Ultraprecision positioning by preload change of lead screws - (Characteristics of fine feed)

Ultraprecision positioning is examined for a fine feed system utilizing the elastic deformation of lead screws accompanying the change in the preload in a double nut. The nonlinear deformation due to Hertzian contact of the b all screw can be ignored within a feed of 1 mum under an adequate initial p reload. No effect of table load on nanometer-order displacement is observed in the range from 10 to 50 kg. The table displacement obtained under an in crease in the preload coincides well with the result under a decrease in th e preload. Feed control with preload change based oil a one-to-one correspo ndence of preload change and displacement is effective for avoiding the hys teresis phenomenon of the piezoelectric actuator adopted as a deformable sp acing part in a double nut. In addition, the preload can be used as a measu re to detect the table displacement in place of a position sensor which som etimes shows unreliability owing to unstable performance in the nanometer r egion. The minimum step feed deduced from preload change is 1 nm for a slid ing screw and 5 nm for a ball screw.