| 摘要 |
A mast base comprises a rigid body (10) and four supporting legs (15), serving to support said body and extending laterally from the body (10) in mutually diverging directions. Each supporting leg (15) comprises an upper arm (17), which, at its inner end, is pivotally connected to an upper portion of the body (10) for pivoting movement relatively to the body around a first horizontal pivot axis (x1), and a lower arm (18), which, at its inner end, is pivotally connected to a lower portion of the body (10) for pivoting movement relatively to the body around a second horizontal pivot axis (x2). At their outer ends, the two arms (17, 18) are pivotally connected to each other for pivoting movement relatively to each other around a third horizontal axis (x3). At least one arm (18) has a variable length. The upper arm (17) of each one of two supporting legs (15), which are located at mutually opposite sides of the body (10) and which extend laterally from the body in mutually opposite directions, is pivotally connected to the body (10) by means of two pivot joints (19), which are located spaced apart in the direction of said first horizontal pivot axis (x1).
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