An Ultraprecision Positioning System using Twist-roller Friction Drive with Fine Adjustment

摘要

For uftraprecision positioning, the Twist-roller Friction Drive (TFD) has been proposed by the authors. The TFD is a kind of lead screw with a minute lead; the rotation of the driving motor is extremely reduced to the linear movement of the machine table. In the present paper, an ordinary servomotor is used for coarse positioning and a piezoelectric actuator is used for fine positioning. The fine adjusting mechanism using the piezoelectric actuator is incorporated into a motor-holding element and the driving motor is rotated slightly around the motor shaft by deforming the piezoelectric actuator. The resolution of the coarse positioning using the ordinary servomotor is 5nm, while the stroke of the positioning table can be as large as several tens of millimetres. On the other hand, the stroke of the fine adjustment using the piezoelectric actuator is only 10nm, however, the positioning resolution can be as small as 50pm. For long distance positioning, the servomotor drives the machine table at first. As the table approaches the destination within several nanometres, the control of the table movement is switched from the coarse positioning to the fine positioning. Finally, the table is positioned within sub-nanometre of resolution under the control of the fine adjustment. Therefore, the positioning system using the ordinary servomotor with the fine adjustment can be used as a sub-nanometre positioning device with long stroke.