The paper presents the development of a system for the measurement of the shapes and dimensions of rotationally symmetric forgings under high temperature. These large semi-finished products are measured with demands for accuracy on the order of millimeters. The challenge is to design a measurement system that overcomes the problems caused by high temperature and provides results instantly without interrupting the production process. The proposed approach exploits the fact, that the measured parts have simple rotationally symmetric shape. It is based on the assumption that (in the simplest case) the actual shape can be determined from four boundary curves which lie in two mutually perpendicular planes. These four boundary curves can be obtained by determining the edges of the forging in two images. The proposed approach has been incorporated into a software application created in Matlab programming environment. Hence the system does not use added illumination resolving edge detection and scale calculation is a crucial step. The main parts of the system, such as calibration, edge detection, spatial orientation, and the evaluation of information about the shapes and dimensions of the measured parts, have been designed so that the entire measurement process takes only a few seconds. The article focuses on the individual parts of the software application. It discusses the suitability of using particular mathematical models and the designed multi-step edge detection method, which is based on thresholding, directional median filtering and validation and correction of detected edge points.
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.