the micrometer screw moves the part being measured to a position where the spherical probing head is touched by piezoelectric nano-positioning stage at the beginning of each experiment, and then the piezoelectric stage drives the moving part being controlled to scan at 5 nm step. Fig. 10 shows that a input/output characteristi ccurve and residual of fitting curve through axial approach and radial approach, respectively in the range of 1 m from touch point.