A globally convergent angular velocity observer for rigid body motion

The problem of obtaining the angular velocity of a rigid body from orientation and torque measurements only, without noisy numerical differentiation, is considered. A novel angular velocity/angular momentum observer for rigid body motion is presented. Using Euler quaternions and a mechanical energy function approach, it is shown that the observer estimates converge globally and that the convergence is eventually exponential. It is hoped that a mechanical energy function approach to rigid body control can be combined with the observer presented to lead to a globally stable, nonlinear, observer-based, rigid-body controller in which the observer and controller errors can be separated, in much the same way as one can separate controller and observer poles in the output feedback controllers of linear system theory.>