  Two-inertia systems are prone to resonance vibrations that degrade their
control performances. These unwanted vibrations can be effectively suppressed
by control methods based on a disturbance observer (DOB). Vibration suppression
control methods using the information of both the motor and load sides have
been widely researched in recent years. Methods that exploit the spring
deflection or torsional force of two-inertia systems have delivered promising
performances. However, few conventional methods have exploited the relative
position information, and the discussion of position control is currently
insufficient. Focusing on the relative position, this study proposes a new
resonance ratio control (RRC) based on the relative acceleration and state
feedback. The structure of the proposed RRC is derived theoretically and the
proposed method is experimentally validated.
