Vibration suppression of two-wheel mobile manipulator using resonance-ratio-control-based null-space control

A two-wheel mobile manipulator has the potential to become a multiskilled robot in the field of robotics, and it is already implemented by using inverted pendulum control. The center of gravity (COG) position is controlled to achieve the balancing of the robot. Since the vibrations of manipulator arms affect the COG positions of the inverted pendulum, balancing of the robot deteriorates. Therefore, the vibration control of manipulator arms of the two-wheel mobile manipulator is proposed in this paper. The virtual double-inverted pendulum is modeled using a 4-DOF manipulator, and it is controlled in work space and null space. Resonance ratio control is utilized for vibration-suppression control. The resonance ratio of a system can be determined arbitrarily by the feedback of reaction torque, and reaction torque observers are implemented for each and every manipulator motor. The feedback signal for vibration suppression is introduced to the null space of the manipulator. Simulations and experiments were carried out to check the validity of the proposed method, and results prove the effectiveness of the proposed vibration controller.