Calibration of a laser reference plane for large-scale dimensional flatness measurement

A laser reference plane for measurement of the flatness of large-scale dimensional surfaces has been proposed. A finely collimated laser beam is swept by rotating a pentaprism in an ideal plane parallel to the surface to be measured. The apex angle error of the pentaprism is the most effective one for measurement of the flatness. In this paper, a practical method of compensating the apex angle error for a precision laser reference plane is presented. The measurement of the flatness of the Japanese Industrial Standard zeroth grade precision surface plate, whose deviation from flatness should be less than 7 mu m in an area of 1 m x 1 m, was performed using the proposed and conventional (Union Jack) methods. The results of the two methods coincided with each other and this clarified the feasibility of the proposed method.