A first conveying unit has a mechanism for advancing rollers, which are pressed against {HEAD ~ the driven portion} of {TAIL ~ 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 
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A first conveying unit has a mechanism for advancing rollers , which are pressed against { HEAD ~ the driven portion } of { TAIL ~ 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
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