Design, Control And Experiment Of Piezoelectric Inchworm Micro Actuator

With the rapid development of precision machining and measurement,optical engineering,biological engineering,modern medicine,aerospace and other high technological fields,the conventional micro displacement actuator is limited by working principle and mechanical structure,the transmission efficiency is low,the output displacement is limited,accuracy is not high and the structure is complex and not easy to control,so it can not meet the requirements of precision positioning and the driving Piezoelectric inchworm micro actuator is a precision micro actuator which is based on the principle of inchworm motion to realize two-way,large stroke and high precision motion.it is widely used in these fields.According to the main problems of piezoelectric inchworm micro actuators,two kinds of micro actuators were designed based on compliant mechanism and their performance optimization and related performance test experiments were carried out.The main contents are listed as follows:In consideration of the issues of small output force and low speed of inchworm linear actuator,a novel inchworm linear micro actuator based on compliant mechanism is presented.The micro actuator is composed of two clamping mechanisms,a driving mechanism and an output shaft.The movement characterization of the actuator is that the drive mechanism drives the clamping mechanism for reciprocating linear motion,and the clamping mechanism takes the output shaft for linear motion.The working principle of the micro actuator is drawn and its movement principle is expounded.The flexible lever structure is adopted to design both the clamping mechanism and the driving mechanism in order to offer enough clamping force and driving force and improve the speed of the micro actuator.The detailed theoretical derivation of the micro actuator is carried out.The relationship between driving voltage and clamping force of the clamping mechanism,and the relationship between input displacement and output displacement of the driving mechanism are established by using the pseudo rigid body method.The relationship between the input force and the driving force is established based on the function principle.The prototype of micro actuator is made and an experimental platform is set up to test the performance of the micro actuator.The experiment results showed that the maximum clamping force is 216.43 N,the maximum driving force is 13.5 N.When the driving voltage is 120 V,frequency is 95 Hz,the maximum speed is 48.91 mm/s.In order to establish the step prediction model of micro actuator and realize the precise control of micro actuator,we need to quantitatively analyze the relationship between the step,driving voltage and driving frequency of the micro actuator.Quantitative analysis of the relationship between step,drive voltage and driving frequency is to determine the nonlinear mapping relationship,and establish prediction model.The nonlinear support vector machine regression theory is used to establish the relationship model between the step,the driving frequency and the driving voltage.Firstly,the key parameters of the drive signal of the micro actuator are optimized by experimental analysis and theoretical deduction,and the waveform of the driving signal is corrected.Secondly,the nonlinear support vector machine regression theory is adopted,and the Gauss radial basis kernel function is selected to establish the theoretical model of the step distance prediction of the micro actuator.Finally,the experimental test system is built to verify the step distance regression model of the micro actuator.The experimental results show that the step distance prediction model of the micro actuator can predict the step distance accurately.The relative error range between the experimental value and the predicted value is 0.275%-3.929%,and the error is small.Inchworm micro actuators can achieve large motion and high precision motion.However,in practice,the minimum step size will affect the accuracy of motion.In order to further improve the motion precision of the micro actuator,a piecewise control system is proposed on the basis of PID control.The piecewise control system proposed is composed of macro motion stage and micro motion stage.In the macro movement stage,the micro actuator moves according to the way of Inchworm crawling.In the micro motion stage,the micro actuator adopts PID closed loop control to get closer to the target position.The output model of the micro actuator is established,and the parameters of the control system are identified by the experimental method.The large stroke and high precision positioning experiment of the inchworm micro driver is carried out by the macro and micro segment control system.The experimental results show that when the driving voltage is 40 V and the frequency is 1 Hz,the positioning error of the micro actuator is between 0.53-0.67?m,which indicates that the proposed piecewise control method can effectively improve the motion accuracy of the inchworm micro actuator.The inchworm linear micro actuator can only achieve continuous linear motion.But in industry,it often needs large stroke rotation.Therefore,a new type of inchworm rotating micro actuator is designed based on compliant mechanism.The micro actuator is consisted of 2 clamping mechanisms,2 driving mechanisms,an output shaft and a bracket.Both the clamping mechanism and the driving mechanism adopt the flexible lever structure,which has the advantages of no friction and no lubrication,and ensures the clamping force and driving torque required by the micro actuator,and improves the movement speed.The calculation formula of magnification and static stiffness of the clamping mechanism is derived based on the virtual work principle.The pseudo rigid body model of the driving mechanism is established,and the relationship between the driving torque and the driving voltage is established based on the torque balance.The prototype is made according to the designed micro actuator,and the experimental test system is built to perform the performance test.The test results show that the design of the micro actuator in the driving frequency of 5 Hz,when the driving voltage is equal to 100 V,the maximum step is 783.5608?rad,at 30 V driving voltage,when the driving frequency is equal to 50 Hz,the maximum speed of 18.54 rad/s,the measured maximum driving torque is 95.04 N?mm.The performance of the designed micro actuator is well,and it can be used for reference for the development of the inchworm micro actuator.