Research On Drive Control Of Piezoelectric Micro Gripper Based On Preisach Model

Piezoelectric ceramics have the advantages of small volume,high displacement resolution and large driving force,so piezoelectric drive is widely used in the field of micro positioning and micro clamping.The tiny displacement generated by piezoelectric ceramic driving can be applied to the micro gripper.It can achieve accurate amplification and positioning of displacement.Hysteretic nonlinearity has great influence on the positioning accuracy of piezoelectric ceramics.It is usually necessary to combine hysteretic model with nonlinear control.It can reduce the errors generated in the driving process and improve the precision of the system.Preisach model can describe the hysteresis nonlinear process of piezoelectric ceramics.At present,it’s the mainstream and most effective method for hysteresis compensation of piezoelectric ceramics.However,the Preisach model is difficult to be combined with real-time control due to its complex structure and large number of operators.The combination of Preisach model and adaptive inverse control method can effectively realize hysteresis compensation and reduce errors.At last,it can improve the displacement accuracy of micro gripper.The micro-gripper is divided into two parts.The first part is the mechanical structure of the micro-gripper.According to the size of the gripper object,it is necessary to design a reasonable micro-gripper structure to realize the tiny displacement generated by piezoelectric stacking to the gripper arm,so it can grip the object.Simulation software was used to simulate the force and displacement generated by piezoelectric stack,observe the displacement of the gripper and the change of the overall stress of the micro gripper,and verify the gripper effect.The second part is the drive control,using hysteresis compensation method to reduce the error,improve the control precision.The Preisach model can describe the hysteresis nonlinear process in most cases,so that hysteresis compensation can be carried out.However,Preisach model has a large number of operators and Preisach model is a complex model,so it is proposed to combine Preisach model with adaptive inverse control method.In the design of control algorithm based on Preisach model,the weight matrix column priority reconstruction method is proposed.This method rearranges the weight matrix of Preisach model,and can ensure the accuracy of Preisach model while reducing the calculation amount of model parameter identification.It can optimize the model and achieve the best hysteresis compensation effect.The adaptive inverse control method can realize the online updating of the weight,feedback the error obtained by subtracting the expected displacement from the actual displacement to the system.Change the learning rate and control the algorithm to change the weight parameters.At this time,the online updating of the weight makes the model approach the hysteresis nonlinearity of the piezoelectric ceramics constantly,and the error is further reduced.By combining the Preisach model with adaptive inverse control,the method can be applied between different frequencies to compensate the hysteretic nonlinearity of piezoelectric ceramics.Simulation analysis was carried out by Labview software,different operator number and frequency were set to simulate the working condition of Preisach model,and the influence of operator number and frequency on the hysteresis compensation effect of Preisach model was analyzed.The results show that with the increase of the number of operators,the more accurate the model is,the smaller the error is.The higher the frequency,the greater the error.However,when the number of operators increases to a certain number,the upper limit of the device is reached,and the error will no longer decrease after the number of operators reaches a certain number.By setting up an experimental platform of piezoelectric twin wafer and piezoelectric stack.The hysteresis compensation effect of the Preisach model based adaptive inverse control method was verified under different frequency,voltage,operator number.Firstly,the feasibility of the Preisach model is confirmed in the simulation of Labview software.Secondly,the effectiveness of the adaptive inverse control method based on the Preisach model is verified in the actual application process through the piezoelectric twin chip experiment.Finally,the piezoelectric stack is used to carry out the micro-clamping experiment.The minimum error of adaptive inverse control method based on Preisach model is obtained.When the frequency is small,the adaptive inverse control error based on Preisach model can be reduced by 68.4% at most,and 82.71% as the number of operators increases,compared with the control error with no control or only using Preisach model.When the frequency is large,the adaptive inverse control error based on Preisach model can be reduced by 74.73% compared with the control error without control or only using Preisach model.With the increase of the number of operators,the error can be reduced by 77.43%.The experimental results show that the Preisach adaptive inverse control method has a good hysteresis compensation effect on the clamping effect of micro-gripper in practical application.