| 摘要 |
PURPOSE:To enable a device to perform higherspeed and further higher accurate positioning, by equipping the device with the first and second nuts screwed by a thread to a feed threaded shaft, spacer provided in a clearance between these first and second nuts further extended and contracted in the axial direction of the feed threaded shaft and a spacer control means controlling this spacer for extending and contracting action. CONSTITUTION:An electrostrictive element 1 is controlled in its amount of extending and contracting in a direction A by voltage applied to this element 1. Accordingly, in the first action when positioning is performed, the electrostrictive element 1 sets its applied voltage so that friction between a feed threaded shaft 8 and nuts 3, 4 decreases as small as possible through a ball 7 in order to enable a table 9 to move in a high speed in the vicinity of a predetermined positioning point. Next in the second action in order to perform stable and high accurate positioning of the table 9, the electrostrictive element 1 sets its applied voltage so that backlash between the ball 7 and the nuts 3, 4 and between the ball 7 and the threaded shaft 8 is completely removed. Subsequently, the table 9, after it is stopped, is fine moved by controlling the applied voltage to the electrostrictive element 1 and extending and contracting it. |
