Patent ID: 8272500

Claim:
A screw driven conveyance device comprising: a conveyance carriage; a plurality of screw shafts that are rotation-driven are placed along a traveling route of the conveyance carriage; the conveyance carriage being propelled by rotation-driving of the screw shafts, the conveyance carriage having a pair of front and rear follower rollers fitted between helical vanes of a screw shaft at two locations, which are front and rear locations, in the axial direction of the screw shaft, one follower roller is a position-fixed follower roller, the other follower roller is a movable follower roller supported movably within a certain range in the axial direction of the screw shafts, urging means for urging the movable follower roller in one orientation of a moving direction of the movable follower roller, the pair of front and rear follower rollers are press-contacted in an opposite orientation to each other, against the helical vanes of the screw shaft to position the conveyance carriage relative to the screw shaft, the plurality of screw shafts are concentrically placed in series with an air space therebetween not wider than an interval between the pair of front and rear follower rollers, second holding means for positioning the movable follower roller at a position when the pair of front and rear follower rollers are fitted between the helical vanes of a single screw shaft so as to be respectively press-contacted to the helical vane on one side, second switching means for switching the second holding means from a non-positioned state to a positioned state upstream of the air space and for returning the holding means from the positioned state back to the non-positioned state downstream of the air space, and while the pair of front and rear follower rollers are transferred from upstream to downstream of the air space between the screw shafts, the movable follower roller being positioned by the second holding means.