Investigation of the Dynamic Characteristics of a Piezohydraulic Actuator

A piezohydraulic actuator is a hybrid device consisting of a hydraulic pump driven by piezo stacks, that is coupled to a conventional hydraulic cylinder via a set of fast-acting valves. Because the performance of the actuator is strongly related to the pumping frequency, a good understanding of the dynamics of the system is essential for designing a high-efficiency actuator. This article describes the development of a frequency domain model to quantify the dynamics of a piezohydraulic hybrid actuator. The analysis treats the hydraulic circuit as a series of fluid transmission lines, each represented by a transfer matrix that determines the relationship between the pressure and velocity at the inlet and at the outlet. The model includes the effects of fluid compressibility, inertia and viscosity. An experimental procedure to measure the frequency response of the device is described, and is used to validate the analysis. The effect of tubing length and fluid viscosity on the dynamic characteristics of the system is investigated. Longer tubing lengths result in lower resonant frequencies of the system, while increasing fluid viscosity results in a decrease in the magnitude of the resonant peak.