the ink ribbon cassette 40 set in a main body of a printer 10, a magnetic sensor 24 takes the position in the middle of the inside of the ribbon-delivery core 50, and detects the magnetic force line 51.