A motor-piezo actuator for nano-scale positioning based on dual servo loop and nonlinearity compensation

This paper presents the design of an ultra precision positioning system, which consists of a coarse stage and a fine stage. Two servo motors moving on recirculating ball screw are used to drive the coarse stage and three piezo actuators are used to provide the nanoscale positioning. The static and dynamic performances of the positioning system are formulated for designing the micro stage. Based on an evaluation of the system's natural frequency, a dual sever loop approach is used as the control mechanism. The main noise caused by the ambient environment is reduced by a vibration-suppressing table, and in the system control software, a digital Chebyshev filter is used to remove the noise caused by the magnetic chuck on the table. To correct the hysteresis and nonlinearity of PZT, Exact Model Matching (EMM) control law has been used, and therefore repeatability of the fine stage's motion can be improved considerably, the positive and negative movement can follow exactly the same path. A positioning accuracy of 8 nm is achieved over a traveling range of 200 mm with this system.