The platform alternatingly moves in either one of a direction substantially similar to the direction of motion of the conveyor, and {HEAD ~ a direction} substantially opposite to {TAIL ~ the direction} of motion of the conveyor 
substantially opposite to
The platform alternatingly moves in either one of a direction substantially similar to the direction of motion of the conveyor , and { HEAD ~ a direction } substantially opposite to { TAIL ~ the direction } of motion of the conveyor
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 REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH