Optical laser reflection borometry

Abstract

A hole diameter measurement is a common task in mechanical engineering metrology. Inner hole dimension is usually measured with contact gauges touching the inner wall. Another approach is the hole diameter estimation by a contact or optical measurement of the diameter at the top or bottom of the hole. Such approach does not allow for the measurement of the real geometry of the hole inner walls. As the hole diameter decreases, small geometry variations along the hole axis lead to a large relative error between the actual and measured diameter value. We assessed several different optical schemes allowing for an optical measurement of a hole diameter by reflection of light towards the hole inner wall. We selected and tested a reflection optical laser triangulation approach for measurement of side wall of a recess and we analyzed the allowable depth of a bore enabling the hole diameter estimation by scanning of the inner wall along the hole axis.