Rotation axis estimation for the derotator calibration with machine vision measurement of the auxiliary laser

A key problem when using the derotator is to ensure the coaxial alignment between the optical axis of the derotator and the rotation axis of the measured object. Moreover, accurate measurement of the rotation axis is the prerequisite of achieving the coaxial alignment. In this paper, we propose a strategy for estimation of the rotation axis with the assistant of an auxiliary laser and a binocular stereo vision sensor. When a laser source is temporarily attached to the measured object or the rotor shaft, the rotation of the laser will generate a ruled surface. The binocular sensor can accurately measure the coordinates of laser dots in three-dimensional (3D) space. The pose vector of the laser in each certain rotation angle can be estimated with measured 3D coordinates of the laser dots. Finally, the rotation axis of the object can be estimated with multiple pose vectors considering the constraint of the fixed axis rotation. The validity and precision of this proposed strategy are demonstrated by means of experiments.