Friction transmission mechanism for a motor-driven blind

A friction transmission mechanism mounted in a motor-driven Venetian blind for controlling lifting of slats and bottom rail of the Venetian blind and tilting of slats of the Venetian blind, comprising at least one cord roll-up unit and a driving unit adapted to drive said at least one cord roll-up unit, wherein said cord roll-up unit comprises:

• an amplitude modulation set, said amplitude modulation set comprising a support, an amplitude modulation lift cord connected to the slats and bottom rail of the Venetian blind and adapted to lift or lower the slats and bottom rail of the Venetian blind, and an amplitude modulation wheel rotatably engaged to said support and coupled to said driving unit for free rotation relative to said support to roll up or down said amplitude modulation lift cord upon operation of said driving unit, said support comprising a shoulder at one side thereof;
• a frequency modulation set, said frequency modulation set comprising a frequency modulation lift cord adapted to tilt the slats of the Venetian blind, and a frequency modulation wheel engaged on said amplitude modulation wheel and adapted to roll up or down said frequency modulation lift cord as the amplitude modulation wheel rotates, said frequency modulation wheel comprising a protruding block adapted to act against said shoulder of said support to limit rotation of said frequency modulation wheel within a predetermined angle after the frequency modulation lift cord has been rolled up or down;
• and
• a linkage, said linkage comprising spring means mounted in between said support and said frequency modulation wheel and forcing said frequency modulation wheel against said amplitude modulation wheel to produce a friction resistance that causes said frequency modulation wheel to be rotated with said amplitude modulation wheel upon rotary motion of said amplitude modulation wheel.