| 摘要 |
Such a trolley comprises rolling assemblies (3), in each of which at least two wheels (5) are mounted on supports (6) having the ability to shift along a track (7) in a closed loop exhibiting a horizontal lower length (70). The movements of the supports (6) inside the track (7) are connected such that when a support engaged in the rear part of the length (70) moves back therein, a neighbouring support enters the front part of the said length. Thus, when a first wheel (5) encounters an obstacle, the assembly (3) and therefore the trolley continue to advance, the support for the said first wheel (5) moving back inside the length (70). Another wheel (5) comes into contact with the ground ahead of the obstacle and becomes a bearing wheel. The first wheel then retracts upwards in order to pass over the obstacle which is thus negotiated without altering the attitude of the trolley or vertically shifting its centre of gravity. <IMAGE>
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