Output Feedback Control of Rigid-Body Attitude with Input Saturation

In this article, the attitude control problem of a rigid body without angular velocity measurement and subject to actuator saturation is solved in a novel way by the combination of the I&I methodology and the dynamic scaling technique. Different from previous literature that utilized ad hoc methods to solve such kind of problems, we construct the observer for the angular velocity directly, where the gyroscopic term is dominated by the dynamic scaling skill. The controller is a simple PD scheme with a saturate restriction on the angular-velocity part. It's shown that the observer and the controlled attitude dynamics compose a cascaded system. By utilizing the cascade-system stability theory, it is proven that the closed-loop system is globally asymptotically stable. Finally, simulations are conducted to demonstrate the effectiveness of the proposed control scheme.