The magnetic coupling can be modelled as a classical two-inertia servo drive, where the “magnetic spring” has dynamic representation as in Fig.3. For a conventional two-inertia servo-drive, the shaft has stiffness K N·m/rad and is linear within its operating range.When considering the magnetic coupling, the linear torsion spring of traditional systems is replaced by the nonlinear torque transfer function given by TC = TG sin(pθD).