Photogrammetry based system for the measurement of cylindrical forgings axis straightness

Dimension measurement of hot large forgings is necessary for manufacturing process and quality control. Conventional non-contact optical measurement methods are not applicable, mainly because of high temperature and large dimensions. A novel approach to the axis staightness measurement of the cylindrical forging, based on the principle of photogrammetry and edge detection, is described in this paper. Proposed system is developing under laboratory conditions, but the actual conditions of steel production are also considered. Demands on the measurement system were set by our industrial partner, producer of cylindrical forgings with length of 4 to 20 m and diameter up to 1.4 m. The system should be able to detect axis straightness deviations higher than 5 mm (system accuracy has to be better than 5 mm). Cylindrical forgings are 4 to 20 m long with diameter up to 1.4 m. The approach is based on the assumption that the actual shape of the cylindrical forging axis can be determined (in the simplest case) using four boundary curves which lie in two mutually perpendicular planes. Four boundary curves can be obtained by detecting the forgings edges in two images. The article provides results of first validation of proposed method in laboratory conditions. Measurement repeatability was validated by carrying out ten measurements of a deformed rod. Each measurement was compared with a measurement performed by industrial fringe projection scanner Atos III Triple Scan in order to verify the accuracy of the proposed method.