Lift lock for blind

A lift lock installed in a blind having a headrail fixedly transversely mounted on a top side of a window, a blind body suspended from said headrail, a spring winding mechanism mounted in said headrail, said spring winding mechanism having at least one spring means and at least one drum, said at least one drum being horizontally rotatable in clockwise direction and counter-clockwise direction to upwardly receive/downwardly extend said blind body, the spring means of said spring winding mechanism imparting a torque in clockwise direction to said at least one drum, the lift lock comprising:

• a shaft pivoted to said headrail for synchronous rotation with the at least one drum of said spring winding mechanism, said shaft having a constraint device;
• a switching mechanism mounted inside said headrail, said switching mechanism having a sliding member movable between a locking position and an unlocking position, said sliding member having an engagement device, said engagement device being forced into engagement with said constraint device to stop said shaft from rotary motion when said sliding member moved to said locking position, said engagement device being disengaged from said constraint device for enabling said shaft to be rotated by an external force when said sliding member moved to said unlocking position;
• and
• a control mechanism having a vertical pull rod, said pull rod having a top end suspended from one end of said headrail and coupled to said switching mechanism for pulling downwardly by the user to switch said switching mechanism between said locking position and said unlocking position alternatively, and a return spring mounted in said headrail and adapted to return said pull rod each time said pull rod been pulled downwards by the user and released.