An electro-hydrostatic actuator for hybrid active-passive vibration isolation

Abstract

A novel electro-hydrostatic actuator (EHA) for active vibration isolation has been designed, modelled and tested. The EHA consists of a brushless DC motor running in oil and integrated with a bidirectional gear pump, driving a hydraulic cylinder. The actuator is designed to be integrated into a flexible strut connecting a helicopter rotor hub and fuselage, to provide isolation at the dominant rotor vibration frequency of around 20 Hz. The resonant frequency of the EHA is tuned to provide some passive vibration isolation. Active control increases the isolation performance by compensating for damping losses, and provides isolation over a broader range of frequencies. Tests on a prototype demonstrated a four-fold reduction of the root-mean-square transmitted force and a near elimination at the fundamental frequency. The advantages of the resonant EHA are a wider range of operating frequencies than a purely passive system, and lower power consumption than a purely active system. received his PhD degree from the University of Bath in 1991, for research into adaptive control of electrohydraulic systems. He has worked for rediffusion simulation on flight simulator control systems, as a Lecturer at the University of Leeds, and as R&D Manager for Instron. He is currently a Professor of Machine Systems at the University of Bath, and Director of the Centre for Power Transmission and Motion Control. His research interests are in the control of mechanical systems, and particularly servohydraulics. 48 J-P. Henderson et al. Nigel Johnston obtained his PhD from the University of Bath in 1988 for research into fluid-borne noise characteristics in hydraulic systems. He has been actively involved in research into efficient fluid power, digital hydraulics, fluid-borne noise, pump and valve dynamics, pipeline and flexible hose dynamics, high precision, high bandwidth actuation, aircraft fuel systems and active fluid-borne noise control. He is an organiser for the Bath/ASME International Fluid Power and Motion Control Symposium.