| 摘要 |
A grating assembly drive means is connected to control the movement of the movable grating between OPEN and CLOSED positions relative to a fixed grating. The drive means moves the movable grating through yieldable connection when moving toward CLOSED position, whereby when such movement is blocked by a foreign object the movable grating stops without damaging the object or the drive. On the other hand movement by the drive means toward OPEN position is direct after removal of any slack caused by a previous yielding.
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