Patent US 6,070,641

An automatically braking mechanism for a rolling door system is used in connection with en elongate support shaft for selectively rolling up or lowering the rolling door formed of a series of connected slats. A driven wheel is fixed on the support shaft and a motor drive is provided for driving a chain drive sprocket wheel and a continuous roller chain couples the drive and driven sprocket wheels. The roller chain normally moves along a predetermined path prior to failure of the roller chain when the roller chain is under tension. A braking mechanism includes a first elongate sensing arm pivotally mounted at one end and carries a follower roller at the other end which is normally in direct contact wit the roller chain. A second elongate actuator arm is integrally formed with the sensing arm so as to be pivotally mounted for sharing common angular movements with the sensing arm. A stop pin is mounted on the actuator arm for sharing movements with the actuator arm and for movements between a normal mode disengaged position in which the stop pin clears the driven sprocket wheel to permit rotation thereof when the follower roller engages the roller chain while the roller chain is under tension. The actuator arm and stop pin move to a failure mode engaged position in which the stop pin engages the driven sprocket wheel to prevent rotation thereof when the follower roller bridges or crosses the predetermined path of the roller chain. A tension spring normally urges the actuator arm to move to the failure position when permitted to do so by the sensing arm. In this way the roller chain maintains the actuator arm in the normal mode position prior to failure of the roller chain.