| 摘要 |
This device comprises essentially at least two assemblies 7, each of which comprises two arms articulated on the same fixed horizontal axle 11, a normally stationary lower arm 8, the free end 8a of which bears on the ground 17, and an upper arm 9, of which the free end 9a, shaped as a cradle 9b capable of receiving and supporting a hub or shank 2b of a beam 2, is connected at the free end 8a of the lower arm 8 by drive means 8 of arbitrarily adjustable length. <IMAGE>
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