PURPOSE: To facilitate changing of the screw rigidity by forming a gear on the external circumference of a spacer which expands/contracts the nut space by pushingly pressing one end of a pair of nuts which are engaged with a ball screw and applies preloading thereto in the feeding direction, and shifting the spacer in the axial direction by means of an expanding/contracting mechanism thorough engagement with the gear.
CONSTITUTION: A ball screw 15 is supported at the holes of flanges 12-14 which are protruded underside of a movable table 11, and a nut 16 fixed to the flange 14 and a nut 18 where the movement in the rotational direction is restricted by means of a lock 17 fixed to the movable table 11 and the axial movement is allowed are engaged with each other. A spacer 20 provided with a gear 20a engaged with a gear 22 is fitted to the nut 18 in a slidable manner. A cam surface 20b is formed to the spacer 20, and the cam surface 21b of the second spacer 21 is fitted thereto. The spacer 21 is fixed to the flange 12, and the flange 13 is provided with the gear 22 and rotated by means of a motor 23. Thus, the spacer 20 rotates by the rotation of the gear 22, the spacer 20 is slided by the sliding of the cam surface, and the rigidity of the screw 15 is increased.
HORI NOBUMITSU
YAMAKAWA YOICHI
TAKAHASHI TOSHIHIRO
SUZUKI HIROHIDE
