The Controlled shutdown of a hydraulic servo-system using acceleration feedback

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Title: The Controlled shutdown of a hydraulic servo-system using acceleration feedback
Author: Jolly, Mark
Abstract: Hydraulic servoactuators have long been used in industry where high performance precision motion control is required. Because of their precision and ability to generate large forces, applications are numerous in industry. One such application provides cockpit motion for flight simulation. This thesis investigates a new emergency shutdown (abort) scheme for such high performance servo-systems. Because flight simulation involves the motion control of both man and machinery (a mock cockpit in motion), it will be used as the standard by which a safe and effective abort is modeled. The justification for motion abort during actuator operation is unsafe actuator accelerations. In order to protect man and equipment, the operation of critical servosystems, such as flight simulators, must be constantly monitored to detect system malfunctions which might cause personal injury or equipment damage. After any malfunction is detected, the appropriate shutdowm hardware must be signaled to safely take command of the servosystem and bring it to rest. The intent of this thesis was to verify the integrity of a new concept in hydraulic actuator abort, which utilizes the mechanical feedback of actuator acceleration. Once verified, critical design parameters can be further optimized and possible design configurations suggested. The abort system was modeled on a software package called Continuous System Modelling Program (CSMP). The actual abort subsystem proved to work as expected, but when integrated into the flight simulation actuation system, instability was observed. This instability occurred due to extremely large inertial forces acting on relatively large volumes of compressible hydraulic fluid. The spring rate imposed by the hydraulic fluid caused high frequency oscillations, superimposed on the desired steady state behavior, to pass through the entire system. Various loop gains in the model were adjusted to minimize the oscillations, but an additional dampening device would be the likely solution to effectively attenuate the instability. Such a device could be the topic of another thesis.
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Date: 1988

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