| 摘要 |
Raisable and lowerable bollard or other access control device has a drive mechanism (6 - 13) normally powered from a local source of power (11) to raise and lower an operative access obstructing part (1). The drive mechanism (6 - 13) relies on mechanical engagement between operative parts (13 etc) that does not obstruct unpowered movement of access part (1) if one of its said operative parts (13) is released, as available using non-self-sustaining leadscrew and nut mechanisms and locking/unlocking (17) of rotation for the leadscrew (13).
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