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