A production line has a plurality of working groups in which {HEAD ~ work operations} are controlled by {TAIL ~ a sequential controller} 
A production line has a plurality of working groups in which { HEAD ~ work operations } are controlled by { TAIL ~ a sequential controller }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL