This paper presents a compliant motion control strategy by using null space. In constraint environment , there is possibility that the object such as obstacle come in contact with not only the end-effector, but also the middle link of manipulator . Then the compliant motion is one of powerful method to avoid such unknown environment because the exact sensing , the calculation of the manipulator configuration against the environment and so on are not required. Furthermore the redundancy makes it

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... possible to accomplish the workspace task while obstacle avoidance. So the compliant motion that the compliance characteristics exists in only null space of Jacobian matrix by definition of compliance center points is introduced . In this paper, the criteria of compliant motion which is useful for more dextrous manipulation is derived and it is guaranteed that the motion is always stable and safe against the external force. The validity of the proposed method is confirmed by several numerical and experimental results by using planar redundant manipulator.