| 摘要 |
PROBLEM TO BE SOLVED: To increase the moving quantity of a moving roller without any increase in the area of a caterpillar storing place. SOLUTION: A caterpillar winding drum 32 is provided in a pit inner storing place of a caterpillar 6 connected to a moving cover 5 moving with the moving roller 1, a winding driving device 36 formed by a winding spring 36 is fitted to a shaft 33 of the drum 32, and the drum 32 is energized in the winding direction. When the moving roller 1 is moved to the drum 32 side, the caterpillar 6 is taken up on the drum by the energizing force of the spring 36. When the moving roller 1 is moved to the opposite side to the drum 32, the caterpillar 6 is delivered from the drum 32 against the spring 36, and the energizing force of the spring 36 is increased. The drum 32 is provided to increase the amount of storing the caterpillar, so that the travel of the moving roller 1 can be increased.
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