The method 42, wherein {TAIL ~ the step} of selecting comprises selecting {HEAD ~ drive units} in response to an actuation of either one of the open limit actuator and the close limit actuator 
The method 42 , wherein { TAIL ~ the step } of selecting comprises selecting { HEAD ~ drive units } in response to an actuation of either one of the open limit actuator and the close limit actuator
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH