| 摘要 |
A counterweight (12) provided at the end of a shaft (8) for winding up the door-raising belts (3) of a concertina type door. The counterweight (12) is designed to open the door to a fraction of its height. It co-operates with the motor (7) when the door is being opened and closed under normal circumstances. A motor and brake unit (14) is provided including both the motor (7) and a brake for locking the shaft (8) when the motor is not in operation. Catch means may also be provided on the bottom of the door. Manual means are provided for releasing the shaft-locking brake means in the event of a power failure. The device is essentially a safety device and in the event of a motor breakdown or a power failure it enables the concertina-type door to be rapidly opened, at least partially. Similarly, in the event of the coupling between the drive shaft and the motor being broken, the device prevents the door from falling to its closed position in a catastrophic manner. The device also makes it possible to use a motor of smaller power than would be required in an installation which does not include a counterweight. |
