| 摘要 |
At least two zones, 21, 22, 23 are established along the course of permitted travel of a movable barrier (typically between a fully open and a fully closed position). After a triggering condition, such as loss of power or momentary disconnection of the barrier from its drive mechanism, the exact position of the barrier may not be known. By determining the zone in which the barrier is located, and driving the barrier in a particular direction based on the determined zone, the barrier can be directed to pass a location at which its position is precisely known (a passpoint), so as to recalibrate the system. Two zones may cover substantially all of the permitted travel of the barrier or there may be three or more zones. Adjacent zones may overlap. |
