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