An inspection technology of inner surface of the fine hole based on
  machine vision
Rongfang He Weibin Zhang Guofang Gao
Fine holes are an important structural component of industrial components,
and their inner surface quality is closely related to their function.In order
to detect the quality of the inner surface of the fine hole,a special optical
measurement system was investigated in this paper. A sight pipe is employed to
guide the external illumination light into the fine hole and output the
relevant images simultaneously. A flexible light array is introduced to suit
the narrow space, and the effective field of view is analyzed. Besides, the arc
surface projection error and manufacturing assembly error of the device are
analyzed, then compensated or ignored if small enough. In the test of
prefabricated circular defects with the diameter {\phi}0.1mm, {\phi}0.2mm,
0.4mm distance distribution and the fissure defects with the width 0.3mm, the
maximum measurement error standard deviation are all about 10{\mu}m. The
minimum diameter of the measured fine hole is 4mm and the depth can reach 47mm.