In this paper the model development, problem specification, constraint formulation, and optimal feedback controller design for a variable-displacement hydraulic pump system are shown using the Quantitative Feedback Theory (QFT) technique. The use of variable-displacement pumps in hydraulic system applications has become widespread due to their efficiency advantages; however, this efficiency gain is often accompanied by a degradation of system stability. Here we develop a QFT controller for a variable-displacement pump based upon a linear, parametrically uncertain model in which some of this uncertainty reflects variation in operating point-dependent parameters. After presentation of a realistic non-linear differential equation model, the linearized model is developed and the effect of parametric uncertainty is reviewed. From this point, closed-loop performance specifications are formulated and the QFT design technique is carried out. An initial feasible controller is designed, and this design is optimized via a non-linear programming technique. In conclusion, a non-linear closed-loop system response is simulated. This paper is intended to have tutorial value, both in terms of the detailed hydraulic system model development, as well as in terms of the detailed exposition of the QFT controller design and optimal loop shaping processes. © 1998 John Wiley & Sons, Ltd.

Quantitative feedback design for a variable-displacement hydraulic vane pump

The use of root-locus-based robust design techniques in the design of a digital controller for a high-performance variable-amplitude fatigue test is described. Evaluation of the resulting controller on a prototype laboratory materials testing system, designed to simulate the mechanical stress loads experienced by certain aircraft components, shows that it meets design performance goals of 0.25% specimen load accuracy while providing robustness to specimen compliance over a 10 to 1 range. This performance significantly exceeds that obtained with traditional hand-tuned controllers. >

J.C. Cockburn

Papers

Robust control for high-performance materials testing