반사된 무늬 관측을 통한 경면반사체의 형상 측정

Abstract

Many components such as automotive panels, silicon wafers, home appliance, etc. have specularly reflective surface. In automotive and any other industries, there is need for accurately measuring the 3-D shape of reflective surface to speed up and ensure product development and manufacturing quality by using non-contact techniques. With specularly reflective surfaces, many existing inspection techniques for surface measurement based upon direct fringe pattern illumination that are traditionally developed for diffuse surfaces are no longer useful. However, reflective surface can be used as a mirror to reflective illuminated fringe patterns onto a screen behind. In this case of implementing fringe reflection techniques, it has been found that phase distribution depends not only on the height of the object but also on the slope at each measurement point.In this setup, a computer generated sinusoidal fringe pattern in the form of linear, parallel fringe lines of equal spacing is displayed on a LCD monitor. The monitor is placed in front of the test object, whose specularly reflective surface behaves as a mirror. A virtual image of the fringe lines is thus formed. For planar surface, the fringe pattern of the image is undistorted. However, the fringes are distorted according to the slope distribution is not flat. By digitizing the distorted fringes, employing a phase shifting technique, the fringe phase distribution is determined, hence enabling subsequent determination of the surface slope distribution. Then, we can reconstruct height distribution by using numerical integrating. Fringe reflection technique showed the ability to provide accurate non-contact measurement of 3-D shapes of the specularly reflective surfaces. We obtained 3-D shape data for known spherical mirror, unknown eyeglass and reflective plastic case. It is simple, robust, and applicable in industrial environments.