| 摘要 |
A shift mechanism (66, 68, 70, 72) for shifting a member (22, 22A', 22B, 27C) for performing an operation at a preselected one of at least two spaced-apart operating positions. The mechanism comprises a threaded screw (10, 10A, 10B, 10C) that is rotated about its central longitudinal rotational axis ("C") by a motor (14, 14A, 14B, 14C) to move a drive nut (12, 12A, 12B, 12C) in opposite axial directions therealong relative the particular direction the shaft is rotating and causes the drive nut to compress a resilient biasing means (20, 20', 20A, 20A', 20B, 20B', 20C, 20C') which is adapted to urge the member (22, 22A', 22B, 27C) to the particular position in a preloaded condition such that the operation is able to be performed by overcoming any resistance incurred in performing the operation or upon removal of the resistance upon the occurance of an event enabling the operation to occur. |
