A driving linkage is coupled between {HEAD ~ the barriers} and {TAIL ~ the parallelogram linkage}, such as a simple bell crank linkage 
A driving linkage is coupled between { HEAD ~ the barriers } and { TAIL ~ the parallelogram linkage } , such as a simple bell crank linkage
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH