| 摘要 |
A boom for earth excavating apparatus comprises a first elongated tubular shaped member, a second elongated tubular shaped tool supporting member positioned within the first member and adapted for telescoping movement therein, a hydraulic cylinder positioned within the outer boom member, means for constraining motion of the cylinder in a longitudinal direction with respect to the outer boom member, a hydraulic piston positioned within the cylinder and coupled to the second member for causing longitudinal motion of the second tubular member when a hydraulic force is applied thereto, means intercoupling the cylinder and the second boom member for guiding motion of said second member in a longitudinal direction and for causing rotation about a longitudinal axis thereof when the cylinder is rotated, and means for providing rotation of the cylinder thereby causing rotation of the second member and the tool about a longitudinal axis.
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