Patent attributes
The present invention relates to a sectional lifting door system. When the system is in normal operation, a door operator drives a cable drum to wind or unwind a cable for lifting or lowering slats. During a process of lowering the slats, if the slats is stopped or slowed unexpectedly (e.g. the slats hit an obstacle below), the door operator is disconnected from a shaft automatically. At this time, even if the door operator is still activated, the shaft does not rotate, the cable drum does not unwind the cable so that a certain tension force can be maintained on the cable and that the cable is prevented from loosening from the drum, thereby preventing the slats from falling off. Also, it can avoid the situation that the weight of the slats is completely applied to the obstacle because the cable drum continuously unwinds the cable.
