One or more barrier members is coupled at a fixed post to a pivot pin or axis oriented parallel to {TAIL ~ the extension direction} of the parallelogram linkage, and thus operable to guide the barrier gate to a blocking position spanning {HEAD ~ the doorway} or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening 
One or more barrier members is coupled at a fixed post to a pivot pin or axis oriented parallel to { TAIL ~ the extension direction } of the parallelogram linkage , and thus operable to guide the barrier gate to a blocking position spanning { HEAD ~ the doorway } or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening
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