Study On Nonlinear Modeling And Control Technology Of Piezo-driven System For Micro-displacement Stage

With the rapid development of high-precision positioning technology,Piezo-driven micro/nano positioning systems have been used widely in the scientific and engineering fields,such as nanoimprint lithography,optoelectronic packaging,cell arrangement and precision machining.Piezoelectric actuator is one of the most important parts of micro/nano positioning system and its positioning accuracy have a great influence on the positioning accuracy of micro/nano positioning system.It is quite necessary and worthy to improve the positioning accuracy of piezoelectric actuator.However,complex nonlinear hysteresis of the piezoelectric actuators considerably degrades the positioning accuracy of the micro/nano system,even lead to system instability.To improve the positioning accuracy,it is necessary to develop hysteresis models to describe nonlinear hysteresis precisely.Most hysteresis models have complex expressions and many parameters which cannot be identified easily.Meanwhile,these models cannot describe nonlinear hysteresis precisely.Moreover,most hysteresis models can describe either rate-independent hysteresis or rate-dependent hysteresis.In order to compensate for nonlinear hysteresis to acquire high positioning accuracy,this dissertation will focus on hysteresis modeling and control technology of piezo-driven system for micro-displacement stage,the main contents are listed as follows.Firstly,for most hysteresis models have complex expressions and many parameters,a new polynomial hysteresis model is proposed.According to the value of input voltage,the model divides the hysteresis curves into two parts which are described by quadratic polynomials and linear equations.Compared with the traditional hysteresis models,the new polynomial hysteresis model has simpler expression and less parameters and its inverse model can be obtained easily.Then,based on this model,a feedforward control and a hybrid control which combines the inverse model and PID controller are designed.Lastly,experiments results demonstrate the validities of the hysteresis model and the designed controls.Secondly,for most hysteresis models describe either rate-independent hysteresis or rate-dependent hysteresis,a generalized hysteresis model which can describe both rate-independent and rate-dependent hysteresis is proposed.Based on the classical Prandtl-Ishlinskii model,the model introduces a quadratic polynomial and the initial displacement of piezoelectric actuator when it is used to describe rate-independent hysteresis.When it is used to describe rate-independent hysteresis,the model introduces the input frequency to the parameters of model.Experimental results demonstrate the validity of the generalized hysteresis model.A direct inverse modeling approach is adopted to obtain the inverse model of the generalized hysteresis model.Combing the inverse hysteresis model and adaptive LMS,two adaptive controls are designed : an adaptive control with an inverse model and an adaptive control with two inverse models.Meanwhile,a feedforward control with an inverse model is designed as a comparison.Three groups of experiments are designed to test the tracking performance of these controls: Point-to-point motion,a sinusoidal motion and a multi-frequency sinusoidal motion.The results show that the adaptive controls can realize high precision motion control and the adaptive control with an inverse model can get the best tracking performance compared with the other two controls.Lastly,combining computer micro-vision measurement system and 3-DOF compliant mechanism,a piezo-driven micro/nano positioning system is designed.Computer micro-vision measurement system has the advantages such as non-contact,high resolution and multi degree-of-freedom measurement ability.Based on a generalized hysteresis model and an adaptive control,a semi-closed loop control and a full-closed loop control of the piezo-driven micro/nano positioning system are designed.To get more high positioning accuracy,anther full closed-loop controls are presented.Experimental results demonstrate the validities of full-closed controls of the piezo-driven micro/nano positioning system.