Reduce Measurement Uncertainty of Ball Crater Method by Using Image Processing Techniques

Abstract

A method of reducing the uncertainty in measuring coating thickness using the ball crater method is proposed in this research. A crucial step of the ball crater method is measurement of the radii of the crater circles from a microscope image. While traditional methods of measuring the radii involve human operators, who inevitably introduce measurement uncertainty, the proposed approach measures a radius by fitting a circle (or an ellipse) to all edge points of a crater circle edge, which is extracted from the microscope image of the crater by using image processing techniques. This eliminates the subjectiveness introduced by human operators and reduces the measurement uncertainty. Experimental results confirm the feasibility of our method and its potential in reducing measurement uncertainty and increasing measurement accuracy of the ball crater method. The use of all edge points in the estimation of the radius in the proposed method also enables accurate determination of coating thickness from an image of a crater taken from a direction other than the normal to the coating surface.