Design And Test Research On The Piezoelectric Stack Pump

In recent years, as a new branch of micro-mechanical hydraulic systems, piezoelectric-driven micro-pump has been widely used in various fields. Compared with the driving motor used in the conventional axial piston pump, new piezoelectric drivers give a higher energy density. The micro-pump based on the piezoelectric materials has a very simple structure, unlike the conventional mechanical form; no moving-parts are involved in generation of motion, volumetric displacement, and fluid flow. The new piezoelectric-hydraulic actuator would be envisaged as a potential actuator for driving flight control surfaces and other unmanned air vehicle (UAV) subsystems.In this thesis, a stack actuator is used as the driving element of the piezoelectric pump because of its larger output displacement and output force. The actuating principle and output characteristics of piezoelectric stack were discussed in detail. A prototype piezoelectric pump was designed and fabricated, and its characteristics were investigated. This thesis is organized as follows:1. The working principle of piezoelectric stack pump is described. The operation of pump relies on a chamber equipped with a moving elastic membrane, the overall form and assembly structure are designed based on the principle of operation. Cantilever-type metal sheet is used as the passive check valve. The valves are clamped on the valve body through the tightening screw. The entire structure is simple and less demanding on the processing technology.2. A steady-state dynamic model of the piezoelectric pump system is established. The electrical/mechanical/fluid coupling behaviors of the pump system are taken into consideration in the dynamic model. The simulation results show that the output capacity of the piezoelectric pump depends on the parameters of the components, the driving frequency of the piezoelectric stack, the driving voltage.3. The prototype piezoelectric pump is fabricated and its structural form can achieve the purpose of transmission fluid. According to the theory of hydro-fluid mechanics, the influence of the sizes of the cantilever valve and the valve orifice on output characteristics was investigated. The piezoelectric pump is tested up to a pumping frequency of 100Hz, developing a maximal flow rate of 288.5ml/min and a maximal output pressures of 68kPa. The output characteristics have greatly improved compared with various types of proposed piezoelectric pump.4. Modal analysis for the elastic membranes and piezoelectric stack assembly in different thickness is discussed based on the FEM software. The numerical results of the first three natural frequencies and vibration mode shapes show that, the additional vibration mode shapes in optimal working frequency point has a great influence on the outflow in the pump chamber. The modal effect can explain the differences between the experimental output flow rate and the simulated steady-state output flow rate. It can be concluded that the thickness of the elastic membrane has a great influence on the optimal working frequency and the maximum pump output flow rate.