A Study on Ultra-precise Positioning over A One-millimeter Stroke Using Differential Ball Screw

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This study aims at realizing a simple positioning mechanism with nanometer level resolution over a one-millimeter stroke using a differential ball screw. Differential screw mechanism using a sliding type screw has been used for positioning with fine resolution. However, there has never been any trial to realize ultra-precise positioning by differential mechanism using ball screw, so that its positioning performance in nanometer range has not been discussed.A differential ball screw with outer diameter of 12 mm was manufactured on trial. The screw shaft has two part of ball screw, part A and B, in the same axis, whose nominal leads are P_A=2.00 mm and P_B=1.95 mm, so that the differential lead (d=P_A-P_B) is 0.05 mm. The lead error of the manufactured ball screw was measured precisely, and the positioning performance of the differential ball screw was estimated. It is clarified that the phase of lead error is not identical between the ball screw A and B. However, it is estimated that th … More e differential lead error can be decreased by adjusting the phase between the two nuts. To discuss the positioning performance of the ball screw, a prototype of positioning mechanism was designed and constructed, and the feed or positioning characteristics were measured in detail. On the basis of the experimental results, it is clarified that the run out error of the screw shaft and the friction of the linear guide ways become critical disturbances for the differential performance.The positioning mechanism was revised to improve the performance avoiding the above disturbances, and an ultra-precise positioning system over a one-millimeter stroke was constructed. Flexible elements are devised to eliminate the effect of run out error of the screw shaft. Rolling guide ways using V-flat shaped groove are designed to decrease the friction of the guide way elements. After the revisal, the effect of run out error is completely eliminated from the travel error of the stage. It is confirmed that the representative travel error is 0.9 μm with the fluctuation less than 0.5 μm. Linear characteristics are obtained in microscopic range that the table displacement is proportional to the rotational angle, and the proportional coefficient agrees with the designed value. On the basis of the above experimental results, a construction of positioning mechanism is established to exhibit the ability of the differential ball screw. Less