US Patent 9121220 Hollow built-in blind

A hollow built-in blind includes two glass plates, an annular spacer cooperating with the glass plates to define a receiving space, and a blind disposed in the receiving space and including a lower rail, a plurality of slats, and two pull cords connected to the lower rail. A transmission unit includes a transmission shaft, a winding mechanism disposed on the shaft, and a belt pulley fixed to one end of the shaft. A drive unit is located at one lateral end of the blind and includes a guide wheel spaced apart from the belt pulley, an internal control device operable to move upward and downward in the receiving space, and a timing belt looped over the belt pulley and the guide wheel and having two opposite ends connected to the internal control device to form a closed loop.