| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to achieve easy diameter expansion of a drum main body by a bladder and to suppress hanging-down of a segment in a diameter reduction state.SOLUTION: A center drum 2 includes: a stem 6 attached to a support shaft 4; a drum main body 7, which comprises plural segments 11 which are guided to the inside/outside in a radial direction by guide means 12, on the stem 6; diameter expansion means 8 comprising a bladder 15 which expands a diameter of the drum main body 7; and diameter reduction means 6 which reduces a diameter of the drum main body 7. Diameter reduction means 9 is equipped with a rubber band 16 which is wound around an outer peripheral surface of the drum main body 7, and a ring-shaped coil spring 18 which is wound along an outside surface of the drum main body 7. A spring fitting part 20 is formed on the outside surface of the drum main body 7.SELECTED DRAWING: Figure 4 |
