US Patent 6883579 Drive system for garage door

A drive system is provided for a moveable barrier, such as a garage door, that limits unauthorized shifting thereof. The drive system includes a flexible actuator for raising and lowering the door. The flexible actuator is tensioned with a biasing mechanism to minimize actuator throw, and a stop assembly of the biasing mechanism limits unauthorized travel of the garage door from the closed position by a predetermined amount that is sufficiently small so as to keep intruders out of the garage. The flexible actuator may for example, be a cable, a belt or a chain.