Inspection of reground drill point geometry using three silhouette images

Worn drills are often reground using a drill pointer. This paper deals with an easy and practical method for inspecting the geometry of a conically ground drill point using CCD camera images. In the proposed method, first, a CCD camera obtains outline images, or silhouette images, of the drill point, viewing from three different angular directions about the drill axis. Then, the three-dimensional coordinate data on the flank (ground) surfaces of the drill are evaluated from the images. Finally, by fitting the coordinate data to a mathematical model of the drill point geometry, five parameters describing the geometry are identified by an optimization technique. The proposed method is virtually unaffected by the lighting conditions and the surface texture because of the use of silhouette images. However, it can be affected by apparatus set-up errors such as angular positioning error of the drill to be inspected. In order to investigate their influence, the error sensitivity of the method has been analyzed through computer simulation.