The block diagram of the robot is shown as above. Here, $\phi$ is the angle between $X_v$ and $X_0$ (Yaw angle of the robot), and $\psi$ is the angle between $Z_b$ and $Z_v$ (pitch angle of the robot's CoM).
Angular velocities of CoM in global coordinate $X_0, Y_0, Z_0$ are given as
$\Omega_g = [-\dot \phi sin\psi \ \ \dot \psi \ \ \dot \phi cos\psi]$
Whereas, according to my understanding it should be simply
$\Omega_g = [0 \ \ \ \dot \psi \ \ \dot \phi]$
I am pretty sure I am wrong, but I could not figure out how did the authors come up with $\Omega_g = [-\dot \phi sin\psi \ \ \dot \psi \ \ \dot \phi cos\psi]$.
Any help would be really appreciated.