Design And Experimental Study On Piezohydraulic Actuator Driven By Piezomembrane Pump

In order to meet the requirement of Micro Linear Actuators, which have the advantage in the terms of achieving large thrust, long travelling distance, high output precision and low consumption synchronously, in the fields of aerospace,robot etc, a new type of piezohydraulic actuator is designed, combining piezoelectric actuation technology with hydraulic transmission technology in this paper. The actuator is driven by piezomembrane pump which adopts piezomembrane as the power source in order to reduce the cost and enlarge the application. With water as the energy transfer medium, hydraulic cylinder as the power output terminal, the actuator completes the conversion of micro-displacement to macroscopic motion and electrical energy to mechanical energy by the way of cyclic compression of micro-droplets of liquid. The piezoelectric hydraulic actuator integrates the superiority of piezoelectric actuation and hydraulic transmission.1. The piezomembrane is one of the most important element of piezoelectric pump, whose performance exerts great influence on the output ability of piezoelectric pump directly. According to the shell theory and piezoelectric theory, the dynamic model of circular piezomembrane had been established. The deflection of the piezomembrane under liquid pressure and voltage were achieved respectively, as well as the change of chamber volume caused by the deflection. The output pressures were obtained when the change of chamber volume were the same under liquid pressure and voltage separately. The influence of radius ratio (piezoelectrice layer radius to piezomembrane radius) and thickness ratio (piezoelectrice layer thickness to piezomembrane thickness) on performance of the piezomembrane pump was studied through numerical analysis and finite element method. Results show that there are optimal structural parameters (radius ratio and thickness ratio) for output thrust and output velocity to obtain maximal values respectively, which provide a theoretical reference for the analysis of output performance of the piezomembrane pump. 2. The parameters related to performance of piezohydraulic actuator was analysed and selected:Though the analysis of several common valves, the umbrella-shape valve is selected; in order to obtain perfect output performance, orifice diameter, chamber-height were selected combining theory with experiment. The output energy of piezoelectric pump is passed through the hydraulic cylinder to the external parts, for which, the output performance of the piezohydraulic actuator is affected by the size of hydraulic cylinder structure directly, the formulas of output capacity of the hydraulic cylindethe were introduced which provided the theoretical basis for the selection of hydraulic cylinder in this paper.3. According to the selected parameters, 5-chamber series piezoelectric pump was fabricated and tested, from which the best driving modes were obtained when the number of working piezomembrane is n (n=1,5). The test results show that there are optimal frequencies for output thrust and output flowrate, and the optimal frequency for output flowrate is higher than that for output thrust; output thrust can be improved by increasing the number of working piezomembrane which has less influence on output flowrate.4. The hydraulic cylinder with the diameter of 25mm was selected and assembled with 5-chamber series piezoelectric pump and other components into piezoelectric hydraulic actuator,the output thrust, velocity of which are tested under the best working mode with 3,4,5 piezomembranes running respectively:1) The velocity against zero external load and thrust against zero velocity were tested at different operating frequencies, the relationship between output thrust, velocity and working frequency, voltage and the number of working piezomembrane were studied.Though calculation of test result, the relationship among output power,step length, driving frequence, voltage and the number of working piezomembrane were obtained.2) The velocitiy under different load were obtained, and the output power,step length were calculated. Result shows that velocitiy and step length decrease with the increasing of load. there is optimal size of load for output power to obtain maximal values; the maximal values of output power, optimal load for output power and the maximum load all rise with the increasing of the number of working piezomembrane.5. Based on the tests above, electromechanical energy conversion efficiency and mechanical energy conversion efficiency of the piezohydraulic actuator were calculated; in order to reduce the energy loss, some suggestions about the improvement of some structures were proposed in this paper.