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