Research On Design And Control Of The Piezoelectric Actuated Compliant Amplification Mechanism

With the application of precision equipment expanding,piezo-actuated displacement amplifier system(PDAS)draws more attention because of its simple structure,diverse configurations and easy control.To increase the amplification ratio is the main method to enhance the stroke of the PDAS.However,since the shaft drift of the flexure hinge,amplification ratio extrema becomes a general issue for PDAS.Although the multi-stage amplifier achieves large amplification ratio,the structure size is bulky.To solve this problem,the design methodology and control method of the large-stroke PDAS are studied in this thesis.Based on the motion direction stiffness,the displacement loss,system stiffness,and energy efficiency of the PDAS is deeply discussed.The research on design and control of the large-stroke highenergy-efficiency PDAS,and expanding the stroke of the PDAS to millimeter level are significant.This thesis simplified the triangular amplifier and the lever amplifier into paralleled flexible chain and serial flexible chain respectively.Use the compliance matrix to describe the elastic deformation of the flexure hinge,apply the D-H method to operate the matrixes for force-displacement calculation,and establish the generalized kinematics and statics models of the flexible chain.As for dynamics,Lagrange's equation is used to establish the dynamics equation,and the natural frequency is calculated by the equivalent stiffness and equivalent mass.The kinematics and load performance of the two-stage bridge and lever amplifiers are compared and the influence of the flexure hinge on the amplification ratio is analyzed,by applying the generalized model.The influence of the motion direction stiffness on the PDAS is studied based on the analysis of the flexure hinge.The motion stiffness design methodology is proposed,which takes the hybrid hinges,hybrid material,and parameter optimization as the main tools,carries on the system stiffness optimizing as guidance,and considers the optimization of the kinematics and dynamics performances as the key aim.The system stiffness of the two-stage flexible amplifier is analyzed by applying this method,and the relations of the amplification ratio and the stiffness ratio is obtained.Based on this,the classical two-stage bridge-type amplifier is improved by applying hybrid hinges,which enhance its relation amplification rate up to 0.9.To compact the structure size of the PDAS,we proposed a hybrid flexure hinge based bridge-lever-type two-stage amplifier whose superiorities of amplification ratio and compactness is validated via FEA and experiment studies.To increase the energy efficiency of the PDAS,the relation of the motion direction stiffness and the energy efficiency is discussed based on the system stiffness analysis methodology.We analyzed the method to enhance the energy efficiency,proposed the concept of negative based high-efficient PDAS,and developed a PDAS with energy efficiency of 80%.To find the optimal working performances of the two-stage bridge-type amplifier,the hybrid hinge based two-stage bridge-type amplifier is optimized based on the stiffness analysis,where the amplification ratio,natural frequency,displacement loss,and load capacity are comprehensively considered.Finally,the design mechanism with amplification ratio of 90,stroke of 5mm,natural frequency of 50 Hz,and load capacity of 50 N is achieved.To achieve nanometer scale positioning precision,we introduce concept of macro/micro driven,where an extra piezo-ceramic is used to compensate the displacement loss caused by amplification effect.Given that the system is MOSI system,the control strategy ‘macro open micro lose' is proposed,where the Gaussian process regression(GPR)is used to model the piezoelectric hysteresis and the input shape technology(IST)is used to eliminate the residual vibration.To solve the contradiction between the large stroke and small structure size of the micro-gripper,the motion direction stiffness analysis method is introduced to the design of micro-gripper,where the amplification ratio is enhanced via flexure hinge individually design,the passive compliance is achieved via stiffness design,and parallel motion is realized via parallelogram mechanism.The GPR and IST are used for dual feedforward control,and hybrid control consists PID and dual feedforward control is used for constant force control.The force/position switch control is used to enhance the compliance effect during the clamping moment.The merit of the proposed microgripper is verified via experiment study.