The doorway barriers are movably mounted to the posts of the fixed frame in {TAIL ~ the doorway} to block passage by protruding into the doorway opening when {HEAD ~ the platform} has moved away from the doorway sill by operation of the parallelogram linkage 
The doorway barriers are movably mounted to the posts of the fixed frame in { TAIL ~ the doorway } to block passage by protruding into the doorway opening when { HEAD ~ the platform } has moved away from the doorway sill by operation of the parallelogram linkage
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH