Patent ID: 9718654
Date: 2017-08-01
CPC Classifications: B66C

Claim:
1. A telescopic boom comprising: a first frame whose section is U-shaped, the U-shaped first frame comprising a curved portion intersecting points on a curve having a constant radius of curvature; and a second frame connected to the first frame so that a closed section is formed, wherein the curved portion includes a plurality of protrusion portions arranged in a circumferential direction of the telescopic boom, each of the plurality of protrusion portions has an arc-shaped section and protrudes from the curve having the constant radius toward an outside of the telescopic boom, the arc-shaped sections of each adjacent ones of the plurality of protrusion portions have radiuses that overlap each other, and a joint is formed at a border between each adjacent ones of the plurality of protrusion portions, the joint comprising a ridge portion provided on an inner surface of the telescopic boom within the radiuses of the arc-shaped sections of the corresponding adjacent ones of the plurality of protrusion portions, wherein each protrusion portion extends in a longitudinal direction of the telescopic boom, wherein the plurality of arc-shaped protrusion portions are continuously arranged toward both sides of a center line of the telescopic boom along the curved portion from a position on the center line of the telescopic boom, the arc-shaped sections of the plurality of arc-shaped protrusion portions are arranged to have different radiuses to each other, the radiuses of the arc-shaped sections of the plurality of arc-shaped protrusion portions increase as the protrusion portions are farther away from the center line of the telescopic boom, and each joint comprises a point intersecting the curve having the constant radius.