  This paper presents hybrid attitude and gyro-bias observers designed directly
on the Special Orthogonal group SO(3). The proposed hybrid observers, enjoying
global exponential stability, rely on a hysteresis-based switching between
different configurations derived from a set of potential functions on SO(3).
Different sets of potential functions have been designed via an appropriate
angular warping transformation applied to some smooth and non-smooth potential
functions on SO(3). We show that the proposed hybrid observers can be expressed
solely in terms of inertial vector measurements and biased angular velocity
readings. Simulation results are given to illustrate the effectiveness of the
proposed attitude estimation approach.
