**Abstract**

A method for detecting the precise 6-degree-of-freedom (6DOF) localization of robotic arms end effectors without referencing any additional feature target during inline robot operation is introduced to facilitate precise robot positioning and monitoring. In this work, a 3D vision probe with digital structured-light projection is integrated with a wafer handling robot to perform online 6DOF location monitoring in semiconductor production. Precise alignment of the robotic arms end effector moving in the 3D operation space is realized by robust point cloud object alignment using regional surface area descriptors and the variant iterative closest point algorithm. Verified and confirmed by experimental tests, the developed method can achieve online 6DOF location monitoring with micron-level accuracy. Moreover, the proposed method can completely avoid the disadvantages of existing methods, namely relying on planar 2D images and demanding an additional target to be embedded with the end effector for localization, which reduces practical application, especially in an in-line operation environment. The major technical breakthrough of the present work is the target-free precise 6DOF localization of moving objects.

**Keywords:** 6DOF localization, iterative closest point, point cloud alignment, 3D vision, robot end effectors
