| 摘要 |
<p>A shutter mechanism for a ventilation fan comprises a number of blades (1,2,16) forming a louvre shutter or an iris shutter, which blades are movable between closed and open positions by a linear or rotary actuator (3,17,18). The actuator includes a spring (14) which urges the blades into the closed position. A synchronous motor (6,21), when energised, causes the actuator to open the blades and to maintain them open against the action of the spring. In the open position of the blades, the motor operates in the stalled condition, and can operate in that condition for indefinite periods of time.</p> |
