Influence of an additional glass pane on an optical 3D measuring system

The number of satellites launched into space is growing from year to year. The amount of defective satellites is increasing as well, as there are only a few proven spare parts available. A specific test of the spare parts could be carried out on Earth with the help of a space simulation chamber. In such a chamber, material testers can generate an ultra-high vacuum and set temperatures between -180 degrees C and +200 degrees C. The influence of the temperature and vacuum on the geometry of the components can be evaluated from the outside using an optical 3D measuring system, that measures the component inside the chamber through a sight glass. By feasibility studies it was proven how strong the influence of an additional glass pane is on the measuring accuracy and the measuring error of a 3D scanner. A Zeiss stripe light scanner was used, which measures a 40 mm gauge block through a 20 mm thick borosilicate pane. For a reference scale of the scanner's measuring accuracy, measurements were initially carried out without the glass pane. The measurements were performed with different angular positions and distances between the glass pane and the scanner. The results showed an expected influence of the glass pane on the accuracy of the measuring procedure, as the bias became steadily larger with larger angles of incidence. A decrease in precision due to the glass pane was not observed for the measurement method. An enlarging statistical error occurred in the evaluation software due to the use of the glass pane. The reason for this is the displacement of the 3D point cloud through the glass pane into an inclined position.