| A quiet hydraulic actuator has been designed and built for use in low-frequency isolation and alignment systems to stabilize the optics in gravitational wave detectors. By comparison to traditional electromagnetic and mechanical actuators, the hydraulic actuator is particularly well suited for this application due to its relatively high force, large stroke, low noise, and low frequency capabilities.; This type of actuator can be adapted to a variety of specifications. We describe a matrix of design trades which are used to characterize an actuator, and we present the set of design criteria used to meet our performance requirements. These trades can be used to scale the actuator design to meet other performance requirements.; Three generations of actuators have been developed. The final design incorporates a passive hydraulic damping mechanism that suppresses an undesirable resonance peak in the open loop response. The absence of the peak is shown to greatly facilitate feedback controller design and robustness.; Eight of these actuators were installed on a platform at LASTI---the LIGO test facility at MIT. A diagonalized MIMO controller was implemented on the platform incorporating both sensor correction and sensor blending techniques. Isolation performance has been demonstrated in translational directions from 70 mHz to 7 Hz.; Large scale installation of the actuators has recently been completed at LIGO-Livingston; one of two LIGO observatories in the U.S. Prior to installation at Livingston, the observatory was inoperable during the daytime because of severe cultural noise. However, with the aid of quiet hydraulically actuated platforms, the observatory may now operate at all times of day. |
