Study Of Fundamental Technologies For Large Range And High Precision 2-D Coarse/Fine Positioner

Ultra-precision positioners with large range, have been widely applied in many fields. Most of these positioner are driven in coarse-fine mode. For 2-dimension positioning, the type, with one dimension positioner added on to another dimension one, is commonly used. Accordingly, one set of measuring system for one DOF's measurement, two set are applied for two DOF(X-Y) displacement measurements, which leads to Abbe error. Here, a new coarse-fine positioning method is put forward, with planar motor as the coarse driving part and giant magnetostrictive actuator (GMA), a smart material actuator, as the fine one, which avoids added-on installation for 2-DOF positioning as mentioned.For coarse-fine mode, fine positioning is decisive for the whole positioning accuracy, though coarse positioning also plays an important role. Therefore, inherent nonlinearity and hysteresis in GMA, greatly affecting the accuracy, has to be handled for the goal of ultra-precision positioning.Hysteresis exhibited by giant magnetostrictive actuator is rate-independent when the input frequency is low and can be modeled by static Jiles-Atherton model. It becomes rate-dependent due to the eddy current effect and the magnetoelastic dynamics when the input frequency gets high. In this case, the eddy current loss represented by eddy current impedance and the estimation of the GMA's eddy current impedance through effective permeability are studied.Before computing the error between the feedback displacement signal and the desired position, the feedback signal should be filtered to minimize the influence of noise and time-variant model parameters, caused by environment or by estimation deviation. To this end, the extended Kalman filter combined with 1^st-order devided difference and strong tracking filtering is established.To attenuate the nonlinear and hysteresis behaviors, the inverse of the Jiles-Atherton hysteresis model for hysteresis compensation, in other words, linearizing the GMA model, is employed. After the inverse hysteresis developed and the feedback displacement signal filtered, feedback control laws are designed to meet the performance specifications. Several adaptive control algorithms, respectively, combined with common PID controller are considered, including Fuzzy-PID control, generalized minimum variant Fuzzy-PID control, multi-mode generalized predictive control PID control. The performance of these control methods are illustrated through simulations and experiment studies.On the other hand, to erase Abbe error for 2-DOF measurement, the principle of the planar capacitive sensor-based 2-D direct-decoupling measurement is proposed. Four methods for the sensor's capacitance computing—equation for infinite parallel capacitor, equation by Hereen's model, equations derived from Maxwell static electric field theory and analysis by finite elements method-are provided, and their results are compared with. Based on capacitance computing, the sensitivity of the designed sensor is figured out. To balance the dimension and the sensitivity of the sensor, structural design is conducted to minimize the sensor area with the given sensitivity. Moreover, the techniques for signal detection and conditioning, increasing displacement computation and anti-interference implementation are discussed.At last, the coarse-fine positioner is established, the planar capacitive sensor-based 2-D direct-decoupling measuring system is constructed, and the according experiments have been conducted to verify above theoretical studies.