In this paper, we propose a sensorless collision-detection method that exploits static redundancy and achieves robustness against unknown manipulation forces. The proposed method does not require additional sensors other than joint position or motor current sensors commonly used in industrial manipulators and collaborative robots. This method enables the detection of collisions at the terminal link under unknown manipulation force conditions that are difficult to detect using conventional methods. By extracting the null-space component of the Jacobian matrix from the joint driving torque, the method achieves low-latency detection with simple computation. Moreover, by limiting the task space in which the manipulation forces are applied according to the task, the proposed method can be applied to general-purpose manipulators. In this study, the effectiveness of the proposed method was validated through simulations using a planar 2-degree-of-freedom (2-DOF) manipulator and experiments using a vertical 6-DOF manipulator.

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