Bi-directional Driving Mechanism And Experimental Research Of Asymmetrical Inertial Piezoelectric Actuator

Piezoelectric actuator is a kind of precision tiny driving device based on piezoelectricmaterials and it possesses the advantages of high positioning resolution, fast response speed,simple structure, low cost and no electromagnetic interference. It has been widely applied inthe fields of precision and ultra-precision machining, medical treatment, vibration control，sensors and et.al. Asymmetric inertial piezoelectric actuator has simple structure and specialdrive type. Compared with the inertial piezoelectric actuator drived by traditionalasymmetric waveform (eg.sawtooth wave), the asymmetric inertial piezoelectric actuator canbe drived by symmetric waveform, which simplifies the power control and saves the designcost. A novel bi-directional rotary asymmetric inertial piezoelectric driving mechanism basedon inertial piezoelectric actuator has been proposed in this paper. The law of conservation ofenergy is applied to analyze the movement process of piezoelectric vibrator theoretically,accordingly the relationship between step-angle and frequency of the bi-directional rotatingactuator is deduced. The propsed piezoelectric actuator can change direction of rotation byusing signal at different frequency. The application areas of this kind of actuator arebroadened and the references for the further theoretical research of asymmetric inertialpiezoelectric actuator are provided.1. The research status of piezoelectric actuatorAccording to the state of the art, the direct drive type, the inchworm type and theinertial impact type actuators are analyzed and a novel bi-directional rotary inertialpiezoelectric actuator with asymmetric clamping locations is proposed based on the inertialpiezoelectric actuator in this paper. The asymmetric inertial piezoelectric actuator not onlyhas simple structure and convenient controll, but also can realize bi-directional driving byselecting different working frequency on the basis of the theoretical analysis.2. Research on piezoelectric basic theory and bi-directional drive theoryPZT material with the vibration mode LE is selected as the drive element of the actuatorin this paper, which is supported through the asymmetric clamping cantilevered manner. Thedriving principle of the actuator is analyzed preliminarily, then the kinetic model of theasymmetric clamping vibrator is established and the equivalent stiffness formula is deducedon the basis of the nonlinear vibration system model. The motion process of the asymmetricclamping vibrator is decomposed and the law of conservation of energy is applied to deducethe step-angle expression of the bi-directional rotary asymmetric inertial piezoelectricactuator. The possible movement form of the actuator is analyzed according to the results of the theoretical analysis.3. Simulation of the piezoelectric actuatorThe comertial finite element software namely Ansys is applied to analyze theasymmetric clamping piezoelectric vibrator. The static deformation and stress distribution ofthe asymmetric clamping vibrator are researched by the static analysis. The modes of theasymmetric clamping vibrator at different frequencies, the harmonic response undersinusoidal excitation and the transient response at different time periods are researched bythe kinetic analysis. MATLAB software is applied to analyze the atuator according to theresults of the theoretical deviration. The effect of frequency, voltage, system quality andclamping stiffness difference on the working performance of the bi-directional rotaryasymmetric inertial piezoelectric actuator is researched in this paper.4. The experimental analysis of the piezoelectric actuatorThe prototype of the actuator is designed and the test system for the actuator is set up.The experimental results show that the minimum driving voltage of the actuator is about25Vand the maximum step-angle of the actuator can reach up to0.0647rad at the voltage of90V.The velocity of the positive directional rotation decrease with the increase of the clampingdifference and increase a little when the claming difference is5mm under the voltage of90Vand the inertial mass of8.2g. The change of the velocity of the reverse directional rotation isnot obvious with the increasing of the clamiping difference under the same condition. Theactuator changes direction at about79Hz when the frequency changes from0Hz to100Hzand can also change direction at about215Hz when the frequency changes from120Hz to300Hz. The maximum step-angles of the actuator toward to each direction with doubleinertial mass are all around0.01rad. The difference between the performance of the positiveand the reverse direction is smaller than the single inertial mass one. The frequency band thatthe maximum amplitude of vibration peak lies in is close to the natural frequency of finiteelement simulation. The minimum resolution of the actuator can reach up to0.3μrad and canrealize smooth rotation. The experimental results show that the actuator can achievebi-directional rotation, which is agrees well with the results of theoretical analysis.