| 摘要 |
An extensible support leg comprising at least two reciprocally-slidable portions (20, 21), a manoeuvring screw (5) axially constrained to a first portion (20) of the portions (20, 21), a threaded volute (4) axially constrained to a second portion (21) of the portions (20, 21) and screwed on the manoeuvring screw (5), and a rotating drive shaft (8) which is connected to the manoeuvring screw (5) by means of a mechanical gear change (70, 71, 80, 81, 86), and is destined to be rotated in order to set the manoeuvring screw (5) in rotation, the mechanical gear change (70, 71, 80, 81, 86) further comprising: two first cogged crown wheels (70, 71), coaxial and rotatably solid with the manoeuvring screw (5); two second cogged crown wheels (80, 81) mounted coaxially and rotatably idle on the drive shaft (8), each of which enmeshes directly with a respective cogged crown wheel of the first cogged crown wheels (70, 71), such as to realise two gears having different transmission ratios; and a cursor (86), which is rotatably solidly associated to a portion of the drive shaft (8) comprised between the second cogged crown wheels (80, 81), and is mobile, in a direction of the axis of the drive shaft (8), between a first enmeshed position and a second enmeshed position, in which the drive shaft (8) is rotatably solid respectively with one of the second cogged crown wheels (80) and with the other (81).
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