| 摘要 |
An apparatus for moving a movable assembly along a mast is provided. The movable assembly has a bore adapted to receive the mast passing through it. The movable assembly has a release and retain mechanism; a uni-directional drive mechanism; and a switching mechanism for engaging the uni-directional drive mechanism. The switching mechanism has a shaft positioned within the movable assembly, generally oriented parallel to the bore, that is capable of rotational movement around the longitudinal axis of the shaft and axial movement along the longitudinal axis of the shaft. The switching mechanism also has a drive pin attached to the shaft of the switching mechanism that is oriented generally perpendicular to the longitudinal axis of the shaft. The switching mechanism also has a mechanism for affecting the axial movement of the shaft that is preferably in the form of a cam. The release and retain mechanism has a biased release lever defining a slot that is sized to receive the mast. The release lever normally engages the mast and when doing so allows movement of the movable assembly in a first direction along the mast while preventing movement of the movable assembly in a second direction along the mast. The uni-directional drive mechanism has a biased drive lever defining a slot, the slot being sized to receive the mast. The drive lever normally is disengaged from the mast. The drive pin is positioned along the length of the shaft so as to cause the drive lever to engage the mast when the shaft is first rotated to position the drive pin proximal to the drive lever and subsequently displaced longitudinally. By engaging the mast, the drive lever provides incremental movement of the movable assembly in the first direction. Free movement of the assembly in both directions can be accomplished by similar employing a release pin on the shaft to engage the retain and release mechanism.
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