Redundant manipulator is useful for posture control with keeping the desired end-effector position by using its redundancy. This makes it possible to realize dexterous motion such as obstacle avoidance motion with achieving the target task. However, the more degree-of-freedom motion increase, the smaller the stiffness of redundant manipulator is. This induces unacceptable vibration in the manipulator motion. To address this issue, this paper describes a strategy of vibration suppression by using workspace observer and resonance ratio control based nullspace control. The validity of the proposed approach is confirmed by simulations and experiments.
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