Theoretical And Experimental Research On Linear Piezoelectric Actuator Based On Inertial Principle

In recent years,micro machinery and precision machinery have become one of the hot topics in the mechanical engineering field,and inertial impact piezoelectric actuator is one of the research focuses.The usual track of inertial impact piezoelectric actuator is horizontal,but in practical applications,the actuaor have to support fast and precise positioning on the inclined rail.Moreover,with the science and technology development,the positioning accuracy,speediness and load capacity of actuator are more demanding.The performance of inertial impact piezoelectric actuator needs to be improved.In this paper a linear inertia piezoelectric actuator with two groups unimorphs is put forward and designed based on the principle of inertial impact,piezoelectric unimorph is used as the drive component.One group unimorphs are called main drive vibrators which provide the pull force along the moving direction of actuator,and the other one are called the assistant drive vibrator,which provide the thrust along the moving direction of actuator.By driving the actuator with two groups unimorphs compared with one group,it can achieve faster average velocity,higher positioning accuracy,more drag load capacity.The main research contents are as follows:The structural optimization of piezoelectric unimorph are performed,and the optimal structural size of unimorph is determined.The length,width and thickness of the beryllium bronze substrate are respectivelyL_cu=80mm?W_cu=30mm?T_cu=0.4mm,The length,width and thickness of the piezoelectric ceramic layer are respectivelyL_p=60mm?W_p=30mm?T_p=0.2mm,and the stiffness ratio of the beryllium bronze substrate and the piezoelectric ceramic is A=2,with these structural dimensions the inertia force of the free end of the vibrator is the largest and the vibrator is called the optimal vibrator.Modal analysis and the harmonic response analysis of the optimal vibrator have been done based on finite element theory and the first order natural frequency of the vibrator has been got which is 75Hz.The dynamic model of the vibrator is established and the MATLAB Simulink is applied to simulate the vibrator dynamics.The simulation results show that the vibrator has the greatest inertia force at its the free end when driven by symmetric square wave,and the second largest driving capacity wave is the sine wave and the triangle wave has the weakest driving capacity.According to the optimal structure size,the piezoelectric unimorph is fabricated and its performance is tested.The experimental results show that the actual first-order natural frequency of the unimorph is 73Hz.Under the same amplitude and frequency voltage,the output inertia force of the unimorph at the free end under symmetrical square wave excitation is the largest,followed by the sine wave,and the triangular wave has the weakest driving ability,which is consistent with the simulation results.The force analysis of the actuator is performed and the balance equations of the actuator when it moves along the horizontal and inclined planes are got.From the analysis the conditions for the actuator to perform bi-directional stable motion on the horizontal and inclined planes are also achieved.?1?The output inertia force of the main drive unimorph free end is greater than the output inertia force of the auxiliary drive unimorph free end;?2?.The excitation voltages of the main and auxiliary drive unimorphs need to have same frequency and a phase difference of 180 degrees;A dynamic model of linear inertial piezoelectric actuator is established and the experimental prototype is manufactured The transfer function model of the actuator prototype is built by MATLAB Simulink.According to the simulation results,the relationship curves about the average speed of the actuator prototype and the main drive vibrator excitation voltage U₁,average speed of the actuator prototype and straight track angle?are obtained.A curve fitting is used to get the rate of change which is excitation voltage of the main and assistant drive vibrators to the inclination angle of the linear track.By using MATLTAB,the excitation voltage control program of the linear inertial piezoelectric actuator and the velocity control program of the actuator are compiled,and the output of excitation voltage which drive the actuator is through the data acquisition card controlled by the Data Acquisition Toolbox in MATLAB.The prototype of a linear inertial piezoelectric actuator is used to do the performance test.The experimental results show that by using two groups unimorphs including main drive and assistant drive vibrators the average speed and the fast positioning ability of the actuator can be increased.When the excitation voltage of the assistant drive vibrator is about 30%of the main drive unimorph exciting voltage,the actuator's ability to drag the load is the strongest.Reducing the difference between the main and assistant drive unimorph excitation voltage,the actuator's step distance decreases,and to the extent the positioning accuracy is also improved.The minimum step that the actuator can achieve is related to the minimum output voltage of the acquisition card.The larger digit of the card analog output port,the smaller step distance the actuator can achieve.Finally in this paper,a uniform speed control experiment is carried out,excitation voltage of the vibrators are increased to compensate for the loss of speed caused by the increase of the tilt angle of the straigh rail.The experimental results show that with the change of the angle of the straight track,the average velocity of the actuator is approximately unchanged,the maximum speed fluctuation is about 12um/s,and the speed control effect is well.