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