Dynamic Displacement Amplification Mechanism And Experimental Study Of Flexible Actuator Based On Solid-liquid Coupling

Piezoelectric materials have been widely used because of its advantages such as fast response,high positioning accuracy and high output force.However its scope of application is limited due to the tiny displacement output.At present,there are two main types of piezoelectric micro-displacement amplifier: flexible hinge micro-displacement amplifiers and hydraulic micro-displacement amplifiers,and the hydraulic micro-displacement amplifiers has attracted wide attention because they can produce greater output displacement,and take up less space.The existing research is mainly based on hydrostatic pressure amplification method,some scholars have also tested the dynamic characteristics of the hydraulic amplification and found that the amplification is more obvious when driving frequency close to the resonant frequency.But they did not carry out an in-depth study of the method of constructing displacement amplifier using dynamic characteristics.In this paper,a flexible actuator based on solid-liquid coupling is designed,which is based on the National Natural Science Fund Project " Design Theory of Fluid Dynamic Coupled Flexible Actuator Driven by Piezoelectric"(Item no.51405189).The actuator uses a piezoelectric oscillator as excitation source,and the piezoelectric oscillator produces the reciprocating bending deformation under the alternating voltage.This deformation drives the flexible diaphragm to reciprocate through the incompressible fluid,resulting in a larger displacement output at the center of the silicone diaphragm.In this paper,there are two indicators to evaluate the performance of the actuator: one is the absolute displacement of the center of the silicone diaphragm,and the other is the ratio of the center amplitude of the silicone diaphragm to the center amplitude of piezoelectric oscillator.The specific contents of this paper are as follows:The whole structure of the flexible actuator is designed and its working process and working principle are discussed.The interaction of the piezoelectric oscillator,the shell,the fluid medium and the software diaphragm are analyzed.The core components of the actuator including the composition of the piezoelectric oscillator,the driving power,the supporting condition and the material of flexible diaphragm is selected,and the experimental prototype is manufactured.The input and output of the flexible actuator are the center displacement of the piezoelectric oscillator and the center displacement of the silicone diaphragm respectively.The amplification ratio is defined as ratio of the output displacement to the input displacement.When the input displacement of the piezoelectric oscillator is constant,the output displacement of the center of silicone diaphragm depends on the shape of the surface of the diaphragm,so the vibration mode in the resonant state of the silicone diaphragm is tested.The experimental results show that the points with zero amplitude forms a circle on the surface of silicone diaphragm,and the movement direction of flexible diaphragm is opposite on different sides of the circle.In the first half of the mode,the fluid in the cavity is flowing to the inner region of the pitch circle,and the volume change of the fluid in the inner circle is larger than that of the piezoelectric oscillator.The displacement of the center point of the silicone diaphragm is larger than that of the piezoelectric oscillator under the action of the fluid.In the second half of the cycle,the movement process is the opposite.The experimental results also show that the number of pitch circles on the surface of silicone diaphragm varies with different driving frequencies,showing different vibration modes.The displacement amplification mechanism of the flexible actuator is analyzed and can be summarized into two aspects: One is to amplify the output displacement using the system resonance,and the change of the centroid displacement of fluid is greater than that of the piezoelectric oscillator.The other is to further enlarge the output displacement utilizing the special deformation of the silicone diaphragm,and this enlargement makes the displacement of the center point of silicone diaphragm larger than the displacement of fluid centroid.Therefore,the ability to enlarge the output displacement can be formed under the condition that the liquid is incompressible and the input area is less than the output area.The electromechanical coupling equation of the piezoelectric oscillator and the vibration mode analytical formula of the diaphragm are used,and the concept of the equivalent rigid body is introduced to discretize the motion of the liquid.The dynamic equations of the rigid-flexible-liquid coupling system including the piezoelectric oscillator,the software diaphragm and the fluid medium are established,and the displacement amplification of the system is analyzed by the equation.The test platform is built to test the prototype with different structural parameters,and the influence of each parameter on the output performance of the flexible actuator and the influence weight are analyzed.The experimental results show that when the thickness of the silicone diaphragm is 0.3mm and the filling water mass is 11.24 g,the amplification is the best for the ?35mm single-chip piezoelectric oscillator without load,and there are two optimal frequencies: At the first resonance point(124Hz)the silicone diaphragm amplitude reached 1.21 mm,the displacement was enlarged by 21.81 times.In the second resonance point(262Hz)silicone diaphragm amplitude reached 1.51 mm,the displacement was enlarged 24.42 times.