Hydraulic actuator force control: Quantitative design and stability analysis
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Date
2015
Authors
Esfandiari, Masoumeh
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Abstract
Automotive active suspension, advanced seismic testing, and force/torque emulations of space manipulators are examples of applications, where the hydraulic actuator force control is required. In double-rod hydraulic actuators, the actuator force is the differential pressure across the actuator multiplied by the piston effective area. The focus of this work is to control the actuator force of a double-rod hydraulic actuator by controlling the differential pressure across the actuator. The double-rod hydraulic actuator of this study is run by two independent circuits: 1) electro-hydraulic actuation and 2) electro-hydrostatic actuation. In general, developing controllers for hydraulic actuators is challenging due to the presence of parametric uncertainties and uncertain nonlinearities. Also, a specific challenge in force control of hydraulic actuators is the limiting effect of environment dynamics on the maximum achievable tracking bandwidth.
Considering the above challenges, in this research for the first time, quantitative feedback theory (QFT) is employed to control the hydraulic actuator force. Using QFT, a robust, linear, fixed-gain, and low-order controller is designed for each actuation system which: (i) keeps the closed-loop response within desired tracking bounds (ii) guarantees the closed-loop stability around desired operating points, (iii) rejects disturbance, and (iv) achieves desired tracking bandwidth. Among the performance criteria, special attention is paid to achieve high tracking bandwidth. Trade-offs between different performance criteria towards achieving high tracking bandwidth, are discussed. Experimental results are presented to validate that the performance criteria are satisfied by the designed QFT controllers.
The QFT controllers are synthesized based on the families of frequency responses of the hydraulic actuation systems, which limits the stability results of the closed-loop system, only for these families of the frequency responses. In this thesis, to investigate the nonlinear stability of the closed-loop systems with QFT controllers, for the first time, Takagi-Sugeno (T-S) fuzzy modeling and its corresponding stability theory are used. The stability conditions are presented in the form of linear matrix inequalities (LMIs). As a result, the nonlinear stability of the designed QFT controllers for both the actuation systems is proven in the presence of parametric uncertainties.
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Keywords
Hydraulic actuators, QFT, Control, Stability, T-S fuzzy models