Study of ultra precision positioning system and linearity compensation

A design of an ultra precision positioning system including a coarse stage and a fine stage is proposed. In this positioning system, the fine stage's relevant design parameters about the static and dynamic performance are assessed and evaluated, and according to the system's natural frequency, dual servo loop control law is adopted. The positioning system is composed of two recirculating ball-screw servo motors and three piezo-actuators. Servo motor's function is to realize the coarse stage's motion, and piezo-actuator's function is to realize the fine stage's motions. In system control software, because Chebyshev digital filter is adopted to remove the noise components from environment, the positional accuracy achieves within 8 nm over 200 mm stroke. To eliminate the influences of hysteresis and nonlinearity of PZT, exact model matching (EMM) is added into control law, and therefore the error of repeatability of the fine stage's motion is decreased to one-fifth of that before compensation, and it almost makes the positive and negative motion paths in the same line.