Patent ID: 8851148

Claim:
A window blind comprising: a stationary seat; a blind mechanism including a linking rod that is mounted rotatable to said stationary seat, and a blind unit wound releasably on said linking rod; a coupling mechanism including a transmission unit that is connected to said linking rod, and that is movable between an operable state, where said linking rod is permitted to rotate for releasing or retracting said blind unit, and a non-operable state, where rotation of said linking rod is not permitted, a stop unit that is disposed for restraining rotation of said linking rod when said transmission unit is at the non-operable state, and a resilient member that is disposed for biasing said transmission unit toward the non-operable state; and a control pole connected to said transmission unit and operable for converting said transmission unit to the operable state against a resilient force of said resilient member; wherein said transmission unit includes a first gear that is connected co-movably to said control pole and that has a plurality of angularly spaced-apart first gear teeth, and a second gear that is connected co-rotatably to said linking rod and that has a plurality of angularly spaced-apart second gear teeth meshing with said first gear teeth of said first gear; wherein said second gear has a plurality of first and second bottom lands, each of which is formed between an adjacent pair of said second gear teeth, said stop unit having a plurality of engaging grooves formed respectively in said first bottom lands of said second gear, one of said first teeth of said first gear engaging one of said engaging grooves when said transmission unit is at the non-operable state, a number of said engaging grooves being less than a number of said second gear teeth of said second gear.