Robust Nonlinear Control System Synthesis Method for Electro- Mechanical Pointing Systems with Flexible Modes

摘要

A novel technique for designing robust nonlinear control algorithms for an electro-mechanical pointing system (a surrogate gun-turret testbed called the ATB1000) is presented. This system poses a very challenging control problem, as aiming accuracy must be achieved in an operational environment characterised by high-level disturbances (e.g., gun recoil) and with severe limitations imposed by the nonlinear behaviour of the drive train and the existence of flexible modes in the gun barrel. The control synthesis approach includes two steps: 1. use of a linear control method to design a dissipative outer-loop control law to make the overall system insensitive to the unmodelled dynamics and parameter imprecision associated with the flexible modes of the wheel-barrel subsystem; 2. use of a set of sinusoidal-input describing function (SIDF) models of the testbed's drive subsystem (which characterises the amplitude-dependent effects of backlash and nonlinear friction) to design an inner-loop nonlinear compensator to make the controlled drive-system response insensitive to input amplitude. This approach represents a major extension of previous SIDF-based techniques that make them applicable to systems with flexible modes. It achieves robustness in two senses: The final system is insensitive to the pointing command input amplitude and to the existence of unmodelled dynamics.