Design And Modeling Of The Actuator Type Piezoelectric Pump

A pump transforms energy of other formations into hydraulic energy,and provides power for the whole hydraulic system.Traditional hydraulic power unit transform electrical energy into mechanical energy with motors,and then pumps transform mechanical energy into pressure energy.Because of the heavy weight and big size of electrical motors and hydraulic power unit,it’s applications in MEMS,micro fluid high-precision transportation,aerospace and walking robots.Under this background,micro hydraulic pumps driven by intelligent material have been developed,whose characteristics of small size,low weight,high power-size ratio and remarkable anti electromagnetic interference performance,and have been focused and studied.Through development of more than 20 years,many types of piezoelectric pump have appeared,but their maximum output flow and maximum output pressure is still relatively low,which becomes a shortcoming in application.By now,its’ application is subjected to precise flow control and occasions which only allow small pump size.This article is aimed to raise the output flow of piezoelectric pumps under the condition of maintaining its’ high output pressure.This article raise out a structure of driving type piezoelectric pump,and construct the mathematical model of the system.Then the influence of port valve on piezoelectric pump is studied with the presumptions that the natural frequency of throttle slice is the main reason of limiting the work frequency and maximum output flow of a valve.Take the throttle slice with of type of cantilever beam for example,then build its’ dynamic model when vibrating in high frequency in the water,find the wet mode of throttle slice vibration,give out the analytic formula of its’ natural frequency and quality factor when first order flexural vibration happens in the waters.To raise its’ output flow of the pump,the ways of raising its’ natural frequency have been evaluated from the aspects of natural frequency of the throttle slice and flow-pressure characteristics,among which a check valve design based on the scaling law can raise up the natural frequency of the throttle slice at the same time without causing big jump of its’ flow resistance.To analyze the flow-pressure characteristic of the pump cavity,this article construct the mathematical model of liquid flow of pump cavity,give out the analytical formulation between loss of pump cavity pressure and flow.Pressure loss comes mainly from viscous drag produced by liquid viscosity,inertial force induced by change of flow area when the liquid is flowing,and inertial force induced by change of liquid speed.Viscous drag is the main source of pressure loss when a piezoelectric pump works at low frequency,when the pressure loss is proportional to its’ work frequency.Whereas inertial force is the main source of pressure loss when the piezoelectric pump-work at high frequency,then the pressure loss is proportional to the square of work frequency.Besides,vortex in the pump cavity and pipe will increase pressure loss.In this article commercial computational fluid dynamics software named CFX is used to analyze the influence of parameters of pump cavity,work frequency of piezoelectric stack have on pump cavity pressure loss.It is found that chamfer at the interface between pump cavity and the pipes can decrease pressure loss.