| 摘要 |
<p>PURPOSE: To simplify the structure of a carrier track assembly by connecting the inner end of a second boom part to the other end of a carrier track with one end thereof connected to a power plant, thereby supporting the second boom part by the power plant for extending/contracting the second boom part. CONSTITUTION: A second boom part 12 is received in a retractable state in a base part 8 by a hydraulic cylinder 13 provided in the base part 8, and a piston rod 14 extended from the cylinder 13 and fixed at its outer end to the second boom part 12. When the second boom part 12 is extended, a carrier track 22 is supported on the hydraulic cylinder 13, in a nearly rigid linear position. When the second boom 12 is contracted, the carrier track 22 is folded upon itself and supported by the hydraulic cylinder 13.</p> |
