Decoupled Control Study Of Multidimensional Platforms Containing Piezoelectric Actuators

With the development of industrial manufacture,the demands for technical target such as control accuracy and sensitivity are becoming higher and higher.There are more and more components as the complexity of controlled objects is added.Some controlled objects can't be regarded as simple linear systems because of the characteristic of nonlinearity existing in them.Even some characteristics of nonlinearity are not smooth,such as hysteresis and coupling,and there are also linear and non-linear parts in the system with a relationship of input and output,which will lead that the objects can't be identified and controlled in a regular way.After the further analysis of such systems,the nonlinearity of them often appears in one or more elements,which,however,is difficult to describe in identification and control.In the thesis,a research is launched on a three-dimensional platform with PZT driver,and the system is analyzed according to the data acquired in the experiments.The hysteresis of the system is described in sandwich model.Similarly,the inter-axis coupling is also described in sandwich model.Finally,a feedforward compensation control method is proposed to compensate and control the inter-axis coupling effectively.Thus,the control accuracy and sensitivity of track movement are improved.The thesis has reached following achievements.First,by analyzing the driving method of single axis on the three-dimensional platform and large amounts of data,the effect of hysteresis on accuracy and sensitivity is obtained.Because hysteresis is an intermediate elements in the system,its input and output cannot be measured directly.Since it can't be modeled alone,the system becomes a non-smooth sandwich system.In the article,after ascertaining the mathematical expressions of the system,the key term separation technical is applied to restructure the general expressions with a parameter linearization structure.Generalized recursive least squares algorithm and iterative algorithm are used to identify the parameters of the system.At last,experiments are done to verify the accuracy of the model.Then,according to the further experiments and analysis,besides the characteristic of nonlinearity existing in single axis,there is also the inter-axis coupling,which has a strong impact on the accuracy of system movement.So studying this characteristic is significant to improve the accuracy.Similar to hysteresis,coupling is a non-smooth and nonlinear characteristic,which has a feature of hysteresis.Based on the research on hysteresis above,the inter-axis coupling is described in sandwich model,and the parameters of the system are identified by Generalized recursive least squares algorithm and iterative algorithm.By analyzing the result of identification,it can be concluded that the obtained model can well describe the characteristic of inter-axis coupling.Finally,a feedforward compensation decoupling control method is proposed on account of the inter-axis coupling on the three-dimensional platform,in which the inter-axis coupling is decoupled in a feedforward coupling mode at first,and then the sandwich hysteresis inverse model is designed as a feedforward PID controller to make feedforward compensation for PZT actuator,obtaining excellent performance of control.