Nonlinear robust control for a passive line-of-sight stabilization system

In this paper, the technique of model reference robust control (MRRC) is applied to a passive line-of-sight (LOS) stabilization system. The system uses a flywheel as a spinning mass gyroscope to stabilize a two gimbal system against base motion. Due to the gimbal geometry, unwanted dynamic coupling exists in the LOS system. The system is treated as a two input - two output system, and it is then decoupled and controlled using only input/output measurements rather than state feedback. The technique used in this paper for decoupling and control of the LOS system is MRRC which is an extension of model reference control to nonlinear MIMO systems. The technique utilizes bounds of plant parameter uncertainties via controller parameter uncertainties and also input disturbances bounds. Specifically, dynamics of the passive line-of-sight stabilization system are described, followed by a perfect knowledge (MRC) control design and then a nonlinear robust control design.