the force–motion characteristics will be symmetrical in the XY plane. The micro capacitive sensor contains a floating plate and a fixed plate, the floating plate is supported by four springs and pillars to keep the gap between two plates. The fixed plate is separated into four equal parts. When a vertical force (Fz) is applied to the probing sphere, as is shown in Fig. 2(a), four separated parts are electrically connected by wires to form a common plate, floating plate has a translational motion along z direction to make capacitance change,