| 摘要 |
<p>PROBLEM TO BE SOLVED: To effectively arrange a sheave with which a boom expanding wire is looped within a boom without being protruded to a clearance between the booms. SOLUTION: In this expansion boom, a sheave 25 is composed of a first sheave 25a with which a first wire 50 is looped, and a second sheave 25b which is formed aside from the first sheave 25a and with which a second wire 51 is looped. The first and second sheaves 25a, 25b are connected with each other so as to individually rotate. In order to guide each one side of the first and second wire 50, 51 to a clearance between first and second booms 12, 13, the first and second sheaves 25a, 25b are arranged in such a way as to partially protrude the outer peripheral portions thereof to the clearance between the first and second booms 12, 13.</p> |
