| 摘要 |
The invention relates to an operating unit (1) for architectural coverings, in particular roller blinds or shades. The unit (1) includes a stationary base member (37), a rotatable driving member (39), a rotatable driven member (29) and a brake mechanism (71, 73, and 75). The brake mechanism (71, 73, and 75) automatically arrests rotation of the driven member (29) in respect of the stationary base member (37), when not rotated by the driving member (39). The brake mechanism includes a first wrap spring (73), adapted to yield a predetermined minimum brake force, and at least one second wrap spring (75), different in size from the first wrap spring (73) and adapted to yield a supplementary brake force, which together with the predetermined minimum brake force amounts to a predetermined maximum brake force. |
