Modeling and feedback control of a tilting-pad journal bearing

The goal of this study is to develop and implement a controllable tilting-pad journal bearing that uses feedback control to reduce the vibration of a rotating shaft. In this new type of tilting-pad journal bearing the radial positions of the pads are independently and continually adjusted using linear actuators, and the shaft displacement is measured for feedback using proximity sensors. The development of the control system begins with the creation of a nonlinear transient simulation of a tilting-pad bearing supporting a rotating shaft. This simulation, based on a one-dimensional Reynolds equation model, allows for radial motion of the pads to control the motion of the shaft. From the nonlinear simulation a new linear model is constructed, consisting of stiffness and damping terms for each pad. The linear model is used to design a linear quadratic regulator for state-feedback control of the bearing and a proportional controller for output-feedback control. Both of the control designs are evaluated using the nonlinear simulation to determine the closed-loop system response. The simulations show that the feedback controllers significantly reduce the orbit of the shaft.; An experimental controllable tilting-pad journal bearing is constructed that uses piezoelectric stack actuators to move the pads. This bearing and the proportional output-feedback controller are tested in an experimental test stand. The results from the experiments using this bearing show a significant reduction in size of shaft orbit along its minor axis.