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