Patent ID: 8893766

Claim:
Operating unit for an architectural covering, in particular a roller blind or shade, that exerts a first rotational force in a fully raised position and a second rotational force in a fully lowered position, the operating unit including a stationary base member, a rotatable driving member, a rotatable driven member, and a brake mechanism for automatically arresting rotation of the driven member in respect of the stationary base member when not rotated by the driving member, wherein the brake mechanism includes a first wrap spring and at least one second wrap spring, the first wrap spring having a first number of windings configured to maximally yield a first brake force that amounts to the first rotational force of the architectural covering, the at least one second wrap spring having a different operating force than the first wrap spring, the at least one second wrap spring having a second number of windings greater than the first number of windings and configured to yield a supplementary brake force, which together with the brake force of the first wrap spring amounts to a predetermined maximum brake force, wherein the supplementary brake force is greater than the first brake force.