| 摘要 |
<p>A mechanism for opening and closing a barrier (10) comprises a first, elongate support member (114) for supporting the barrier (10) for pivotal movement between a closed and an open position; a second, barrier support member (102) mounted for pivotable movement about the first support member (114) between the closed and open positions; a first drive means (118) operable for moving the barrier support member (102) from the closed position to the open position under the action of gravity; a second drive means(120) operable to move the barrier support member (102) from the open position to the closed position under the action of gravity; and a control mechanism for selectively maintaining gravitational potential of the barrier during operation of the second drive means for subsequent operation of the first drive means.</p> |
