Design, test and model of a hybrid magnetostrictive hydraulic actuator

Abstract

The basic operation of hybrid hydraulic actuators involves high frequencybi-directional operation of an active material that is converted to uni-directionalmotion of hydraulic fluid using valves. A hybrid actuator was developed usingmagnetostrictive material Terfenol-D as the driving element and hydraulic oil asthe working fluid. Two different lengths of Terfenol-D rod, 51 and 102 mm, withthe same diameter, 12.7 mm, were used. Tests with no load and with load werecarried out to measure the performance for uni-directional motion of the outputpiston at different pumping frequencies. The maximum no-load flow rates were24.8 cm3 s−1 and22.7 cm3 s−1 with the 51 mm and 102 mm long rods respectively, and the peaks were noted around 325 Hzpumping frequency. The blocked force of the actuator was close to 89 N in both cases. Akey observation was that, at these high pumping frequencies, the inertial effectsof the fluid mass dominate over the viscous effects and the problem becomesunsteady in nature. In this study, we also develop a mathematical model of thehydraulic hybrid actuator in the time domain to show the basic operational principleunder varying conditions and to capture phenomena affecting system performance.Governing equations for the pumping piston and output shaft were obtainedfrom force equilibrium considerations, while compressibility of the working fluidwas taken into account by incorporating the bulk modulus. Fluid inertia wasrepresented by a lumped parameter approach to the transmission line model,giving rise to strongly coupled ordinary differential equations. The model wasthen used to calculate the no-load velocities of the actuator at different pumpingfrequencies and simulation results were compared with experimental data for modelvalidation.