| 摘要 |
A device with at least a supporting means (1, 2, 3, 4) coupled to a movement-system making the upper-plate moving. The device is characterized in that it includes a mechanism by which the supporting means (1, 2, 3, 4) can be moved vertically thanks to the operation of a movement-system, whereby this mechanism comprises at least the following elements: a ball-housing (6) with a ball; a threshold-block (7) with a bearing surface on which the ball rests.
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