Hydraulic Servo-Mechanisms with Nonlinear Mechanical Loads: Robust Performance with Analysis and Control of Bifurcation Behavior

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David F. Thompson, University of CincinnatiProposal No. 9978704Hydraulic Servo-Mechanisms with Nonlinear Mechanical Loads: Robust Performance with Analysis and Control of Bifurcation BehaviorMotion and force control systems involving hydraulic servo-mechanisms (such as a piston-and-rod actuator) represent vitally important components of the nation's manufacturing, transportation, and civil infrastructures. However, the advantages afforded by hydraulic actuation are accompanied by a penalty in the form of significant nonlinear dynamics; this behavior is often further complicated by coupled mechanical system nonlinearities. Recent studies by other investigators have focused primarily upon the application of nonlinear control techniques (e.g., adaptive control, variable-structure control). The paradigm which is developed in this project is to characterize the nature and degree to which conventional linear feedback controllers are effective in achieving nonlinear robust stability of hydraulic servo-mechanisms, with specific nonlinear structural loads, and under specific operating conditions. The research plan is summarized as follows: (1.) Develop feedback designs for linear robust performance and robust stability with and without feedback linearization of the inner loop hydraulic servo-mechanism characteristics; (2.) Check for nonlinear robust stability, primarily through bifurcation analysis; (3.) Check actual performance of the nonlinear system (via simulation and experimental methods); (4.) For specific applications and operating conditions, define the acceptable ranges/limits over which the aforementioned approach is valid. The expected impact and significance of the project lies in the development of better techniques for the design of simple, low-order controllers which would yield well-defined nonlinear stability margins and higher bandwidths than would be achievable through adaptive control or similar techniques. Potential applications of this work would lie the control of automotive and aerospace power transmission elements such as brakes and clutches, machine tools, and hardware-in-the-loop control of structural test specimens.