a sensor mechanism for scanning {HEAD ~ the ends} to determine whether each end extends parallel to the path without regard to {TAIL ~ the length} of the piece being scanned; and 
a sensor mechanism for scanning { HEAD ~ the ends } to determine whether each end extends parallel to the path without regard to { TAIL ~ the length } of the piece being scanned ; and
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD 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