Control of Articulated Structures on Maneuvering Platforms

This paper describes approaches to modeling, system identification, control design and testing of a heli-borne automatic gun turret system. Nonlinear dynamic modeling from physical data, linear and nonlinear system identification, model validation, control design, simulation, implementation and testing are described. Firing dispersion is reduced by supressing effects of recoil in barrel tip motion at the firing instances. Quasi-periodic nature of the recoil disturbance is exploited in the control design by assigning frequency dependent weights to the output. The nominal controller reduces recoil response of the barrel tip, while allowing the turret/fork system to move around. The nonlinear portions of the dynamics, i.e. backlash and coulomb friction, introduce significant degradation of the linear controller performance. Further improvements to the nominal linear controller is achieved by using an estimator to track the barrel tip position, learning the actual deviation of the tip at firing instances during a burst and using the learned values to correct for the next burst. The scheme works remarkably well on the nonlinear simulation model under a variety of model parameter variations.