| 摘要 |
One embodiment has a pulley 22 freely running on a shaft driven by a motor 20. A cable around the pulley 22 is connected to the opening portion of the window or door which is biassed to the open position by spring 13. An electro-magnetic clutch 23 rotates with the shaft 21 and is energised to engage the pulley 22 so that the motor 20 may close the window or door, or allow it to open. With complete power failure, for instance because of a detected fire, the clutch 23 disengages automatically and allows the window or door to open under spring bias. In other embodiments, a motor drives a rack and pinion (Fig. 6, not shown) or a lead screw (Fig. 7, not shown) to move an electromagnetic device to move a window or door. The electromagnetic device holds a spring compressed, but in the event of fire allows the spring to expand to automatically open the window or door. The spring is re-compressed using the motor. <IMAGE> |
