Correction of measurement accuracy for optical measuring machines depending on the direction vector of the point

• Published in: Measurement. Sensors 2025-01, p.101659, Article 101659
• Main Authors: Harmatys, Wiktor, Gąska, Adam, Gąska, Piotr, Gruza, Maciej
• Format: Article
• Language: English
• Subjects: CMM; Measurements; Optical; Vision
• ISSN: 2665-9174; 2665-9174
• DOI: 10.1016/j.measen.2024.101659

Optical measurement techniques are one of the most frequently used coordinate measurement systems in factory conditions. Due to their continuous development and miniaturization, this allowed them to be installed in various types of coordinate measuring machines, as a result of which, the machine equipped with a classic contact head and an optical head enables multi-sensor measurement. The growing popularity of optical heads is due to the fact that they enable non-contact measurement of even small and sensitive objects, which in many cases is impossible to do with a contact head. In addition, they owe their popularity to the fact that a significantly smaller number of precise mechanical and electronic elements are used in their construction. Another advantage is that they enable collecting a large number of points in a short time, which is more difficult with traditional contact systems, and with the development of these techniques, optical heads offer increasingly higher accuracy. However, the disadvantage of this method is that the stability and accuracy of measurements using this method depend on a large number of factors, including: lighting conditions, quality of measured surface and its reflectivity. Another problem that has not been fully solved is the lack of direct correlation between contact and non-contact measurements due to the fact that it is very difficult to obtain a measurement of exactly the same point using these two measurement techniques. Another problem related to the measurement accuracy of this type of measuring heads, especially for the end user, is that the metrological software of most manufacturers is closed software, i.e. no one other than the manufacturer has access to the source code and therefore the techniques and algorithms for detecting a point in the image are known only to the manufacturer. Due to the fact that different algorithms may detect a point in the image in a different way, especially if the direction vector is not fully consistent with one of the main measurement axes it may additionally affect the measurement results. In this article the dependence of the measurement error on the direction vector of the measurement point was investigated. For this purpose, a special rotary table was developed and manufactured, the central part of which is transparent. With such solution the measurement of points on the axis of rotation of the table using the optical method using the backlight from the bottom of the object. A g