| 摘要 |
PROBLEM TO BE SOLVED: To provide a function of detecting cutting or coming off from a sprocket of a chain to stop rotation of a sprocket. SOLUTION: Retchet teeth 7 are formed around on a part of circumference of a boss 2b of a driven sprocket 2. An arm 10 has a shaft 8 parallel with a rotation shaft 2a of the sprocket 2, an idle sprocket 11 on one of two rotation ends across the rotation shaft 8 and a fork hook 12 to be meshed with the ratchet teeth 7 on the other end. A coil spring 13 is wound around the rotation shaft 8 of the arm 10 to keep the idle sprocket 11 meshing with a chain 3 and to prevent the hook 12 on the other end from meshing with the ratchet teeth 7. When the chain 3 is cut, the idle sprocket 11 moves away from the track of the chain 3 and the arm 10 rotates clockwise to make the hook 12 of the arm 10 mesh with the ratchet teeth 7 of the driven sprocket 2. Rotation of the driven sprocket 2 is thus stopped.
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