A first conveying unit has a mechanism for 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 {HEAD ~ the driven portion} when {TAIL ~ the object} enters the intersection 
A first conveying unit has a mechanism for 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 { HEAD ~ the driven portion } when { TAIL ~ the object } enters the intersection
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