Precise positioning in the in-situ deflectometric measurement of optical

Phase measuring deflectometry is a powerful in-situ measuring technique for complex specular surfaces. Its measuring accuracy depends on the quality of geometric calibration. An in-situ deflectometric measuring system is integrated into a single point diamond turning machine. An accurate self-calibration method is proposed to refine the positions of the camera and the screen. A world coordinate system is established by introducing a flat mirror without markers. The geometric positions are solved by minimizing the deviations of the traced screen pixels. The tracing deviations caused by the form errors behave differently with those caused by the position errors. Precise localization of the measured surface can be realized by error separation, so that detecting of feature points can be avoided. Experimental results demonstrate that the measurement error is below 300 nm.