  Aiming at the accurate and effective coaxiality measurement for twist drill
with irregular surface, an optical measurement mechanism is proposed in this
paper. First, A high-precision rotation instrument based on four core units is
designed, which can obtain the 3-D point cloud data of full angle for the twist
drill. Second, in the data processing stage, an improved robust Gaussian
mixture model is established for accurate and rapid blade back segmentation. To
improve measurement efficiency, a rapid reconstruction method of the twist
drill axis based on orthogonal synthesis is provided to locate the axial
position of the maximum deviation from the benchmark by utilizing the extracted
blade back data. Finally, by calculating the maximum radial Euclidean distance
from the benchmark, the coaxiality error of the twist drill is obtained.
Comparing with other measurement methods, experimental results show that our
proposed method is effective with high precision of 3 um and high efficiency of
less than 3 s/pc. The result demonstrate that the proposed method is effective,
robust and automatic, it can be applied in many actual industrial scene.
