A first conveying unit has {HEAD ~ a mechanism} for {TAIL ~ advancing rollers}, which are pressed against the driven portion of an object, toward an intersection, when the object travelling on the first rails nears an intersection, and for retracting the rollers from the driven portion when the object enters the intersection 
for
A first conveying unit has { HEAD ~ a mechanism } for { TAIL ~ advancing rollers } , which are pressed against the driven portion of an object , toward an intersection , when the object travelling on the first rails nears an intersection , and for retracting the rollers from the driven portion when the object enters the intersection
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH